Variation of the Hydraulic Conductivity of Clayey Soils in Exposure to Organic Permeants

Clayey soils are the most common material used in waterproofing and play an essential role in waste and contamination control. Permeability is a key parameter in such problems and its determination is needed in ensuring the satisfactory performance of the soil. Research has shown that a permeant fluid with a low dielectric constant can shrink the double layer around the clay particles which will, in turn, increase the permeability of the soil. In this paper, the permeability of two types of clay with different plasticity, exposed to the flow of water and methanol as polar and miscible solvents and gasoline and car oil as non-polar and immiscible solvents is investigated. In addition, the effect of soil properties such as plasticity and compaction water content on permeability of the samples is examined. To this end, soil samples are prepared and compacted at various water contents. Then, permeability tests are conducted according to the modified constant head method and the effects of parameters such as the fluid dielectric constant, water content of the samples and soil plasticity are examined. The results demonstrate that the lower dielectric constant of the organic fluid decreases the thickness of the double layer, providing more space for the flow of the permeant and as a result, the permeability of the clay increases. The reduction of the permeant dielectric constant from 80.4 to 2.28 led to a remarkable increase in soil permeability

An ANN Based Sensitivity Analysis of Factors Affecting Stability of Gravity Hunched Back Quay Walls

This paper presents Artificial Neural Network (ANN) prediction models that relate the safety factors of a quay wall against sliding, overturning and bearing capacity failure to the soil geotechnical properties, the geometry of the gravity hunched back quay walls and the loading conditions. In this study, a database of around 80000 hypothetical data sets was created using a conceptual model of a gravity hunched back quay wall with different geometries, loading conditions and geotechnical properties of the soil backfill and the wall foundation. To create this database a MATLAB aided program was written based on one of the most common manuals, OCDI (2002). Comparison between the results of the developed models and cases in the data bank indicates that the predictions are within a confidence interval of 95%. To evaluate the effect of each factor on these values of factor of safety, sensitivity analysis were performed and discussed. According to the performed sensitivity analysis, shear strength parameters of the soil behind and beneath the walls are the most important variables in predicting the safety factors

The seismic resistance simulation for cracked clayey backfill

Applying nonlinear multidirectional forces to the earth retaining structure causes expansion and compression of existing soil crack and this phenomenon occurs in complicated form for clay. The cracked clayey backfill subjected to multi-directional seismic loads has not been reported in the literature. An analytical method was used for identifying the length of the crack. Two types of models with 7 and 15 cracks were assumed and simulated. By introducing the nonlinear extended finite element method (NXFEM), the nonlinear displacement, strain, and stress of the models were simulated. The results revealed that the number of the soil cracks modifies the vibration mechanism, nonlinear displacement, stress, and strain behavior of the model. The research methodology was validated by comparing the results of the numerical simulation with those available in the literature. The novelty of the present study is related to introducing NXFEM

Crack simulation for the cover of the landfill – A seismic design

The stability of the landfill is an environmental issue. The collapse of the landfill causes environmental pollution and influences human life. In the present study, the crack on the cover of the landfill was simulated. Rankine’s theory and the Phantom Node Method were used for the simulation length of the crack and the mechanism of the crack propagation in the nonlinear extended finite element method (NXFEM). Artificial Neural Networks (ANNs) based on Levenberg-Marquardt Algorithm and Abalone Rings Data Set mode were used to predict displacement in critical points of the model. The vibration mechanism of the landfill was changed in each model. During applying seismic load on the model, the optimized thickness of the clay cover on the landfill was discussed. The thickness of the landfill cover controls the seismic response of the landfill. The numerical simulation shows differential displacement of the landfill impacts on the crack propagation and the need for the appropriate design of the cover thickness of the landfill

Prediction of the displacement mechanism of the cracked soil using NXFEM and Artificial Neural Networks

The stiffness and strength of the soil foundation govern the seismic safety of the structure. Estimating the influence of the soil crack on the nonlinear displacement of the soil foundation needs to be investigated in detail. In the present study, the cracked soil foundation subjected to the seismic load has been simulated. The nonlinear extended finite element method (NXFEM) was applied for the prediction of the crack path on the soil foundation considering the mechanical properties of the soil as the main parameters. In addition, the impact of the crack morphology on the differential displacement of the soil model was investigated. To examine the validity and prediction of the displacement range of the cracked soil foundation, Artificial Neural Networks (ANNs) were employed by using MATLAB. Considering the results of the numerical simulation and ANNs were observed that there is a direct relationship between the morphology of the soil crack with the soil with displacement mechanism. The morphology of the soil crack has a considerable impact on the vibration mechanism of the soil mass subjecting to the seismic loading. The novelty of the present study is related to the prediction impact of crack morphology on cracked soil foundation differential displacement. The prediction crack morphology of the soil significantly supports geotechnical earthquake engineering design

Crack simulation for the cover of the landfill – A seismic design

The stability of the landfill is an environmental issue. The collapse of the landfill causes environmental pollution and influences human life. In the present study, the crack on the cover of the landfill was simulated. Rankine’s theory and the Phantom Node Method were used for the simulation length of the crack and the mechanism of the crack propagation in the nonlinear extended finite element method (NXFEM). Artificial Neural Networks (ANNs) based on Levenberg-Marquardt Algorithm and Abalone Rings Data Set mode were used to predict displacement in critical points of the model. The vibration mechanism of the landfill was changed in each model. During applying seismic load on the model, the optimized thickness of the clay cover on the landfill was discussed. The thickness of the landfill cover controls the seismic response of the landfill. The numerical simulation shows differential displacement of the landfill impacts on the crack propagation and the need for the appropriate design of the cover thickness of the landfill

Shearing Rate Effect on Mechanical Behavior of MSW Materials

Recent catastrophic failure in different regions of the world is an indication on the poor level of engineering knowledge on the mechanical behavior of MSW materials which are the main materials in the landfill body. However extensive researches have been made to represent a clear frame work to describe the behavior of these materials but clearly all of these attempts had not been enough. In the region with high seismic activity, mechanical response of MSW materials under quick and dynamic loading condition is one of the issues which should be addressed however there are some evidences concerning the higher resistance of MSW materials under dynamic loading condition. As a part of an extensive research, using large triaxial apparatus and large direct shear box, the effect of shearing rate on the mechanical response of these materials were evaluated. Effect of this factor also estimated on the pore water pressure generation pattern using large triaxial tests performed in un-drained condition. The results confirmed the achievement of Augello et al. (1995, 1998), Zekkos (2005) and Zekkos et al. (2007) regarding higher level of shear resistance of MSW materials under dynamic loading condition. The results also showed that however the rate of pore water pressure generation decreases with increasing the loading rate but final level of pore water pressure is independent of loading rate