Advances in Unsaturated Soil, Seepage, and Environmental Geotechnics

The paper stresses the fundamental role of soil suction in applied problems involving unsaturated soils. Suction gradients largely control water flow and mechanical and hydraulic behavior depends on the current value of suction. The solution of practical problems requires first a correct identification of the causes of suction change, its quantification and its effect on properties. A review of applications has been made for soils covering a wide range of grain size, from rockfill aggregates to very active and expansive clays. Some case records are presented to illustrate specific features of behavior, which may be appropriately handled by modern tools of coupled flow-deformation analysis. The paper stresses also the value of suction controlled testing and field monitoring to get a proper insight into the different cases presented.

Significant advances have been made in our understanding of the mechanical properties of Municipal Solid Waste (MSW) in the past 15 years. MSW property values used in engineering analyses have evolved from unsubstantiated guesses to informed estimates based upon laboratory and field data. Recent findings of importance with respect to MSW properties have included the development of characteristic unit weight profiles, measurement of the at rest lateral earth pressure coefficient (K₀) in the field and laboratory, reconciliation of shear strength values from different types of laboratory tests and from back analyses of landfill failures, insight into the role of liquids and pore pressures on shear strength, and evaluation of the dynamic modulus and damping in isotropically consolidated triaxial tests. Despite this progress, many important questions on MSW properties remain unanswered, including the effects of waste composition, waste processing, and waste degradation on most of the mechanical properties of interest, the values of the active and passive earth pressure coefficients for MSW, the cyclic behavior of saturated MSW, and quantitative evaluation of the secondary compressibility of MSW. Furthermore, changes in waste streams, waste processing, and landfill operations suggest that typical values for waste properties will continue to evolve over time.

Recently, a new soil-water characteristic curve model for unsaturated soils was proposed based on a fractal model for the soil pore surface. The air-entry value and the surface fractal dimension of soil pores were used to determine the soil-water characteristic curve in this new fractal-based soil-water characteristic curve model. The experimental results found from literature can testify the new model. The new experiment on unsaturated loess is conducted to compare with the new model. The soil-water characteristic curve drawn with experiment data is in satisfactory agreement with the curve predicted by the new model.

The contribution of matric suction to the stability of an unsaturated soil slope must be properly accounted for in order to evaluate the slope stability with reasonable accuracy. It is also essential to develop a better method to analyze the stability of unsaturated soil slope instead of the conventional slice method commonly used in practice so far. In this paper, previous research work on strength of unsaturated soil is reviewed and a strength formulation for unsaturated soil is proposed in the three-dimensional effective stress space. The implementation of the strength reduction method for stability analysis using Finite Element Method (FEM) is described in this paper. A case history of unsaturated soil slope failure is analyzed by the developed strength reduction FEM and the results clearly indicate that the global factor of safety decreases as the matric suction decreases during rainfall leading to final slope failure. The numerical analysis clearly demonstrates the important effect of suction on the stability of unsaturated soil slope.

Rainfall-induced landslides are caused by an accumulation of water infiltration into unsaturated soil slopes. This paper reports trends of wetting front suction (psi) of weathered soil-clay mixtures that are commonly found in Korea. Both tensiometer tests and numerical analyses are performed to evaluate the effect of wetting front suction loss on unsaturated mixture soil slopes with a certain amount of clay fractions. It is found that until 10% clay content is the limit in weathered soil showing different wetting front suction which plays a key role in the stability of soil slopes.

Geo-sequestration (geological sequestration) is showing us the enormous potential of permanently storing CO₂ underground to reduce greenhouse gas emission from fossil fuels. Hydro-mechanical evaluations of the storing formations are essential to such CO₂ geo-sequestration projects. This paper focuses mainly on studying relationships between CO₂ saturation and pore pressure change of rocks during the dilatation process. In order to investigate how much the injected CO₂ can influence the pore pressure change of rocks when the dilatation phenomena happen, rock samples were treated with CO₂ saturated water under triaxial high pressure and compressive experiment conditions. In this paper, a time dependent porosity method was firstly put forward to study the dilatation process of rocks, and it was successfully implemented by a finite element method associated with multiphase characteristics. The results show that CO₂ saturated water plays a key role in the acceleration of dilatation process of rocks. The dissipation of pore pressure is seriously controlled by the porosity magnitude of rocks. If the rock has larger magnitude of the porosity, the rock behaves fast dissipation of the pore pressure.

Soil water characteristic curves (SWCCs) relate matric suction and water content in unsaturated soils. SWCCs exhibit hysteresis during drying and wetting cycles and the behavior is path dependent. An elastoplastic model is developed using the bounding surface plasticity theory to predict the SWCCs including the hysteresis. The SWCCs predicted for a fine Ottawa sand are compared with measured results and good comparisons are achieved.

Unsaturated soils comprise of three phases: soil solids and pores filled with water and air, whereas in saturated soils the pores are completely filled with water only. Conventional techniques of measuring volume changes in saturated soils cannot be used unsaturated soils because under loading the changes occur in both the volumes of air and water for unsaturated soils. The measurement of these volume changes poses additional challenges and complexities compared to saturated soils. In this paper, key issues in measuring of changes in volume of unsaturated soils in triaxial testing are outlined and discussed.

This paper presents comprehensive results of a series of collapse tests on unsaturated compacted clay using a suction-controllable triaxial apparatus for identifying the collapse behaviour, which includes deformation characteristics such as volume changes and hydraulic characteristics such as degree of saturation changes. The collapse tests were conducted by decreasing the imposed matric suction from 147 to 0kPa step by step under constant isotropic net stresses. Experimental data show that the wetting-induced collapse deformation mainly depends on the initial density and mean net stress at which the collapse occurs, i.e., the denser the specimen or the larger the mean net stress, the smaller the collapse deformation. In addition, the soil-water characteristic curve obtained for an initial denser specimen tends to shift upwards in the S_r - lns plane, compared to an initially looser specimen. It is shown that the collapse mainly occurs in the suction range from 20 to 80 kPa for the tested soil.

Loess collapsibility is closely interconnected with its microstructure feature. The kinds of pores in loess can significantly influence on its properties. In terms of the scanning electron microscopy analysis, the pores in loess can be divided into four types based on their sizes. According to the shape of grain arrangement, it can be classified into open pore, embed pore, and inner-particle pore. The existence of open pore in loess is the fundamental reason for causing loess collapse. The effects of the pores on loess collapsibility are various with different diameters. The diameter of 20 micrometers can be taken as a distinguishing standard. The more contents of the pore larger than 20 micrometers exist, the higher the collapsibility is.

Based on one-dimensional deformation tests of Nanning expansive soils, the relationship of deformation versus time was studied. The results indicate that swelling ratio is of a hyperbolic relationship with time in single-logarithmic scale and it could be divided into two stages: during a short time at the beginning, the swelling ratio increased dramatically; and after that, it trends to be stable. Using linear regression to analyze the relationship between swelling ratios and time, simple hyperbola functions to fit the swelling ratio curves can be easily obtained and the results are much agreeable. As for shrinking-time curve, it is almost linear with time in logarithmic scale. The simple linear functions to fit shrinking curves can also be obtained, which are much agreeable. Therefore, the paper provides a new simple way to analyze the relationship of expansive soils' deformation versus time. In practical engineering, those simple relationships could be used to predict the volumetrically changes with time.

On the basis of the double-stress-state variable theory, the consolidated drained shear tests on undisturbed unsaturated loess with suction control were conducted using direct shear apparatus. From the tests results, influence of net vertical pressure and matric suction on the shear strength for undisturbed unsaturated loess was found directly. Thus measuring soil-water characteristic curve was avoided to obtain the shear strength indirectly and the test process for unsaturated soil strength was simplified. Based on these tests results, we have obtained the shear strength characteristics of undisturbed unsaturated loess and relevant relationship curve under different matric suction and proposed a new equation for shear strength expressed as a function of net pressure and matric suction .All coefficients in this equation are determined.

This paper shows the results of a serious of high-pressure consolidation tests on the collapse loess samples with various moisture contents. The deformation delta and moisture content omega curves show that the deformation increases with the moisture content increasing. There is an abrupt rising stage in the delta - omega curve, and the deformation appears much sensitive to the moisture increasing this stage. Finally, two empirical formulae are put forwards to calculate settlement of collapse loess foundation by considering the moisture content increasing.

In this paper, the electrical resistivity properties of the compacted expansive soils sampled from Hefei of China are measured using the equipment namely ESEU-1 developed at the Institute of Geotechnical Engineering, Southeast University, China. The effects of water content, pore fluid chemistry and temperature on the electrical resistivity of the compacted expansive soils are discussed. The axial swell, axial shrinkage and swelling pressure of the compacted expansive soils are found to have a good relationship with the electrical resistivity of the soils, indicating that the electrical resistivity method can be used as a reasonable method to evaluate the swell-shrinkage properties of expansive soils.

Saturation effects of subsoil on the propagation of Rayleigh waves in a half-space have been studied in this paper. Based on Biot's theory, the secular equations of Rayleigh wave are rigorously derived for pervious and impervious surfaces, which are defined as a function of frequency, Poisson's ratio and the degree of saturation. The results show that a slight decrease in degree of saturation can lead to a substantial effect on the velocity, displacement and energy-flux distribution of Rayleigh waves in the low-frequency case, and the influence depends on the Poisson' ratio and the frequency. The propagation depth of Rayleigh waves is about 1.5 times the Rayleigh wavelength and the propagation characteristics of Rayleigh waves are mainly dominated by the shear wave. It is suggested that one may need to carefully take into account the saturation condition in performing SASW method.

The change in shear strength of expansive soils with the amount of swell was experimentally investigated. Series of swell tests were carried out using a hydraulic triaxial stress path cell on expansive shale samples having different initial water contents and subjected to different confining pressures. The samples were sheared under strain controlled loading using a motorized screw control cylinder connected to the triaxial apparatus. For each value of confining pressure, five shear tests were performed. In the first test, the soil sample was sheared without allowing for swell to take place (i.e. 0% swell) which is considered as a reference test. In the second test, shearing was conducted after the sample was allowed to swell until the vertical swell ceased (i.e. 100% swell). In the third, fourth, and fifth tests, the samples were sheared when the vertical swell reached, respectively, 25%, 50%, and 75% of the ultimate vertical swell measured in the second test. The ratios of the shear strength of the swelled samples to the shear strength of the sample in which no vertical swell was allowed were calculated. Test results have shown a significant influence of the amount of swell on the measured shear strength of the tested soil. In particular, the average value of the shear strength for samples allowed to reach ultimate vertical swell was only about 10% of that for samples that were sheared before swelling.

Desiccation cracks are assumed to be the consequence of an excess of tensile stresses induced by shrinkage of the drying body with a constrained kinematics. Free and constrained desiccation shrinking tests on silt samples are compared and simulated using linear hygro-elasticity. The results reveal diverse patterns of stress depending on the external constraints and presence of moisture gradient. The linear hygro-elasticity captures well the drying process before the appearance of the cracks. For the tested material, the tensile axial stress at the first crack (w = 24%) was estimated at about 3.7 kPa.

This paper presents development and validation of a numerical model for simulation contaminant transport in soils under different mechanisms. In the model the nonlinear system of the governing differential equations is solved using a finite element method in the space domain and a finite difference scheme in the time domain. The governing equations of the miscible contaminant transport including advection, dispersion, diffusion and adsorption effects are presented. The mathematical framework and the numerical implementation of the model are described in detail. The model is validated by application to standard experiments on contaminant transport in soils.

Filtration behaviour of subballast material was investigated in the laboratory using a new cyclic filter test apparatus. Tests were conducted on subballast-subgrade materials having a constant piping ratio of 9 and a cyclic pressure of 75–140 kPa at 2–15 Hz frequency. Results from this study showed a considerable influence of loading frequency on the filtration behaviour of subballast material. In particular, the loss of subgrade soil was observed to increase with the increase in loading frequency. This implies that subballast-subgrade interface which is stable at lower frequency may be unstable at much higher frequency typical of fast modern train. Therefore, the effect of frequency in the design of subballast material under cyclic loading needs to be considered.

Based on Biot consolidation theory and pore water continuity principle, differential equation groups and boundary conditions for seepage field and stress field were established respectively. By using Galerkin variation theory and eight-node isoparametric element, differential equations were discretized in terms of both space and time, the coupled finite element equations of seepage field and stress field were established and the solution of the coupled finite element equations was introduced. An example was given to show the effect of seepage in this coupled model. The coupled model analysis can present some base for theoretic research in fluid-solid coupling analysis and reference value for prevention and cure in slope engineering.

Based on the fractal pore-space theory, fractal models of the water flow and the solute diffusion for unsaturated soils are proposed. The fundamental relationship for hydraulic conductivity between unsaturated and saturated soils is investigated. The ratio of solute diffusion constants in porous media to their values in water is determined. The threshold moisture content of affecting solute diffusion is analyzed by using fractal model. The water and solute transports through unsaturated soils are numerically simulated. The model development, simulation studies and model validation are presented and discussed.

One-dimensional consolidation theory proposed by Terzaghi is widely used for the analysis of consolidation. Seepage force is ignored in the derivation of the consolidation theory. However, flow of water through a soil mass results in seepage force being exerted on the soil. This paper addresses the influence of seepage force on consolidation and clarifies whether the seepage force can be neglected in practical engineering. The basic matrix equations for coupling analysis of seepage force and consolidation using finite elements are derived based on the principle of virtual work and Galerkin's weighted residual method. Corresponding program is coded in FORTRAN. A case is analyzed using the program for one-way drainage. The results are compared with that obtained by classic Terzaghi's one dimensional consolidation theory. It is shown that seepage force has influence on pore pressure dissipation of one dimensional consolidation. The immediate increase of the pore pressure is about 3/4 of the applied load when seepage force is considered. Because of the existence of seepage force, consolidation rate is decreased.

Thermoelastic deformation due to a point heat source is the analog of poroelastic response caused by a point sink. In this paper, Biot's three-dimensional consolidation theory is introduced to derive the analytical solutions of the transient consolidation deformation with a point sink in saturated isotropic porous elastic half-space. The transient ground surface displacement produced by a point heat source is described through analog quantities between poroelasticity and thermoelasticity. Closed-form solutions of the horizontal and vertical displacements are obtained by using Laplace and Hankel integral transforms. Attention is focused on the maximum surface horizontal displacement compared to the maximum surface settlement. Results show that the horizontal displacement is about 30% of the maximum ground surface settlement. The study concludes that horizontal displacement is significant and should be considered in prediction of the transient settlement induced by groundwater withdrawal.

Understanding pore fluid distribution in porous media is an essential task in exploring plant growth under microgravity. This paper presented experimental and modeling investigations on pore fluid distribution at residual saturation in porous media in microgravity. First, experiments were conducted aboard NASA's KC-135 flights, which provided gravity conditions of 1g, 2g, and 0.01 g. Glass beads were used as porous media. Hexadecane, a petroleum compound immiscible with and lighter than water, was used as wetting fluid at residual saturation. Nitrogen freezer was used to solidify the discontinuous Hexadecane ganglia in glass beads to preserve the pore fluid changes during different gravity conditions. Particle separation and increased bulk volume of samples under microgravity were observed. In the modeling phase, a 3D pore network model was developed to investigate the spatial distribution of pore fluid. Cubic packing (the loosest packing) of Ottawa sand was used to represent the particle separation under 0g. The modeling results revealed non-uniform spatial distribution of pore fluid under 0g.

This paper reported the bench-scale experimental study of using a patent pending compost soil (developed by Earth Solutions) as a rainfall erosion control material on roadside embankment. A rainfall simulator, which simulated natural rainfall of 10-year event in Kansas, was constructed for this study; and a soil box was designed and built to accommodate the erosion tests. First, loam base soil was tested for erodibility, the soil loss significantly exceeded the tolerable soil loss. Then the compost, as surface erosion control layer, was applied on the base soil. Two configurations were tested: (1) filtered compost — composts of three different pellet sizes were laid on up-slope, mid-slope, and down-slope, respectively, with finer compost on upslope and coarser compost on down-slope, (2) vegetated compost — the compost layer was vegetated using grasses. Experimental results showed that soil loss was within the tolerable limit in the two compost applications. It was concluded that the proprietary compost soil could be a suitable material for roadside embankment rainfall erosion control.

Biological clogging of porous media by metabolically active bacteria is an important issue in Geoenvironmental engineering. In this paper, the role of two important factors influencing biological clogging is evaluated. Results are presented from two different series of percolating experiments: (1) experiments conducted with sterile and unsterile soil, (2) experiments conducted with soils subjected to low and high hydraulic head. A. mixture of Ottawa sand and Kaolinite was used as the porous medium and Pseudomonas aeruginosa as the bacterial culture. Results indicated that filtering as well as clogging by bacteria occurred in soil samples, as reflected by the reduction in the CFUs (Colony Forming Units) of the effluent compared to the influent CFUs. Comparisons of pore size distributions (PSD) of the soil before and after clogging revealed that both biomass growth and biogas generation were responsible for the permeability reduction. Experiments conducted with sterile and unsterile soil revealed that higher reduction in permeability could be achieved in unsterile soil because of the presence of indigenous soil microbes. Experiments conducted with sample subjected to high hydraulic head revealed that high heads would result in biofilm rupture formed on the surface, which would result in subsequent increase in permeability.

Based on a fully coupled thermoporoelastic formulation, the elementary solutions of thermal consolidation with the conjunctions of instantaneous point heat source, instantaneous point fluid source and constant volume force are deduced by heat source function method. Using the method of fictitious heat source and method of images, the solutions of a semi-infinite saturated porous medium subjected to a local heat source with variable intensity with time on its free surface are developed. By numerical integral methods, the fluctuation characteristics of temperature, pore pressure and displacement under cyclic temperature loading are studied. The results also show that the magnitudes of the field quantities are decreased greatly along the depth of soil layer, and the corresponding phases are delayed.

Capillary relaxation is an important effect that must be properly characterized in modeling subsurface flow and transport processes. Here we present a continuum theory of porous media that accounts for the effects of capillary relaxation. A new procedure is proposed to determine relaxation times based on the acoustical technique. By virtue of the notion of linear viscoelasticity, a new model is developed to take into account the hereditary effects of capillarity. Numerical examples are presented to illustrate the time-dependent effects of the soil moisture characteristics (SMC). It is shown that increase in the rate of matric suction shifts upward the drying SMC curve and that this effect diminishes with decrease in the capillary relaxation time. Numerical results are consistent with experimental observations, implying that the proposed theory can be used to simulate the nonequilibrium flow in unsaturated soils.

To evaluate the potential use of Ariake clay from the Kyushu area of Japan as a landfill barrier material, a series of batch sorption tests are performed. Two heavy metals, Cd²⁺ and Pb²⁺, were selected as key contaminants. The effect of solid-solution contact time, solid-to-solution ratio and pH of solution on the sorption of Cd²⁺ and Pb²⁺ on Ariake clay are investigated. The batch test results show that the sorption of Cd²⁺ and Pb²⁺ to Ariake clay reached equilibrium in less contact time than prescribed by ASTM and US EPA standards. The sorption also was significantly controlled by the solid-to-solution ratio. With increase in the solid-to-solution ratio, the sorption of Cd²⁺ decreased. Sorption of Cd²⁺ increased with the increase in the pH of solution. The influence of pH on the sorption also was found to be solid-to-solution ratio-dependent. At relatively lower solid-to-solution ratio, the sorption of Cd²⁺ increased with increasing pH, whereas it marginally increased at relatively higher solid-to-solution ratio. The solid to solution ratio was found to be the crucial factor for controlling the sorption of heavy metals on the Ariake clay.

In this study, using established geotechnical methods, electrokinetic geosynthetics (EKGs) were installed directly in the heavy metal contaminated soil specimen and the electrokinetic (EK) process used to move the ionic contaminant species through the treatment zones. The EK technology, coupled with water flushing at the anode, was applied at bench scale on Zinc (II) laden kaolin soil for a period of five weeks. Completed tests indicated that the technique can significantly reduce contaminant species concentration in treated soil, by remobilisation of the target cations towards the cathode electrode, where they are extracted from the soil through the effluent. The data indicate that the combination of EK and soil flushing shows considerable promise as an in situ method for contaminated land remediation. The study also highlights the potential of the EKG system for widening the applicability of soil flushing techniques to fine-grained soils.

Iron oxides are known to have cementation and aggregation behaviours in soil. They are present as very fine particles between 20 nm to 100 nm at various levels of concentration in natural soils and rocks. This paper describes an experimental programme conducted to examine the index properties of iron oxides rich soils, which are affected by iron oxides aggregation, cementation, and magnetic properties. In addition, the effects of curing and different measuring devices (e.g. Casagrande cup and fall cone) are discussed. The soil samples for the above experimental work were prepared from synthetic powders such as speswhite kaolin, bentonite, keuper marl, and iron oxides (e.g. haematite and goethite) and were tested in various proportions. The results show the Casagrande cup underestimates liquid limit compared to fall cone, whereas the magnetic property of iron oxides has minor effect on different cone materials (e.g. stainless steel, brass, aluminium, and acrylic). The liquid limits of the curing samples are decreased significantly due to the growth of iron oxides cementation and aggregation in soil. Besides, there are some differences between the coefficient of the regression line and the flow lines generalisation for soils with and without iron oxides.

The scope of this paper is to present the development of the calculation methods of limit equilibrium analysis for translational failure of landfills. Four leachate buildup conditions are considered during the development of the calculation methods for analyzing translational failure to represent various conditions in landfills. The factor of safety for an interface with a high friction and low apparent cohesion generally drops much more quickly than that with inverse conditions when the leachate level is increased. The critical interface with the lowest FS for a multilayer liner system can be transferred from one interface to another with changes of the leachate level.

In recent times sequestration of carbon dioxide (CO₂) into unmineable coal seams has been investigated extensively, including field trials in USA, Canada, Japan and Poland. Economic feasibility studies have indicated that the cost of sequestration can be offset to some extent by harvesting the methane (CH₄) in the coal seam. Besides issues with injectivity of low permeability coals, the long term safety, such as potential leakage of the sequestered gas, needs to be assessed. This requires an understanding of the geomechanical behavior of black coal. Some initial studies suggested that CO₂ may have a softening effect on coal. This paper outlines some experimental results obtained in the investigation of the effects of CO₂ on the strength and deformation properties of black coal. Preliminary laboratory results obtained from acoustic emission and standard stress strain plots indicate a softening effect of CO₂ on black coal under uniaxial compression test conditions.

Investigations were carried out to bring out the effect of varying concentration of caustic alkali, NaOH, solutions on the volume change behaviour of two swelling soils containing different types of clay minerals. The effect of contamination is studied not only during contamination but also on already contaminated samples. Bentonite and natural Indian black cotton soil containing interstratified illite-smectite mineral were contaminated with caustic soda solutions of 1 N and 4 N concentration. The oedometer tests revealed abnormal volume change behaviour in Black cotton soil during unloading. This has been attributed, to mineralogical alterations as suggested by XRD and DTA studies. Dissolution of interlayer potassium from interstratified illite-smectite due to interaction with alkali solution has led to the separation of unit layers of the interstratified mineral causing swelling. In bentonite characteristic swelling is restricted and compressibility has decreased due to changes in the thickness of diffuse double layer rather than mineralogical changes.

The leaching column test is a very useful and versatile tool that can be used to study the interactions between soils and various contaminants. This paper presents the results of leaching column tests conducted to examine the interactions of arsenic with soils. The migrations of arsenic through compacted soil columns are monitored for both the sorption and desorption phases of the leaching column tests to study the arsenic-soil interactions during these phases. The effects of varying amounts of organics in the soil on the sorption and desorption of arsenic are also investigated. While low contents of organics appear not to have too much effect on the sorption/desorption characteristics of the admixed soils, higher organics contents significantly affect these characteristics.

Gas-containing layers distribute widely in Shanghai Area, in which soil is unsaturated duo to the high-pressure gas. The data obtained from the laboratory tests is analyzed. A consolidation law of the unsaturated soil is obtained as the gas drained out slowly. The empirical formulas of stress-strain and strain-time are obtained as well. The test results show that the plastic deformation occurs first, then following the elastic deformation. The mechanism of engineering disasters caused by the high-pressure gas are also discussed. Furthermore, some countermeasures are proposed.

The relative merits of cementitious materials applied in the field of soil stabilization have long been accepted. This practice involves exposing a problematic soil with cementitious slurry to meet the requirements of a specific geotechnical response. The physico-chemical principles of stabilizer design across a range of geochemical and mineralogical conditions have been examined with the use of hydrated lime as an alkaline activator and an industrial by-product as a supplementary pozzolan. It was determined that a complex variety of processes occur to specific elements within the soil fabric that contribute to a potent overall geotechnical response. As such, a method for quantitatively assessing stabilizer components must reflect specific soil conditions and geotechnical requirements at the project site.

The paper presents the geotechnical investigation, instrumentation and analysis of some geotechnical problems of a landfill. The stability of the cascade embankments for slope stabilization is studied by the slice method and by the finite element method. The results of the geotechnical instrumentation are briefly discussed. The landfill settlement is investigated by finite element method. The numerical calculations are compared with the results of the geotechnical instrumentation.

One of worsening environmental problems is contamination of groundwater by nitrate-nitrogen supplied by excessive amounts of agricultural fertilizer. In order to remove such nitrate-nitrogen at a site, installation of a permeable reactor barrier (PRB) is thought to be a solution. A sulfur/limestone autotrophic denitrification (SLAD) system is known to be closer to a natural system of removing nitrate from groundwater. In this research, application of this SLAD system to the PRB was examined. Feasibility of the SLAD system was evaluated from a series of experiments using three column reactors. Consequently, nitrate- and nitrite-nitrogen first-order reaction rate constants were obtained from the column experiments and the nitrate- and nitrite-nitrogen profiles were clarified based on the first-order reaction rate. By calculating the designed thickness of the PRB, the application of the SLAD system to the PRB was confirmed to be feasible.

This paper presents the results of a series of laboratory tests investigating on properties of a new mixed soil, Xiaoshan Clay, sticky rice juice, and Tung oil. Though the original Xiaoshan Clay has already met the 10^–7 cm/s clay liner requirement, it can not efficiently block up diffusion of hazardous wastes. To decrease the pollution to the natural earth, sticky rice juice and Tung oil are added into Xiaoshan Clay. It was observed that near the optimum water content of the original soil, the permeability coefficient of the mixed soil is lower than that of the original clay by 2 orders of magnitude. Under the optimum water content, the mixed soil has the largest shear strength, including cohesion and friction angle. The optimal ratio of Xiaoshan Clay, sticky rice juice, and Tung oil, is 90:5:5 in this study. When the water of sticky rice juice is not calculated for water content, the mixed soil has lower permeability and higher strength, hence it is better to regard sticky rice juice as an addictive, and so does Tung oil.

The long-term stability of landfill final covers becomes a challenge when a combination of significant slopes and geomembranes are present together. The extreme weather generated by `El Niño' has generated significantly higher precipitation than what USEPA HELP model predicts. The resulting large amount of infiltrating water produces a zone of saturation that generates significant seepage forces in the overlying soil. These seepage forces if not controlled can result in a slope failure during a design surface water event. Such failures have proven to be very costly. This paper focuses on a review of the design of geocomposite drainage layers to satisfy critical design considerations and demonstrates how geocomposite drains can be designed to control these seepage stresses. Actual examples of landfill failures resulting from inadequate drainage are described, and design changes that would have alleviated problems are also discussed.

Accurately measuring the in situ hydraulic conductivity (permeability) of a clay liner is a major factor in the construction of landfill containment systems. Laboratory and large-scale field test methods are often utilized on test pads constructed prior to placement of the production liner to determine the hydraulic conductivity of the clay. While these test methods provide reliable results, the time required to run the tests can be lengthy. To avoid potential problems, it is important to be able to correlate laboratory and large-scale field test results with more rapid field test methods. This paper discusses in detail the standard laboratory and large-scale field permeability test methods that are commonly used on landfill clay liners. In addition, several rapid field permeability test methods are also described. Four case histories are then presented in which both long-term and rapid field permeability test methods are conducted on clay liner test pads and the correlation between the various procedures is provided. Based on the correlation between the long-term and rapid permeability test methods, the production clay liner can be evaluated using only the rapid test methods reducing the potential for construction delays.