Geotechnical Frontiers 2017: Geotechnical Materials, Modeling, and Testing

At the granular scale, use of fibers mixed within a soil is a demonstrated means of reinforcing both clays and sands, increasing strength, stiffness and ductility of the composite material. At a large scale, use of geosynthetic elements like geotextiles and geogrids provide an increase in composite strength and behavior by confining a reinforced soil mass with evenly placed tensile inclusions. Within this study, concepts of fiber-reinforced soil and geogrids are fused, focusing on randomly-oriented, small grid inclusions (“microgrids”), of various concentrations and aspect ratios mixed within dry sand. The addition of microgrids enabled improved strength and ductility of reinforced composites due to frictional interlock with small grid apertures and the tensile strength of the inclusions. Application of microgrid reinforcement increased soil strength soil by 5 to 10 degrees. Factors that affected behavior included aspect ratio, microgrid concentration by weight and confining pressure. The interlock behavior of microgrids and soil grains are based on frictional mechanisms similar to those of geogrids, demonstrating a dependence on grid transverse member thickness and aperture size in comparison to grain size. However, unlike large-scale reinforcements like geogrids, true soil composite behavior may be better exhibited upon homogenous admixing.

A laboratory study was conducted to investigate the addition of randomly distributed discrete fiber on shear strength of MICP-treated soil catalyzed by bacteria. Specimens were prepared at four different fiber ratios in full contact flexible molds. Unconfined compression tests and triaxial compression tests have been conducted on the fiber reinforced soils. The results showed that improvements in shear strength, ductility, and failure strain were achieved with fiber addition. The shear strength increased gradually with an increase in fiber content up to the optimum fiber content of 0.3%. The failure strain of MICP-treated sand at the 0.3% fiber is nearly 3 times higher than that without addition of fiber. Cohesion and angle of internal friction of fiber-reinforced sand increased by 29–45 kPa and 7.6–11^o, respectively. The inclusion of fibers increases the residual strength and decreases the brittle behavior of the MICP-treated soil.

This study investigates the effects of the type and size of randomly oriented polymeric fibers on the strength and failure strain of fly ash stabilized high plasticity soil. Three different lengths of 13 mm, 25 mm, and 50 mm of two types of fibers, one with low (polypropylene) and the other with high (polyethylene) tensile strength were mixed (1%) with high plasticity clay soil and Class C fly ash (10%). The mixtures were compacted to prepare specimens for unconfined compression test and split tensile test at the same dry unit weight. The fiber inclusions increased the compressive and tensile strength of fly ash stabilized soils significantly. The 25 mm fiber specimens with an aspect ratio of 0.45 that is the length of the fiber to the diameter of soil specimen, showed the maximum enhancement of strength for both compressive and tensile strength. Although all the specimens failed due to pullout of the fibers, the specimens with different fiber showed different strains at failure. The 13 mm fiber specimens (aspect ratio of 0.22) showed minimum increase in failure strain, whereas the specimens prepared with 25 mm and 50 mm fibers showed the maximum increase in failure strain, and failure did not occur even at 15% strain. The length of fiber has a relatively lower impact on gaining strength, but has pronounced effect on the ductility of the soil. The failure strain increased at least 132% when the 25 mm fiber was used. The polyethylene fiber stabilized soil showed slightly higher strengths because of its higher tensile strength and elastic modulus.

In order to combat issues related to expansive soils, chemical stabilization augmented with use of synthetic fibers is gaining focus in recent times. However, in most of these applications, the practicing field engineers face difficulty in selecting the right mix of fiber size, fiber dosage and stabilizer content. The decision becomes more typical, as the target is to achieve or enhance multiple geotechnical properties which differ with fiber dosage and stabilizer content based on governing mechanisms. Addressing these issues, in this study an attempt is made to present an approach for selecting fibre dosage and lime mix for a typical expansive semi-arid soil. In this article, the effect of randomly oriented polypropylene fiber inclusion in enhancing various geotechnical properties of a typical expansive semi-arid soil is studied. The addition of lime is considered in order to ensure proper bonding between clay particles and discrete fiber elements. PROMETHEE is adopted in order to assist in multi-criteria decision-making process. The approach evaluates multiple geotechnical properties for possible alternatives viz., untreated soil; lime treated soil and other including combinations of fiber dosage and fiber size in the presence of lime. The response measures being the targeted geotechnical properties which include, linear shrinkage tests, unconfined compression strength test, California bearing ratio behavior, compressibility characteristics and hydraulic conductivity. The study revealed the best possible alternative considering all the selected response measures.

The geotechnical community is shifting towards promoting sustainable technologies. One of the select applications in this domain consists of clays that are reinforced with natural or synthetic fibers. Extensive experimental work has been reported in the literature on the response/behavior of fiber-reinforced clays. This work led to, and/or was complemented by, several analytical and empirical strength prediction models. In this paper, an application involving the use of fiber-reinforced clays is selected for analysis from a reliability-based design perspective. The application involves a probabilistic assessment of the bearing capacity of shallow foundations on fiber-reinforced cohesive soils underlain by unreinforced clays of the same nature. Monte Carlo simulations were conducted to quantify the impact of model uncertainty and inherent variability in the input parameters on the probability of failure of the foundation. Based on the results, recommendations are made regarding the required factors of safety and/or thickness of the “fiber-reinforced” replacement layer, which need to be adopted for the design of spread footings in order to achieve target reliability levels.

Over the past 60 years, numerous studies have been conducted on the shear strength behavior of compacted clays. Most important for practical purposes are the influence of moisture content during compaction, and strategies for developing laboratory testing programs to evaluate shear strength for design. This paper provides a summary of the state of knowledge regarding the strength of compacted clays to aid in selection of design parameters and the development of compaction specifications. The compaction process and the structure of compacted clays are reviewed as they affect shear strength and volume change behavior. The influence of compaction conditions on shear strength and volume change are illustrated using the results of triaxial tests and consolidation tests on compacted Oak Harbor clay, a lean clay of medium plasticity from Oak Harbor, Ohio.

This paper presents a modified constitutive model to predict post-construction movements of compacted fills due to wetting based on the results of anisotropically-consolidated undrained (ACU) triaxial compression tests. The constitutive model is coded in the FISH language of the finite difference numerical software FLAC. The model allows deformation along the major and minor principal stress directions instead of the vertical and radial directions and user-defined wetting fronts to predict movement with time. The lateral and vertical progressive surface movement induced by top-down wetting is simulated and the results illustrate how the differential vertical and lateral movement at the ground surface can change during the course of top-down wetting.

Brazilian tensile strength (BTS) tests were conducted to measure evolution of tensile strength for compacted kaolinite disks at saturations (S) ranging from 0.02 to 0.73. Tensile strength and stiffness prior to failure followed non-monotonic trends marked by general increases as saturation increased from 0.02 to ~0.40, followed by general decreases as saturation further increased. Strain at failure increased monotonically with saturation. Evolution of the strength, strain, and stiffness response was interpreted to reflect corresponding evolution of interparticle stress components active in unsaturated soils, including capillary forces and double layer forces. Results provide experimental evidence for evolution of internal stress state in unsaturated soils over a wide range of saturation.

A comprehensive investigation of the shear strength of Beaumont clay was undertaken to support the design of a new off-channel reservoir in Texas. Testing of intact, remolded, and compacted clay provided the basis for establishing soil shear strength parameters used in conducting slope stability analyses of the embankment dam. This paper focuses on characterization of the shear strength of remolded and compacted clay. Remolded clay was tested using direct shear, torsional ring shear, and consolidated-undrained triaxial methods. Compacted clay was tested using unconsolidated-undrained and consolidated-undrained triaxial methods. Specific topics of the paper include: (1) comparison of fully softened strength measurements from direct shear, torsional ring shear, and consolidated-undrained triaxial testing methods; (2) comparison of fully softened strength measurements with empirical correlations; (3) factors affecting the undrained strength of compacted clay from unconsolidated-undrained triaxial testing; and (4) summary of drained and undrained shear strength parameters of compacted clay for consolidated-undrained conditions. The laboratory testing addresses common misconceptions about the actual factors affecting shear strength characteristics of normally consolidated and compacted clay. Undrained strength of clay is primarily related to the void ratio during shearing (and degree of saturation for compacted clay), whereas drained strength parameters are not significantly affected by void ratio or compaction conditions.

The study presented in this paper was aimed at investigating the use of thermogravimetry (TG) to quantify the amounts of various hydration products, particularly calcium silicate hydrate (CSH) and calcium hydroxide (CH), in stabilized soils and establish correlations between them and strength gain over time. For that purpose, a pure kaolinite was chosen as the soil for this study and Portland cement was the selected stabilizer. Kaolinite samples and cement-stabilized samples were compacted at their optimum conditions and cured for different periods of time up to 90 days. The unconfined compression test, which is a relatively simple and commonly used test, was performed to measure the unconfined compressive strength (UCS) for all the samples and record the macroscopic behavior. Then, a portion of soil from each set of samples was recovered and subsequently subjected to the TG test which was performed at a constant heating rate of 10 K/min until 1000 ^oC, while being connected to a mass spectrometer (MS) for simultaneous evolved gas analysis. The thermal decomposition was divided into four major regions i) desorption of adsorbed water below 105 ^oC, ii) dehydration of CSH phases between 105 and 440 ^oC, iii) dehydroxylation of kaolinite and CH between 440 and 580 ^oC, and iv) decarbonation of calcium carbonate at temperature between 580 and 1000 ^oC. The quantitative analysis revealed that strong linear correlations exist between the amounts of CSH and CH, and strength gain.

Compressed air energy storage (CAES), in which surplus energy is utilized for compressing ambient air that can be released later to provide necessary energy, is being actively pursued in a last decade. This technology has a potential to strengthen the efficiency of renewable energy generation, such as solar and wind power. In addition to the large-scale energy storages, CAES can be operated at a small-scale to support facilities such as residential buildings. In this case, closed-ended steel piles can serve to provide the space where pressurized air is stored during off-peak periods, which leads to an idea of small-scale CAES pile. To continue pursuing the idea of using pile foundation system as an energy storage vessel, we need to examine long-term stability of CAES pile. In this pilot study, we investigate a finite element model of an axisymmetric CAES pile that is subject to the internal uniform pressurization while supporting a constant structural load. Long-term stability of the CAES pile is assessed from the first 10 pressurization-depressurization cycles at the various initial dead load conditions. Elasto-perfectly-plastic constitutive law is employed at the pile-soil interface for simplicity. We are able to observe that vertical displacement of the CAES pile accumulates with negligible radial deformation as the number of pressure cycle increases.

This paper presents a numerical model and its application to analyze thermally induced pore fluid flow in saturated soil surrounding geothermal piles. Coupled effects of heat conduction and convection on thermal performance of heat exchanger piles in saturated soil are considered. Heat transfer energy equation and Brinkman’s momentum equation that considers a Boussinesq buoyancy term are coupled to analyze convective heat transfer through pore fluid flow. A hybrid explicit-implicit approach is employed in the finite difference solution scheme to calculate pore fluid velocity and temperature increments within the ground. Results indicate that thermal operation of geothermal piles alters pore fluid density, buoyant flow occurs (even under hydrostatic condition) within saturated soil in the vicinity of heat exchanger piles, and thermally induced pore water flow under saturated condition facilitates pile-soil heat exchange.

In recent years, there are applications of geothermal foundation for near surface geothermal energy utilization in geotechnical engineering. However, significant uncertainties exist in design of such foundations and affect the thermal-mechanical behaviors. To consider these uncertainties explicitly, it is desirable to develop a reliability-based design methodology for geothermal foundations by quantifying the uncertainties in thermal-mechanical soil-structure interaction of the geothermal foundation design. In this paper, the deterministic analysis for geothermal foundation is performed using a numerical model. A series of advanced moment methods are used for assessing the probability of exceedance in terms of both factor of safety and displacement requirements of geothermal foundations by combining the reliability method with the deterministic numerical model. A case study for a geothermal foundation design is presented to demonstrate the significance of the proposed framework for reliability-based design of geothermal foundations.

Tidal energy converters (TECs) provide a means to extract energy from the horizontal flow of water resulting from the rise and fall of tides. It is critical that the behavior of all aspects of the TEC, including the foundation, be understood to optimize not only its reliability but also its cost efficiency. Unlike the majority of offshore energy structures that attempt to minimize the interaction with flowing water, a TEC is designed to interact with this flow through a rotating turbine. The rotating turbine blades, fluctuations in the tidal current speed and direction, wave loading, turbulence, and vibrations all result in a combined cyclic loading of the foundation or anchoring system. A suction caisson is a suitable foundation type to secure tidal current turbines to the seabed. In soft marine clays, the suction caisson provides an ideal foundation for TECs that can be installed without the need of equipment for pile driving or mobilizing gravity base foundation while allowing for the removal of the foundation, contributing to the overall “green” nature of the device. When configured in the monopod configuration the TEC will apply significant horizontal loading on the suction caisson. Therefore, the response of a suction caisson in the monopod configuration in soft clay with an aspect ratio of 1 is investigated under monotonic and cyclic horizontal loading.

An investigation was performed on the suitability of abandoned wells in California for enhanced geothermal systems (EGS). The study identified three counties characterized by high numbers of abandoned wells, medium to high crustal heat flows (75-100 mW/m²), and suitable sedimentary geology: Santa Clara, Monterey, and Santa Barbara. Temperature gradients ranging between 4 and 7.3 ^oC/100 m access bottom hole temperatures between 40-73 ^oC for an average 1,000 m deep well. These rock temperatures are sufficient for the extraction of low-temperature geothermal energy for direct use such as district heating, greenhouse heating, and aquaculture. The mitigation of drilling costs and the documented lithology both reduce the risk associated with EGS. However, hydraulic fracturing of loosely to moderately consolidated sedimentary rock in transitional stress regimes remains one limitation to the EGS conversion of these abandoned wells.

Ground-source heat pump systems consist of heat exchanger boreholes, embedded with circulation pipes, buried in the ground and connected to a heat pump for heating and cooling of buildings. Due to the changes in seasonal energy demands of the building, sustainability of borehole heat exchangers depends on the seasonal load balance. As the soil can be gradually heated up or cooled down considering the unbalanced thermal loads, long-term performance of heat exchanger boreholes is closely related to maintaining a constant ground temperature as progressively changing temperatures indicate loss of heat exchange efficiency in the long term. In order to address the long-term thermal performance for different unbalanced climatic conditions, ground thermal loads were estimated and representative equivalent half-sine waves of thermal loads from a hypothetical four floor medium size office building are created for 100+ different locations. Total required heat exchanger lengths for each location are then estimated for the proposed building. Findings suggest that for different seasonal energy demands, amplitudes and durations of the sine waves change significantly, consequently suggesting different loop lengths. For unbalanced climates, loop lengths found are considerably higher than balanced cases. Ultimately, numerical analyses were simulated for 30 years of heat exchanger operation to investigate the thermal performance under different climatic conditions.

Energy piles are deep foundation elements designed to utilize the relatively constant temperature of the ground for efficient heating and cooling of the buildings while at the same time serve as foundations. The temperature changes during the operation of energy piles result in axial displacements, a part of which is restrained by the surrounding soil or the building on top. The restrained part of the axial displacements induces compressive stresses during temperature increase and tensile stresses during temperature decrease along energy piles. Moreover, the unrestrained part of the displacement results in changes in the mobilized shaft resistance, which need to be taken into consideration during design of energy piles. With the aim of quantifying these effects, a series of full-scale field tests on three energy piles with different end-restraint conditions was carried out in Richmond, TX. The field test program included conventional pile load tests and application of temperature. Temperature changes were applied to the test piles with and without maintained mechanical loads to investigate the effects of structural loads on energy piles. Moreover, the lengths of the test piles were determined to represent different end-restraint conditions at the toe. In this paper, a comparison of the thermally induced axial stresses and mobilized shaft resistance of two identical, end-bearing test piles with and without maintained mechanical loads are presented along with the details from the full-scale field test.

Geothermal foundations (energy piles) combine the structural function of deep foundations with the ground source heat exchangers to transfer geothermal energy to superstructures. The intermittent operation of the geothermal energy pile system results in cyclic thermal loading on the soil-pile interface. To investigate the effects of cyclic thermal loading on soil-concrete interface properties, a conventional direct shear device was modified by replacing the bottom shear box with a concrete plate that has embedded aluminum tubes to heat and cool the interface. A series of tests were conducted with interface temperatures of 4.5, 22.5, and 42.5 ^°C, respectively. The normal stresses of the direct shear tests were 27.6, 41.4, and 100 kPa. The tests were performed both under cooling and heating with thermal cycle numbers of 0.5 and 10.5. The aforementioned tests were conducted at a shearing rate of 3 mm/min, and the water contents of all the samples were approximately 18.5%. The responses of soil-concrete interface at different temperatures and temperature cycles are presented in this paper.

Manufacturing data record (MDR) has traditionally been the basis of compliance assessment and approval of geomembrane material for use in construction works. Acceptance of the MDR data has strong reliance on the quality control management following industry recognized international standards. 250,000 m² of conductive geomembrane material was approved on the basis of compliant MDR for use in a project in Australia for lining a process water storage dam. The conductive geomembrane material was manufactured with a non-conductive edge to assist with the welding of the material. Frequent seam failures during the installation phase triggered rigorous investigation of the geomembrane material properties. During the process of investigation of the extent of this inconsistency, it was detected that the non-conductive edge of the geomembrane material is under gauge (occasionally 15% or more) and non-compliant with the technical specification. Significant investigation and root cause analysis were undertaken by the designer and the manufacturer. The investigation detected that the inconsistency is as a result of production anomaly, that has been able to bypass the manufacturer’s quality assurance process and possibly applicable to all geomembrane rolls supplied for the project. In order to eliminate the deficiency, all susceptible seams were eliminated.

The soil survey methodology is used for the detection of leaks in geomembranes. Although little known in Brazil, it is well suited to minimize the risk of placing waste on a damaged liner system. A Canadian study indicates that the density of damages on installed geomembranes is on average between 4 and 22 leaks per hectare. Quality Control measures currently used in Brazilian landfills do not include this type of testing. As the existence of lined landfills is relatively new in Brazil, the impact caused by damage in the protective layers cannot be perceived. The landfill of CTR-RIO, in Rio de Janeiro, Brazil, adopted this methodology for quality control. The results after 4 years of operation indicated the amount of leaks found range between 0.5 and 8 leaks per hectare for an inspected area of approximately 310,000 m². All identified damages could be repaired before the beginning of the waste disposal.

Waste containment facilities can experience elevated temperatures for a variety of reasons such as hydration of combustion ash, aerobic biodegradation, and smoldering combustion. Elevated temperatures can reduce service life or effectiveness of geomembranes by accelerating antioxidant depletion and polymer degradation. A case history is presented to illustrate the potential effects of elevated temperatures and time-temperature history on a high-density polyethylene geomembrane and the associated reduction in service life or effectiveness. The impact of peak temperature, e.g., 60–80°C, the duration of peak temperatures (time-temperature history), and the time to complete antioxidant depletion were found to significantly reduced by increasing temperatures investigated. The effect of tensile strains, thickness, and leachate characteristics on estimated service life is also discussed.

This investigation was conducted to evaluate effects of temperature on swelling and bentonite extrusion properties of GCLs. The swelling characteristics were determined using standardized test procedures and extrusion characteristics were determined using a new test method developed by the authors. Tests were conducted on a conventional medium-weight woven/nonwoven GCL. The range of test temperatures was 2 to 98°C (swelling tests) and -5 to 100°C (extrusion tests). The extrusion tests were conducted under stresses between 100 and 400 kPa and moisture contents between 50 and 150%. Temperature had significant effects on both swell and extrusion. The swell index ranged from 21 mL/2g at 2°C to 36.5 mL/2g at 98°C, with the largest increase occurring from 20 to 40°C. The amount of extrusion ranged from nearly 0 to 40.5 g/m² with generally decreasing extrusion with temperature from 2 to 100°C. At a given temperature, extrusion increased with increasing stress and moisture content.

Geogrid-aggregate interlock provides enhanced local stiffness in the vicinity of the installed geogrid and is a responsible mechanism for the improved performance of geogrid base reinforced pavements. The objective of this study was to establish innovative approaches to quantify the local stiffness increase of geogrid-stabilized aggregate samples. Two pairs of bender elements were installed at two different heights of cylindrical specimens in a repeated load triaxial testing device. Resilient modulus testing was conducted on both geogrid reinforced and unreinforced specimens. Through the use of bender elements, the shear waves were measured during the resilient modulus tests. Experimental results show that the shear moduli estimated from the shear wave velocities increase with bulk stress, regardless of geogrid reinforcement. The shear modulus estimated in the vicinity of the geogrid was always greater than that estimated farther away from the geogrid. According to the preliminary tests conducted so far, geogrid-aggregate interlock related local stiffness increase in unbound aggregate base layers can be effectively quantified by using shear waves.

Thermal expansion is a critical property of geomembranes as it can affect the formation of wrinkles during their installation as well as for exposed applications. When an excessive number of wrinkles has developed because of an excessive dilatation of the geomembrane, these wrinkles may become interconnected, which increases the risk and extent of leakage. This paper introduces the test procedure that should be followed to permit the evaluation of thermal expansion characteristics of geomembranes using a dynamic mechanical analyzer. It is shown that the test should be conducted with low applied stress and very low heating rate. In addition, the effect of the specimen width and length is analyzed. Finally, differences in behavior between machine and cross direction are characterized. Overall, it is concluded that this technique provides an effective tool for measuring the linear thermal expansion of geomembranes under conditions simulating their use in the field.

This paper presents the effect of aperture size on the low displacement stiffness response of geogrids subjected to pullout loading. The aperture size of geogrid was varied by cutting ribs of geogrids in the pullout tests. Two types of geogrids were tested at two normal pressures (21 kPa and 35 kPa). The soil-geosynthetic composite (SGC) model was used to compute the low displacement interface stiffness (K_SGC) of the geogrids. Based on the analysis of laboratory tests using SGC model, the results showed response of geogrids was highly dependent on the aperture size. The geogrid with original aperture size showed the highest K_SGC value. As the size of the aperture increased, the K_SGC decreased possibly due to reduction in the passive resistance of transverse members and the loss of confinement at the junctions of the geogrid.

Recent storm events, such as the storms in the fall of 2009 and Superstorm Sandy in 2012, have eroded beaches and dunes in the downtown Montauk, NY, area. The culmination of these storms have created a potentially imminent hazard that has left many commercial buildings along the shoreline vulnerable to damages from future storms. Beach and dune erosion caused by Superstorm Sandy has partially undermined several shorefront structures in downtown Montauk, leaving the area vulnerable to damage from future storms. A stabilization project was developed in cooperation with the Army Corps of Engineers, New York State Department of Environmental Conservation, and East Hampton, NY town officials. A unique component of this project was the use of modular geotextile containers instead of geotextile tubes for the core of the dunes. Geotextile containers can provide an alternative over traditional geotextile tubes; they are fabricated with high capacity seams to produce bag or pillow shaped containers. When filled with sand or other soils, the geotextile containers are used to construct revetments and other hydraulic structures such as filling in scour holes, closing breached dykes, and as basic armor units for erosion protection works. Geotextile containers are engineered to provide strength, durability, and soil tightness to perform during installation and during operational life. They are easy to use and can be rapidly mobilized if necessary for emergency works. This paper will discuss the material selection, development, construction, and installation of this stabilization effort utilizing geotextile containers for dune protection.

Recently the Environmental Protection Agency established national regulations for the safe disposal of coal combustion residuals (CCRs) from coal-fired power plants. These CCR byproducts, such as fly ash and bottom ash, can be a real challenge for both small and large facilities to remove and manage. The Environmental Protection Agency’s comprehensive set of requirements addresses the risks from coal ash disposal like leaking of contaminants into ground water, blowing of contaminants into the air as dust, and the catastrophic failure of coal ash surface impoundments. Geotextile tube dewatering technology can provide a unique approach for the management of coal combustion residuals. By incorporating geotextile tube technology, coal-fired facilities can dewater and contain CCRs. This technology can be utilized in the operation of existing surface impoundments, efforts to beneficially use consolidated ash, and the continued operation of coal-fired operations by direct sluicing the daily flows from the plant into geotextile tubes. This paper will discuss several unique approaches involving the remediation or clean closure of surface impoundments, beneficial use of dewatered CCRs, and direct sluicing operations incorporating geotextile tube technology for the safe disposal of by-products from coal-fired power plants.

Torsional ring shear tests were conducted to investigate Soil/Geosynthetic Interface Strengths of various geomembranes. A selection of seven smooth and three textured geomembranes (10 total) that can be factory fabricated were sheared against two soils to investigate the range of soil/geosynthetic interface strengths. The two soils are: (1) a clayey glacial till; and (2) Ottawa fine sand. Smooth PVC and both smooth and textured HDPE geomembranes were also tested so the fabricated geomembrane interface strengths could be compared to previously published interface strengths and commonly used geomembranes. The effect of texturing and material properties on shear strength and soil interaction are presented herein and compared with existing interface strength values. To facilitate the testing, programmable video cameras were used as a data acquisition system.

Geotextile filters are an interesting solution to dewater tailings as they can be installed on existing ponds or be deployed during operation. However, filtration of the fine-grained tailings that are encountered in the oil sands and other mining industries raises several issues: blinding or clogging of the geotextile by the fine particles, or piping. Since the hydraulic conductivity of fine-grained tailings is generally too low for the ASTM D5101 standard test method for soil/geotextile system filtration compatibility, a test setup has been specifically developed and used to study the filtration behavior of needle-punched and heat-bonded nonwovens with various types of oil sands tailings. The permittivity of the geotextile/tailings systems was always several orders of magnitude lower than the water permittivity of the geotextile. On the other hand, no clogging or blinding was observed over more than 100 days. These results show that geotextiles offer great promise for the filtration of fine-grained tailings.

The self-healing capacity of 25.4, 30.2, 34.9, 41.3, and 50.8 mm-diameter circular fully penetrating holes in geosynthetic clay liners under 2 kPa applied stress is compared after full hydration using deionized water and 10 mM CaCl₂ solution. In deionized water, holes with diameters up to 41.3 mm self-healed but with an indentation about 1~2 mm-deep at the center of the larger self-healed zones. The hole with a diameter of 50.8 mm self-healed but the hole was filled with a layer of bentonite slurry with a 4~6 mm-deep indentation. Submerged in 10 mM CaCl₂ solution, holes with diameters less than 34.9 mm self-healed with a 1~6 mm-deep indentation. The 41.3 mm-diameter hole did not close up, leaving a 26.5~28.5 mm-diameter hole. This study shows the importance of the hydrating fluid on the potential for self-healing.

The use of geosynthetic clay liners (GCLs) in barrier systems for waste containment can expose GCLs to different internal stress conditions and elevated temperatures. Thus, evaluation of the internal shear strength of GCLs as a function of normal stress and temperature is important to the design and integrity of barrier systems. In this study, internal shear strength of GCLs was evaluated in stress-controlled shear tests at a range of temperatures from 20 °C to 80 °C and under 20, 40, and 60 kPa normal stress. Horizontal shear deformation increased with increasing temperature, but decreased with increasing normal stress. Increased deformation with increasing temperature was attributed to reduced tensile strength of the needle-punched reinforcement fibers. The ratio of shear-to-normal stress at failure decreased from approximately 1.5 to 1.2 with an increase in temperature from 20°C to 80°C, and was independent of normal stress.

Geosynthetics have been extensively used to reinforce soil structures, such as embankments, slopes, walls, foundations and roads. Proper evaluation of the interaction between geosynthetic reinforcement and backfill is important to understand the mechanisms of geosynthetic-reinforced soil (GRS) structures. Pullout tests have proven to be an effective way to study such interaction. In a pullout test, a geosynthetic reinforcement layer is buried in backfill within a test box. Vertical pressure is applied on top of the backfill to simulate the normal stress on top of the geosynthetic reinforcement in a GRS structure. The geosynthetic reinforcement is then pulled out from the backfill through an opening in the front wall of the box. The pullout test results are influenced by boundary conditions due to the thickness of the backfill, as well as the roughness of the interface between the backfill and the walls of the pullout box. This paper discusses the results of a numerical study performed to investigate the boundary effect on pullout test results. A two-dimensional numerical simulation was conducted using a finite differential method program, FLAC, using the Mohr-Coulomb model to describe the behavior of the backfill. The geosynthetic reinforcement was modeled as a linearly elastic and perfectly plastic material. The numerical model was calibrated and verified against pullout tests of geogrids. Boundary conditions, such as backfill thickness, and the roughness between the bottom of the backfill and the wall of the pullout box, and how these affect pullout test results are analyzed and discussed. The numerical results show that the pullout forces at the large pullout displacement calculated from the numerical simulation with the fixed bottom were closer to the measured pullout forces than those with the free bottom.

One-dimensional compression tests and triaxial shear were performed on two high plasticity resedimented clays from the offshore Gulf of Mexico: Ursa clay (liquid limit, w_L= 52 %) and Eugene Island Clay (w_L= 79 %). The resedimentation technique was used to prepare fully saturated samples of identical composition for laboratory testing at effective stresses ranging from 0.1 MPa to 85 MPa. For a given stress level, increasing pore fluid salinity causes a reduction in void ratio, compressibility and coefficient of lateral earth pressure at rest (K₀) but an increase in permeability. Increasing salinity has no discernible effect on the friction angle measured at critical state, but increases undrained strength at low effective stresses. These variations in properties are correlated to clay plasticity and mineralogy. Tests performed on specimens in which the natural salts had first been leached out and NaCl subsequently reintroduced showed little difference in measured properties.

In addition to density and stress, fabric is also a key state variable strongly affecting soil behavior. While fabric influence on mechanical behavior of soils has been investigated experimentally, the available database is limited in terms of boundary conditions and soil types tested. Offshore carbonate sediments are of special interest for offshore geotechnical analyses due to their prevalence in tropical waters and unique mechanical behavior that stems from their mostly biogenic origin. A key gap in the availability of experimental data on soil fabric relates to the anisotropy of offshore carbonate sediments. In practice, anisotropy studies (whether rigorously correlated to fabric or not) are typically carried out experimentally for simple boundary conditions such as idealized plane strain and axisymmetric states. In real geotechnical applications, stress paths subjected to soil elements in the field are far more complex, often involving the combined variations of both the orientation and magnitude of all three principal stresses. This paper presents a new multi-scale approach to assess soil fabric at the micro-scale level and relate it to the macro-mechanical response observed for generalized loading conditions. A new sampling method is illustrated that enables preservation and evaluation of the fabric of offshore sediments specimens following generalized stress disturbances imparted by a hollow cylinder apparatus. The link between fabric evolution and the observed stress-strain behavior of sand is discussed along with preliminary results. The approach is part of a broad framework that will be used to systematically study the evolution of soil fabric and anisotropy and their relationship to multi-directional loading scenarios.

This paper investigates the monotonic and cyclic response of offshore carbonate sediment and silica sand using two different types of simple shear apparatus (referred to as ‘rigid’ boundary and ‘flexible’ boundary simple shear apparatus in this paper). In the ‘rigid’ boundary apparatus a series of concentric rings were used around the specimen to transfer the shear strain from the bottom to the top of the specimen, whilst in the ‘flexible’ boundary apparatus an unreinforced membrane was used to confine the specimen. All the tests were carried out on reconstituted specimens with similar initial conditions. The effects of these different boundary conditions on the monotonic and cyclic shearing response are presented in this paper. Comparisons between inferred and directly measured pore-water pressures and shear strain responses are also presented in this paper. This paper demonstrates that there are significant differences in the results obtained using the two types of simple shear apparatus. The difference is more pronounced for silica sand compared to the fine grained carbonate sediment used in this study.

Combined resonant-column/torsional-shear tests were performed on four specimens of marine clay collected at varying depths over a range of confining pressures commensurate with the specimen depths. Using the small-strain measurements from these tests, the influences of stress state and void ratio on the small-strain shear stiffness, shear-wave velocity, and material damping ratio were studied. As the confining pressure increases and the specimen consolidates, both the shear stiffness and velocity increase. The rate of this increase follows typical trends of consolidation curves: less sensitive during recompression and unloading, and more sensitive during virgin compression. The laboratory-measured V_s showed good agreement with the field values with little evidence of sample disturbance. The influence of stress on G_max and V_s was also found to be in good agreement with the laboratory. The relationship between the stress state, void ratio, and material damping is more complicated and does not show as consistent a behavior.

This paper compares laboratory element test results on kaolin clay reconstituted by two different methods. One method was to consolidate a slurry in a large consolidation box producing a block sample that could be cut into triaxial-sized specimens. This produced consistent specimens near the liquid limit. The other method was to use a pug mill, a device used to mix, de-air and extrude clay that can be used for pottery. Consistent specimens with a water content below the liquid limit could be prepared in this way. The testing program presented herein included one-dimensional incremental loading oedometer and undrained triaxial compression loading tests on the two reconstituted specimen types. The results show that the two reconstitution methods significantly influence the test results because of kaolin particle arrangement. The slurry-based specimens show more compressibility and contractive shearing behavior while the pug mill specimens show less compressibility and somewhat dilatant shearing behavior.

The bishop ring shear (RS) apparatus is typically used to obtain interface residual friction angles (δ_res) of marine sands for design of either axial pile capacity after the ICP-method or pipeline design at shallow depths. Past research studies have proposed either a fixed value of δ_res = 29° for pile design, or correlations between δ_res and the mean particle size (D₅₀). In current design practice δ_res is mostly assumed to be equal to 29° and RS tests are only performed to clarify whether δ_res can be increased or not. This paper presents a database of RS-tests on offshore North Sea sands that suggest that δ_res could be stress dependent when the vertical effective stresses are less than 50 kPa, while the fines content are of secondary importance. Moreover, δ_res is affected by the roughness of the chosen steel interface and D₅₀, but the effective stresses effects can also be predominant. The aim of this paper is to assist practitioners with the evaluation of a realistic value of δ_res for the design of offshore infrastructure in North Sea type of sands.

Locating and tracking buried objects underground can be a difficult task especially in the case of plate anchors in soft clays. These plates, used offshore, gain their large vertical capacity by being embedded deep into the seafloor. Most commonly they are installed by either dragging horizontally tens to hundreds times their fluke length (drag embedment anchors) or by a suction caisson, which is then removed, and then dragging the anchor multiple fluke lengths, (suction embedded plate anchors). They can be extremely cost effective given their capacity to weight ratios, but they also have significant uncertainty in their capacity since plate anchor installation depths are exceedingly difficult to measure and predict. These difficulties exist not only in the field, but also in the laboratory. In the past decade significant progress has been made towards measuring plate anchor kinematics in 1-g laboratory experiments with the development of magnetometer tracking systems and translucent soil simulates. However, these methods are not easily transferable to the geotechnical centrifuge, where models with field scale effective stresses can be tested. In this paper we propose a new method for tracking plate anchors within a soft clay small scale model using an acoustic transponder attached directly to the plate anchor. We demonstrate the systems feasibility with analytical calculations and a prototype experiment in water. Though this active acoustic system is being developed for plate anchors in clay it could be used to detect the location and trajectory of any object buried in soil.

Portable free-fall penetrometers (PFFP) are used as an innovative approach to investigate the uppermost seabed stratification, including the mobile layer. The aim of this study is to design an add-on sampler for PFFPs to collect simultaneously sediment, with focus on the mobile sediment layer. Here, we present three prototype designs and preliminary tests, based on the lessons learned from other systems such as gravity and piston corers. The prototypes differ in shape, sampling tube dimensions, wall thickness ratios, and core catching mechanisms. In preliminary tests, the sample quality was assessed based on visuals, recovery ratio and volume change. Promising results were achieved using suction only to hold the material in the sampling tube, causing the least sample disturbance. Still, the results showed that core catcher increased the chance of recovery of sand. Based on the results, recommendations for further sampler improvements, and particularly, a new core catcher design are given.

Rapid penetration of torpedoes into the sea floor encompasses a host of complex phenomena. Determining the kinematics of soil-torpedo interactions, needed for development and validation of state-of-the-art numerical simulations, remains one of the major challenges in design and analysis of torpedo anchors. In this study, results of rapid penetration tests in reduced scale physical models of synthetic soils are presented. The granular media consists of saturated refractive-index-matched transparent quartz particles. High-speed imaging is used to capture images during the penetration event. Digital image correlation is then performed to investigate soil-torpedo interactions. Results of the analyses provide high fidelity data with regards to kinematics of soil-torpedo interaction at various stages of penetration. These data reveal a deviation of the soil response ahead of the torpedo from both cylindrical and spherical cavity expansion.

Sediment dynamics cause continuous changes in nearshore morphology and play a major role in coastline evolution as well as for engineering activities in the coastal zone. A portable, free-fall penetrometer was used to investigate the geotechnical characteristics of surficial seabed sediments in the energetic nearshore zone of the U.S. Army Corps of Engineers Field Research Facility at Duck, NC. Penetrometer deployments were carried out along four cross-shore transects in water depths of 0.8-14.3 m. Duplicate deployments demonstrated the reproducibility of the results. The derived maximum quasi-static bearing capacities ranged from 8.7-251 kPa, with a decrease in the qsbc and in the scatter in the seaward direction. Significant differences in sediment strength were observed in the vicinity of the actively migrating, shore parallel sandbar. The study shows a strong relationship between geotechnical characteristics and active morphodynamics of the nearshore seabed. The depth of closure was reflected in the penetrometer results.

Two vertically aligned pressure transducers were embedded at a sandy beach at a sediment depth of 5 cm and 20 cm, respectively. Pore pressure buildup, and the impact of horizontal and vertical pressure gradients were assessed with regard to the ocean wave forcing. The results indicated that all three processes may impact and enhance sediment erosion. Excess pore pressure built up, and exceeded the initial mean effective stress at both measurement sediment depths. However, the pore pressure build-up appeared interrupted by irregular wave forcing. The critical instantaneous Sleath parameter for sediment mobilization by horizontal pressure gradients was exceeded for many wave cycles, suggesting a contribution to sediment erodibility. Upward directed vertical pressure gradients exceeding the buoyant specific weight were measured, being likely associated to the formation of wave groups. The field study represents a proof-of-concept for future field investigations regarding pore pressure response to wave forcing.

Sediment instability and erosion in coastal wetlands has been identified as a major concern, particularly in locations such as coastal Louisiana. In order to model coastal zones, an improved understanding of sediment transport, erodibility, and morphologic evolution is crucial. The geotechnical sediment behavior in areas of active sediment dynamics is still poorly understood, and rarely integrated in predictive models. During field investigations at three locations in coastal Louisiana, loose and likely mobile sediment surface layers were characterized using a free fall penetrometer. The predictive capabilities of numerical tools need to be validated against datasets from such investigations, before numerically investigating the evolution of mobile layers, their geotechnical characteristics and the resulting potential impact on increasing sediment erodibility during extreme events. In this paper, a brief literature review is presented on current methodologies of numerical simulations of field testing processes. Preliminary results from a three-dimensional simulation in finite difference platform of the field-testing method at a generic soil profile are presented in order to evaluate current capabilities and limitations of numerical platforms and protocols. Areas of future research are identified and a discussion is presented on the prioritized fronts.

Coastal areas are vulnerable to the earthquake-tsunami multi-hazard, which can cause significant sediment instability near the shoreline, leading to potential damage or collapse of critical coastal infrastructure. During the earthquake, sediment instability can occur via residual liquefaction, and the water level can rise following the cessation of strong shaking. The water level rise has significant implications for the ensuing tsunami-induced sediment instability. Herein, a modeling framework for the aforementioned problem is established using two different pore water pressure generation models. The water level rise is estimated for a hypothetical sediment profile and earthquake motion for both fully saturated and partially saturated conditions. The results show that water level rise can be significant just onshore, which is validated with post-earthquake field reconnaissance. The results imply that tsunami-induced sediment instability will be significantly affected by the earthquake-induced sediment instability. Future work will focus on the interaction between earthquake-induced and tsunami-induced sediment instability.

This paper describes the rationale behind using strain-dependent stiffness values for settlement analysis. Normalized elastic stiffness versus axial strain curves are presented for several soil types. Comparisons are made between the predicted settlement using (1) strain-dependent soil stiffness; and (2) single value high-strain soil stiffness for each layer beneath a major soil-supported structure using different soil profiles. Although the predicted settlement using strain-dependent soil stiffness is smaller in each case, the differences vary depending on various factors, including the level of loading (and hence strain) in the soil, and the ratio of low-strain to high-strain elastic modulus.

The present study theoretically explores instability behavior of medium dense sand under both drained and undrained biaxial test. The instability analysis has been posed as a plane strain bifurcation problem within a large deformation framework. A generalized pressure-dependent 3D constitutive model has been employed to simulate the drained and undrained biaxial tests on a medium dense sand sample assuming two types of lateral boundaries, namely rigid and flexible. The lateral boundary condition can influence significantly the onset of undrained soild-fluid instability and drained diffused intabilities. Localization gets delayed with increasing lateral confinement for both drained and undrained cases. Elastic parameters have strong impact on the instability onset.

The aviation industry in mainland china is growing rapidly and to cater to this growing demand numerous airports have been planned and constructed in the hilly and mountainous regions of mainland China. The formation of the airport is commonly based on a high embankment. The filling material for the high embankment possesses large self-weight and experiences seasonal variation in water content and temperature, and various external loadings. The variation in water content renders the fill material to be unsaturated. This paper presents the experimental results obtained by performing a series of tests on a poorly-graded sandy gravel using a newly designed suction controlled oedometer apparatus. Special emphasis is given to study the stress-strain behavior of fills for different stress paths. Particularly, the creep behavior of fills is investigated under different stress state variables. The results show that the matric suction increases the soil strength until the plastic deformation state is reached. Several important observations and findings from the study are presented and discussed in detail.

The mechanically stabilized earth (MSE) approach embankments for a new state highway bridge across the Indian River were founded on 8–9 m of dense sand overlying a 20 m thick layer of soft, normally consolidated, high plasticity clay. Consolidation of the clay was accelerated through an array of prefabricated vertical (PV) drains. The instrumented 13.8 m high fill was monitored during staged construction and for a period of 1.25 years after construction. The embankment settled more than 2 m, while large lateral spreading (~0.5 m) was restrained by overlying sand layers. The available site investigation data was carefully reinterpreted and a 2D finite element analyses was performed using rate-independent, effective stress models (Modified Cam-Clay and MIT-E3). The numerical predictions are generally in very good agreement with measured ground settlements and lateral deflections. This study highlights the importance of careful parameter selection in modeling the performance for soft ground construction in order to predict key features such as the asymmetric lateral spreading of the clay during consolidation.

In the first part of this research, centrifuge model testing was used to investigate the relationship between the coefficient of lateral earth pressure at rest, K₀, and overconsolidation ratio, OCR, for clean sand for the whole loading-unloading-reloading cycle. Tactile pressure sensors were used to measure the change in K₀ in two saturated centrifuge models conducted on Ottawa sand_. A relationship was developed between the change in K₀ and OCR both for unloading and reloading conditions. In the second part of this research, the same tactile sensor was used to test the influence of extensive liquefaction on K_0. A centrifuge model was subjected to very strong shaking causing extensive liquefaction. Lateral earth pressure was measured before and after liquefaction. It was found that there is a significant reduction on K₀ due to extensive liquefaction which explains the increased vulnerability of sandy deposits after liquefaction, as observed by many researchers.

Migration of fine particles through constrictions between coarser fabrics by seepage force is the process termed suffusion. A coarser soil structure resulted from fines loss will lead to change in hydraulic and mechanical properties such as increased permeability, decreased strength and stability which can cause significant settlement or failure of the levees, embankments and dams. This paper presents a coupled computational fluid dynamics and discrete element method (CFD-DEM) approach to model the suffusion process. The concept of transition layer is defined and used to explain the suffusion process and patterns. The effects of particle size distribution, seepage velocity, fines content and initial void ratio on the transition layer in suffusion are investigated.

Nanoindentation testing was performed on 121 fractured core and drill cutting shale samples to investigate the mechanical properties of samples. With a twofold goal to examine the possibility of obtaining mechanical properties from small intact core fragment and to hereafter establish an understanding for upscaling relationship between cuttings and cores. A new hardness-based method for clay matrix is proposed to reasonably process and interpret indentation data. Results reveal that the clay matrix’s mechanical properties including Young’s modulus, hardness, and fracture toughness can be obtained. Such a hardness-based method for processing indentation data proves to be convenient and feasible. Weak anisotropy is observed for the studied shale samples. The fracture toughness exhibits stronger anisotropy. Comparison of the results from fractured core blocks and shale cuttings shows encouraging agreement in their mechanical properties, hence intact drill cuttings may be advantageously used for nanoindentation testing in cases where intact core samples are unavailable.

Sinkholes pose a hazard socially, economically and environmentally. In Florida, sinkhole-related insurance claims between 2006 and 2010 amounted to $1.4 billion. The scope of this study is to develop a sinkhole simulator (soil-groundwater physical testing) that can assess the qualitative behavior of the hydrogeological mechanism of sinkhole formation. The physical model setup incorporates an unconfined and confined aquifer system with constant head controls for each. Water level transducers are used to monitor variations in the water table during the sinkhole process. The study investigates effects of sinkhole affecting parameters such as soil type and compaction level. Scenarios involving adjustments in soil type and compaction are employed to collect data on water table drawdown and erosion characteristics, as well as the type of sinkhole formation, either cover-collapse or cover-subsidence. A strong relationship between soil compaction, cohesion and the type of sinkhole formed was observed.

Shear banding is generally viewed as a form of instability that occurs when the observed states of a system permit a bifurcation in the solution path to two (or more) solutions. The mechanics of shear bands have been studied extensively both experimentally and analytically, yet mostly in a qualitative manner and in two-dimensions. The evolution of the micro-deformation mechanism leading to the development of shear bands is still not well understood and has important implications in three-dimensional analysis. Presented herein is a promising method of modeling the micromechanics of the shear band phenomenon in plane strain using parallelized discrete element method (DEM). The preliminary results show the DEM’s capability of responding correctly to different loading conditions giving an accurate depiction of the behavior of real soil. The preliminary results from the DEM simulations are presented and discussed.

Based on the results of recent studies, comprehensive characterization of the behavior of infilled rock fractures under saturated and unsaturated conditions requires knowledge of morphological details of fracture surface, as well as state of stress of infill materials and their initial innate conditions (e.g., void ratio, water content, degree of saturation and dry density). This paper describes a semi-empirical equation to interpret the effects of wall-roughed nature of the fractures and presence of partially saturated fine materials within the fractures on the behavior of infilled rock fractures during shear. The proposed equation incorporates the soil-water retention curve parameters as well as hardening due to changes in either volume or degree of saturation into existing models originally developed for fractures with saturated infills. The literature data is also used to evaluate the reliability of the proposed equation in predicting the shear strength of infilled rock fractures in unsaturated conditions.

An apparatus was constructed for testing the response of contacts between silica sand grains subjected to sustained loads. Testing results clearly indicate the delayed convergence of grains, likely caused by fracturing of asperities at the contact. The resolution of measurements was about 150 nm, and the difficulties in testing will be discussed. With the development of a constitutive law for time-dependent behavior of an individual contact as a future goal, the distinct element method (DEM) was adopted as a simulation tool. An individual grain was simulated as an assembly of bonded sub-particles. The true texture of a silica sand grain surface was scanned using atomic force microscopy, and the contact region was replicated in simulations by “carving” the surface from high-resolution assembly of sub-particles. Simulations indicate that the near-contact regions of grains are subjected to time-dependent micro-fracturing, leading to an increase in the number of interaction points within an individual inter-granular contact area. This, in turn, leads to an increase of contact stiffness. Increase in the small-strain stiffness of sand is then a consequence that has been observed in the field.

High-speed trains (HST) bring about special problems compared to typical freight and passenger trains. These special problems include the train passing the Rayleigh wave barrier and associated large deformations, particularly when the HST travels on soft soils. Results from instrumented tests performed with an HST on soft soil at different sites and associated numerical analyses have indicated that a large dynamic amplification appears in the vertical dynamic movement of the high-speed railways (HSR) as the train speed approaches the Rayleigh wave speed; this is attributed to a resonance phenomenon. This Rayleigh wave speed is the equivalent Rayleigh wave speed of the rail/embankment/ground system. This threshold speed is called the critical speed and is known as Ground Mach 1 or GM1. The question is to quantify this dynamic amplification to be in a better position to decide if it can create some serious ride discomfort or even derailment. A 4-D finite element model, developed in LS-DYNA, was used to simulate this problem. The model included the full train length and the raised embankment. The results of this study show that the critical speed is controlled by the Rayleigh wave velocity of the subsoil and that the maximum deflection occurring at the critical speed is about three times larger than the static deflection.

Numerous empirical correlations are available to estimate shaking-induced settlement of saturated, coarse-grained soils. These correlations, widely used in practice, were developed using laboratory cyclic shear tests of small specimens tested under either drained or undrained conditions. In particular, settlements of liquefiable soils are estimated using correlations derived from undrained laboratory element cyclic tests. However, simultaneous settlement and porewater pressure increase in dynamic centrifuge tests suggest that partial drainage may occur in the field. In this study, we compare shaking-induced settlements measured in dynamic centrifuge tests with settlements computed using three correlations for drained conditions and three correlations for undrained conditions. The comparisons illustrate that correlations based on drained conditions typically underestimate significantly the measured settlements, while correlations based on undrained conditions typically overestimate significantly the measured settlements.

Shale formations have been widely characterized in recent years due to their importance in different petroleum and civil engineering applications, especially unconvential shale gas recovery. Hydraulic fracturing in these reservoirs requires having a complete understanding of the petrophysical, static-dynamic, ductile, and anisotropic properties of the shale. Creep deformation of these formations affects the state of regional stresses (impacts the success of hydraulic fracturing) and the transport properties of shale rocks (important in the long term). This paper presents preliminary results from an experimental program that explores ductile behavior of specimens of the Marcellus Shale formation from Allenwood, Pennsylvania, through a series of hydrostatic and triaxial experiments. Experiments were performed at 20 and 30 MPa following the same deviatoric stress (DS) path. The results show that the magnitude of creep is directly proportional to the deviatoric stress level and the confining stress does not significantly affect the creep response.

Weathering degrades the mechanical properties of rocks causing failure or large settlements in many rock-engineering structures. Rock weathering commonly expected to develop on a geological time scale. Tropical climates where there is a dynamic weathering environment (thermal, hydrological, mechanical and chemical (TMHC)) can have a rapid weathering rates. As weathering process continues, specific minerals leached out, altered and newly formed minerals are deposited in fractures. In advanced stages of weathering, large deformations can be produced even under very low loading conditions because of weaker bonding and development of voids. In this study different degree of weathered basaltic volcanic rocks from Deccan Traps formations in India are studied under uniaxial and triaxial compression testing with confining pressure up to 10 MPa. The study introduces a weathering index i.e. Strength ratio (Rs) and rebound number value (R_N) related to the GSI Chart (along with Jcond89 and RQD) for rock mass classification. The estimated GSI values for each stage of weathered rock mass are presented in this paper.

Reproducibility of inter-specimen soil water characteristic curve (SWCC) measurements was quantified for four soil samples collected from the Sagehen Experimental Watershed near Truckee, California. The hanging column method, the UMS HYPROP apparatus, and the dew point potentiometer method provided measurement of the SWCC. The van Genuchten SWCC function was parameterized using regression on data from 10 HYPROP trials per soil and individual measurements from the hanging column. Variability in water content (θ) was ± 0.03 to ± 0.13 at any given suction (Ψ), indicating random variability in SWCC prediction despite identical specimen preparation. Variability in replicate parameter estimates for a single soil may be greater than 14% of median estimates. This variability could affect strength testing reliant upon replicate specimen preparation. Additionally, this result may impact testing programs that commonly rely upon a single SWCC measurement and subsequent parameterization.

Mudflow deposits have a distinct fabric consisting of a mixture of clay and large dispersed rock-like particles. The evaluation of the mechanical properties of these mixtures is challenging. Very little is known about the changes in fabric experienced by these mixtures when subjected to shear, and how these changes influence the failure of the mixtures. In this, study the fabric changes will be studied using simulated clay-rock mixtures. Clay samples containing wooden rods were subjected to direct shear in a plane stress direct shear apparatus (PSDSA). The tests indicated that the clay developed regions of intensified compression at the interface between the clay and the rods. Failure took place in these regions. If more than one rod was present in the samples, the regions of failure interacted producing a continuous failure surface. Also, clay regions near the rods developed voids that influenced the permeability of the simulated clay-rock mixtures.

The principle of effective stress states that the strength and volume change behaviors of soil are governed by intergranular forces expressed in terms of a continuum quantity called effective stress. Past research on effective stress formulations has identified a tensorial quantity that characterizes the liquid phase of unsaturated granular geomaterials. This quantity was named fabric tensor of the liquid phase and was shown to be anisotropic and to have an intrinsic association with the evolution of the effective stress tensor. It was also shown that its variation is random and can be depicted with microstructural image analysis. In this study, two past micromechanical effective stress formulations are discussed in comparison with Bishop’s effective stress. The extended Mohr-Coulomb and effective stress approaches are used in interpreting shear strength parameters and effective stress parameter for partially saturated granular soils. Correlations are identified for some material variables. The nonlinearity observed in the angle of friction associated with the matric suction was discussed in relation to the fabric tensor of the liquid phase.

The direct shear test is one of the oldest and simplest tests used for determining the shear strength of granular soil. The common boundary plate inserts used in the physical tests are either porous stones or grid plates, which ensure drainage, as well as the transmission of shear stress across the soil sample. Often in discrete element method (DEM) simulations, however, a fixed-particle boundary or sawtooth boundary are used. At present, there is limited information available regarding the effects of these boundary types on the observed response. The current study focuses on the laboratory response of the granular material, under four different boundary conditions (fixed-particle, saw tooth, and two sizes of grid inserts). Direct shear tests were conducted on samples of metal ball bearings for each of the boundary types. The influence of these boundaries in relation to the peak shear stresses and friction angles are compared and evaluated. The data collected in this study will serve as experimental validation for DEM simulations of similar direct shear tests.

Cyclic wetting and drying of compacted highly plasticity clays and shales cause volume change through shrinkage and swelling. This eventually may decrease the shear strength to the fully softened state. The objective of the current study is to determine the change in strength as well as physical properties of high plasticity clay due to repetitive swelling and shrinking over time. During this research, the effects of cyclic wetting and drying on the shear strength of the clayey soil were investigated. Soil samples were collected from a slope located on I 35 near Mockingbird, Dallas, to prepare test specimens which were subjected to 1, 3, and 5 wet-dry cycle before the direct shear testing. It is observed that the angle of internal friction decreased by 6^o and cohesion decreased by 55% of initial compacted stage after the fifth wet-dry cycle.

Cone penetration test is a field investigation technique to characterize soils. However, most of the correlations have been developed for dry or saturated soils. Unsaturated soils are mostly available above the water table where suction stresses can influence the cone resistance. Thus, ignoring the partial saturation could result in inaccurate estimation of mechanical properties from the cone resistance. In this paper, cone penetration is simulated inside soil layers with various ground water levels using finite element method. Mohr-Coulomb constitutive model is modified for unsaturated soils. Material parameters are updated according to the stress state and suction profile in depth using user-material subroutines. Lowering the water table increases the cone resistance above the water table due to the presence of suction stresses that contribute to the effective stresses in the soil. However, this difference diminishes passing the water table where suction goes to zero and effective stress decreases in saturated soil.

Ultrasonic wave monitoring methods are among the most promising proven methods in investigating the shear failure of rock discontinuities (fractures or joints). In this study, ultrasonic waves recorded during direct shear experiments on rock joints were employed to investigate the shear failure processes. A series of direct shear experiments was performed on gypsum specimens where shear waves were transmitted through and reflected off the discontinuity as the rock was subjected to shear failure. Distinct peaks in the dominant frequency of transmitted and reflected waveforms were systematically observed prior to the shear failure of the rock and were considered as “precursors” to the shear failure. This study shows that a rock discontinuity behaves as a low pass filter that attenuates the high frequency components of the signal. Such attenuation depends on the stiffness of the rock discontinuity which can be affected by the applied shear stress and the damage at the asperity contact points.

Previous research indicates that significant changes in engineering behavior of cohesive soils may occur if the soil undergoes cycles of freezing and thawing. Understanding this behavior would prove useful to engineering practice as soils subjected to freeze-thaw cycles is a common occurrence during and subsequent to construction or its placement. This research effort focused on the impact of a single freeze-thaw cycle on the deformation characteristics of a resedimented Boston Blue Clay (RBBC). A RBBC specimen was subjected to one freeze-thaw cycle while maintaining vertical stress conditions with a goal to evaluate changes in stress-strain behaviors of the resedimented soil during and after the freeze-thaw cycle. Results indicate that the RBBC heaved 1.6% during freezing but compressed 6.8% upon thaw – all under the same applied vertical stress – this represents a four-fold difference from movements during freezing, indicating that the behavior of cohesive soils subjected to freezing and subsequent thaw warrants careful evaluation and consideration. Additional research is warranted to better understand other factors, such as the influence of stress history and freezing-thawing temperature, on potential expansion and compression movements.

Load carrying capacity of bedrock is needed for the design of foundations for structures in the Dallas-Fort Worth area. The load carrying capacity of bedrock can be estimated by testing rock core samples and by pressuremeter testing. These methods are time consuming and/or rather expensive to implement. An alternative method is to estimate the loading carrying capacity of bedrock in the field using Texas cone penetration’s (TCP) measurements (number of blows per 12 inch cone travel distance or cone travel distance per 100 blows) and charts developed by Texas Department of Transportation (TxDOT). Moon et al. (2004) have developed empirical equations to mathematically predict the compressive strength of shale in Dallas area. However, the rock quality designation (RQD) and rock percentage recovery, which measure the degree of jointing or fracture in a rock mass, have not been included in the published correlations. This study presents a new approach to incorporate RQD and rock percentage recovery as another contributing factor in new empirical correlations along with the TCP’s measurements to better estimate the unconfined compression strength of Eagle Ford shale in particular. This new strength correlation that was developed has a better statistical fitness compared to other previously developed correlations by other researchers.

Previously, researchers have examined phase interactions in multi-phase systems such as geomaterials at different degrees of saturation. Some studies have measured the angle made by the solid-liquid and liquid-air interfaces using physical laboratory tests. The lack of technological advancements that enabled microstructural inter-phase examination has largely impeded results from such efforts. In addition, the measurement of contact angle has largely been dominated by user interference. Recent developments in image acquisition and associated advanced image processing platforms have enabled automated quantification of microstructural features. This study proposes two image-based contact angle-measurement approaches: the “liquid-pixel” and “regression” approaches. The study also investigates “center” identification for contact angle measurement. Statistical evaluation of the measurements is performed for both methods and the observed results are discussed. It is concluded that the “non-zero-intercept” approach, one variation within the regression-based techniques, gave the most reliable angle measurement.

Experiments were conducted to compare two laboratory techniques for measuring thermal conductivity of unsaturated soils: (1) a modified transient plane source (MTPS) method for non-destructive measurements using a planar, interfacial heat reflectance sensor; and (2) a transient line source (TLS) method utilizing a single-probe heat source. Thermal conductivity and thermal conductivity dry out curves (TCDCs) were measured for two sands, including a poorly graded sand, and a well-graded sand with silt. The MTPS sensor resulted in larger thermal conductivity values than the TLS sensor for pore water saturations greater than 50%. At low pore water saturation, the MTPS sensor potentially underestimates thermal conductivity due to poor sensor-soil contact potentially resulting from the absence of water bridges between the sensor and soil surface.

This paper presents the results of computer modeling to predict the response of GS (geological sequestration) reservoirs to CO₂ injection. Coupled H-M (hydro-mechanical) modeling is conducted using the computer code FLAC (Fast Langrangian Analysis of Continua) developed by Itasca (2011) and applied to the CO₂ GS project in the In Salah Gas Field in Algeria. The modeling focused on the H-M response such as the spread of the CO₂ plume, time history of pore pressure increase, and ground surface uplift, which are compared with available field monitoring data and previous modeling studies of the In Salah CO₂ GS Project. In addition, the potential for mechanical failure and eventual CO₂ leakage through the caprock in the In Salah field is analyzed using a critical pressure approach.

This paper aims at clarifying destabilization of volcanic embankments caused by piping phenomenon in which fine particles migrate within void networks. In order to accomplish the purposes, field observation of a full-scale embankment was firstly carried out. Thereafter, a series of upward seepage test was conducted to grasp features of seepage behavior in volcanic soils and to investigate effects of differences in compaction conditions on its behavior. In consideration of test results, it was shown that destabilization of soil structures due to seepage flow is derived depending on an increase of amount of finer soil particles. Additionally, internal stability of compacted volcanic soils under geometric condition was investigated based on Kenny and Lau’s, Kezdi’s and Li and Fannin’s criteria in detail. From the results, a geotechnical evaluation was discussed for the stability of soil structures constructed by volcanic coarse grained soils subjected to seepage flow.

Seepage of water through soil media, if not controlled, may lead to erosion of earth dams and their foundations and eventually can result in instability and failure. Thus, understanding of flow of water through porous media and accurately modeling of this phenomenon are of great importance in geotechnical engineering. In this study, smoothed particle hydrodynamics (SPH) method is utilized to simulate a 2D pressure-driven vertical flow through fixed porous media. To model fluid motion, the spatially averaged Navier-Stokes equations are implemented into SPH formulations. The spatial heterogeneity and anisotropy of pore space are introduced in the model using local porosity values imported from granular samples created using the discrete element method (DEM). Fluid-solid coupling is considered using classic semi-empirical equations. A SPH model is developed using one-way coupling method, to simulate flow of water through fixed porous media under various hydraulic gradients caused by different mechanisms (e.g., pressure gradient, body force). The effects of porosity values and hydraulic gradients on discharge velocity are studied. The results are compared against published simulation results to validate the developed SPH model.

Stormwater control measures (SCMs) are used to control runoff volume and peak flow rates. Rain gardens are one type of vegetated SCM which can utilize engineered or native media. Hydraulic conductivity, which can be measured in the field or laboratory, is a major design parameter for infiltration SCMs. The double-ring infiltrometer (ASTM D3385) is the most commonly used technique to determine hydraulic conductivity in the field; however, it can be cumbersome because of its considerable size and large water usage. In this study, various infiltration techniques, such as Modified Philip-Dunne, single-ring, and double-ring infiltrometers, were used to determine the hydraulic conductivity at different sites. In addition, the UMS KSAT Benchtop laboratory method was used to find hydraulic conductivity. Preliminary results indicate that the Modified Philip-Dunne provides results similar to the other tests methods.

Artificial ground freezing has been used for over 100 years to provide temporary earth support and groundwater control for deep excavation in both unconsolidated soils and rock. Time dependent thermal numeric models have been used to evaluate the required freezing time for ground freezing systems and to evaluate the required refrigeration loads. Groundwater velocity through the freezing system is a mechanism that introduces additional heat energy into the system that can retard or even prevent the formation of a frozen earth barrier. Recent software developments have introduced models that couple the traditional heat transfer model with groundwater flow models. These models allow the design engineer to evaluate the effects of the groundwater velocity on the freezing system. It permits the design engineer to modify the ground freezing system or to reduce the permeability of the soils with ground improvement techniques thereby reducing the groundwater velocity permitting timely ground freezing operations. This paper discusses the application of these models and compares them to actual field results on key ground freezing projects. The results of these comparisons indicate the commercially available models are reliable thereby establishing a standard method of design for ground freezing projects.

Degree of water repellency significantly influences the infiltration behavior of water-repellent soils. In this study, the chemically treated water-repellent kaolin clays with different concentrations (C_O) of an organosilane solution are examined to explore the effect of water repellency on its infiltration characteristics. Experimental results show that the soil-water contact angle tends to increase with increasing C_O until C_O = 5%, and then shows an almost constant value with increasing C_O. The water infiltration time (WIT) results show that water infiltration resistance is significantly improved by organosilane treatment (C_O ≥ 5%) under low hydrostatic pressure (WP). However, as the hydrostatic pressure increases, WIT is converged (C_O = 5%) or exacerbated (C_O = 10% and 20%) to the WIT of untreated clay. The different behaviors of infiltration are discussed in terms of wetting patterns. The findings can be used to improve a conventional hydraulic barrier system.

Numerical simulations of water flow through unsaturated soils have been well studied but very few studies have addressed water movement across soil interfaces by imposing continuity of both flux and pressure head. Imposing continuity of both head and flux leads, at a local discrete level, to a nonlinear interface equation which may exhibit multiple solutions if the spatial discretization is not fine enough, for example during infiltration with sharp fronts or in the presence of very dissimilar soil layers. The non-uniqueness of solutions of the interface equation can lead to numerical errors and/or numerical oscillations. We use a staggered finite difference approach with cell-centered hydraulic conductivities estimated by averaging nodal conductivities. We evaluate the impact of several averaging schemes (arithmetic, harmonic, geometric and log-mean) on the occurrence of multiple solutions and associated numerical issues. The resulting numerical schemes are compared in terms of their propensity to trigger multiple roots at soil interfaces. Our results show that the choice of averaging scheme does affect the occurrence of multiple solutions and long term behavior of the numerical solution. In particular, our simulations confirm that the averaging schemes associated with larger interface conductivities (log-mean and arithmetic mean) are less likely to suffer from non-uniqueness issues of the interface problem.

Coupled heat and water transport has found to be relevant in unsaturated soils because of increasing interest in disposal of radioactive wastes, geothermal energy, hydrology and agricultural problems. In an unsaturated soil, heat can be either latent or sensible or both and water may take the form of either liquid or vapour or both. The impact of thermal gradient on water vapour movement in terms of both vapour and liquid flow is essential and it requires accurate experimental quantification and representation for modeling of coupled heat and water vapour flow. Although it is possible to calculate the total water vapour flux, it is difficult to distinguish experimentally between liquid and vapour fluxes in unsaturated soils. This paper focuses on providing a critical review on heat and water vapour transport in unsaturated soils.

In this study we developed a numerical model based on isogemoetric analysis (IGA) to simulate variably saturated flows. A head-based formulation and mass-lumping technique are used to determine the wetting front progress in unsaturated soils. This study shows that the IGA-based method is able to use higher order non-uniform rational basis functions (NURBS), extensively used in computer aided design (CAD), to model highly nonlinear problems. Unlike Lagrange shape functions, NURBS have non-negative amplitude even for high order approximations. It is shown that higher order NURBS are able to predict wetting front in highly nonlinear problems. To demonstrate this capability, a highly non-linear transient unsaturated seepage problem is simulated in both IGA and finite element analysis (FEA). The results show that the IGA model performs properly over a wide range of unsaturated flow problems while higher order FEA model diverges especially in problems with high level of nonlinearity.

Gas hydrate plays a critical role in new energy resource, global carbon budget, and submarine instability. Enhanced understanding on how gas hydrates influencing these issues largely depends on in-depth understanding of multiphase flow in hydrate-bearing sediments particularly during hydrate formation and dissociation processes. However, appropriate selection of flow parameter values for hydrate simulators is not available. Published parameter values show large discrepancies among hydrate simulators as well as between numerical and experimental studies. Based on experimental results of single-phase flow in hydrate-bearing sediments, recommended flow parameters for hydrate-bearing sediments are λ = 1, S_rw = 0.1, and S_rg = 0.55 for the Brooks and Corey model and m = 0.7, S_rw = 0.1, and S_rg = 0.5 for the van Genuchten model. In general, current hydrate simulators underestimate residual gas saturation S_rg, which will lead to overestimated rate of gas production from hydrate deposits. These results are also relevant to multiphase flow in porous media undergoing diagenesis, bio-clogging, or mineral precipitation and dissolution.

The physical properties of granular materials, such as hydraulic, strength, and thermal properties, are dependent on the density (or porosity) and particle size distribution of materials. Among others, the understanding in thermal properties of granular materials is still in immature stage. In this study, the thermal conductivity, one of important thermal properties, of Silica sands with varying porosity and particle size are experimentally investigated using the transient method. Based on experimental results, the thermal conductivity of granular materials was presented as the function of porosity and proportion of finer particles. It was found that the thermal conductivity tends to become lower under higher porosity and lower proportion of finer particles, and vice versa. Further study on the thermal conductivity of granular materials regarding their packing condition and particle size distributions should be required more in mechanical or generalized terms.

The freeze-thaw cycles in unsaturated frozen soils can cause serious damage to civil infrastructure. In this paper, a microstructure-based four-phase clay model is generated in Matlab. The model is then converted into a finite element software Comsol. The thermal, hydraulic and mechanical properties of each phase (soil particle, ice, water and air) of the clay are applied randomly to each pixel of the image model based on the volumetric content of each phase. The simulation results show that: (1) The thermal and hydraulic flow are observed during the freeze-thaw cycle. (2) The temperature, matric suction and potential head are obtained during the thawing process of the clay model. (3) The internal stress distribution versus time are calculated during the freezing process. The simulation results agree well with the engineering experience, which provides a simulation model to microstructurally analyze the thermal, hydraulic and mechanical properties of unsaturated frozen soils.

Study on soil thermal conductivity draws much attention recently since it is a governing soil thermal property in heat transfer process for geothermal applications. The variation of soil thermal conductivity at shallow depth is less understood because it is affected by various environmental factors (e.g. temperature, humidity, precipitation, etc.). This paper presents the measurement of thermal conductivity dry-out curves (TCDCs) for sands using a modified hanging column device (MHCD). Thermal conductivity of three sands was measured continuously from fully saturated condition to dry condition using a KD2 Pro (i.e. TR-1 single probe). A thermo-TDR probe was also used to measure sand moisture content. TCDCs of test sands were established with respect to degree of saturation, and then compared with the measured thermal conductivities obtained by multiple-specimen method (MSM). A good agreement of measured thermal conductivity was found between the MHCD and the MSM. The predicted TCDCs by three alternative thermal conductivity models were also compared with the measured curves. Recommendations have been provided to improve the models for wider applications.

The effectiveness of two models to estimate the thermal conductivity of sands is reviewed. Haigh (2012) proposed an analytical model based on unidirectional heat flow through a three-phase soil element. Using a database of 155 test measurements, his model performed with similar effectiveness to the empirical model proposed by Chen (2008). The database used by Haigh (2012) depended largely on the measurements conducted by Chen (2008). Eighty of the 155 measurements were conducted on 4 high quartz content sands presented by Chen (2008). In this study thermal conductivity tests were conducted on 3 sands at dry and wet conditions. The effectiveness of the Haigh (2012) and Chen (2008) models are reviewed using the new dataset. Overall, both methods performed reasonably well and the conclusion of Haigh (2012) that his model out performed the empirical models was confirmed.

In this study, soil critical temperature was measured using two distinct approaches: (1) a temperature profile established from a heating element located at the top of a vertical column and (2) temperature and moisture profiles induced from a centrally placed heating source in a ‘horizontal’ apparatus. Steady-state thermal and moisture equilibrium took longer to establish in the horizontal apparatus (on average, nine hours longer); however, the resulting temperature and moisture profiles were more consistent in the horizontal apparatus and with easily discerned slope discontinuities between the dry and moist zones. More ambiguous temperature profiles were observed in the vertical apparatus, even with insulation and heat tape applied to minimize horizontal boundary losses. This is indicative of the difficulty in maintaining one-dimensional heat flow in a vertical column. As soil critical temperature is an important parameter used in designing underground infrastructure impacted by significant heat transfer, such as buried power cables, refinement and standardization of equipment and protocol for determining this parameter in a precise and mechanistically sound manner is of prime concern.

A deep geological repository, DGR is an underground disposal facility for the safe disposal of high-level radioactive wastes. In DGR, the radioactive waste is vitrified and placed in metallic canister, which is encrusted with a thick layer of engineered geomaterial called buffer material. As the radioactive waste generates moderate amount of heat due to its decay, a thorough performance evaluation of the buffer material demands the knowledge of their thermal properties and rate of moisture loss. With this in view, it is proposed to investigate the coupled flow of heat and moisture. Experimental study involves imposing heat flux to the buffer material using a constant heat source representing radioactive waste contained canister. Thereby, the soil near the vicinity of the heat source is subjected to a higher temperature when compared to the rest, causing heat and moisture migration from the surface of the heat source towards the periphery. From the spatial and temporal variation of temperature and relative humidity (RH) obtained experimentally by means of deploying sensors over varying depth and radial distance, the vapor flow within the system is demonstrated in terms of its isothermal vapor diffusion coefficient.

Lightweight cellular concrete has been utilized in many geotechnical applications including as the backfill in retaining walls, lightweight pavements, land slip repairs, bridge approach fills and to provide shock absorption in earthquake zones. The use of this material in seismic regions requires an understanding of its dynamic properties. In this study, five different mixes of lightweight cellular concrete, with varying unit weights were tested in a cyclic simple shear apparatus. The samples were subjected to four different consolidation pressures followed by a series of fifteen strain-controlled undrained sinusoidal cyclic loads. The cyclic strains were varied from 0.08% to 1.0% double amplitude shear strains. From the results obtained, the maximum shear modulus was found to increase as the dry unit weight of the material decreased and as the consolidation pressure increased. The damping ratio was found to decrease with increasing shear strain until a threshold shear strain was reached beyond which the damping ratio increased with an increase in the shear strain. This threshold shear strain ranged from 0.25% to 0.35% for the specimens tested.

Recent studies in soil improvement have shown that the use of biopolymers are capable of significant enhancements to various engineering properties of the soil. Strengthening efficiencies, reduced permeability, and improvements to friction angle are all benefits that biopolymer use have onto the soil. However, in order to fully utilize the biopolymer technology into the fields, a full understanding of the geotechnical properties is necessary. In this study, one dimensional oedometer consolidation tests were performed with attached p and s wave sensors for elastic wave property measurements. Gellan gum biopolymer was used in this study, and its effects on the elastic properties and consolidation behavior for sandy and clayey soils were observed. Results showed that due to the high electrical sensitivity and hydrophilic properties of the biopolymers, the elastic properties and consolidation behavior of the biopolymer treated soils varied greatly from the untreated soils.

A more sustainable destination for water treatment sludge (WTS) is its use in earthworks and as landfills liners. However, because of its high water content and plasticity, the investigation of WTS workability in construction procedures is mandatory. As a contribution for this purpose, this paper investigated the thixotropic effect of Cubatão WTS by means of laboratory vane tests. The experimental procedure consisted in preparing triplicate samples of sludge remolded at the liquid limit and storing them for different times to determine the gain of undrained shear strength. Results indicate that Cubatão WTS is thixotropic. The very low remolded undrained shear strength triples after five months of storage. Despite the thixotropic regain reaching 200%, the strength is still insufficient for geotechnical purposes and additional treatments will be necessary to turn the sludge into a reusable material for earthworks.

This paper pertains results of experimental studies carried out on reinforced bottom ash based geomaterial. The proposed geomaterial is prepared by blending bottom ash with expanded polystyrene beads, waste plastic water bottle strips and a binder such as ordinary Portland cement. The mix ratios used in the experimental study were 0.2%, 0.6%, and 1.0%. The plastic strips were used in two different aspect ratios 0.1 and 0.2 with different mix proportions 1%, 2%, and 3%. The cement to bottom ash ratio was considered as 10%. The effect of mix ratio, percentage of plastic strips and curing period on the compressive strength, stress-strain behaviour, density and secant modulus were studied and results are incorporated in the paper. The result indicated that for a particular mix ratio, the compressive strength increased with increasing aspect ratio. Nonlinear relationship was observed between compressive stress and axial strain for all the mix ratios and curing periods.

The rapidly emerging sub-discipline of biogeotechnics is comprised of both bio-mediated and bio-inspired technologies. Research and development over the past decade have focused primarily on bio-mediated technologies, while research on bio-inspired geotechnical technologies is still in the early stages. This paper synthesizes the advances in the broader field of bio-inspired design and highlights aspects particularly relevant to the exploration of new geotechnical engineering innovations. The structure, advantages, and challenges of both problem-based and solution-based design methodologies are presented. A hierarchical framework for the characterization of biological systems is discussed in the context of how the framework facilitates the use of bio-inspired methodologies. Finally, an example application of the bio-inspired design methodology to tree root inspired foundation and anchorage systems is explored and discussed.

Microbially induced calcite precipitation is bio-mediated calcite precipitation process that can improve the geotechnical properties of granular soils. Bio-cementation offers an environmentally conscious alternative to more traditional ground improvement methods by utilizing natural microbial activity to induce calcite precipitation on soil particle surfaces and at particle contacts. Previous research studies have demonstrated the ability of bio-cementation to increase soil shear strength, initial shear stiffness, liquefaction resistance, and reduce hydraulic conductivity and porosity; however, few researchers have examined the shearing behavior of bio-cemented sands at the particle scale. In this study, four poorly-graded sand specimens were treated to different levels of bio-cementation and subjected to drained triaxial compression. During shearing, the internal structure of soil specimens was examined using X-ray computed tomography and various digital image correlation techniques. Results demonstrate that various levels of bio-cementation can increase peak shear strength by 47% to 1487%, reduce internal deformations required to mobilize peak strength, and change the onset of shear banding from a gradual and widespread development to a more abrupt and narrow feature after failure.

Recently, chemical stabilization has gained attention for high moisture fine-grained soils, due at least partially to increased sustainability and beneficial use desires. As defined herein, very high moisture soil (VHMS) is at a moisture content at or above the soil’s liquid limit. Cases where VHMS is chemically stabilized with 5% or more cementitious material by total VHMS mass is referred to as cemented VHMS (C-VHMS). A primary objective of this paper is to compare portland cement to blended portland and slag cement for C-VHMS at early ages. Another objective is to determine strength, modulus, and ductility properties of C-VHMS over a period of several months to establish strength to modulus correlations. All other factors constant, slag cement’s strength gain potential is greater at later ages than at early ages, and as such, sluggish early strength gain that can be problematic was evaluated a considerable amount in this paper.

Recently, chemical stabilization applications seem to be expanding, in particular stabilizing fine-grained soils with elevated moisture. In this paper, very high moisture soils (VHMS) chemically stabilized with 5% or more cementitious material by total mass are referred to as cemented VHMS, or C-VHMS. This paper’s primary objective is to evaluate strength gain of C-VHMS over time and use the measured properties to evaluate usefulness for various applications. A secondary objective is to compare properties of Portland cement to blended Portland and slag cement within C-VHMS. C-VHMS strength properties were reported from mixing through 180 days of curing on two soils. Results showed Portland and slag cement blends were able to produce on the order of 67% of compacted soil-cement (albeit with considerably different total dosage rates) in one of the soils. Overall, C-VHMS, when allowed sufficient curing time, was shown to be more robust than intuition might suggest.

With no more than a couple of thousand years of experience, humankind has developed some innovative techniques to leverage the subsurface for a variety of beneficial functions. In contrast, nature has had the benefit of several billion years to initially design and subsequently evolve the manner in which flora and fauna practices soil mechanics. This paper uses two examples of biota to compare how nature has evolved its solutions in contrast to what humans have done and identifies enhancements that humans could exploit through a deliberate mimicking of what nature has done (i.e. bioinspiration). In particular, a comparison of selected aspects of ant-soil interaction and root-soil interaction are used to illustrate where significant potential exists in the emerging field of bio-geotechnics. The paper describes the salient characteristics of the framework by which nature designs its technology, and in turn, a methodology by which humans can augment our current design processes.

The reliability analyses of one rockfill embankment dam in Norway are presented. The event tree analysis and the Bayesian network approaches, the latter combined with Monte Carlo simulations, were used to obtain the annual probability of dam breach. The analyses were run partly in a workshop format, as a process to reach consensus among several experts on the parameters to consider in the calculation of probabilities. The analyses illustrate that the reliability analyses enabled the identification of an unexpected mode of failure and later quantified the effect of rehabilitation measures on the estimated probability of dam breach.