Geo-Chicago 2016: Sustainable Geoenvironmental Systems

Anchor trenches for MSW landfills subject to various uncertainties arising from inconsistency in parameter measurement and determination, placement of fresh waste on the geomembrane (GM) liner, improper compaction of cover and backfilled soils, construction practices, assumption of relative slippage, and invention of new design methods. A wide range of variability is associated with the design parameters of the anchorage. Conventional factor of safety approach cannot account for the uncertainties involved. The drawback can be well addressed through reliability based approaches. The objective of the analysis discussed herein is to produce estimates of the probability of anchor trench failure as opposed to the conventional factor of safety. Therefore, a framework for the target reliability based design optimization (TRBDO) methodology is presented for the design of anchor trenches. This paper emphasizes the importance of allowable design strength of the liner considering the variability for rectangular and L-shaped rectangular anchor trenches.

A review is presented on the long-term internal shear strength of geosynthetic clay liners (GCLs). Existing experimental data were evaluated to identify key attributes of long-term shear strength behavior. In particular, evaluations and discussions have been developed on aspects of GCL behavior that have received limited attention in previous studies; e.g., immediate and creep deformation behavior, deformation at the end-of-immediate shear deformation, rate of creep deformation, and deformation as a function of creep stress ratio. Analytical models were applied to evaluate GCL shear deformation behavior. Analysis of available data suggests that shear deformation behavior and model parameters are dependent on aspects such as specimen dimensions, reinforcement type (e.g., needle punching or stich bonding), test temperature, short-term peak shear strength, and method of shear stress application (i.e., stepwise loading versus constant creep stress).

The mechanisms governing the shear behaviour of sand and sand-geomembrane interfaces is studied by carrying out large scale symmetric loading direct shear tests on three sands of different sizes with similar morphological characteristics and a smooth high density polyethylene geomembrane. To focus on the effect of particle size on the shear behaviour, the morphological properties of sand particles, measured from microscopic images, were kept same. Surface topographical profiling of the geomembranes before and after interface shear tests was carried out to understand the extent of indentation due to shearing along the interface. The representative samples of smooth geomembranes after tests with three sands of different sizes at one particular normal stress were selected for damage analysis/surface roughness measurements through 3D optical profilometer. 3D contours of surface roughness of the geomembrane before and after the tests are presented and compared. Interface shear strength was observed to hugely depend upon the effective contacts formed on the surface of the geomembrane, which are a function of the number of particles in contact and the depth of the grooves formed by these particles on the surface of the geomembrane.

This paper reports the engineering behavior of proposed expanded polystyrene (EPS) geofoam unit cells with fly ash inside the core of cell. EPS geofoam unit cell were prepared with four different densities of EPS geofoam material i.e. 15, 20, 22, and 30 kg/m³ with heights 50, 75, and 100 mm. The fly ash was compacted inside the core of unit cell at its optimum moisture content in layers of 25 mm height. The compression tests were performed on proposed composite material to study the stress-strain behavior, effect of density of EPS geofoam and height of unit cell along with the failure patterns. Compressive stress-strain curves for EPS geofoam showed increase in compressive strength with increased density of material. On the other hand, EPS geofoam unit cell with fly ash showed a decrease in the compressive strength with increase in the density of EPS geofoam material. Also, increase in the height of EPS geofoam unit cell resulted in decrease in the compressive strength. For a particular height of the EPS geofoam cell, compressive strength decreases marginally with increase in the density of EPS geofoam. Different failure patterns were observed for the each height of the unit cell tested.

Pennsylvania Department of Environmental Protection (DEP) and Department of Community and Economic Development (DCED) officials welcomed the recent creation of an entity that collects and reprocesses geomembranes used in various aspects of Marcellus shale oil and gas drilling, development, and production. These various aspects include well pad liners, above ground impoundments, secondary containment, and floating covers. Well pad liners are placed over a large area (usually 60 m (200 ft) by 60 m (200 ft)) around the drill well to contain drilling fluids, provide an anti-slip surface for drill workers, and contain oil and gas products. Above ground containment ponds are used for a variety of containment purposes, e.g., drill pad water, well flowback water, and shale derived liquids. Secondary containment geomembranes are used around oil and gas storage tanks to contain any leaks from these tanks. Floating covers are used to prevent contact with the environment and wildlife of various liquids associated with the shale play.

Transport of odiferous hydrogen sulfide (H₂S) gas was evaluated using column tests simulating interim covers for waste containment consisting of a thin geomembrane overlain by cover soil. Tests were conducted with co-extruded geomembrane (GM) comprised of a thin inner layer (0.05 mm) of ethylene-vinyl alcohol (EVOH) sandwiched between two layers of linear low-density polyethylene (LLDPE), a 0.1-mm-thick polyethylene (PE) sheet, a 0.76-mm LLDPE GM, and a 0.76-mm polyvinyl chloride (PVC) GM. In each case, the GM or sheet was overlain with a thin layer of silt intended to protect and anchor the GM. Breakthrough of H₂S occurred from the column with an EVOH GM (≈ 30 d) was five times slower than from columns with LLDPE and PVC GMs (≈ 6 d). Relative concentrations on the cover surface from the column with the EVOH GM was lower than for all other GMs (relative concentrations were in the following order: PE > PVC > LLDPE >> EVOH). The diffusion coefficient for H₂S in the EVOH GM back-calculated from the column test data was approximately 100 times lower than diffusion coefficients for the PE sheet and other GMs (1.1 × 10^-12 m²/s for co-extruded EVOH GM, 1.14 × 10^-10 m²/s for 0.1-mm PE GM, 0.87 × 10^-10 m²/s for the 0.76-mm LLDPE GM, and 1.06 × 10^-10 m²/s for the 0.76-mm PVC GM). These findings suggest that interim covers with co-extruded EVOH GMs can be effective at reducing emission of odiferous H₂S relative to interim covers with other geomembranes.

Multicomponent geosynthetic clay liners (GCLs) have recently been introduced to the market to perform sealing in landfills, dams, dikes, ponds, etc. As they are combining a GCL to a coating or film, their hydraulic properties are falling between geomembranes (GM) and GCLs. In order to evaluate the importance of performing the experimental quantification of the diffusion of phenolic compounds in multicomponent geosynthetic clay liners, which will be a time consuming and expensive operation, a preliminary modelling was undertaken. The objective of this paper is to present the results of this modelling performed based on the quantification of the diffusion in geosynthetic clay liners, polyethylene films and geomembranes in order to evaluate the performance towards diffusion of a multicomponent geosynthetic clay liner. Diffusion was quantified for 2,4-dicholophenol, 2,3,5,6-tetrachlorophenol, and pentachlorophenol. Results show sensitivity to the thickness of the film or geomembrane used in conjunction with the GCL, more important than to the nature of the phenolic compound under study. The protection at field scale by a multicomponent GCL would thus not be ensured with the same level as with a more classical composite liner containing a geomembrane, which remains the best performing solution towards diffusive transfers.

Friction is determined experimentally in modified laboratory direct shear (interface shear) tests. Results of these tests vary greatly due to several factors including test equipment, configuration, and setup. Recently, two round-robin test series were performed by the German Geotechnical Society (DGGT). Both series show significant variations in the characteristics of friction stress vs. displacement curves and the peak friction stress values. For the second test series the boundary conditions of the tests were specified more precisely. However, the results showed nearly the same variation. Additionally, in 2013 a round-robin test series was performed with ASTM D5321 after a significant revision of this ASTM test standard was published. One interface was tested. This round-robin test program was set-up to evaluate the effectiveness of the current test method. However, similar variation was found in this test series as the two series initiated by the DGGT. This paper will present results of the round-robin test programs and identify ways in which to improve the current interface shear test standards. Particular attention will be given to the test equipment and setup including boundary conditions, clamping, gripping, etc.

The water uptake and the hydraulic conductivity behavior of a low quality (LQ) GCL were determined in this study. The term “low quality” refers to the physical properties such as liquid limit rather than the chemical properties of bentonite used in GCL. For this purpose, GCL samples were hydrated over compacted silty sand subsoil which was taken from the landfill liner. After 7, 17, 30, 62, and 90 days of hydration, GCLs were removed from the flexible-wall permeameters and subjected to the hydraulic conductivity tests with deionized water. Results illustrated that GCL water contents increased up to 7 days of hydration period and then, leveled off. The relationship between final water contents and liquid limits were also evaluated. The data from this study together with the literature suggest that the greater the liquid limit, the greater is the GCL final water content. However, the hydraulic conductivity behaviors of GCLs were rather different from the literature. Increase in the hydration duration led to decrease the required PVF for the equilibrium hydraulic conductivity (2.4×10^-11 m/s). However, initial hydraulic conductivities of LQ-GCL were about 2.0×10^-6 m/s. Although they decreased to ≈ 2.4×10^-11 m/s over time, higher initial hydraulic conductivity seems to be significant when LQ-GCL is installed in the field.

The recovery and emission of landfill gas (LFG) is an important topic in landfill management. Horizontal wells are extensively used to control the escape of gases and achieve effective gas recovery before landfill closure. A two-dimensional analytical model for layered landfills with horizontal wells was used in this study for the analysis of gas pressure. The model, with a horizontal layered structure, was solved using separation of variables and double finite integral transforms. The gas pressure distribution and well pressure were then calculated to analyze the influence of horizontal well layout. The result shows that a smaller horizontal well spacing is more suitable for the waste layers with high gas generation rates. Even for different well layouts, it can be designed independently in the presence of low-permeable cover. To distinguish the optimal horizontal well spacing, a cost index was defined considering the cost of well installation and vacuum pressure. The cost index has a minimum value and the corresponding spacing is the optimized one. With the help of one parameter C_ratio (cost ratio of well installation to vacuum pressure), the optimal selection of horizontal well spacing becomes possible and effective. These results provide helpful guidelines to the design of horizontal LFG collection systems.

For sanitary landfill design, the geotechnical properties are usually necessary during landfilling for stability of slopes, leachate and gas management and utilization. In this study, shear strength behavior of synthetic MSW samples were investigated with large scale direct shear tests in different compositions. In order to determine composition effect on the shear strength behavior, three synthetic MSW average compositions of Europe (E), Turkey (T) and USA (U) were composed by using 11 different waste materials. In addition to these compositions, six modified compositions were produced by reducing the percentage of the predominant material or completely removing from the composition. The test results have shown that, the highest internal friction angle belongs to E composition which has the highest paper and cardboard waste ratio. On the other hand, maximum cohesion value belongs to T composition which consists higher amount of organic waste than other compositions. When fiber waste content increases, internal friction angle also increases. The cohesion values of the samples are high which have high organic matter content.

A prototype heat extraction system was designed and installed at a MSW landfill located in region with a temperate climate in California. The heat extraction system consisted of a heat extraction well equipped with closed-loop vertical piping network, a fluid storage tank located at the ground surface, and a pump/generator assembly. A monitoring system also was installed to assess the influence of the heat extraction system on the waste mass. The heat extraction system and monitoring system extended to depths of 23.5 m and 24 m, respectively. The prototype system was operated for a period of approximately 1 year. Turbulent flow conditions were maintained during system operation. Temperature decreases on the order of 5°C were measured at a radial distance 1 m from the heat extraction well along the entire depth of the extraction well. Less influence was observed at greater distances from the heat extraction well. The selected design and installation of the system described herein was effective for extracting appreciable amounts of heat as demonstrated by the preliminary data obtained during early stages of operation of the system.

Dynamic properties of municipal solid waste (MSW) from a dump site located at Delhi, India dump site that has been operational since 1994 have been evaluated using field and laboratory testing. Shear wave velocity profiles were measured at locations close to sample collection points. Undrained cyclic triaxial testing was conducted on 150 mm diameter specimens reconstituted at their in situ composition and in situ unit weight and on specimens prepared with the <20 mm fraction only to study the effect of fibrous waste constituents on dynamic properties. Less cyclic degradation due to excess pore pressure generation was observed for specimens with greater fibrous material content. Dynamic properties obtained from this study are observed to be consistent with the data reported from USA landfills.

Municipal solid waste (MSW) landfills can generate significant amounts of methane. There is considerable interest in quantifying surface methane emissions at such facilities. Numerous techniques exist for the evaluation of methane emissions from landfills. These techniques are either based on analytical emission models or on measurement methods. This paper presents a method to estimate methane emissions using ambient air methane measurements obtained on the surface of a landfill. Genetic algorithms (GA) based optimization combined with the standard Gaussian dispersion model are employed to identify locations as well as emission rates of potential emission sources throughout a MSW landfill. A case study is employed to evaluate the performance of the proposed methodology. GA-based search techniques are proven to be useful in estimating source locations and emission rates using methane concentration measurements.

The 50,600 m² (5.1 hectares, 12.5-acre) Astoria municipal solid waste (MSW) landfill opened in 1965 for disposal of household and select commercial and industrial waste. Oregon Department of Environmental Quality (DEQ) ordered the closure of the landfill in 1978 due to failure to prevent landfill-created leachate from impacting the nearby creek and associated wetland. Through a partnership of Columbia Memorial Hospital, the City of Astoria, and Astoria school district, plans were developed to create a 6.9 hectares (17-acre) athletic field complex at the site. The biggest geotechnical challenge was characterizing the variable, and highly unknown, content of the landfill upon which structures would be founded. A number of design challenges were addressed, including: characterizing the strength and compression properties of the landfill debris, the high live loads imposed by the grandstand due to its cantilevered roof with associated wind and seismic loads and the occupancy, the relatively light luminaires, and scoreboard with very high overturning loads due to high winds. These issues were addressed with a combination of surcharging, deep foundations, soil improvement, and special foundations using conventional engineering analyses and existing published data.

Geophysical surveys were conducted over a municipal solid waste (MSW) cell that uses leachate recirculation lines (LRLs) to enhance MSW degradation. Changes in the waste over time during and after leachate injection were recorded using 2D resistivity tomography, electromagnetic conductivity, ground-penetrating radar (GPR), well-logging and seismic methods. Results obtained from the GPR surveys and geophysical well logging are the focus of this paper. It is recommended that GPR surveys utilize a 50 MHz antenna frequency since the 100 MHz antenna has too shallow a penetration depth (< 2 m), whereas the 25 MHz antenna, while achieving better depth penetration, was low resolution, was cumbersome to use in the field, and strongly affected by noise. Signals from the 50 MHz antennas penetrated into the refuse and imaged deeper reflections that could represent intermediate cover, different types of refuse, LRLs, or leachate accumulations. Geophysical well logging with natural gamma and electromagnetic conductivity (induction) probes was conducted in 75-mm diameter boreholes along the perimeter of biogas extraction wells. MSW (1-2 years old) produced count rates of 20-30 counts-per-second (cps) on natural gamma logs. Electromagnetic conductivity logs obtained in boreholes identified buried metals in the waste and hardware associated with the pipes. Increased conductivity at about 7 m depth was related to an accumulation of leachate at this depth.

A fiber-optic distributed temperature sensing (FODTS) system was developed and installed for the first time in an elevated temperature landfill (ETLF) in 2014. Various other options for in-situ instrumentation were evaluated, the analysis of which resulted in the development of a system that combines FODTS and vibrating-wire (VW) temperature and pressure sensor components. Installation was performed using sonic drilling methods/techniques. Challenges included safety precautions, logistical handling of materials and equipment, and flexible equipment mountings at the landfill surface. Vertical profile plots depicting temperature versus depth at various times after installation show changes in temperature over time. Three-dimensional (3D) images of the temperature distributions illustrate how the data can be used to visualize the expansion or contraction of heat within the waste mass and identify the location of the possible heat-source zones. The combination of FODTS plus VW technology has provided a redundant system of data verification and a more complete understanding of the temperature-pressure regime.

One of the main issues delaying the field implementation of landfill biocovers is the lack of a proper field technique to assess the level of CH₄ oxidation. Gas push pull test (GPPT) was used to assess the level of methane oxidation. GPPTs consist of the injection of a gas mixture containing a reactive gas (CH₄) and a non-reactive tracer (SF₆) into the soil and the extraction of the pushed gas mixture from the same location over time. To quantify in-situ rates of methane oxidation, eleven GPPTs were performed in different locations of an active landfill in Florida. Quantification of first order reaction rate is based on the comparison of breakthrough curves of the different gases in accordance with (1) well mixed reactor, complete mixture of gases, and (2) plug-flow reactor model, no mixing of the injected gases. Using the data collected, a mass balance approach was also performed to express methane reactions as a percent oxidation and the Michaelis-Menten parameters were also determined. The first order methane oxidation reaction constant varied from 1.04 to 36.90 hr^-1 and 0.65 to 28.04 hr^-1 when the data was reduced using well-mixed reactor and plug-flow reactor, respectively. The average first order reaction constant averaged 17.52 hr^-1 for the well-mixed reactor analysis and 12.3 hr^-1 for the plug-flow reactor analysis. The mass balance analysis yielded a methane percent oxidation from of 13 to 76% with an average of 47%. The Michaelis-Menton parameters, V_max and K_m, for the oxidation reaction were determined to be 4950 g.m^-3soil gas.hr^-1 and 5%, respectively.

Generation of municipal solid waste (MSW) is huge in cities of developing nations, mainly due to rapid industrialization and urbanization. To cope up with this situation, apart from resorting to various methods of treatment and disposal of MSW (viz., landfills, composting, biomethenation, incineration and pyrolysis), aerobic bioreactor landfills, which are gaining popularity for economical and effective disposal of MSW, are being installed. However, as the efficiency of the bioreactor landfills primarily depends on the rate of decomposition of the MSW, which could be manipulated by appropriate microbial activity, under ambient conditions of moisture and temperature, the leachate recirculation should be modulated, primarily, based on the amount of moisture and temperature of the MSW in the bioreactor landfill. This calls for development and implementation of advance instrumentation for continuous monitoring, which would facilitate controlling moisture content and temperature in the bioreactor landfill. With this in view, the response of the MSW in such landfills was simulated under anaerobic conditions, by employing the frequency domain reflectometry (FDR) probe and multilevel thermocouples. The study successfully demonstrates that these instrumentation are quite effective in modulating the decomposition rate of the MSW by adequate scheduling of the ‘leachate circulation’.

In recent times, rapid urbanization and industrialization has created a scarcity of land space in the cities. This has led to renewed interest in finding means to extend the life of existing municipal solid waste (MSW) landfills, as it is becoming increasingly difficult to find new landfill sites for future waste disposal. In this regard, dynamic compaction (DC) is a viable technique to reduce the volume of MSW and increase the storage capacity of an existing landfill system. The objective of this paper is to model numerically the densification of municipal solid waste landfills using a dynamic compaction technique. For this purpose, dynamic compaction was numerically simulated on the components of a typical homogeneous fresh MSW fill using Abaqus (2014), and the corresponding reduction in waste volume, crater depth, depth of the improvement and strains in the MSW fill after the impact was computed along with the energy imparted during dynamic impact. Fresh MSW with a particular age was modelled by adopting available constitutive relationships. The analysis and interpretation of numerical model results indicate the effectiveness and relevance of dynamic compaction in densifying the MSW landfill. Larger ratio of tamper radius to print spacing is found to be more effective in increasing the storage capacity of landfills.

In the present study, custom designed apparatus was developed to estimate the gas permeability of soil barrier considering advective flow condition. A blend of Kaolin clay and Kalpi sand in the ratio of 4:1 by dry weight was selected as an ideal soil barrier material. The gas permeability of the soil barrier was determined at various placement water contents with respect to standard Proctor compaction and initial relative gas pressures. The gas permeability of the soil barrier material was found to decrease from 1.52 x 10^-13 m² to 9.68 x 10^-16 m² at a relative gas pressure of 10 kPa when the molding moisture increases from 14.7% (4% dry of optimum) to 20.7% (2% wet of optimum). Beyond 2% wet of optimum, an increase in the gas permeability was noticed. It was also found that initial relative gas pressure does not have significant influence on the gas permeability of the soil barrier irrespective of the placement water content.

Phytocaps are vegetated soil landfill covers that are designed primarily to reduce the drainage of rain water into the waste through water balance mechanisms instead of the resistive mechanism employed by conventional landfill caps. The potential superior capability of phytocaps to reduce fugitive release of methane to the atmosphere can encourage their use in Australia and elsewhere. A multiphase transport model was used to study and characterize the methane oxidation potential of phytocaps and to estimate methane abatement generated as a result of installing phytocaps at a given landfill. Phytocaps were simulated in four locations of Australia. For each location, daily estimates of soil water content and soil temperatures were predicted and then used in a gas transport model to simulate methane oxidation. Several simulations were performed on each phytocap using methane loading flux (MLF) varying from 2 to 200 gm^-2d^-1. The results of the gas transport model simulations were used to develop methane oxidation curves for each climate, by correlating oxidation fraction (OF) to the MLF. The potential abatement, in Australian carbon credit units (ACCUs), for a typical two hectare landfill site was then estimated. The installation of a phytocap at the example landfill can result to an abatement potential value in the range of approximately $56,000 and $114,000 AUD/year and an approximate present market value (2015) of $76,000 AUD/year.

Elevated temperatures in municipal solid waste landfills can pose health, environmental, and safety risks because they can generate excessive gases, liquids, pressures, and heat that can damage landfill infrastructure. This paper discusses mechanisms that can lead to elevated temperatures in the landfill and presents a case history to establish trends in gas composition, leachate collection, settlement, and slope movement. In general, landfill gas composition changes from predominantly methane (50-60% v/v) and carbon dioxide (40-55% v/v) to a composition of carbon dioxide (60-80% v/v), hydrogen (10-35% v/v), and carbon monoxide (> 1,500 ppmv) as temperature elevate. As waste temperatures increase, gas and leachate pressures also increase, resulting in odors, leachate outbreaks, and potential slope instability. These observations are summarized in a progression of elevated temperature indicators that are related to field manifestations and possible remedial measures.

This paper focuses on one of the major environmental concerns of urban centres of developing countries, i.e. the remediation or closure of waste dumps. Data was collected and analysed for 62 waste dumps sites from 26 cities of India. Eight remediation/closure alternatives were considered for containment of the dumps. A multi-criteria analysis (MCA) approach was adopted to select the most appropriate alternatives for different sites. The proposed method uses the concept of modified and normalised scores to relatively rank the alternatives. The method was applied to 11 dumps with varying site conditions and observed to be sensitive to changes in conditions and perform satisfactorily in identifying different options for distinctly different sites. The decision-making method performs well with the available limited information on the waste dumps rather than elaborate geo-environmental parameters.

For the past 40 years, non-woven geotextiles have been used as filters and drainage materials in geo-environmental works, especially on sites such as municipal waste landfills. Proper selection of non-woven geotextile filter layers is essential to ensure efficient operation and durability of drainage systems. Geotextiles are easy to transport and install, their main advantage is to help to minimize clogging effect of drainage. The growing use of geotextiles in environmental projects needs research on performance of geotextiles in leachate collection systems on landfills. It appears that non-woven geotextiles may not drain water as effectively as was initially expected. This paper presents results of laboratory tests of water permeability, in the normal direction to the plane of unworn and worn non-woven geotextile samples taken from the Radiowo landfill after more than 15 years of exploitation. The permeability tests were performed under different loads. The measurements were conducted according to national standards. The aim of the research was to determinate water permeability under various exploitation and loading conditions. The results obtained allowed to trace changes in water permeability of non-woven geotextile samples and to verify the effectiveness of applied geofilters on old municipal-waste landfill conditions.

Understanding the mechanical behavior of municipal solid waste (MSW) is still a major challenge in engineering. The purpose of this paper is to critically review published literature on MSW shear strength from the past 20 years, including the major strength mechanisms and failure criteria, so a landfill engineer can access key behavioral concepts, beyond just the raw values of friction angle and “cohesion” parameters that are required for design. In addition, this paper explores the relationship of shear strength parameters with MSW composition and urban population, which are useful proxies for economic development. To revisit the state of the practice since the introduction of commonly used design charts, an enhanced database of shear strength parameters as well as Mohr-Coulomb envelopes was compiled. Also, a relationship was developed between strength parameters, MSW composition, and population data for a number of cities in a developing country. This study supports the concept that the consumption habits of an urban area are very relevant when it comes to designing landfills. Furthermore, instead of introducing a new recommended range of design parameters or a new strength envelope, the compiled data are interpreted under a simple statistical basis, so the designer can make informed decisions on which parameters to choose for design.

Elevated temperature events are problematic for Subtitle D landfills because they: (1) are challenging to identify and delineate; (2) can remain undetected for a relatively long period of time; (3) are difficult to extinguish; (4) may damage engineered components, (5) direction and rate of movement are not uniform, and (6) produce side effects that may damage a facility enough to warrant permanent closure. In addition, slope instability and movement have occurred at these landfills with elevated temperature, leachate, and/or gas pressures. This paper discusses the mechanisms for slope instability, including elevated gas pressures, perched leachate surfaces, and reduced MSW shear strength. Based on a case study, slopes are found to move outwards of up to 15 m. In addition, the slope can reverse backwards into the settlement bowl if settlement is excessive.

In the United States, FEMA estimates that 8,400 fires occur at Subtitle D (municipal solid waste; MSW) landfill facilities every year. This paper uses landfill indictors, such as gas composition, temperature, slope movement, and settlement, to the effectively delineate the three-dimensional boundaries of elevated temperatures and monitor the growth and/or movement with time. In addition, a conceptual model is proposed to classify a MSW landfill into three zones to determine the transition from normal operating areas to the elevated temperature region, which is important for public health, environmental safety, and appropriate response by landfill personnel, first responders, and regulatory agencies.

Biodegradation of municipal solid waste (MSW) is enhanced in bioreactor landfills via active leachate recirculation. Biogas consisting primarily of methane and carbon dioxide is generated during this process and can be recovered as an energy source. The physical, chemical, geotechnical and hydraulic characteristics of the waste are altered during active biodegradation. However, changes in these characteristics have not been examined closely in the field due to limitations in field measurements. Three laboratory simulators with diameters of 0.3 m and volumes of 42 L were filled with characterized MSW from landfills in Michigan and California to investigate the impact of waste composition on the degradation process. Leachate was recirculated frequently and the progression of MSW biodegradation was monitored via measurements of generation rate of biogas as well as chemical oxygen demand and pH of leachate. The total volume and total weight of the MSW were recorded continuously. The total unit weight, and volumetric water content were calculated. Hydraulic conductivity of the MSW was tested within the same simulators over time. Active biodegradation lasted for approximately 200 days. While significant changes of the physical characteristics were observed during active biodegradation, the changes continued at lower rates even after 800 days. Changes in the physical and biochemical characteristics of the MSW are correlated with the initial waste composition through parameter B that is defined as the percentage of biodegradable constituents in the waste mass.

In this paper, the tensile capacity and anchorage required for making the geomembrane–soil interface stable against sliding have been evaluated for an old MSW waste dump. Four methods of analysis have been used–two infinite slope analysis (ISA) and two finite slope analysis (FSA) methods. Slope inclinations are varied from 3.0H:1.0V to 1.5H:1.0V and heights between berms are taken as 5 m and 10 m. The tensile capacity required to stabilize a slope as steep as 1.5H:1.0V, calculated from all the methods, varies between 33 to 85 kN/m for berm height of 5 m and 90 to 170 kN/m for berm height of 10 m. Estimation of anchorage capacity for run–out and trench anchor has been done by four methods–Koerner (2005), Qian et. al. (2002), Sharma and Lewis (1994) and Villard and Chareyre (2004). For run–out anchor, the anchorage capacity for 2 m wide berm is observed to lie between 30 to 46 kN/m. This increases to the range of 48 to 110 kN/m for trench anchor. These capacities are adequate for anchorage of geosynthetics when height between berms is limited to 5 m. The present study demonstrates the wide variation in results obtained by different methods and the need for improving the current practice.

Permeable reactive barriers (PRBs) are used worldwide for the remediation of contaminated groundwater in the subsurface. This paper showcases a PRB installed in an acid sulfate soil rich ground to neutralize acidic groundwater. Recycled concrete has been used as the reactive material. Its performance is monitored over 8 years and has shown promising results for treatment in the long-term by maintaining a neutral pH and removing heavy metals from groundwater. Heavy metals (Al and Fe) precipitate out of solution and armor the reactive surfaces of recycled concrete, which leads to a decrease in the efficiency. Longevity of the PRB is predicted considering the rate of exhaustion of reactive material, rate of precipitation of secondary minerals and the groundwater flow at field site.

Sodium bentonite (Na-bentonite) commonly is used as a barrier or a component of a barrier to limit contaminant migration into the environment. Results of experimental research to date indicate that Na-bentonite may exhibit significant membrane behavior resulting in restricted solute migration (also known as anion exclusion) and development of chemico-osmosis, leading to reductions in both liquid and contaminant flux through the bentonite. Thus, bentonite-based engineered barriers may exhibit improved containment performance, which has motivated the development of laboratory research to further evaluate and quantify membrane behavior. The purpose of this paper is to provide a summary of recent and current advances in the ongoing evaluation of the significance of membrane behavior in bentonites, including chemically modified bentonites (e.g., dense pre-hydrated geosynthetic clay liners, multiswellable bentonite, bentonite polymer nanocomposite, HYPER-clay) and bentonite-amended clays. In addition, the development of an innovative apparatus to measure membrane behavior under unsaturated conditions is described. Recent research regarding the limiting concentrations at which membrane behavior continues to persist is summarized. Finally, recommendations for future research on the relevance of membrane behavior in practical applications are provided.

A landfill liner as designed to be a barrier of low permeability is required to achieve a hydraulic conductivity lower than 1×10^-7 cm/sec in Ohio. A test pad of soils must be used to ensure that this requirement is met, and subsequently soil layers to be used for landfill liner must be compacted to achieve similar properties as those of the test pad. Currently two different methods are used to ensure that the properties of the compacted soil layers are similar to those the test pad; the dry corner method specifies the acceptable ranges of grain size distribution, and the best fit line of optimums (BFLO) method designates an area for acceptable dry density vs. moisture content data points. The present study first briefly surveys these two methods. The dry corner method may be overly simplistic and often inefficient in practice, whist the best fit line of optimums method frequently leads to over-conservative compaction demands, thus inducing higher costs. A newly improved method is proposed in the present study based on percent deviations of compacted soil properties compared with the properties of the test pad. These properties include clay, silt and sand fractions, index properties, maximum dry density and optimum moisture content. Data of over 130 soils in the past landfill projects are analyzed. The results of this new method are also compared with the two current methods. The present study shows that this method is of great potential for more efficient quality control for landfill liner construction.

Chemical oxygen demand (COD) is one of the important indexes of landfill leachate. The shale is a kind of mineral with a high specific surface area, which potentially can serve as an additive for the clay liner to retain the COD from leachate. Sorption experiments showed that the crushed shale with the grain size of 0.075-2.0 mm displayed higher sorption rate (41.1-47.3%) for COD than the others. The hydraulic conductivity tests showed that the permeability of the mixes of crushed shale and clay could be less than 1×10^-7 cm/s when the crushed shales and clay ratio was appropriate. Based on the convection-diffusion equation and column test, the parameters of diffusion and retardation for COD through liners were obtained. Both of them increased gradually with the increase of the volume of the added shale. The forecasting duration for COD breakthrough deduced by the theoretical equation with above parameters first increased and then decreased with the rising ratio of shale in the mixes. When the ratio was about 5%, the duration for COD breakthrough was the longest period as compared with that of the other ratio.

This study discusses and compares the hydraulic conductivities of GCLs to those of sand-bentonit mixtures (SBMs)/zeolite-bentonite mixtures (ZBMs). ZBMs had 20% and 30%, whereas SBM had 20% bentonite contents. The effective stress applied on GCLs was greater than bentonitic mixtures. Neither GCLs nor bentonitic mixtures were prehydrated with water. The results showed that hydraulic conductivities of non-prehydrated GCLs were significantly greater than those of ZBMs and SBMs. Applying greater effective stress did not reduce the hydraulic conductivities of GCLs. Although bentonitic mixtures were non-prehydrated during hydraulic conductivity tests, they had been hydrated with water before compaction. In order to figure out this condition and to make better comparison between the hydraulic conductivities of GCLs and bentonitic mixtures, two brand new GCLs were prehydrated with DI water (DIW). Then, permeation was begun with DIW until one pore volume of flow was passed through the samples. Finally, the permeant was switched to landfill leachate and hydraulic conductivities were determined. The results showed that initial permeation of GCLs with DIW decreased the hydraulic conductivity when GCLs were further permeated with landfill leachates. Also, the hydraulic conductivities of GCLs were less than those of bentonitic mixtures. This may be attributed to greater effective stress applied on GCLs.

The objective of the present study is to evaluate the effect of geofibers in restraining desiccation cracking of expansive clay, through controlled laboratory tests. In the study, the soil was reinforced with polyester fibers of lengths 15 mm, 30 mm, and 50 mm, at fiber contents of 0.25%, 0.5%, and 0.75%, by dry weight. Saturated soil specimens were allowed to dry at a constant temperature and relative humidity. The loss of moisture, crack initiation, crack propagation, crack morphology, and surficial crack measurements were studied. Digital image analysis was employed to measure the surficial cracks. The results indicate that the desiccation cracking of soil is significantly restrained by geofiber reinforcement due to the bridging effect. The crack area increased with an increase in the length of the fibers. The surficial crack formation of the soil is reduced by 66% when reinforced with 15 mm fibers at a fiber content of 0.5%.

Bentonite is a naturally occurring clay-rich sediment that has a high cation exchange capacity and swells upon contact with water. Owing to these characteristics, highly compacted bentonite (HCB) is often used as an engineered barrier system (EBS) to protect used nuclear fuel containers (UFCs) that are stored in deep geological repositories (DGR). Nutrients present in the bentonite may support microbial activity and growth leading to possible microbial influenced corrosion (MIC). To evaluate the potential extent of MIC in a DGR, a bulk chemistry approach was employed, accounting for nutrients in the bentonite, backfill, and groundwater, and established limiting nutrients (LNs) for microbial growth. The methodology was applied to one UFC encased in HCB and to an entire placement room containing 341 UFCs. The method was also applied to both crystalline and sedimentary rock environments, typical of Canadian geologies. Nitrogen and phosphorous were identified as the LNs, depending if one UFC or the entire placement room was considered. The results show that there is limited carbon and nutrients available for microbial growth in a DGR. The results also highlight the need for construction and operating procedures to control nutrients and organics additions to the repository.

Addition of polyacrylate to enhance the chemical resistance of Na-bentonite (NaB) was investigated. To boost the swelling of NaB, and thus boost the mechanism by which NaB derives low hydraulic conductivity, superabsorbent Na-polyacrylate (SAP) was investigated as an additive. Mixtures were tested by direct permeation (i.e., permeation without prehydration with a dilute solution) at low effective stress with 50 mM CaCl₂ or 500 mM CaCl₂. These solutions are known to result in substantially reduced NaB swelling, wider and more direct flow paths, and orders-of-magnitude increases in hydraulic conductivity in NaB. Dry-blended mixtures of granular SAP and NaB did not exhibit improved hydraulic conductivity to 50 mM CaCl₂ or 500 mM CaCl₂ relative to barriers composed of 100% NaB or SAP. Wet-blended mixing of SAP with NaB did not result in improved hydraulic conductivity relative to barriers composed of 100% NaB or SAP when directly permeated with 500 mM CaCl₂, however, a one mass-percent addition of SAP resulted in up to a two orders-of-magnitude reduction in hydraulic conductivity when permeated with 50 mM CaCl₂. The use of non-crosslinked (i.e., non-super absorbent) polyacrylic acid was also investigated by permeation of granular mixtures of NaB and polyacrylic acid with 50 or 500 mM CaCl₂. When the weight-average-molecular weight of the polyacrylic acid additive was less than 1,080,000 g/mol, mass-percentage additions as low as 0.75% (the lowest mass fraction tested) resulted in a greater-than three orders-of-magnitude reduction in hydraulic conductivity to 50 mM CaCl₂. Granular mixing of polyacrylic acid did not improve hydraulic conductivity with 500 mM CaCl₂. Polyacrylic acid is hypothesized to clog hydraulically governing (intergranular) porosity.

Geosynthetic clay liners (GCLs) are factory manufactured barriers, typically consisting of sodium bentonite clay between two geotextiles. Because of their low hydraulic conductivity, GCLs are frequently used as a replacement for regulatory prescribed compacted clay liners. With their many benefits, GCLs have their limits. Several field studies have assessed the in-service performance of GCLs in landfill covers. In some cases, GCLs exhibited high in-service hydraulic conductivities as compared to initial preconstruction laboratory results. Past research has demonstrated that GCLs which undergo both wetting and drying cycles combined with cation exchange can experience increases in hydraulic conductivity over time. To prevent this, the current industry standard is to either test the adjacent soil for chemistry to evaluate compatibility, or to install an overlying synthetic membrane to prevent clay desiccation. This study exposed prototype polymer-modified GCLs to several wetting and drying cycles in a calcium solution, representative of aggressive landfill cover conditions. GCL samples were then tested for hydraulic performance, and results were compared to traditional GCLs that underwent the same conditions. This study demonstrated that certain polymer-modified GCLs can be a solution to offset the effects of desiccation and cation exchange.

Over 300 million tons of municipal solid waste (MSW) has been produced in China every year. So far landfilling has been the major form of disposal for the MSW and hazardous industrial solid wastes. Horizontal liner becomes the key barrier structure preventing contamination, which consumes large amount of clays and cause land and environmental problems. This paper investigates the feasibility of using solid waste as landfill liner material with laboratory experiments. Powdered coal gangue was studied. Hydraulic conductivity tests, batch adsorption tests, and column leaching tests were conducted to investigate the permeability coefficient and the adsorption performance against heavy metals and organic pollutant. The results show that the permeability coefficient could be as low as less than 10^-7 cm/s and meet the requirements of the applicable criterion, with good adsorption properties to ions of Pb, Cu, Zn, Ba, and several organic pollutants. The powdered coal gangue has shown good potential as landfill liner material.

Application of soil-water treatment sludge (WTS) mixtures in earth works may reduce land disposal of WTS and exploitation of natural soils. This paper includes the geotechnical characterization and properties of a WTS and a soil-WTS mixture. The sludge was collected in a water treatment plant that generates 60 tons per day of sludge with 20-25% of solids. The investigated soil was a lateritic clayey sand, representative of a significant area of the state of Sao Paulo, Brazil. Compaction curve, plastic and liquid limits, and specific gravity of solids were obtained for WTS, soil and mixture. WTS and soil were also subjected to chemical and mineralogical characterization by X-ray fluorescence and diffraction, respectively. Compaction parameters were determined at standard proctor energy, and one-dimensional consolidation tests were carried out on compacted specimens. Results indicate that the geotechnical characteristics of the mixture are slightly different from those of the soil, and previous air-drying affects the compaction parameters of the mixture: the maximum dry unit weight increased and the optimum water content decreased for lower initial water contents in the compaction tests. Compression index C_c of the mixture is higher than that of the soil, however acceptable for a compacted soil in geotechnical works.

Bentonite is widely used in contaminant resistant barriers, the primary problem with bentonite is its decreased chemical compatibility when reacting with high concentrations of inorganic solutions. To improve the chemical compatibility of bentonite and maintain its low hydraulic conductivity, two polymer (P1 and P2) additives are added to bentonites individually. In this study, the swell index (SI) and hydraulic conductivity to deionized water (k_w) and to CaCl₂ solutions (k_c) of polymer modified bentonite filter cakes (denoted BP1 and BP2) are measured and compared with traditional sodium bentonite. The results indicate that the performance of polymer modified bentonites is different from that of conventional sodium bentonite. Polymer modified bentonite #2 (BP2) displays the maximum free SI ratio, and the minimum increase of hydraulic conductivity. This demonstrates that P2 has superiority in maintaining relatively low hydraulic conductivity in calcium chloride solutions up to 60 mM. It is found that the hydraulic conductivity of BP2 maintains 10^-9 m/s though SI decreases sharply.

Hydraulic conductivity tests were conducted on two geosynthetic clay liners (GCLs) containing bentonite-polymer mixtures (BPMs) to investigate long-term hydraulic conductivity to coal combustion product (CCP) leachates. Permeant solution chemistries were synthesized to represent typical CCP leachate, predominantly divalent cation ash leachate, flue gas desulfurization residue leachate, high ionic strength leachate, and trona ash leachate. Hydraulic conductivity tests were conducted on non-prehydrated GCL specimens at an isotropic effective confining stress of 20 kPa in flexible-wall permeameters. Low hydraulic conductivities (<10^-11 m/s) were maintained for both of the BPM GCLs in each of the permeant solutions. In contrast with what is commonly observed for conventional sodium bentonite GCLs, hydraulic conductivity of the BPM GCLs did not vary systematically with ionic strength of the permeant solution. Hydraulic conductivity of the GCLs was also not related systematically to swell index or fluid loss of the BPM, suggesting that index test procedures commonly adopted as surrogates for hydraulic conductivity for conventional GCLs may not be applicable to GCLs with BPMs.

The paper presents the influence of alkaline alteration on shear characteristics of bentonite-sand mixture. The Ca-type bentonite and the bentonite-sand mixture were immersed in NaOH or Ca(OH)₂ solutions. Triaxial compression tests were executed using the immersed specimens. Mineral composition, leacheable cation and microstructure of the sample after the testing were investigated. Dissolution of minerals and precipitation of secondary materials by alkaline solutions changes shear strength. For the bentonite, dissolution of minerals significantly occurred, residual stress decreased, on the other hand, decrease in the residual stress in the bentonite-sand mixture was relatively small. The mixture of sand, remarkably, plays a role in controlling decrease in residual stress.

Fluid conduction in the soil liner materials in landfills and underground storage tanks are of critical importance for the confinement of landfill leachate and fuel leakage. Most commonly, clay alone or clay with amendments can be used as soil liner materials due to their low hydraulic conductivities. Previous research indicates conventional compacted clay liners tend to have less compatibility and retention capacity for organic liquids or liquids with non-polar solute. The objectives of this study were: to evaluate how various fractions of organobentonite amendments in the compacted silty clays can alter their permeability for pure water; and to quantify how organic permeant liquids properties (e.g. density, viscosity, polarity) can affect their conduction in compacted silty clay-organobentonite mixtures. The experimental results show that the hydraulic conductivity of compacted silty clay-organobentonite mixtures increases with the addition of the organobentonite fraction. Furthermore, the permeability of a mixture with 50% organobentonite decreases as the permeant liquid changes from water to methanol.

Bentonite-polymer mixtures (B-P) used in geosynthetic clay liners (GCLs) have been shown to maintain low hydraulic conductivity in aggressive (e.g., high ionic strength) permeant solutions detrimental to untreated sodium-bentonite (Na-B). While a number of hypotheses have been proposed, the underlying physical and chemical mechanisms for improved chemical compatibility and low hydraulic conductivity of B-P GCL remain poorly understood. This paper describes a suite of scanning electronic microscopy (SEM) analyses conducted to observe pore-scale structure of B-P hydrated with deionized water and saline solutions. Polymer observed in B-P exposed to deionized water had a remnant three-dimensional network structure, with polymer chains forming bridges among clay clusters and filling large voids in the inter-cluster pore space. Polymer observed in specimens exposed to 20 and 200 mM CaCl₂ solutions had a remnant contracted structure with less bonding to clay clusters and higher occurrence of open channels and potential flow paths. The SEM observations provide a basis to support conceptual frameworks establishing relations among pore fluid chemistry, bentonite fabric, polymer hydrogel, and macroscopic hydraulic conductivity of B-P.

Compacted clay soils are commonly used as landfill liners. This research work was aimed at investigating the suitability of sawdust amended lateritic clay as a landfill liner to adsorb Pb and Cd, thereby protecting underground water. Index properties, compaction, strength and permeability tests were conducted on the unstabilized and stabilized clay in order to determine the effects of the sawdust on the geotechnical properties of the lateritic clay. Batch kinetics tests were utilized to determine the capacity of the clay and sawdust-amended clay to adsorb Pb and Cd. The soil, classified as A-7-6 and CH by AASHTO and unified soil classification systems, respectively, was admixed with 0%, 5%, 10%, 20%, and 30% sawdust by dry weight of the soil. Test results show that the specific gravity, plasticity index, maximum dry unit weight and unconfined compressive strength of the soil decreased with increasing sawdust content while the optimum moisture content and hydraulic conductivity increased with increasing sawdust content. The stabilization of the lateritic clay with ≤10% sawdust content was recommended for use as landfill liners, as they meet the standard hydraulic conductivity requirement and present a good adsorption of Pb and Cd.

In this study, soil-water characteristic curves (SWCCs) for lateritic soil treated with up to 10% bentonite content developed as liner for landfills were measured in the laboratory by sequential desorption of saturated soil mixtures using pressure plate extractors. Test specimens were compacted using standard Proctor (SP), West African standard (WAS), an intermediate effort commonly used in the region and modified Proctor (MP) over a range of moisture contents (2% dry of optimum, optimum and 2% wet of optimum). The experimental SWCC data were fit to the van Genuchten equation for the water content–pore water suction relationship. Analysis of test data indicate that greater air entry suctions were obtained for soil mixtures with higher bentonite content and when compacted at wet of optimum water content or greater compactive effort. It was however observed that the changes in compactive effort proved more influential than water content.

Polymer-modified bentonites have been introduced in recent years to improve the chemical compatibility and performance of hydraulic barrier systems (e.g., geosynthetic clay liners) permeated with aggressive leachates. Laboratory experiments were conducted using a rotational torque viscometer to determine the viscosity of pure polymer and polymer-bentonite mixtures in suspension with saline solutions. Viscosity depends on the polymer-to-bentonite ratio, ionic strength, and anion and cation species. The bentonite fraction controls viscosity at polymer-to-bentonite ratios radi about 5% by mass. Polymer fraction controls viscosity at ratios approaching 10%. Low viscosity is interpreted to reflect a coiled polymer conformation, less effective hydrogel formation, and less effective bridging between polymer and clay units. Ongoing research is establishing potential links between the viscosity of polymer-bentonite suspensions and hydraulic performance of polymer-modified barrier systems in aggressive permeant solutions.

Water vapor sorption behavior of clays gives valuable information on mineralogy and surface properties, and consequently on macro-scale engineering behavior of clays. Sorption isotherms can also indicate functional groups in polymers, and therefore their hydrated behavior. This paper evaluates the water vapor sorption behavior of polymer-modified bentonites prepared to be representative of materials used in composite systems for hydraulic barrier applications. Bentonite-polymer (B-P) mixtures were dry-mixed in mass-controlled ratios denoted by their respective polymer content (P) (0% P, 2% P, 4% P, 6% P, and 100% P). Hysteretic water vapor sorption isotherms for pure polymer, pure bentonite, and the B-P mixtures were obtained along adsorption and desorption paths using a dynamic water vapor sorption analyzer. Isotherms for bentonite-rich (≤ 6% polymer) mixtures at relative humidity (RH) less than about 70% are essentially identical to the bentonite end-member, suggesting that the bentonite fraction dominates the initial sorption response. At RH greater than 70%, adsorbed water content systematically increases with increasing polymer fraction.

Geosynthetic clay liners (GCLs) are widely used to isolate pollutants because of their low hydraulic conductivity to water. However, the performance of clay barriers may be impaired by prolonged exposure to electrolytic liquids which may lead to the compression of the diffuse double layer. The consequences are the increase of permeability and the loss of self-healing capacity. Moreover, the efficiency of the liners can further deteriorate by repeated wet and dry cycles, which may lead to desiccation of the bentonite and associated cracking. Modified bentonites have been introduced to improve the resistance of clay barriers to aggressive solutions. This study deals with a polymer-amended clay, HYPER clay. HYPER clay is treated with an anionic polymer and dehydrated and it shows enhanced performance in presence of electrolyte solutions. The effect of wet and dry cycles on the hydraulic conductivity to seawater of needle-punched GCLs prototypes of treated and untreated bentonite was investigated. The prototype samples containing HYPER clay 8% showed lower permeability compared to those containing untreated bentonite. However, the temperature suggested from the standard used in this study is extremely high and it does not represent the temperature in the field.

Soil-bentonite backfills (SBB) have been widely used in geotechnical engineering applications to control the migration of contaminants in the subsurface. As an essential parameter, the compressive modulus (E_s) impacts the stress-state behavior of the consolidated backfills, which influences hydraulic conductivity. It is therefore important to estimate the E_s value of cutoff wall in landfill site. The compressibility of SBB is characterized by piezocone penetration tests (CPTU). In this study, a landfill site in Jiangsu Province of China was selected to predict the compressive modulus of SBB. Nine CPTU soundings were carried out at different locations in cutoff wall. Based on the CPTU data, the compressive modulus can be calculated using different methods. The values of E_s were then compared with the results of high-quality laboratory tests and they correlated well. This study confirms the potential for use of CPTU to obtain valid predictions for compressive modulus of soils in cutoff wall.

Soil-bentonite (SB) vertical cutoff walls composed of sandy soil and Na-bentonite (NaB) are commonly used as in-situ engineered barriers for the containment of groundwater contamination. In countries where high quality NaB is scarce, commonly available Ca-bentonite (CaB) is considered as an alternate material for use. However, CaB exhibits lower swelling capacity than that of NaB, leading to unacceptable higher hydraulic conductivity, k, of soil-CaB backfills. The purpose of this study is to investigate phosphate dispersant additive to decrease hydraulic conductivity of soil-CaB backfills. A series of viscosity, density, and filtrate loss tests are conducted using phosphate dispersant amended/un-amended CaB-tap water slurries to determine the optimal phosphate dispersant dosage. Subsequently, slump and flexible-wall hydraulic conductivity experiments are conducted using backfills consisting of sand and amended/un-amended CaB. The results show that k values of un-amended soil-CaB backfills are higher than typically required hydraulic conductivity of 10^-9 m/s for backfill in vertical cutoff walls. In contrast, amended soil-CaB backfill can possess k of 8.3×10^-10 m/s to 2.7×10^-10 m/s, which is lower than 10^-9 m/s. This study demonstrates that phosphate dispersant is a potential amendment for achieving low hydraulic conductivity sand/CaB backfills in SB cutoff walls.

Soil-bentonite slurry trench cutoff walls are the most common type of vertical cutoff walls used in the US. The hydraulic conductivity of bentonite slurry wall backfill is typically required to be equal to or below 1x10^-7cm/s. Backfill is made by mixing excavated and/or borrow soils with bentonite slurry and, as needed, additional dry bentonite. Publications have provided guidance for mix designs to achieve the desired characteristic of low hydraulic conductivity. Previously, no systematic studies have been undertaken to investigate the hydraulic conductivity of soil-bentonite slurry wall backfill formulated with different grain size distributions and bentonite contents all as a function of stress. This paper describes the results of studies undertaken to evaluate the effects of grain size distribution, bentonite content and effective stress on the hydraulic conductivity of soil bentonite slurry trench cutoff wall backfill. Three base soils were used representing a range of fines content for soils found on typical construction projects along with four bentonite contents for each base soil. The hydraulic conductivity was measured in consolidometers adapted for falling head permeability tests at the end of each load increment. These experiments yielded the relationships between effective stress and hydraulic conductivity and allowed examination of the influence of base soil characteristics and bentonite content. In summary, a decrease in hydraulic conductivity due to increasing stress is evident for all base soils and for all dry bentonite contents except for the low fines content with 0% dry bentonite which showed hydraulic conductivity to be independent of stress. Increasing the dry bentonite content resulted in a decreased hydraulic conductivity at all stress levels and for all base soil fines contents. Increasing the fines content of the base soil from low to medium decreased hydraulic conductivity regardless of stress or dry bentonite content. However, a further increase from medium to high fines content base soil showed little additional benefit from the additional fines.

Microbially induced calcite precipitation (MICP) is a bio-geochemical process that induces urea hydrolysis and the resulting calcium carbonate precipitation by ureolytic bacteria within porous media matrixes, including but not limited to soil, concrete and rocks. MICP has been widely studied over the past decade for its potential applications in cementation of porous media, hydraulic control, and environmental remediation. Preventing unwanted fluid or gas migration via fracture networks in low-permeability formations (e.g. fractured rocks) is one of the priorities in many of the engineering applications. For example, it is necessary to properly seal the host and cap rocks for subsurface containment of captured CO₂, and it is critical to seal the access shafts while constructing nuclear waste disposal facilities. MICP offers an attractive alternative to traditional grouting technologies due to its advantages as a low viscosity and low-pressure technique. The success of MICP implementation for rock fracture sealing and permeability reduction needs to be comprehensively investigated. This study reports encouraging results from preliminary experiments conducted on artificially fractured sandstone specimen, suggesting permeability reductions as high as 80% after being treated with MICP method. Visual inspection of micro x-ray CT images revealed evidence of precipitation, in particular at sections closed to the top and bottom of the specimen.

This study presents a series of modified fluid loss tests to investigate the hydraulic conductivity of bentonite filter cakes when exposed to heavy metals. Both high quality calcium-bentonite and natural sodium-bentonite are used in this study. Lead-cadmium (Pb-Cd) mixture and hexavalent chromium (Cr(VI)) are selected as representative heavy metal contaminants that are commonly found in contaminated groundwater. Total metal concentrations in bentonite-chemical liquid slurry range from 0 to 15 mmol/L. The result shows that the hydraulic conductivities of bentonite filter cake formed by bentonite-water slurry range from 1.1×10^-11 m/s to 3×10^-10 m/s, which are 3 to 90 times lower than the commonly used value for the slurry-trench wall backfills (10^-9 m/s). Hydraulic conductivity increases with an increase in Pb-Cd concentration. In contrast, the impact of Cr(VI) contamination on the hydraulic conductivity is insignificant, and the hydraulic conductivity shows a maximum of 2.3 times increase when target Cr(VI) concentration increases to 15 mmol/L. The result is due to the different chemical species of lead, cadmium, and chromium that exist in bentonite-chemical liquid slurry.

The effectiveness of containment of coal combustion residual (CCR) impacted groundwater using soil-bentonite (SB) cutoff wall was evaluated in this study. First, the slurry tests were performed with bentonite-water slurries prepared with tap water, simulated groundwater, and CCR impacted groundwater to investigate potential use of different types of in-situ water for preparing the slurry. Next, the free swell, liquid limit, flexible wall permeability, and one-dimensional consolidation tests were conducted to evaluate chemical compatibility of soil-bentonite backfills with contaminated groundwater. The results indicated that CCR impacted groundwater had little impact on slurry properties, as well as basic engineering properties of the backfill materials. For example, the liquid limit and swell index of the bentonite tested with tap water were 411.8% and 26 mL/2g, respectively; while that for bentonite tested with CCR impacted groundwater were 375.5% and 30 mL/2g, respectively. The hydraulic conductivity, k, for backfill permeated with tap water was 4.2×10^-10 m/s, whereas that based on CCR impacted groundwater was 3.5×10^-10 m/s. Similarly, the compression and swell indices for backfill prepared with tap water were 0.15 and 0.017, which was close to that for backfill prepared with CCR impacted groundwater. The results of the study suggest that SB cutoff walls have potential to be an effective containment system for coal ash disposal site groundwater.

Filter press tests are widely used for field quality control of bentonite slurry in slurry trench excavations and often are incorporated in technical specifications for assessing filtrate properties of initial (freshly mixed) slurry and occasionally for in-trench slurry. In some cases, the results of filter press tests conducted on in-trench slurry are directly or indirectly used to assess the hydraulic performance of the cutoff wall. However, specifications for maximum filtrate loss from filter press testing of in-trench slurry can result in unnecessary construction delays and costs. The authors examine the reasons for specifying filtrate parameters for slurry and present the results of filter press tests conducted on lab and field samples to evaluate the utility of filtrate loss as an appropriate quality control measure for soil-bentonite cutoff walls. These results show no evidence to support that excessive filtrate loss of in-trench slurry (i.e., above the maximum value employed in typical specifications) compromises trench stability or contributes to an overall higher permeability of the completed vertical barrier. Higher in-trench filtrate loss is associated with higher sand content, which results in higher slurry density and improved trench stability. Furthermore, the permeability of all filter cake specimens created in this study from in-trench slurries with sand contents as high as 35 percent were less than 10^-7 cm/s, which is the lowest target permeability typically specified for soil-bentonite cutoff wall backfill in hydraulic or geoenvironmental containment applications. The authors do not recommend using filtrate loss of in-trench slurry as a quality control parameter for assessing the effectiveness of slurry trench cutoff walls.

In the reliability analysis of earth slopes considering spatial variability of soil, the few models of discretization of random fields into finite random variables, available in the literature, have certain shortcomings. This paper presents a newly developed discretization model which is free from most of the shortcomings of the existing models. The developed discretization model has been incorporated in a computational scheme for slope reliability analysis based on the first order reliability method (FORM) in conjunction with the Spencer method of slices valid for limit equilibrium analysis of general slip surfaces. To elucidate the entire computational procedure as well as to examine the efficacy of the new discretization model, the safety of the Cannon Dam, USA, has been re-analysed. The results of reliability analyses have revealed that the proposed model yields the lowest value of the reliability index among all the models used in the analysis. Using the proposed model, a parametric study on the variations of the reliability index with the variations of magnitudes of the scales of fluctuation has also been carried out and reported.

Accurately calculating earth pressure acting on retaining wall from fillings is the key to ensure the safety of retaining wall design. Although Coulomb earth pressure theory has been widely used for many years, inevitably it has some shortcomings. Embankment fillings are layered and limited in road construction. Based on the assumption of movement associated flow rule, for the movement mode of translation, formula of active earth pressure acting on retaining wall from semi-infinite two-layered backfills was obtained by using the method of level-layer analysis. For two-layered and limited backfills embankment, taking the effects of bedrock excavation faces into consideration, calculation analysis of active earth pressure acting on retaining wall was carried out in different cases. By an example, feasibility of this method had been validated.

Earthquakes are one of the most serious natural calamities that can induce failures of slopes such as landslides and dam breaks. Therefore, it is an important research topic to evaluate the co-seismic stability level of soil slopes. Such a method should be based on a thorough understanding of the progressive failure process of soil slopes. A few centrifuge model tests were conducted to investigate the progressive failure behavior of slopes. The load and top settlement of the slope were measured using a load transducer and a laser displacement sensor, respectively. An image-based displacement measurement system was used to record the images of the slope and accordingly determine the displacement field of the slope during loading. The deformation and the failure process of slopes were examined according to the measurement results.

The shear strength properties of municipal solid waste (MSW) are of special importance when evaluating the stability of landfill slopes. Geoenvironmental engineers are well aware of the existence of many sources of uncertainties associated with shear strength parameters of MSW due to various reasons. The significant uncertainties associated with the shear strength and shear stresses render deterministic modeling potentially misleading. The traditional engineering approaches like method of slices used for evaluating MSW slopes are frequently questionable as they do not adequately account for uncertainties included in analytical modeling and natural variability. In order to quantify the slope stability precisely by taking into account the variability, the reliability based design optimization (RBDO) framework is presented. The mean and standard deviations associated with unit weight, cohesion and angle of internal friction of the MSW are taken into account in the probabilistic optimization. Reliability analysis is performed using first order reliability method (FORM). A limit state function is formulated against sliding slope failure using Spencer method of slices. The influence of coefficients of variation (COV) of stability number and friction angle on critical center coordinates and reliability index is presented in the form of charts.

Hill areas in northern India are developing at a rapid pace, resulting in construction of multi-storeyed buildings on hill slopes in large numbers, in spite of unfavourable conditions for construction. The buildings transmit their load to the hill slope through foundations. It results in increase in shear stress, which may cause instability of hill slopes, when exceeding the shear strength of the soil. The present study is focused on stability of hill slopes subjected to foundation loads. The investigation reveals that the foundation can cause either a local failure, or an overall instability of hill slope, or a mixed failure involving both the modes. The maximum foundation loads representing the number of storeys in the building, which can be sustained by slopes of different inclination angles, and the effect of foundation width and location, are discussed.

Design and construction of highway and railroad embankments across the Chicago/Calumet Lacustrine Plain must often tackle challenges related to excessive total and differential settlements due to the presence of compressible clays and/or uncontrolled fill. Engineering works related to the extension of the Gary-Chicago International Airport runways required relocation of a rail line and construction of an embankment section over a former sand pit dug out through Holocene-age beach deposits in the early 1900s. By 1990s the 6.6-acre site included about 275,000 cubic meters of solid waste—foundry sand, incinerator ash, slag, and auto and demolition debris—indiscriminately placed below and above the water table without compaction control. The uncontrolled fill material was dynamically compacted to meet strict settlement tolerances. The design characteristics and performance verification of the ground improvement are presented in this paper.

The soil tends to be evaluated as a homogeneous material and rocks as solid or continuous media. However, there has always been a great uncertainty when evaluating materials with a high degree of heterogeneity; such materials are referred as bimrocks. In this paper the implementation of multiscale numerical modeling is shown for the study of materials with discontinuous nature. Triaxial tests using DEM were developed, where the resistance variation parameter, according to the block volumetric proportion (BVP) and the blocks shape was shown. Slopes in FEM were modeled with the inclusion of individual blocks and compared with limit equilibrium slope analysis using parameters from homogenized resistance. It was established that it is possible to define the parameters of homogenized resistance as dependent exponential functions of the surface area ratio of the blocks. It was showed a decreasing friction angle trend as the sphericity of the blocks decreased, in addition to conventional friction angle increase and decrease in cohesion with increasing volume ratio of blocks. A comparison of the factor of safety obtained by finite elements and limit equilibrium is performed. Finally, the need of a multiscale approach for heterogeneous materials analysis is established.

Landfill stability is one of the most important concerns in the landfill design and operation. Several slope failures in the past decade highlight the need for the detailed analysis of landfill stability. These failures are attributed to reasons such as heterogeneous composition, improper evaluation of shear strength parameters and the effects of mechanical creep and biodegradation on strength response as well as non-consideration of material variability issues. MSW properties vary due to heterogeneous nature, overburden pressure, and degradation. This heterogeneity and uncertainty in MSW characteristics makes the analysis and design of landfills complicated. In the present study, stability as well as deformation of a typical lined landfill is analyzed using the Mohr Coulomb model for MSW, implemented in FLAC2D. The objective is to demonstrate the influence of variability in strength and stiffness parameters on stability of MSW landfill slopes. To capture the effect of variability, response surface method (RSM) is used in conjunction with Mohr-Coulomb model to develop multi-linear relationships among all the design variables. The influence of variation of unit weight with depth on stability analysis of landfill systems has been particularly studied and discussed. Results show that reliability index decreases with increase in variability of parameters and consideration of unit weight variation with depth provides more reliable estimates of factor of safety and deformations.

This paper reports a series of laboratory model tests conducted on homogeneous unreinforced and reinforced fly ash slopes under uniformly distributed loading (UDL) and strip loading with slope angle 60 degree overlaying fly ash bed. The construction industry is making an attempt to become sustainable because production of fly ash is likely to be increase. In order to minimize the amount of fly ash to be disposed without causing environment pollution hence fly ash to be used as backfill material. The rectangular steel reinforcements having grid thickness 1.2 mm with square openings of 15 mm were placed along the width of the slope in continuous form (coverage ratio = 1) as well as coverage ratio of 0.6. The coverage ratio is defined as the ratio of gross width of reinforcement strip to the center-to-center horizontal spacing between the strips. For all the cases, length of the reinforcement was varied as 0.6H and 0.7H (H = Height of the slope). Test results indicate improved load carrying capacity along with better stability of slope with increase in the length of steel grid for all cases. Finite element analysis (FEM) was also carried out for numerical simulation in finite element based software PLAXIS 3D. The numerical results show reasonable agreement with the experimental study.

One of the most frequently occurring geo-environmental problems around the world is rainfall-induced slope failures. A good understanding of unsaturated soil mechanics (i.e. soil-water characteristic curve and unsaturated shear strength) is required for the analyses of rainfall-induced slope failure mechanisms. Rainfall-induced slope failures are commonly observed in residual soils. Some of the residual soils show bimodal characteristics in their grain-size distribution, called gap-graded soils. The results of the soil-water characteristic curve (SWCC) tests demonstrated that gap-graded soils may exhibit either unimodal or bimodal SWCC depending on the dry density and the water content of the soil. This paper focuses on the unsaturated shear strength characteristics of soils with bimodal SWCC, called dual porosity soils. The results from the unsaturated shear strength tests indicate that the characteristics of ϕ^b angle of dual porosity soil are different from those of soils with unimodal SWCC at matric suctions beyond the air-entry value. For dual porosity soils, the desaturation process occurs first within the macro pores of soil while the micro pores of soil are still saturated at suctions between first and second air-entry values. Air starts to enter the micro pores of the soil at suctions beyond the second air-entry value.

This paper discusses the results of study conducted on sand column constructed in soft expansive clay. The length to diameter ratio (L/d ratio) of the sand column was varied, from 2 to 10 with an interval of two. Floating sand column encased with geogrid were also formed in the soil. The load tests were carried on a circular footing placed over the sand column to study the load settlement behavior in the two cases of floating sand column; the one with ordinary sand columns and the other with geogrid wrapped sand column. The soil beds were prepared in a model tank of diameter 173 mm and height 605 mm. The sand column of diameter 55 mm was constructed at the center of the soil bed. A load test on the footing placed directly on the soft soil bed was also conducted to compare the results of load tests of sand column and geogrid encased sand column. The improvement in load carrying capacity of sand column was expressed as a non dimensional parameter, improvement ratio (IR), which is the ratio of ultimate load carried by the footing on sand column (Qult. column) to that obtained for unreinforced soil i.e. Q. It is found that IR increases with L/d ratios up to 8 then the increment is marginal.

The author was engaged to review three projects where either settlement or instability had occurred thereby resulting in costly repair operations. The problems arose for a number of reasons including an oversight where geotechnical issues were not properly addressed or overlooked, extending the state of the practice beyond proven techniques without adequate confirmation, and less than acceptable monitoring during construction. Case 1 involved an attempt to achieve ground improvement of buried weak deposits below deep fill by dynamic compaction without consideration of the depth of improvement achieved and the compressibility of the underlying deposits. Another example includes the improper use of dynamic compaction to densify fill deposits containing large portions of lumber. Case 2 involves a residential structure supported upon compacted silty clay fill that is on the order of 4.6 m thick under one portion of the building with only a shallow fill under the other portion. Differential settlements resulted in cracking in the structure and the floor slab and the need for underpinning. Case 3 involves an excavation for a future landfill through over consolidated clayey glacial till soil with a compacted clay liner on the slope face. During construction, a number of shallow sliding surfaces developed resulting in the need for removal of the clay liner, providing adequate drainage discharge, and reconstruction of the slope face.

National Exhibition and Convention Center (NECC) is the largest single block building and exhibition complex constructed with large span structures in the world. The NECC, which has a footprint of more than 0.86 million square meters, involves nearly 0.35 million square meters ground improvement work. Depending on the soil properties, adjacent environmental condition, types of foundations, and floor loading as well as stress histories, different ground improvement techniques were adopted. Rigid pile composite foundation with a large pile spacing was adopted on huge indoor exhibition buildings for the first time in China, while the outdoor exhibition venues were improved by preloading. Considering the overconsolidation stress history and small floor loading, only soil replacement technique was adopted for the 35 kPa working load area. The monitoring results agree well with the calculated values. The ground achieved adequate overall bearing capacities as designed and the estimated ultimate ground settlement are within accepted values.

Four soils, three low plasticity clays and one high plasticity silt, were treated with a chemical admixture that creates a hydrophobic composite material when mixed with soil. Specimens were subjected to cycles of wetting and drying to assess durability. Volume change, water content, and mass loss were studied over the course of up to four wetting and drying cycles. Unconfined compression tests were performed to evaluate changes in modulus and strength following each wetting and drying cycle. From the results, there is some measurable volume expansion (<3% in all cases) and mass loss (<3.5%) when submerged in water even though the soil is treated to create a hydrophobic composite material. Increases in strength were observed after 1 and 2 cycles of wetting and drying for three of the treated soils. With additional cycling, the strength and moduli decreased. Compared to untreated specimens, specimens treated with the chemical admixture had greater volumetric stability, less soil mass loss, and for the three low plasticity clays, had a higher maximum stress and a larger modulus.

This study was performed to show the effects of incorporating different sizes and different percentages of shredded rubber tire into the local soil found in Memphis, TN and the surrounding area. Approximately 300 million tires are disposed of each year in the United States, which has led to significant environmental concerns all over the nation. As a remediation to this negative environmental impact, the geotechnical engineering community has been working to use rubber tires in soil modification projects to improve the engineering properties of soils. In this study, compaction and permeability tests are performed on brown loess, the primary soil found in the Memphis, TN area. To gain insight on the use of shredded rubber tire as a fill material, varying percentages of different mesh sizes of shredded rubber tire are mixed with the local loess to form a basis of comparison. Results are presented that show the effect of different amounts and sizes of shredded rubber tire on the engineering properties of Memphis loess. The maximum dry unit weight of the soil/tire mixture decreased as more shredded tire was added yet the optimum moisture content remained relatively unchanged. The permeability of the soil/tire mixture also saw an increase as the percentage of tire increased.

The encased stone column technique is a sustainable, energy saving and geoenvironment friendly effective alternative approach to the conventional reinforced concrete pile foundations. Geosynthetic materials are generally suited as encasements owing to the excellent tensile properties enabling those to produce sufficient circumferential stress around the column and prevent the bulging failure in very soft soil having undrained shear strength below 12-15 kPa. Different types of geotextiles and geogrids of different tensile stiffness are used as the encasement material. Encased stone columns are easy to install as well as cost of the project gets enormously reduced. This study focuses on the influence of encasement stiffness and its varying lengths to the stone column behaviour through numerical modelling of a floating encased stone column installed in very soft soil of undrained shear strength 6 kPa. Results indicated enhanced capacity of the stone column with increase in encasement stiffness. Also with increase in encasement length, the column capacity increases. Providing a partial encasement length, four times the column diameter, improved capacity around 2.25 times that over only stone column was achieved at a settlement 12% of footing width. Providing an encasement of adequate length and stiffness, around three folds enhanced capacity was achieved compared to that of only stone column. Small scale model tests were also performed on encased stone column in laboratory and the same were modelled in the finite element software for validation purpose. The finite element results were found in good agreement with the experiment results.

The fatigue characteristic of a lightly stabilized granular material under traffic loading is an important consideration for the design of a pavement containing such material. This paper presents the evaluation of fatigue behavior of lightly stabilised granular materials using flexural and indirect diametral tensile (IDT) testing. The experimental program included cyclic load flexural and IDT testing to determine the fatigue life of a typical granular material stabilized lightly with 1-3% cement-flyash. Fatigue life was estimated using the approach of approximate energy ratio method and empirical relationships were proposed to relate the fatigue life with tensile strain similar to that proposed in the literature. Details of the experimental investigation, the analysis carried out to determine the fatigue life of the lightly stabilized granular material and comparisons of fatigue characteristics determined from two test methods are discussed in the paper.

The interaction of ions (calcium, alumina, silica, and sulfate) in the presence of water is very complex to indentify, and hence, to predict the behaviour of soil. An attempt has been made to understand the mineralogical and micro–structural changes due to soil–lime–gypsum reactions. Further, the associated mechanisms behind changes in the properties of lime treated gypseous soil with fly ash are presented. A series of experimental works are performed to find out the compaction characteristics, strength and swell behaviour of lime treated soil with gypsum and fly ash. The samples collected after completion of experimental works are used for micro–analysis (X–ray diffraction and scanning electron microscope). The results show that use of fly ash enhances the strength of lime treated gypseous soil by 1.92 folds. Also, the rapid swell, which is observed in gypseous soil with lime treatment, is reduced by 33% after using fly ash. The micro–analysis confirms that formations of cementitious compounds such as calcium silicate hydrate (CSH), calcium aluminum oxide hydrate (CAOH), calcium aluminum silicate hydroxide hydrate (CASHH) and ettringite needles lead to change in the geotechnical properties of soil. Further, it has been found that availability of water influences significantly on the formation of ettringite minerals and, thereby subsequent changes in properties of soil.

In underground spaces under high water pressure, the need to seal the periphery and face of the working environment and establish a stable front is a challenging issue. One method of creating a stable working front and sealing it against underground water pressure is ground freezing. In this study, application of a freezing method for underground space utilization is investigated. A case study related to part of a comprehensive underground expansion project in a Tokyo suburb is considered. Construction includes a junction of a main tunnel with a rampway that connects the underground tunnel route to the ground surface. At this construction site, the segment connecting the main route and rampway needs to be widened. Because of this enlargement and sequence of tasks below the water table, a temporary stable working front and hydraulically waterproof zone are necessary. As an effective method of ground improvement, freezing is used. Ground behavior around the underground expanded periphery and on the greenfield level due to freezing and thawing action is predicted, and a parametric study of the effect of the surrounding soil stiffness on the freezing behavior is conducted. Additionally, the closing time between freezing pipes is also predicted.

Property owners along the Houston ship channel have been developing dredge spoil disposal sites for use as tank farms and industrial facilities. The undocumented dredge spoils, obtained during channel maintenance operations, are not compacted and highly variable materials which are not suitable for foundation support. Ground improvement systems, such as deep soil mix columns and stone columns, have been successfully used throughout the Gulf Coast region to improve unsuitable dredge spoils and weak soils for tank and foundation support. The following paper presents a case history review of the hydrotest performance of fourteen new storage tanks constructed on a dredge spoil disposal site located near the inlet of the ship channel. Both stone column and deep soil mix ground improvement systems were utilized at the site due to the highly variable subsurface conditions encountered at each tank location. Field verification testing, data acquisition monitoring, and modulus testing (stone columns only) were utilized prior to and during construction to confirm design assumptions and settlement predictions. Perimeter settlements were also recorded during the tank hydrotests to compare with the predicted tank settlements, and allowed a direct comparison of the performance of the stone column and deep soil mix column ground improvement systems.

Carbonation using reactive MgO is employed for treating soft soils, which has received attention in the ground improvement as an innovative technology. This manuscript studies the influence of initial water content on engineering properties of carbonated soil admixed with reactive MgO, including physicochemical and strength characteristics. The natural silty soils treated with reactive MgO (20%) and different water contents (from 15% to 30%) were carbonized by carbon dioxide (CO₂). Afterwards, their physicochemical properties and unconfined compression strengths were measured. Moreover, the scanning electron microscopy (SEM) was conducted to explore the mechanism. The results show that the reactive MgO-admixed soil can consume some CO₂ and water; the unconfined compressive strength decreases with increasing initial water content and achieves the strength of cement-treated soils (28 days) due to the formations of carbonation products.

The use of sand or gravel column which is generally called a stone column is an effective method in modifying soil in order to increasing the bearing capacity or decreasing soil settlement and reduction of soil liquefaction in the earthquake. In stone column construction, usually 15 to 35 percent of weak soil volume is replaced with stone column material. In most equations of stone columns design it is used of the unit cells concept to model granular columns and surrounding soft soil. Laboratory study was conducted to better understand the reinforcing impact of sand column in the fine soil on stress strain behavior and shear strength of soft soil. The laboratory experiment consisted of series of the triaxial tests with a diameter of 100 mm and height of 200 mm. to simulate the effect of soil reinforcing, sand column with diameter of 37.5 and 51 mm was introduced in the center of the soft soil. The results indicate that by using of sand column the shear strength of fine soil has increased substantially. The results also showed increasing the diameter and confining pressure increases the shear strength of the soft soil reinforced by sand column. Details of tests including testing methods and results of the experiments and description of diagrams are provided in the original paper.

Cementitous grout is often used in permeation grouting applications, such as in seepage cutoff. However, ordinary Portland cement can be ineffective for permeation grouting of fine-grained sands or in sands with significant amounts of fines. Ultrafine cement grout thus becomes a viable alternative material for grout applications in these types of soils. While a major benefit of ultrafine grout is its penetration ability into the soils with relatively low hydraulic conductivity, the strength of the ultrafine grouted soil mass is not thoroughly discussed in literature. This study investigated initial conditions that could affect grout application effectiveness. An apparatus was developed so that a controlled volume of grout could be injected into a soil specimen. This study found that increases in water-to-cement ratio have a significant effect on the unconfined compressive strength of the neat grout. Grout penetration rates through the samples decreased as matric suction increased. The observed grout penetration rates were observed to be an inverse function of the unsaturated hydraulic conductivity. Also, the strength of the grouted sand was observed to increase as the matric suction increased. The results of this study suggest that knowledge of matric suction may be useful for estimating injection penetration rates and strength of ultrafine grouted sand.

Prestressing the geosynthetics offers a very quick and safe method of improving the poor ground conditions. This paper aims to find out the effect of prestressing the geogrid layer and the effect of adjacency of footing for unreinforced (UR), geogrid reinforced (GR) and prestressed geogrid reinforced (PGR) soil on the load bearing pressure and the settlement characteristics by using the software PLAXIS 3D. The PGR soil has enhanced the bearing pressure of the UR soil by almost 500 % and reduced the settlement by almost 88 % whereas the bearing pressure has increased 200 w.r.t. conventional GR soil and the settlement has reduced by 67%. The zone of influence has also gone up by 67 % for PGR soil w.r.t. UR soil and 25% w.r.t GR soil.

Vacuum preloading is a typical method used to induce consolidation settlement in clayey soils prior to construction. Vacuum pressure is used to increase effective stress in soil by decreasing the pore water pressure. This is in contrast to traditional surcharge loading, which increases effective stress by increasing the total stress on the soil. This mechanism of increasing the effective stress without increasing the total stress makes vacuum preloading a safer option if shear failure is a concern when working on very weak soil. This paper presents a numerical model for large strain consolidation under combined vacuum and surcharge preloading. The model is based on a readily-available radial consolidation model, known as RCS1, which is able to account for vertical and radial flow, soil self-weight, unload/reload effects, time-dependent loading, hydraulic conductivity anisotropy, soil smear, and partial prefabricated vertical drain (PVD) penetration. Additional capabilities of vacuum-induced consolidation are added to the original RCS1 to consider combined vacuum and surcharge loading. The developed model is utilized to simulate a well-published case history of combined vacuum and surcharge preloading at the Second Bangkok International Airport under flexible and rigid surcharge loading conditions. Good agreement is observed between the simulated and recorded settlement vs. time and excess pore pressure vs. time.

A series of plate load tests have been carried out on a square footing 30cm x 30cm resting on waste tire fiber reinforced sand in a tank of size 1.5m x 1.5m x 1.5m to investigate improvement in bearing capacity and reduction in settlement. The granular soil was reinforced with fiber contents of 0.25%, 0.50%, 0.75%, and 1.0% by weight of thickness of reinforced layer at relative densities (RD) 50%, 60%, 70%, 80%, and 90%. Thickness of reinforced layer was kept as 1.5B (B is the width of the footing). The aspect ratio of the fiber used was 22.5. It has been observed that bearing capacity improved at all the fiber contents. Maximum improvement in bearing capacity and reduction in settlements in terms bearing capacity ratio (BCR) and settlement reduction factor (SRF), has been achieved at fiber content 0.75%. The study signifies the use of non polymeric inclusions from recycled waste tires in geotechnical engineering in place of polymeric inclusions.

A FORTRAN based first-order reliability program was employed to evaluate the suitability of tropical black clay (black cotton soil, BCS) - iron ore tailings (IOT) mixture compacted with British Standard light, BSL or standard Proctor (relative compaction = 100%) energy as road pavement sub-base material..Using regression models for compaction characteristics, and established distributions for the relevant soil parameters, reliability indices were computed. The results indicate that for the laboratory-based model, reliability index is sensitive to variability in all the soil parameters. Observed trends indicate that IOT content, silt content, sand content and specific gravity are greatly influenced by the coefficient of variation (COV) and therefore must be strictly controlled in IOT treated BCS for use as sub-base material. Clay content has little effect. Stochastically, the compactive effort used did not produce acceptable safety index value. Therefore, higher compaction energy and more potent additives such as cement or lime are recommended to model compaction characteristics of BCS-IOT mixtures for use as sub-base material in road pavement.

Determination of swell potential is important for geotechnical and geo-environmental designs involving expansive soils. A new soil water retention based methodology is proposed for qualitatively classifying the swell potential of soils. The method is based on the expansibility coefficient (EC) of soils which quantifies the hysteric behavior of specific moisture capacity curve due to the crystalline swelling. The criteria for classification of soil expansibility based on EC index are established by calibrating measurements with other existing methods. Swell potentials of a suite of soil samples ranging from non-expansive to expansive are characterized using different methods for comparison. The EC results show that the proposed methodology can capture the effect of different factors on swell potential, particularly the type of exchangeable cation.

Dispersive soils are exceptional clayey soils which exhibit erosive behavior and known as vulnerable to severe erosion failure, even in quiet water. These soils can be chemically stabilized using various additives such as fly ash, lime, cement, pozzolans, and polymers. Among them, the stabilizing mechanism and characteristics of black coal fly ash has been studied by various researchers. However, in Australia a unique type of brown coal fly ash is produced as a solid waste by the power stations located in Latrobe valley, situated approximately 150 km from Melbourne in Victoria. These brown coal fly ashes are comparatively low in self-cementing characteristics than the black coal fly ash. In this paper, the influence of brown coal fly ash produced from Hazelwood power station on stabilizing dispersive soil found in Hazelwood mine is investigated. The Hazelwood brown coal fly ash is typically high in calcium sulphate, calcium oxide and magnesium oxide. In addition, the hydrated lime was added as a secondary binder to the brown coal fly ash and the combined effect of these two binders on stabilizing dispersive soil was studied. Here the effect of various proportions of Brown coal fly ash and hydrated lime on the rate of erosion, compressive strength, and compaction are discussed. The erosion rate was evaluated using the pinhole test and the crumb test while the compressive strength was evaluated using the unconfined compressive strength (UCS) test. The test result revealed that the brown coal fly ash is effective in reducing the rate of erosion of dispersive soil. However, the strength gaining is comparatively low while using brown coal fly ash without the influence of hydrated lime. Moreover, the addition of hydrated lime as a secondary binder to the brown coal fly ash exhibited a positive behavior in terms of reducing erosion rate and strength gaining.

Every year millions of bottles of polyethylene terephthalate (PET) are wrongly discarded into the environment. In order to reduce the disposal of this polymer in nature, this study aims to evaluate the mechanical behavior of a clayey soil-PET mixed with fine crushed PET. The potential use of this waste material in geotechnical applications may ultimately reduce the problem of wrong disposal. This paper presents an experimental study to evaluate the mechanical behavior of pure soil-PET and mixtures with different contents of PET waste by triaxial tests, in order to obtain the strength parameters of the soil-PET mixtures. The clayey soil-PET used was mixed with 3 and 5% of PET flakes by dry weight. Characterization tests such as grain size, Atterberg limits and compaction test were performed on the clayey material. Triaxial tests at confining stresses of 50, 150 and 300 kPa were done on the soil-PET and mixtures. The results show that the soil-PET strength parameters are influenced by the addition of the PET flakes, thus improving characteristics such as friction angle and cohesion of the soil-PET mixtures. This improvement also depends upon the confining level, which the samples were submitted. These mixtures may be used in landfill and other geotechnical works, so this paper proposes to contribute to a better understanding and interpretation of the behavior of soil-PET reinforced with PET waste.

In this paper, the use of the recycled concrete aggregate (RCA) material in the performance of granular column construction is investigated through laboratory model tests. In the study, firstly, geotechnical properties of RCA material are investigated and some basic tests including particle size distribution, permeability, Los Angeles abrasion test, water absorption, specific gravity, triaxial test and direct shear test are conducted in order to characterize the RCA material. Following these tests, a series of laboratory model tests are carried out by using RCA and NA (natural aggregate) as a granular column material in soft soil deposits having different undrained shear strength. At the end of the model tests, it is concluded that reuse of recycled concrete aggregate can be considered in the construction of granular columns and play an important role in sustainable geotechnical design.

Blasting of liquefiable soils is usually performed to induce densification (i.e., ground improvement) or to conduct field experiments for the evaluation of the consequences of liquefaction, such as deformations, loads on foundations, and changes in small-strain stiffness. However, the use of geophysical techniques to evaluate post-blast change in shear wave velocity (i.e., small-strain stiffness) is rare, particularly when performed over significant time periods to establish the initial effects of aging. This paper describes the use of the multichannel analysis of surface waves (MASW) technique to observe changes in shear wave velocity at a test site in hollywood, South Carolina. The purpose of this study was to evaluate time-dependent changes in shear wave velocities caused by blast-induced liquefaction in unimproved, liquefiable soils to provide a benchmark for comparison to various treated areas improved by installation of driven timber piles. MASW measurements were made prior to and following blasting for a period of up to six months to evaluate changes in stiffness. Following the presentation of the subsurface conditions and blast test program, the blast-induced excess pore pressures are described, and the results of the MASW surveys are provided and compared against previously reported observations. Unlike other studies, it is shown that the aged deposits tested in this study did not regain their initial stiffness after six months due to the loss of soil fabric that developed over several hundred thousand years. However, it is shown that the immediate post-blasting loss of stiffness reduces following an initial blast, indicating that “newly deposited”, denser soils will experience reduced loss of stiffness.

This paper describes the results of laboratory static plate load tests conducted on small diameter PVC (polyvinyl chloride) pipes buried in geocell and geogrid reinforced soft clay bed. The aim of the study was to evaluate the suitability of the combination of geocell and geogrid reinforcement system in protecting the underground utilities and buried pipelines. Commercially available neoweb geocells and biaxial geogrids were used as the reinforcements. A pipe with external diameter 75 mm and thickness 1.4 mm was used in the experiments. Results suggest that the use of the combination of geocell and the geogrid reinforcement system considerably reduces the deformation of the pipe as compared to unreinforced bed. More than 40% reduction in the pressure and more than 60% reduction in the strain in the pipe were observed in the presence of reinforcements as compared to the unreinforced bed. Conversely, the performance of the foundation bed was also found to be marginally influenced by the position of the pipe, even in the presence of the relatively stiff reinforcement system. The study revealed that the depth of placement of pipe can be significantly reduced in the presence of the geocell and geogrid. The outcome of the study has the huge financial implications in the large projects, where the pipelines are laid for several hundred kilometers.

A concern with the disposal, use, and general management of coal fly ash (CFA) is the potential for leaching of trace elements. Leachate from CFA can be reduced through transforming its wettable surface to a non-wettable one. The degree to what the surface has been transformed to non-wettable is measured through contact angle (CA) measurement. However; the technique how to measure accurate CA, particularly on rough and non-homogenous surfaces is challenging. This study provides the first published results of dynamic contact angle measurements for a modified coal fly ash (CFA) and compares the results with static contact angle measurements using three organo-silane (OS) chemicals. The dynamic approach reduces the standard error of contact angle measurements from 20⁰ to 2⁰-5⁰. Results indicate that OS has the ability to transform CFA from a hydrophilic material (contact angles less than 90⁰) to one which is hydrophobic (contact angle greater than 90⁰) with values as high as 148⁰. The data can be used by engineers to evaluate induced water repellency as an approach to increase ash use in applications where leachability is a concern.

Use of industrial by-products in geotechnical engineering projects, such as in the construction of highway embankments, is advantageous because large volumes of these materials can be utilized. Basic oxygen furnace (BOF) steel slag is one of these industrial by-products. This paper provides a brief background on the characteristics of BOF steel slag and presents the results of a series of laboratory tests (grain-size analysis, maximum and minimum dry density, compaction, large-scale direct shear tests (LDS) and isotropically consolidated-drained triaxial compression (CID TX) performed on fresh and aged BOF steel slag generated from an Indiana steel plant. BOF steel slag samples from three different batches of production were tested, which allowed an evaluation of both aging processes and the effect of changes in gradation on the mechanical properties. The BOF steel slag tested in this study contained sand-size particles with varying percentages of gravel- and silt-size fractions. The moisture-density relationships for BOF steel slag were irregular with two peaks. Based on the LDS and CID TX test results, the BOF steel slag exhibited superior strength and stiffness characteristics than conventional geo-materials. The mechanical properties of fresh and aged BOF steel slag are discussed in the context of its use in geotechnical applications.

Due to intense moisture fluctuations, expansive soil subgrades exhibit swelling and shrinkage behavior which results in the damage of lightweight structures such as pavements, single storied buildings etc. resting on them. Frequently, lime or cement is used as a stabilizer to improve the expansive soils. In addition, low calcium based stabilizers such as fly ash, grounded blast furnace slag etc. have been promoted to treat the expansive soils. In this study, an attempt has been made to study the influence of addition of fly ash on the dynamic properties of expansive soils. A class C fly ash is used to treat a moderately expansive soil having a free swell index of 50 %. A series of resonant column tests were performed to determine the small strain dynamic properties, shear modulus and damping ratio, of the untreated and fly ash treated expansive soils at different curing periods. Results indicate that with an increase in fly ash content, the shear modulus increases and damping ratio of the expansive soil decreases. In addition, with the increase in curing period there is an increase in shear modulus and decrease in damping ratio.

The effect of salt concentration on undrained shear strength and index properties of Indian soils is investigated in this study. The soils were collected from 10 regions spread across the industrial belts of Maharashtra and Gujarat. Sodium chloride and calcium chloride were the two chosen salts in the tests. These salts are the known leachate effluents in some of the above polluted regions. Salt concentration of up to 1N was added to several parts of distilled water and mixed with the soils. Each mix was sealed in plastic bags and kept in a desiccator for overnight curing. Care was taken to maintain the salt concentration of each mix. Atterberg limits of the amended soils were determined and the results compared to the available literature. It was observed that the soils with high clay content and montmorillonite as the dominant mineral, shows decrease in plasticity index in the electrolyte solution. This was associated with significant reduction in its undrained shear strength. This observation was attributed to the reduction in the diffused double layer thickness of the clay crystals which lead to the increase in the number of contact points and hence the increase in its strength. This was supported by the micro-fabric study of SEM photographs. The mineralogical composition was also investigated using the x-ray diffraction (XRD) and interpreted along with the above results. As an immediate consequence of the above study is the adjustment in classification of the soil.

The objective of this study is to evaluate the hydraulic properties of RAP materials in highway shoulder applications collected from different locations in Maryland. In order to determine the hydraulic properties, a series of grain size distribution tests and bubble tube permeameter tests were performed on the samples. The results of grain size distributions indicated that the RAP samples collected from different locations within Maryland can be identified as well-graded sand sized with gravel sized material and poorly-graded sand sized with gravel sized material. The obtained hydraulic conductivity coefficients of as-received RAP samples ranged from 8.3x10^-3cm/s to 5.5x10^-2cm/s suggesting that the hydraulic conductivity of as-received RAP is similar to that of conventional granular material with similar gradation. However, the hydraulic conductivity of the RAP is significantly influenced by the particle size distribution. It decreased 10 times with an increase in fines content from 0% to 8% by weight. Similarly, an increase in sand-to-gravel ratio and a decrease in D₁₀ yielded lower hydraulic conductivity values.

In this study red mud was stabilized along with different lime and gypsum content. The variation of lime in the samples had been made 2%, 4%, 6%, and 8% by and gypsum in the samples had been fixed at 1% and 2% by weight of dry red mud. 13 samples of varying lime and gypsum content by dry weight of red mud were prepared and tested for index and engineering properties. The unconfined compression strength samples were cured for 1, 3, and 7 days to study the effect of longstanding curing at room temperature. The CBR tests on unsoaked and soaked samples were carried out to understand the mechanism of lime and gypsum as stabilizing materials. Based on the experimental investigations it is found that addition of lime (up to 6%) to red mud increases the maximum dry density and decreases the optimum moisture content. The optimum mix was RM+6L+2GP which increase the unsoaked CBR by 302.36% and soaked CBR by 939.62%. For the same mix the increase in UCS for curing period 1, 3, and 7 day were 193.71%, 494.41%, and 668.05 % respectively. High strength can be achieved if longer curing period is allowed. The formation of C-S-H and C-A-H gel may be the reason for the higher strength of red mud specimen stabilized with lime and gypsum and red mud stabilized with lime.

North Carolina has recently been facing issues associated with the storage of coal ash, specifically preventing trace elements found in coal ash from leaching into the local groundwater. The research program presented herein focuses on reducing the leachability of trace elements found in coal ash using bio-mediated methods. Microbial induced calcite precipitation (MICP) is used to immobilize trace elements within the fly ash. The MICP process is initiated within ponded fly ash material set up in soil columns, and effluent is collected from the treated fly ash material. The concentrations of the trace elements are measured using inductively coupled plasma mass spectrometry (ICP-MS). The concentrations within the MICP-treated fly ash effluent are compared to baseline fly ash effluent. The MICP treatment process is also applied to dry fly ash material that may be used within construction projects. The MICP treatment process was applied to fly ash material in a similar manner as moisture conditioning during compaction. The MICP treatment process was allowed to take place, then effluent samples were collected from percolating water. The MICP-treated leachate was compared to that of a baseline compacted fly ash sample and compared to the results from the ponded fly ash.

Field water quality data collected from roadway substructures constructed with fly ash was assessed for any potential risk of groundwater and surface water trace element contamination. Trace element concentrations constituting the water quality data were compared to federal and state drinking and surface water quality limits. Elements requiring further evaluation were assessed indirectly to conservatively assess predicted field concentrations at a point of compliance (i.e., edge of right-of-way). Overall, the use of fly ash stabilization and fly ash fill in roadway applications described in this study do not impact groundwater and surface water quality making these beneficial reuse applications suitable with respect to trace element leaching based on obtained water quality data. Water quality data used in this study spans seven locations in four states, three substructure applications (subgrade stabilization, base stabilization, and fly ash fill), 18 monitoring points, and many years of monitoring (some more than a decade). These applications are indicated to be low risk and should not be prohibited by future regulations regarding the beneficial reuse of fly ash.