Geo-China 2016: Geosynthetic Civil Infrastructure, Disaster Monitoring, and Environmental Geotechnics

This paper presents a numerical investigation of the effects of large strain consolidation on contaminant transport in multi-layer soils. Numerical simulations were conducted using the CST3 model, which accounts for one-dimensional coupled large strain consolidation and contaminant transport in saturated multi-layer porous media. The consolidation algorithm accounts for vertical strain, soil self-weight, general constitutive relationships, relative velocity of fluid and solid phases, changing compressibility and hydraulic conductivity during consolidation, unload/reload, time-dependent loading, time-dependent boundary conditions, external hydraulic gradient, variable preconsolidation stress profiles, and multiple soil layers with different material properties. The contaminant transport algorithm accounts for advection, diffusion, mechanical dispersion, linear and nonlinear sorption, equilibrium and nonequilibrium sorption, porosity-dependent effective diffusion coefficient, and first-order decay reactions. Simulation results indicate that layered soil heterogeneity can have significant effects on both consolidation behavior and contaminant transport behavior. Characterization of a multi-layer soil stratum as a homogeneous single layer with average properties may result in significant errors in the analysis of consolidation-induced contaminant transport in multi-layer soils.

The design approaches in shallow square foundations generally based on Prandtl and Terzaghi bearing capacity theory. Other investigators who deal with this subject have already developed their design with adding or changing design parameters on this approach. Within thirty years investigators try to find out effect of saturation degree on bearing capacity of foundation. Especially, in semi-arid and arid region determination of bearing capacity using saturated state bearing capacity equations produces over design for foundations. In this study, using commercially finite element analysis software (SIGMA/W), the effects of suction pressure and saturation degree on shallow foundations have investigated. The necessary design parameters, which are used in the finite element program, are obtained in the laboratory studies in İstanbul Technical University. According to this research, it is recognized that the bearing capacity of foundation using unsaturated soil parameter has increased comparing to design with saturated state design parameter. These results encourage the designers using unsaturated soil parameters especially in arid and semi-arid regions.

The influence of external applied stress on permeability of hydraulic barrier soils has not received adequate attention from researchers in recent times. The method of determining the coefficient of permeability (k) from back calculation from consolidation test is presented in this study. Special effort was made to derive a relationship between the coefficient of permeability and applied stress. Clay soil samples with potential for use as clay liners were taken in Akure, Southwestern Nigeria. Preliminary laboratory tests carried out on the samples include natural moisture content, particle size distribution test, pocket penetrometer test, and unconfined compression test. Consolidation test were performed on the soils, carefully simulating natural in-situ compression and the coefficient of permeability obtained ranged between 1.89 x 10-9 m/s and 1.35 x 10-11 m/s. Experimental results reported in this project indicate that permeability is inversely proportional to applied stress. For sample 1 when the pressure was 100 KN/m2, the coefficient of permeability was1.89 x 10-9 m/sec. however, when pressure rose to 3200 KN/m2, the coefficient of permeability dropped to 5.12 x 10-10 m/sec. Variation of voids ratio with progressive increment of applied pressure was monitored during the experimental programme. Statistical linear regression equation for the relationship between coefficient of permeability and the applied pressure gave a high coefficient of determination (0.985) with cubic polynomial best fit, which is close to 1, hence the best model for describing the relationship. Using the Samarasinghe, Huang and Drnevich, empirical relation between voids ratio and coefficient of permeability to validate the experimental results, log {k (1 + e)} - log e relationships have been obtained for the Akure clay soils. A comparison was made between the result obtained from the laboratory, the empirical Samarasinghe equation, and those reported by other authors. There was reasonable agreement to suggest that the coefficient of permeability values obtained from consolidation tests are reliable.

Oedometer and suction tests were performed in the laboratory on samples of black cotton soil of North-Eastern Nigeria compacted by static compaction to various degrees of saturation and moisture content to determine the compressibility and hydraulic conductivity characteristics at different states of stress in the pore-water. The goal is the evaluation of pavement performance and hydraulic barrier behaviour of semi-arid/arid soils under varied soil moisture and applied stress conditions. From the results, the basic index properties of the black cotton soil such as fines content, plasticity index, clay activity and predominant clay mineral were discussed against the backdrop of the pollution barrier potential of this tropical black clay. Soil suction decreased from 5.2 pF at 20% saturation to 1.8 pF at 100% saturation. Soil suction has been identified as a major factor controlling the expansive nature of black cotton soil i.e swelling- shrinkage properties. The coefficient of consolidation, which is an indication of the rate of consolidation, increased from 0.088 at 20% saturation to 0.324 at 100% saturation. It was observed that the hydraulic conductivity increased only by an order of magnitude from 2.83 x 10^-8 m/s to 2.15 x 10^-7 m/s as the degree of saturation increased from 20% to 100% when voids ratio varied between 0.305 and 0.338. This reveals that change in the hydraulic conductivity of the black cotton soil with increase in degree of saturation was not as remarkable as the change in compressibility. However the highest hydraulic conductivity value at 100% saturation (2.15 x 10^-7 cm/s) is within the upper acceptable limit requirement for leak-proof waste containment liners (1 x 10^-7 cm/s).

Two compaction energies, the Reduced British Standard Light (RBSL) and British Standard Heavy (BSH) covering a wide range of compactive efforts were used to investigate the variations in the hydraulic conductivity with compactive effort and bentonite content for sand-bentonite mixes. In this study the Patani sand from South-South Niger Delta, Nigeria was mixed with bentonite at varying percentages of 0%, 2.5%, 5.0%, 7.5%, and 10% by weight of sand. The index properties of the Patani sand are: specific gravity - 2.65, fines content (<0.075mm) - 4.65%, and SiO₂ content – 97.01%. The bentonite has fines content (<0.075mm) of 83.5%, liquid limit of 176.4%, and plasticity index of 115.3%. Test results indicate that hydraulic conductivity (k) of mixtures decreased by three orders of magnitude from 3.919×10^–7 m/s to 3.792×10^-10 m/s with increasing of bentonite content from 0% to 10% under the RBSL compaction, and from 3.704×10^–7 m/s to 2.700×10^-10 m/s with increasing of bentonite content from 0% to 10% under the BSH compaction. The hydraulic conductivity values at 5% bentonite content of 7.518×10^–9 m/s and 5.673×10^-9 m/s for RBSL and BSH compaction satisfied the specification of hydraulic conductivity, k ≤ 1×10^-9 m/sec for landfill liners by the United States Environmental Protection Agency. Mixing sand with appropriate bentonite contents and adequate compaction yielded a sand-bentonite mixture having low hydraulic conductivity that could be useful as a hydraulic barrier/waste containment liner for the Niger Delta coastal areas.

Effective treatment of mercury contaminated soil is highly challenging due to high toxicity, volatility and environmental mobility and the varied nature and composition of industrial waste products. Conventional stabilization /solidification methods include fixation of metals using Portland cement and fly ash. However it is difficult to stabilize mercury with cement based processes because it does not form a low solubility hydroxide surface. Hence the use of lime as a prospective soil amendment to retain mercury is studied. In this study, locally available semi-arid soils (Al-Ghat and Al-Qatif) having different chemical and mineralogical characteristics are considered and their response to mercury adsorption at varying initial concentrations, pH conditions, temperature and dilution ratios are studied. Empirical models (Langmuir and Freundlich) are applied to ascertain monolayer or heterogeneous adsorption. The adsorption studies are even carried out after amending the soils with lime. Kinetic models are employed to validate the type and nature of sorption taking place (whether pseudo first-order or second-order). It was found that both Al-Ghat and Al-Qatif soils when amended with lime attenuate mercury and the experimental results correlate well with selected empirical models.

Soils are known to retain heavy metals through a number of processes. Human exposure to highly nickel polluted environments has the potential to produce a variety of pathological effects. Some of them are skin allergies, fibrosis of lungs and cancers of the respiratory tracts. In this study four different leaching methods viz. ASTM D3987, Toxicity characteristics leaching procedure (TCLP), extended TCLP, and caged TCLP have been used to study the leaching behavior of Ni²⁺ on red soil and red soil amended with nano calcium silicate (NCS). It was found that as per ASTM D3987, Ni²⁺ with red soil was retained well in the short term and over a long term period the metal ion was released back. Red soil was amended with NCS and it was found that over a period of time the retention was satisfactory which proved that NCS was responsible for encapsulation of Ni²⁺ in its matrix. Extensive leaching tests were further performed; it was found that as per TCLP, extended TCLP and caged TCLP tests the retention of Ni²⁺ with amended soil was 88%, 90% and 94% better than soil respectively Hence it can be concluded that NCS amended soil is a prospective material to attenuate Ni²⁺ taking into consideration the long term effect of heavy metals on soils.

Li-Shing Estate Road is a mountain road that plays an important role in communication between mountain villages and allows the transport of agricultural products from mountain villages to urban areas. However, Li-Shing Estate Road is located in a fracture zone, and landslides occur regularly along the road. Identifying the possible areas of landslide occurrence is an important issue in the prevention of disasters associated with landslides. This study employs the modified multiphase segmentation method to segment the normalized difference vegetation index (NDVI) generated using infrared and red-band information provided from SPOT satellite images. Low NDVI values can be grouped together to form a series of sub-regions. These sub-regions indicate regions that are either villages or landslide areas. The proposed approach imposes edge information in the multiphase segmentation method proposed by Vese and Chan, such that a series of NDVI data over different years can be efficiently segmented. By eliminating village areas, the landslide areas can be located. The located areas are compared with suspected areas provided by Moh And Associates Group Consulting Engineers to verify the segmented results. The MAA Group carried out geological exploration and drilling along Li-Shing Estate Road, such that suspected areas where landslide phenomena could occur have been located and reported. In addition to the modified multiphase approach, another segmentation approach called statistical region merging is employed to demonstrate that the landslide phenomena can be identified by employing an objected-oriented segmentation approach.

The purpose of this study is to obtain the horizontal displacement field of Nantou County 89^th County Road 12.3K’s landslide and its surrounded area based on particle image velocimetry (PIV) technique. The obtained orthophotographs, which were taken in 2008 and 2009, were analyzed by using the PIVview2C software to do the PIV analyses. The results show that the maximum horizontal displacement is about 6.07m in this study area, but 90.4% of the calculated displacement magnitude is less than 2.5m. The major moving direction is toward the azimuth 247.5°-292.5°. The results of PIV analysis can quickly obtain the surface movement magnitude and direction compared with the traditional methods.

Land use and climate change are both important drivers for ecosystem degradation. Human-driven land use changes, such as deforestation and urbanization, reduce ecosystem resilience to disasters. The impacts of climate change include global warming and the increasing frequency of extreme weather events such as storms, flood, and drought. In order to understand how land use change and climate change affect the ecosystem services in the Chenyulan Watershed, Taiwan, we first classified the satellite images during 2008-2013 for land use maps. The impact of cumulative natural disturbances on watershed was quantified by using a hydrological model, SWAT (soil and water assessment tool) under various historical (1996-2013) land use conditions. Based on our results, we could further develop an integrated plan including ecosystem service management, land use management and climate change adaptation to increase the resilience of the ecosystem in the Chenyulan Watershed.

Long-term water immersion weakens slope rocks and degrades rock-layer parameters such as cohesion (c) and friction angle (ϕ), causing slope failure. The traditional analyses of slope failure generally set fixed values to the required parameters by limit equilibrium, but omit uncertainties of the parameters. These methods fail to fully reflect the slope safety factor, causing unreliable calculated safety factors. We examined the collapse of the Cidu section (3K+100) dip slope on Taiwan Formosa Freeway for the sensitivity analysis of c and ϕ and uncertainties related to the variation of the safety factor before and after water immersion and slope rock weakening. The sensitivity analysis results showed that c has greater effects on the slope safety factor compared with ϕ. In the uncertainty analysis, we used three different point estimate methods and the Monte Carlo simulation to calculate the corresponding slope safety factors. This method established the probabilistic analysis of slope stability. We also explored the effect of ρ (correlation coefficient of c and tan ϕ) on safety factors. The traditional analysis results found that the factor of safety is approximately 1, but the probability of failure of slopes reaches 50%, indicating urgency in using stabilizing measures.

Geosynthetic reinforced soil retaining structure has gradually replaced the old-style gravity retaining structure the world over and become the mainstream of soil retaining structure technology. In recent times, the geosynthetic reinforced technology is broadly used in the construction project for slope in Taiwan. It is essential to understand the response of geosynthetic reinforced slope for the dynamic behavior under seismic forces, especially in the region that earthquakes occur frequently. In this study, the seismic monitoring system on the geosynthetic reinforced slope built in FoGuang University is set up to record the seismic data. PLAXIS finite element program is utilized to simulate the seismic response of the geosynthetic reinforced slope under earthquakes. The recorded seismic data from the site monitoring system are applied to the PLAXIS finite element analysis program for validating and exploring the PLAXIS dynamic simulation program. The technique of seismic numerical simulation for the geosynthetic reinforced slope by the PLAXIS finite element program is described briefly. The seismic simulation process is also performed for investigating the maximum acceleration overall the study slope. Both the monitored and the predicted results show that the acceleration amplification of geosynthetic reinforced slope does occur under earthquake from the bottom to the top.

MSE retaining structures with polymeric strips reduce project cost and environmental impact compared to traditional methods. High tenacity polyester strips represent an alternative solution to soil reinforcement in MSE walls. A wide range of strips tensile strength, width and LLDPE coating thicknesses allow the optimization of the design and the use of backfill materials such as lime treated soils, untreated ash fills and cohesive soils. This paper presents the design method, tests results and installation considerations related to three case studies of MSE wall projects recently realized in Texas and Florida, with non-standard soil materials.

Laboratory model tests were carried out to study the behavior of strip footing resting on a geogrids-reinforced dune sand. The tests were performed on a rigid steel tank having glass side with inner dimensions of 1 m by 0.64 m by 0.23 m. Footings were placed at different depths from the surface of sand. Geogrids were placed at different depths below the footing starting at 0.25B to 1.25B. The sand was placed in the tank using raining method. The use of geogrids improved the bearing capacity of strip footings by a factor of up to 4 times. The improvement depends on depth of the footing, the depth of the geogrids below the footing and the number of the geogrids layers. For two layers of geogrids the highest improvement is when the depth of first reinforcement below the footing is between 0.25 to 0.5B, the spacing (h) is between 0.25 to 0.5B and the overall depth of the reinforcements (d_r) is about 0.5 to 0.75B. The geogrids modified the load-settlement curve for the footing by increasing the strains at failure to up to three times that of unreinforced sand. This means with geogrids the footing will undergo more elastic settlements before failure.

The long-term performance of any construction project is influenced by the underlying soil properties. Unstable soils can create significant problems for pavements, structures and slopes. Soil can be stabilized by using a wide range of materials, such as cement, lime, fly ash, and others. When lime and water are mixed with a clay soil, modification of the soil properties and stabilization reactions begin. These reactions occur in the highly alkaline environment (pH >12 for a short period of time). This paper presents a solution to the corrosion of steel reinforcements in alkaline environment through the use of planar high tenacity polyester strips LLDPE coated as MSE walls with concrete facing panels reinforcement. Case studies are referenced with particular focus on the soil parameters, on lime percentage in the reinforced backfill, on the behavior and the durability of the LLDPE coated reinforcement, and on the installation procedure.

This paper numerically investigates the performance of geosynthetic-wrapped and -layered soil commonly used for constructing retaining structures by the discrete element method. First, the geotextile and the soil that make up the reinforced soil are calibrated with tensile, shear box, and triaxial test results. The discretization of two reinforced soils are then introduced, which considers geotextile as an assembly of particles linked with stretching springs. Second, the discrete models of two reinforced soils in periodic boundary condition are examined in triaxial compression in order to evaluate the effect of reinforcement form on soil behaviors. Three geotextiles that vary in tensile stiffness are considered. The simulations show that the wrapped soil is able to sustain greater stress than the layered one. Though similar global volumetric change is found in both cases, the soil wrapped in a container dilates less than that sandwiched between a pair of sheets. In the reinforced domain, stress paths and strain localization are analyzed, from which the reinforce mechanisms are better understood.

Cantilever retaining walls with lengthy free heights are usually required in several geotechnical applications. Compacted soil is the typical backfill behind such walls, yet soil has high unit weight that imposes large lateral loads and may lead to wall outsized dimensions. Expanded polystyrene (EPS) or Geofoam can substitute the soil backfill due to its lightweight and high compressibility, and can reduce the lateral static loads imposed on walls. In this paper, the EPS main parameters were measured after conducting a series of laboratory tests to determine the mechanical and interface properties. Also, a reliability analysis was conducted to calibrate the partial resistance factors for the EPS mechanical properties. Then, a flexible cantilever retaining wall with EPS inclusion was modeled using finite element. From the main outcomes, the lateral pressure was significantly reduced after using the EPS inclusion by up to 75%.

Laboratory sand box tests were performed in this study to investigate the improvement in bearing capacity of a strip footing reinforced with woven geotextile in dry sand. The test cell is 0.9m wide, 0.9m long and 1.0m high. A hydraulic loading system was used to apply the normal force to a 0.85m × 0.1m × 0.05m (length × width × height) strip footing. The unreinforced bearing capacity was obtained and compared with value calculated using Terzaghi’s equation. Various parameters such as: burial depth, length of reinforcement, number of layers and distance between layers were varied to investigate their effects on the bearing capacity. Results of these tests indicate that the optimum burial depth of reinforcement is about 0.4 times the width of footing, with a bearing capacity ratio (BCR) of about 1.67. The optimum reinforcement length is about 3~4 times the width of footing with a BCR value of 1.81. The improvements in bearing capacity obtained from laboratory testing are in accord with previous numerical simulation. However, the loading behaviors are quite different due to the failure mechanism assumed in the numerical simulation.

Reinforced earth is an kind of composite soil composed of soil and reinforcement. In this paper, two methods to analyze the mechanical behaviors of geosynthetic reinforced soil are introduced. In one method, soil and reinforcement are considered separately and they interact with each other through the interface between them. In the other method, the reinforced earth is considered as an anisotropic homogeneous composite. The shortcomings of the two methods are discussed, and on this basis, a new method to analyze the mechanical behavior of reinforced earth is presented.

Vegetation restoration method is a kind of new technique to protect the stability of slope, which has been widely used in railway, highway and hydropower projects in China. In this paper, the history of vegetation restoration method is firstly summarized, then the factors influencing the success of this method are analyzed, and the interaction between soil and vegetations, which is the most important factors, is discussed. Finally, applications of vegetation restoration method in practice are introduced.