Proceedings of the 8th International Congress on Environmental Geotechnics Volume 2

This study investigated the pozzolanic capacity of MSWI fly ash in the solidification process. The MSWI fly ash were solidified by using three kinds of activators, i.e., Na2CO3, CaSO4 and Na2SiO3, they were all cured for 7 and 28 days. Each of them involved two cases, i.e., the activator mixing proportions were 3 and 6% in dry mass basis, respectively. After that, the unconfined compressive strength (UCS) test and water immersion test were conducted on the solidified samples, to investigate the influence of the kind and proportion of activator on MSWI fly ash solidification. The results showed that all the three kinds of activators had played a role in promoting the solidification process, and the Na2CO3 performed best. The UCS value of the samples with the action of Na2CO3 enhanced with the increase of activator mixing proportion and curing time. The 28-day UCS value of the sample with Na2CO3 mixing proportions of 6% reached 2.924 MPa, and the solidified sample also showed a good water tolerance. The effect of CaSO4 on the MSWI fly ash solidification was complex. The UCS value increased with the curing time when the CaSO4 mixing proportion was 3%, however, it decreased with the curing time when the CaSO4 mixing proportion was 6%.

Heat is one of the primary byproducts of biodegradation of municipal solid waste (MSW). Biodegradation of MSW in landfills induces changes in physical properties, mechanical response of MSW, and flow of leachate within the MSW pore spaces. Moreover, biodegradation of MSW in landfills is temperature dependent and consequently the engineering properties of MSW are all influenced by waste temperatures. Thus, landfills are complex systems with interrelated processes and it is crucial to account for all these interdependencies to accurately predict the coupled behavior of MSW. In this study, a coupled-thermo-hydro-bio-mechanical model was formulated that incorporates the effect of temperature on heat generation and biodegradation of MSW. The model integrates a two-phase flow hydraulic model, a plane-strain formulation of the Mohr-Coulomb mechanical model, a first order decay biodegradation model, and a one-dimensional heat conduction model with temperature-dependent heat generation. Numerical simulations were carried out using a typical landfill configuration with leachate injection simulating a bioreactor landfill. The simulations were carried out with and without temperature effects to determine the influence of temperature on MSW behavior. The results indicate a significant influence of temperature on the MSW response (degradation and settlement) and underscore the importance of incorporating thermal effects in numerical modeling of MSW landfill systems.

The slope stability of an existing dump at Delhi has been analyzed for (a) dry waste, (b) with pore water pressure, and (c) with earthquake. The results show that existing slopes are just stable in the dry case and instability is triggered by development of pore water pressures due to infiltration in rainy season as well as by seismic forces. In order to stabilize the slope of the dumps, the traditional way is to flatten the slope by extending the toe of the slope outward in horizontal direction or by moving the crest inwards. This is not a feasible solution in Delhi where there is a scarcity of land and waste heights and volume are very large. The alternative considered in the paper is the construction of reinforced soil (RS) berm at the base of Municipal Solid Waste (MSW) dumps. A parametric study has been carried out considering the influence of the following factors (a) height of waste and (b) slope angle of waste for three cases viz., original slope, slope with 10 m high RS berm and slope with 20 m high RS berm. Apart from internal stability, the external stability of the complete system is analyzed using the limit equilibrium method of analysis. An optimum solution is suggested based on the results of the study. The study shows that RS berm offers a more acceptable solution for stabilizing the slopes of waste dumps where limited space is available beyond the toe of the existing dump.

Slope stability was carried out on the Tianziling landfill to investigate its safety at current and subsequent landfilling stages. The investigation was based on an understanding the high leachate generation rate and waste mechanics of the municipal solid wastes with a high content of kitchen wastes. The slope stability analyses indicate that the potential failure mode at the current state is a shallow slip induced by the high perched leachate mound. With the increase in the height of landfill, the failure mode will change from shallow slip to an overall slip along the bottom composite liner, which is lying on the sloping ground with an inclination of 1:4. The early warning levels for both the perched leachate mound and the main leachate mound in landfill were determined at different stages when the landfill is filled to different elevations. Engineering measures are proposed to enhance the slope stabilization as well as to increase landfill capacity. The measures include improving the configuration of liner system to be lined on the sloping ground, establishing three-dimensional drainage system to drawdown leachate level, raising the height of the downstream retaining dam, applying 10 m thick surcharge layer on the downstream slope, and setting up a safety monitoring system. Landfill stability analyses indicate that with these measures it is able to fill the landfill to the design height of 130 m, which will be the highest landfill in China.

For municipal solid waste (MSW) landfills that are situated in seismically active regions, the response of MSW under dynamic loading is critical to landfill design. In this study, a large-size simple shear device is utilized to perform cyclic testing on MSW under constant load (CL) and constant volume (CV) conditions which are considered equivalent to drained and undrained conditions respectively. The MSW sample was excavated from a California landfill located in a seismically active zone and was fully degraded in the laboratory in controlled conditions. Degraded MSW specimens were compacted and consolidated, and then sheared cyclically using cyclic stress ratios (CSR) of 0.1, 0.2, 0.3 and 0.4 sequentially. For a given number of cycles, higher CSR and higher vertical stress result in higher vertical strain and shear strain under CL conditions, and higher excess pore pressure ratio and shear strain under CV conditions. When subjected to cyclic loading, MSW is found to experience significant vertical strain under CL conditions (i.e., compression), or generate potentially significant pore pressures under CV conditions.

Monitoring subsurface soil movement is important in many geotechnical engineering applications such as stability of slopes, road embankments and settlement in foundations. Soil displacement measurement is also helpful in understanding the formation of shrinkage cracks. Clay soils undergo shrinkage during drying and experience substantial stresses and strains, which results in shrinkage cracks. This paper presents a novel approach to measure soil strain using Fibre Bragg grating (FBG) sensors. In the experiments described, FBG sensors have been used to investigate the strain development in clay during drying.FBG sensors are fabricated in the core region of specially fabricated single mode low-loss germanium doped silicate optical fibres. The grating is the laser-inscribed region with a periodically varying refractive index, which reflects a specific light wavelength. Due to the applied strain, ε, there is a change in the wavelength which can be measured and is directly proposal to strain.Kaolin clay, mixed with water close to the liquid limit, was allowed to dry under room temperature. The specimens were prepared in thin, long linear shrinkage moulds. FBG sensors were placed inside soil at the centre of the specimen. The strain development during drying underwent four phases moving from compression to tension. An oscillating nature of strain was also observed throughout the drying process. Results obtained are useful to develop analytical solutions to describe stress-strain behavior of drying soil.

Landfill odorous gas emission has been a serious environmental problem. In this paper, in situ monitoring and numerical analysis model Calpuff were adopted to analyze the odour nuisance problem near a large-scale landfill in Hangzhou, east of China. The static chamber technique was used to measure the odorous gas emission intensity on the working area surface in the landfill during the Sep. 2016 to Apr. 2017, irregularly. The obtained results indicated that the emission rate of H2S varied from 6.14 mg/m2/h to 91.7 mg/m2/h. The average emission rate in each month was then used in the Calpuff model to analyze the emission pattern of the H2S. The terrain and meteorological conditions at the site were also considered. Concentration of H2S at the community which is 4.2 km away from the landfill is 15 times greater than its olfactory thresholds (0.62 μg/m3). In order to keep the odorous influence area within landfill site, proper engineering measures should be taken to ensure the emission rate of H2S drops to the 15% of its original value.

Considering exponential decreases in landfill gas (LFG) generation and gas permeability of waste with depth, a design method for vertical gas well spacing to achieve a 90% recovery rate is proposed through a quantitative analysis of over 500,000 scenarios calculated using a normalized analytical solution. Both increasing cover resistance and pump capacity can allow an increase in the well spacing while maintaining a 90% recovery rate but may result in a maximum gas pressure below the cover ranging from −5 kPa to tens of kPa. A balance between cover and pump effects is to be achieved in this paper by constraining a maximum gas pressure of 1 kPa below the cover and a recovery rate of 90%. With this goal, the design cover resistance is shown to be strongly related to LFG generation and vertical gas permeability at the top of the waste and the non-homogeneity of LFG generation with depth, but is independent of vacuum pressure and non-homogeneity of gas permeability with depth. A chart suitable for designing to meet these objectives is proposed and illustrated by a practical application.

Kitchen waste refers to waste which is degradable and with high content of organic matter such as lettuce, flesh, peels, etc. Kitchen waste is more easily degraded than non-kitchen waste and produces a greater amount of leachate and landfill gas. It is vital to study the consolidation of municipal solid waste landfills with high kitchen waste content. A new consolidation model for unsaturated high-kitchen-waste-content MSW is proposed after summarizing the consolidation model for unsaturated porous media and high-kitchen-waste landfill.The model takes pore gas pressure and matrix suction as variables. The model is based on hydro-mechanics coupled model for unsaturated porous media, taking bulk modulus of solid particles in waste into account. The porosity and relative permeability of waste change during loading process. A typical example is simulated using OpenGeoSys software to study the influence of age, bulk modulus, permeability on consolidation of municipal solid waste. The model is instructive.

The dramatic development of municipal solid waste (MSW) incineration recently has brought a surge in the generation of air pollution control (APC) residues, a kind of hazardous waste. Landfilling after stabilization of APC residues plays an essential role in the hazardous waste management. Few studies have focused on the leachate quality of mono-landfills for stabilized APC residues in China. This investigation concentrates on simulating mono-landfills by percolation leaching tests in a pilot scale, the leachate quality data from which could offer fundamental basis both for the design of mono-landfill sites (if leachate would be generated) and chemical stabilization processes. Moreover, granulation of the stabilized APC residues could offer a fairly better working condition for transportation and landfilling operation; thus, another purpose of this work is to analyse the leaching behaviour of contaminants and tentatively conclude the effect of granulation on the leachate characteristics of stabilized APC residues in mono-landfill site. Three models were used to describe the leaching rate of the specific contaminants in landfill sites.

An earthen landfill cover test site, consisted of a 0.9 m thick compacted loess layer underlain by a 0.3 m thick gas distribution layer, was constructed at the Jiangcungou landfill in Xi’an, China. Nine methane emission test points were evenly arranged in the test area, and methane emissions were measured at each test point for approximately 35 days. The atmospheric pressure was recorded by the weather station installed near the test site. During 2015, the atmospheric pressure decreased first and then increased with time, and was basically symmetrical about the middle of the year. Methane emission from the earthen landfill cover could be directly related to atmospheric pressure changes, and a significantly negative relationship was found between the measured methane emissions and surface atmospheric pressure. An improved understanding of the atmospheric pressure variations and the influence of atmospheric pressure on methane emission from earthen covers are meaningful for developing a methane emission model and for mitigating methane emissions.

Landfill has become one of the main atmosphere methane sources. Biocover systems were proposed to mitigate methane emission by utilizing the biodegradation existing in landfill cover soils. The methane emission from landfill should be estimated by considering the methane oxidation and migration process in the biocover system. For the typical biocover system consisting of a gas distribution layer and a methane oxidation layer, an analytical model is proposed to investigate the mechanism of methane emission. The model is effectively verified against the published experiment results. The influence of effective diffusivity of each layer and advection is investigated. The results reveal that the existing single-layer analytical model cannot be applied to double-layer biocover. Putting soil with high effective diffusivity on that with lower value can better mitigate methane emission from cover. The upward advection in cover soils has significant negative effect on mitigating methane emission and should be strictly controlled.

Waste placed in landfills may produce pollutants with a high concentration of complex components from chemical and biological degradations. The hydraulic conductivity and threshold gradient of the clay liner are affected by the high concentration of complex components. In order to study the influence of leachate concentration on permeability of compacted clay, three pollutants namely Na+, Pb2+ and COD were selected to conduct permeability study for compacted clay. COD is abbreviation of chemical oxygen demand. COD solution was prepared from dissolved glucose for the experiments in the paper. Flexible wall permeameter was adopted to perform a series of laboratory experiments. The results showed that Na+, Pb2+ and COD concentration increased, the hydraulic conductivity increased and the threshold gradient decreased. When three solutions were provided with the same concentration, Pb2+ had the greatest influence on hydraulic conductivity and threshold gradient of saturated compacted clay, followed by Na+ and COD solution. In the specific environment of landfills, COD had the greatest influence on hydraulic conductivity and threshold gradient of saturated compacted clay, followed by Na+ and Pb2+ solution, which meant it was necessary to conduct further studies on the effect of COD solution on hydraulic conductivity and threshold gradient of saturated compaction clay.

The paper refers to the closure of two old dumps, one for hazardous waste and one for non-hazardous waste. The hazardous waste landfill is bordered by perimeter dykes with dimensions of 80 × 80 m. Its closure was achieved by the execution of a closure system in accordance with the European legislation in force. In order to design and execute the closure of the non-hazardous waste landfill it is necessary to relocate waste in order to obtain 1: 3 slopes. Under these conditions, the maximum capacity of the closed landfill is 89500 m3, resulting a deficit of 191100 m3 of waste for which there is no possibility of relocation to the site. An alternative solution to waste relocation is to build a support structure on the eastern side of the existing landfill to ensure waste stability. A classical support structure (retaining wall, piles, etc.) will have very large dimensions and will involve significant economic efforts. An optimal solution is to build a filling up to the level of the existing deposit, i.e. to make an ecological landfill of non-hazardous industrial waste. The paper deals also with the regulations that had to be followed and the difficulties to obtain construction authorization.

This report describes a pilot test at Tianziling MSW landfill to assess the feasibility of lowering the leachate level using horizontal wells. Three horizontal wells S01, S02 and S03 (length 50 m, 56 m and 55 m, respectively) were successfully installed using the improved directional pipe-protected drilling method. The average leachate flow rate of S01 and S03 were 10.66 m3/day and 3.93 m3/day, respectively after installation of the pipes. After 94 days draining of S01, the maximum and average leachate level drawdowns around S01 were 2.7 m and 1.7 m, respectively. After 42 days draining of S03, the maximum and average leachate level drawdowns around S03 were 1.5 m and 1.1 m, respectively. The radius of influence for S01 and S03 were in the range of 40–50 m. This test in general demonstrates the effectiveness of horizontal wells in lowering leachate level of MSW landfills. The obtained experience can be useful for civil projects that have similar concerns of draining the ground water.

Settlement in municipal solid waste (MSW) in landfills and its change with time is a complex process, because of the break-down potential of solids, heterogeneity of the material, variable particle size, and decomposition processes of organics induced by biodegradation. Waste properties, composition, distribution, and load applied vary significantly with depth and location. Various models have been proposed to predict the long-term settlement of landfill. This paper investigates the variation of settlement predictions of a landfill site using 11 different models proposed in the literature. Time required for 50% and 90% (t50 and t90) settlement to finish is also investigated. The coefficient of variation of t50 and t90 can be as high as 0.8 and 0.6 respectively. This investigation demonstrates the necessity of using probability-based method for long term settlement analysis and landfill design.

Heat generation occurs in municipal solid waste (MSW) landfills due to degradation of the organic fraction of the MSW, which results in elevated temperature. There is a great influence on the temperature distribution from leachate migration in landfills. Therefore, it is beneficial to the operation and management of the landfill to study the thermal evolution in a landfill under the effect of heat generation and heat convection. In this paper, the heat convection-diffusion model of landfill is established, and the analytical solution of the equation is obtained. The solution is used to analyze the variation of temperature under the effect of heat generation and heat convection in a landfill. The existing theory is verified by the measured data, and the influencing factors are analyzed. The calculation results show that convection in the landfill and heat generation parameters all have great influence on the temperature of the landfill. When the convection velocity becomes larger, the influence of depth of the atmospheric temperature increases. The temperature of the landfill increases with the increase of peak heat generation rate factor A.

This paper aims to investigate the compression and pore characteristics of underlying stratum in landfill. Batch tests were conducted to measure the compressibility as well as the pore, mineral, and microstructure characteristics of the undisturbed loess polluted by landfill leachate under different concentrations. Results show that the compressibility and compressive deformation of undisturbed soil increased as the landfill leachate concentrations increased. The reduction range of the void ratio was from 22.1% to 30.8%. The leachate pollution caused a decrease in the content of illite and montmorillonite, which reduced by 4.59% and 3.8%, respectively. The NMR signal of undisturbed soil increased as the landfill leachate concentrations increased. The pore radius of the undisturbed soil was mainly distributed in the range of 0.01–1 μm and can be divided into two ranges. The inter-particle pores and intra-aggregate pores mainly existed in undisturbed soil polluted by landfill leachate. Leachate caused an increase in inter-particle pore, whereas a decrease in intra-aggregate pore radius.

The increase of municipal solid waste (MSW) and the reduction of available urban land lead to the development of large-scale landfill. The landfill foundation is assumed to be rigid in existing models for calculating landfill compression. The self-weight of MSW increases with landfill expansion, and the landfill foundation settlement should not be ignored anymore. The estimation of landfill foundation settlement is of great importance in predicting landfill storage capacity and for the design of effective long-term landfill facilities. The implemented model for calculating landfill compression displacement and storage capacity is able to consider increase in foundation settlement induced by landfilling process. A calculation program is developed base on this proposed model, which can estimate landfill storage capacity. The quantitative effects of initial compaction on MSW landfill settlement and storage capacity are investigated by using the program via consideration of a hypothetical case. According to the investigation, a significant increase in storage capacity can be achieved by rational use of landfill foundation compression and intensive initial compaction. The quantitative investigation presented aims to encourage landfill operators to improve management to enhance storage capacity. Furthermore, prediction of landfill foundation settlement is helpful to protect leachate and gas management infrastructure at bottom of modern landfills.

Leachate leakage has become a widespread problem in most landfills due to the increasing service time. The soil property, water quality and residents’ safety around the landfill was seriously affected by the leachate leakage of landfill. A physical simulating set-up was created to simulate the leakage of leachate in the layer under the influence of flowing water. The monitoring of leachate leakage was conducted using improved electrical resistivity tomography (ERT). The result showed that the accuracy of improved ERT was more than 85% and the laboratory test relying on the simulating set-up and improved ERT was feasible. The laboratory test provides material basis for investigate the leachate diffusion quantitatively.

In Brazil, conventional covers of sanitary landfill are consisted of fine soils compacted with tractor treadmill. Nonetheless, some clays have swelling behavior and present shrinkage cracking when they are dry, impairing their performance with relation to control the flow of water into the waste mass and the flow of gases out of the waste mass. This control is necessary to minimize the leachate and gas volume generated into de waste mass. This research aimed to evaluate the performance of two conventional covers of two lysimeters filled with municipal solid waste (MSW) of Campinas city, Brazil. For this, the concentration of gases (CO2 and CH4) that was coming out of covers was obtained using flux chamber and correlate with the concentration of gases that were drained by central pipe. Disturbed soil samples from two covers were characterized by geotechnical tests such as grain-size distribution, consistent limits, unit weight and moisture content. Permeability testes were also performed with specimens trimmed of undisturbed soil samples collected of two covers. The soil samples were classified as silt clayed-sandy and they presented micro aggregation. Saturated permeability coefficients presented orders of magnitude of 10−4 and 10−5 cm/s. Gas concentrations from central drain were greater than gas concentrations from the cover, twice for CO2 and 30% for CH4, approximately. The precipitation influenced the gas concentrations from central drain and from covers differently and this fact is discussed.

The United States Environmental Protection Agency (EPA) characterizes the wastes generated during the exploration, development, and production of crude oil, natural gas, and geothermal energy as “special wastes” that are exempt from federal hazardous waste regulations. This study is based on a landfill in the state of Louisiana permitted to dispose four types of exploration and production (E&P) wastes. Due to the nature of some E&P wastes received at the landfill, a solidification agent, usually sawdust, is added and mixed prior to final disposal. E&P wastes can have an impact on the slope stability of landfills due to their distinct shear strengths and the concern of development of additional pore pressures due to the reduction of the hydraulic conductivities caused by the utilization of some solidification agents (e.g., sawdust). From this study, the authors developed the necessary geotechnical parameters to conduct a slope stability analysis for the design of future disposal cells and proposed general operational and monitoring guidance concerning the expansion of the landfill. One of the main conclusions of the study was that even though the utilization of sawdust/E&P waste (water-based) may improve the shear strength of the total waste mass, the development of inexorable pore pressures may reduce the safety factor of the landfill slopes.

Landfill gas (LFG) is a product of the biodegradation of municipal solid waste (MSW) under anaerobic conditions. LFG primarily consists of methane (CH4) (40–60%) and carbon dioxide (CO2) (40–60%), both greenhouse gases. Methane has high energy potential that remains largely untapped as a national energy source. In order to recover LFG for energy generation purposes, a reliable estimate of gas generation at landfill sites is necessary. To that end, numerous LFG generation models have been developed with different assumptions made. In this study, three gas generation models – two first order decay (LandGEM and IPCC) and one sigmoidal model (Modified-Gompertz) are considered. The cumulative methane yield prediction of these models is fitted against three degradation experiments on well-characterized MSW specimens with significantly different waste composition ranging from “waste-rich” to “soil-rich”. The results indicate that the sigmoidal model better captures the evolution of methane yield compared to first order decay model and majority of the model parameters follow a systematic trend as a function of waste composition.

Laboratory measurements of the coefficient of earth pressure at rest, K0, of municipal solid waste were made in a large-scale testing device using tactile pressure sensors. The effects of waste composition, compaction and overconsolidation ratio (OCR) on the coefficient earth pressure at rest, K0 of municipal solid waste were evaluated. The tests results showed that K0 of municipal solid waste decreased with increasing fiber content and OCR of the waste. K0 decreased at first with increasing of applied vertical stress and then became approximately constant value at 0.48, 0.35, and 0.23 for MSW 100% < 20 mm, MSW 65% < 20 mm and MSW 35% < 20 mm respectively. Compaction effort also affected the initial value of K0. However, with increasing vertical stress the effect of compaction decreased and was finally eliminated.

Mechanical biological treatment (MBT) waste from the Tianziling landfill in Hangzhou, China, was collected for composition analysis, sample preparation, and conduction of triaxial unconsolidated-undrained and consolidated-undrained tests in an environmental geotechnical laboratory. The principal findings were as follows. (1) The component analysis indicated that the MBT waste comprised plastics, textiles, glass, lime soil, unidentified materials, and so on. (2) The triaxial compression test results showed that the deviatoric stress gradually increased with an increasing axial strain. The relationship between the deviatoric stress and axial strain took the form of a strain hardening curve. (3) The stress–strain relationship of the MBT waste conforms to the Duncan–Chang model. The ranges of the model parameters a and b were obtained. A power function relationship between the model parameters a and b and the confining pressure was established. (4) The values of the cohesion, internal friction angle, effective cohesion, and effective internal friction angle of the shear strength parameters were obtained. The cohesion c was 28.6 kPa, the internal friction angle φ was 23.3°, the effective cohesion c′ was 33.5 kPa, and the effective internal friction angle φ′ was 32.2°. These results can provide a theoretical basis for the stability analysis of MBT landfills.

Soil-water characteristic curve (SWCC) is used to describe the relation between water content and matric suction in porous media, and reflects to some extent the pore size distribution. However, a complete SWCC of municipal solid waste (MSW) is difficult to achieve by direct measurement because of the existence of macropores. For this reason, SWCCs of the matrix region in MSW were measured by a pressure plate extractor, and SWCCs of the macropore region were determined from water breakthrough tests in this paper. Water retention characteristics and pore size distribution of MSW were analyzed based on the complete SWCC. The results show that the residual water contents of municipal solid waste were high. Field capacity of shallow, middle and deep waste were 38.5%, 42.2% and 46.8%, respectively, corresponding to a matric suction range of 3–8 kPa. As the depth and age increase, the effective water content interval and specific yield decrease. Taking 1-kPa matric suction as a limit, pores in MSW can be divided into macropores and micropores. The probability density function of pore radius is bimodal. As the depth increase, the amount of macropores and their radius decrease, and the amount of micropores increases with the average pore size becomes smaller.

Flow slide is a form of landslide that can pose a great threat to the surrounding population and buildings. The collapse of buildings is an important cause of injury and death, so it is highly important to understand the failure process of buildings under the impact of flow slide and put forward effective methods for the hazard mitigation. In this paper, complex fluid-structure interaction between flow slide and buildings is simulated using SPH-FEM method. Flow material is modeled by SPH method which is a powerful tool for handling fluid problems, while the buildings are modeled by FEM elements with erosion algorithm. The runout characteristics and failure process of buildings under the impact of flow slide are both simulated. Different failure mechanisms are identified at different locations. The results indicate that this method is an applicable tool for analyzing the failure process of buildings and is promising to be used to assess the risk of buildings to flow slide.

Aeration is an effective method to repair old landfills and reduce the post-closure charge. Before designing the aeration systems, reliable prediction of aeration systems performance is important because operators could optimize the system based on it. This study proposes a three-dimensional CFD model of vertical aeration systems using ANSYS Fluent platform. Multiphase flow, multicomponent transports and biochemical reaction are considered to simulate the hydro-biochemical process when aeration occurs in aerobic landfills. This model was verified by experimental data successfully. The results focus on the influence of aeration frequency and well depth in terms of intermittent aeration in landfills.

The aim of the present research work is to characterize in situ municipal solid waste (MSW) of Pirana landfill, Ahmedabad and study the flow of water through MSW. A series of compaction test were carried out on dry and wet side of optimum and its structural mobility was determined. Suction characteristics, compressibility characteristics and soil microscopy under constant mobility of moisture and its variational flow path into solid surface and subsurface was evaluated. The results indicate that structural compactness of solid particles which are covered with moisture and chemical diffraction of partial organic matter and its overall effect can be well studied through this type of approach. Suction of MSW is affecting the compression characteristics of MSW and soil microscopy helped in understanding role of drying and wetting under constant degree of compactness and its effect on MSW as hydrodynamic force.

A constitutive model for the stress-strain-time behavior of municipal solid waste (MSW) that accounts for waste degradation has been developed. The model is developed within the critical state soil mechanics framework. The model decomposes the total strain into a time-independent elasto-plastic strain and a time-dependent plastic strain. The time-independent strain, including both the elastic part and the plastic part, is characterized by the ellipsoidal yield surface of the Modified Cam-Clay model using the normality condition and the law of associated flow. The time-dependent strain consists of a mechanical creep part and a biodegradation part. The mechanical creep part is evaluated by Taylor’s secondary compression equation, the normality rule, and the Modified Cam-Clay yield surface. Biodegradation strain is assumed to be isotropic and is characterized by first order kinetics and mass that decays loss exponentially with time. The decrease in the compressibility of MSW as it biodegrades is accounted for by changing the slope of normal consolidation line and the value of the specific volume at the reference pressure based upon the mass loss due to decomposition. A method for obtaining the model parameters is provided.

There are many kinds of geomaterials such as mixtures with clay, silt, sand or gravel. Solid waste materials are also classified as a geomaterial. Generally, strength parameters of cohesion and frictional angle on the geomaterials are obtained from direct shear test or triaxial compression test. It is difficult to perform with ordinary laboratory tests on samples including a large size of soil particles or waste materials with different size and shape, especially on in-situ condition. The authors developed a large size direct shear test for solid waste material. However, it takes a time for preparing specimen and performing the in-situ test. In this study, the corn penetration test and the spiral pile pull out test were performed for estimating strength constants of various kinds of geomaterials as a simple method. Cohesion of geomaterial is obtained from spiral pile pull out test with different length of the pile. Internal frictional angle is calculated from the cohesion and test result of corn penetration test with Terzaghi bearing capacity formula. Estimated strength parameters by proposed method were compared with the values obtained from the direct shear tests. The applicability of this method is confirmed based on the test results of various geomaterials such as sand, decomposed granite soil, and solid waste materials in laboratory. This proposed method is also applied on in-situ ground.

In order to have a better understanding of solidified sludge in a sewage sludge disposal pit, field and laboratory investigation were conducted on the geotechnical properties of the solidified sludge at the Qizishan Landfill in Suzhou, China. The field investigation included borehole sampling. The laboratory test involved the measurements of water content, organic matter content and shear strength for the borehole samples taken from Qizishan landfill sludge pit. The tests results demonstrated that the cohesive intercept (c) of the solidified sludge mostly range from 15 to 60 kPa; friction angle (φ) mostly range from 6° to 40°. The unconfined compressive strength for sludge normally about 180 kPa, but the unconfined compressive strength for some cement-like samples up to 250–300 kPa. Above analysis are useful for the in-situ sludge reinforcement methods, such as first in-situ vacuum preloading combined with subsequent solidification treatment. And it can provide the necessary geotechnical parameter and partly basis for sludge disposal design.

The amount of construction and demolition waste is enormous and still in rapid growth especially in the mega-city like Hangzhou, PR China. However, effective management and technical regulations for dealing with the construction waste are still not available, simple landfill is the main disposal method of C&D waste. In order to reduce the consumption of land spaces by simple landfills, this paper explores the possibility of reclaiming landfills into forest land or farmland. After analyzing the concentration and pollution degree of six heavy metals and two pesticides, the C&D waste landfill can fully satisfy the soil application function corresponding to a third-level standard of Soil Environmental Quality Standard (GB15618-1995). Thus, it can be used for forest land and farmland (except planting vegetables).

This paper presents the results of a study undertaken to enhance the stability of a landfill on sloping ground of a hilly region. The base of the landfill has a significant elevation difference from one end to the other causing an overall inclination of the base with the horizontal. The study highlights the influence of the following factors on the base sliding stability along the geomembrane interface as: (a) leachate head; (b) pore water pressures in wet waste; (c) seismic forces and (d) smooth versus textured geomembrane (GM). Limit equilibrium methodology is adopted for analyses and three types of failure surfaces are analysed – circular, planar (single straight line) and planar (two straight lines). The study reveals that stability against sliding along liner is low, whenever (a) pore pressures/leachate head are high; (b) earthquake forces are large and (c) smooth GM are used. Usually planar failure surface (two straight lines) is observed as the critical surface.Furthermore, it is also observed that the stability of the sloping liner can be enhanced significantly by providing adequate size of earthen berm at the toe. After application of the berm at the toe, the possible critical failure surface may pass over the back slope of the berm or pass under the bottom of the berm. This depends on the geometric dimensions (height & base-width/back slope) of the berm. Planar failure surfaces (two and three straight lines) are analysed to check the stability. The study reveals that by varying the berm height as well as the base width, one can arrive at an optimal solution for stability.

An alternative liner system utilizing geosynthetic clay liner (GCL) in lieu of the permitted compacted clay liner (CCL) was proposed for a vertical expansion at a hazardous waste landfill sitting over an existing unregulated landfill. An assessment was conducted to demonstrate that the proposed system is technically-sound and effective and meets all federal and state rule requirements. Two critical equivalency assessment items including (i) steady state solute flux and (ii) chemical adsorptive capacity and solute breakthrough time were evaluated and are discussed in this paper. Based on the evaluations and discussions, the proposed alternative GCL system is equivalent or superior to the currently permitted CCL system and is capable of preventing the migration of hazardous constituents into the groundwater or surface water at least as effectively as the CCL system.

The objective of this paper is to present a comparison of measured hydraulic conductivities (k) for soil-bentonite (SB) backfill within a 60-m-long section of a 200-m-long, 7-m-deep cutoff wall constructed and instrumented for studying SB backfill properties and variability at the field scale. Backfill k was measured using flexible-wall tests (70-mm diameter) on remolded specimens prepared from surface grab samples collected during construction; flexible-wall tests on undisturbed specimens collected from the wall; larger-scale rigid-wall tests (150-mm diameter) on remolded specimens prepared from grab samples; and slug tests conducted within the wall. Applied effective stresses in the laboratory tests ranged from 4–35 kPa, encompassing the range of in-situ stresses measured in the backfill after load transfer and consolidation (8–13 kPa). The results indicate low spatial variability in k for a given test type, consistent with the observed homogeneity of the backfill. Modest variability in k was observed among the different test types, with the slug tests and rigid-wall tests generally yielding slightly higher k relative to the flexible-wall tests at field-representative stresses.

Sanitary landfilling is nowadays the most common way to eliminate municipal solid wastes. However, the durability of landfill is mainly determined by the anti-seepage property of vertical cutoff walls. As microorganism has proved effective in plugging micro-pores, and greatly enhance the barrier performance of cutoff wall for MSW landfills. In this study, Escherichia coli. was selected for preconditioning towards compacted soil specimens and the hydraulic behaviours of the specimens were evaluated. According to the results, the huge amounts of microbial exopolysaccharides produced by Escherichia coli. encountered in the soil pores and formed a pore plugging, eventually caused 81–95% decrease in the hydraulic conductivity, from the initial value 5.3 × 10−5–5.6 × 10−6 cm/s to the stable value 3.1 × 10−6–2.9 × 10−7 cm/s (dropped by 1–2 orders of magnitude). The introduction of clay leads to the increase of surface roughness inside the internal pores as well as the diminution of shear forces, resulted in more effective adhesion between microorganism colonization and the surface of the particles. Subsequently, an extensive parametric analysis was conducted by numerical simulation to investigate the transport behaviour of contaminant through vertical cutoff walls. Several decrease of orders of magnitude in the hydraulic conductivity from 1 × 10−8 to 1 × 10−10 m/s resulted in the dramatical increase of the breakthrough time by 431.2% which revealed that a low hydraulic conductivity was of significance for vertical cutoff walls to achieve desirable barrier performance.

In the USA, municipal solid waste (MSW) landfills constitute one of the major anthropogenic sources of methane emissions. In the landfill cover soils employed at MSW landfills, aerobic methane-oxidizing bacteria (MOB) convert CH4 to CO2, thereby partially mitigating the CH4 emissions to the atmosphere. In this study, culture-dependent and culture-independent techniques were employed to evaluate methane oxidation capacity and to characterize the microbial community in landfill cover soil. Microcosms with synthetic landfill gas headspace were used to measure potential methane oxidation rates in landfill cover soil and in methanotrophs-enriched microbial consortia. The results demonstrate that the enriched landfill cover soil supported the growth of a diverse group of methanotrophic and methylotrophic microorganisms, and were dominated by Type I methanotrophs showing positive correlation with CH4 oxidation rates.

Granular bentonite materials are some types of buffer/backfill materials with good performance, which are constituted by bentonite pellets or by pellets and bentonite powder. The dry density is the key parameter which controls the engineering properties of buffer/backfill materials. The grain size distribution will influence compressibility and dry density of the compressed granular bentonite materials. In the present work, four types of granular bentonite materials and bentonite powder had been selected and the compressibility and the degree of compaction of these packing materials had been studied. The results showed that the granular bentonite material contains 30% (in weight) powder and 70% (in weight) pellets sized between 2 and 5 mm had the best cost performance, such as, higher dry density, higher compacted dry density, easy to produce.

To unveil the effect of powder particle size on the water retention characteristic (WRC) of compacted GMZ bentonite under a state of constant volume, powder particle size and shape distributions of two GMZ bentonites (GMZ01 and GMZ06) were investigated by employing the dynamic digital imaging technology and WRC tests related to these two bentonites were conducted with both osmotic and air phase methods used for suction control. It turns out that under a state of constant volume, the water content increases gradually with the decreasing suction, and the effect of powder particle size on the WRC seems quite faint within a high suction range but relatively obvious within a low suction range.

A composite cutoff wall consisting of HDPE geomembrane combined with soil-bentonite backfill can be effectively applied to site remediation projects. This technique was firstly successfully applied by Beijing GeoEnviron Engineering & Technology, Inc. (BGE) in a copper-containing acidic liquid leakage project in China in 2011. Then, BGE successfully applied and promoted this technique in many other projects in recent 7 years. Some specific key sealing materials were developed to achieve the effective bonding between geomembrane and bedrock and clay aquifers. In addition, a special machine for installing geomembranes was also designed. The maximum geomembrane inserting depth on site reached to 32 m. Geomembrane composite cutoff wall is considered to be currently the safest and most effective vertical barrier technique to block horizontal pollution migration.

Relative hydraulic conductivity is an important input parameter for water balance models, which are commonly used to evaluate the performance of soil covers. In this paper, pore-network modeling was utilized to analyze the influence of pore distribution characteristics on relative hydraulic conductivity at various water saturations in soils. A drainage process of water slowly invaded by air was simulated to assign various saturations in pore networks. The pore networks have 30 × 30 × 30 pores, with log-normally distributed pore diameters in different mean values and standard deviations. Numerical results indicated that the increase in standard deviation and the decrease in the mean value of the pore diameters lead to a decrease in saturated hydraulic conductivity. Larger standard deviation or lower mean value of the pore diameters can result in more evident right-skewed pore diameter distribution. This provides more throats for water to flow at a given saturation, and thus a larger relative hydraulic conductivity in the pore network.

Study of soil suction is important in design and implementation of slope stability and erosion control measures. In order to conduct a realistic analysis of performance of sustainable green infrastructure, it is essential to address the uncertainties in suction induced by vegetation due to variability in their leaf and root characteristics, evapotranspiration (ET) and initial conditions of the soil. The objective of this study is to investigate the combined influence leaf area index (LAI), root depth, ET rate and initial suction of soil on root water uptake-induced soil suction. A parametric numerical study was performed with 480 simulations using HYDRUS to carry out the finite element analysis. The study was done on completely decomposed granite (CDG) soil and vegetation species used was Schefflera heptaphylla. It was observed that although if independently considered, vegetation with higher LAI provided greater mechanical stability, when combined with higher ET rates or initial suction, the suction induced may lead to wilting of the vegetation. Artificial intelligence technique such as Artificial neural network (ANN) was used to predict matric suction at any given depth using the results obtained from the numerical simulations. Performance of the best model indicated that ANN was able to successfully predict the vegetation-induced matric suction.

Electrical resistivity measurements provide potentially powerful tool for detection of heavy metal contaminated soil, which is on the rise in the whole world with the boost of industrialization and urbanization. A four-electrode resistivity cone penetrometer (RCPT) test (non-destructive, continuous, reliable, and demonstrates strong correlation with subsurface information such as soil properties, stratigraphy, and the location of anomalies) was used to detect metal contaminated soil layers in this study. To investigate the relationship between electrical resistivity and unsaturated subsurface conditions with varying physical property and metal contamination, the polluted clays were synthesized with controlled metal ions concentration and moisture content of loading in a chamber. A series of tests of polluted clay was performed and the mechanism of these tests were analyzed by electrical conduction theory. For all tested soils, the results show that increasing the degree of saturation and metal ions concentration on the clay led to a reduction in the electrical resistivity of clay, while increasing the porosity led to a higher electrical resistivity for the clay. It indicates that altering the porosity and saturation of polluted clay sample changed the ionic movement within the clay’s interlayer. In addition, data gotten by four-electrode soil resistivity box test was used to compare with the data measured from RCPT. The results showed that a linear approximation was sufficient in relating resistivity ρs of soil resistivity box to resistivity ρr of RCPT. In general, the RCPT was well used to examine the pollution of soil and the effects of remediation effectively in-suit.

The concept model of high-level radioactive waste (HLW) repositories in deep geological media is based on a multi-barrier system. Buffer material is considered as an important artificial engineered barrier between the canister and the surrounding rock. Coupled thermo-hydro-mechanical (THM) phenomenon will occur in the buffer material under conditions of the heat generated by the radioactive decay and of the underground water and geo-stress supplied by the surrounding rock, et al. Therefore, it is considered of fundamental important for the evaluation of long-term behavior that the processes taking place in the near filed for the safety operation of the HLW repository. Following the need of understanding the coupled THM behaviors of bentonite, mock-up test is considered as one of the most effective approach. An experiment at middle scale whose internal diameter is 20 cm and inner length 45 cm is proposed as a complementary step for the China-Mock-up test. The middle one is carried out to obtain the bentonite parameters and to identify the processes by simulating the conditions of the China-Mock-up test. The aims intended are to know and understand the long-term behavior of the bentonite submitted to thermal and hydraulic gradients at the opposite direction. The characteristics of the bentonite related to swelling pressure, relative humidity and temperature are presented and interpreted. The results can provide design parameter and theoretical basis for HLW repository.

Soil-bentonite slurry trench cutoff walls have been employed widely in the US as engineered barriers to control groundwater flow and contaminant migration in the subsurface. The hydraulic conductivity of the soil-bentonite backfill is stress dependent and to better understand the in-situ stress state of soil-bentonite slurry trench walls, a wall with a length of 194 m, depth of 7 m, and width of 0.9 m was constructed, instrumented, and investigated in-situ. As a part of the in-situ investigation, vane shear tests were conducted at different locations and depths to evaluate the shear strength distribution within the wall. The results indicate that the peak undrained shear strength value, Su, exhibits a consistent trend with increasing depth. In general, two stages of Su were observed: (1) at depth from 1 to 2.5 m, the Su decreases as depth increases, presumably due to the effects of the cover soil and groundwater level; (2) at depth of 2.5 to 7 m, the Su shows insignificant change with depth and falls into the range of 5 to 10 kPa. Using a constant shear strength to effective stress ratio, Su/σ′, the stresses predicted from the vane shear strength tests were in good agreement with those measured using earth pressure sensors embedded at the time of wall construction.

In order to better understand the performance of silty clay under different conditions, an assessment of the water retention characteristics under different temperatures is required. Laboratory tests were carried out to measure the soil-water characteristic curves (SWCCs) of the silty clay at different temperatures by the filter paper method. The soil-water characteristic curves (SWCCs) in this study were shown in terms of moisture content, void ratio and degree of water saturation (Sr). Temperature has great influence on the SWCCs of the silty clay. Water retention capacity decreases with the increase of temperature, particularly at low suction range (0–500 kPa for matric suction). For a fixed suction value (e.g. 100 kPa), when the temperature increases from 20 to 60 °C, the water retention capacity of the soil decreases from 22.5% to 13.0%. It is also found that temperature has greater influence on matric suction for the case with Sr ≥ 0.2 than that for the case with Sr < 0.2. The curve indicated that the correlation between silty clay void ratio and suction is approximately linear. It is noted that the values of soil matric suction with temperature of 40 °C appeared to be larger than the case with 20 °C and 60 °C for a given void ratio.

The piezocone penetration test (CPTU) is now widely used as an efficient and economical in-situ geotechnical investigation technology. The CPTU not only can provide the data of conventional cone penetration test (CPT), but also give a continuous profile of pore pressure. Furthermore, when the piezocone is halted in soil with a specific depth, the excess pore pressure produced by penetration will be dissipated until the value of zero. This paper investigates the consolidation processing after the piezocone is penetrated into soil-bentonite cutoff wall in a landfill site, China. A finite-element procedure is also used for simulating the consolidating processing of soil-bentonite backfills. The coefficient of consolidation and hydraulic conductivity of soil-bentonite backfills can be evaluated from the consolidation processing of excess pore pressure. The paper gives the necessity and importance of simulation of consolidation processing by finite-element procedure.

There is no leachate level testing method for a landfill with multiple intermediate cover layers. This paper provides an in-situ testing method for multi-layer perched leachate levels. In-situ tests were carried out at a landfill with multiple intermediate cover layers and the perched leachate level on each intermediate cover layer were obtained. The testing results showed that: (1) by drilling to a position 1–2 m away from the cover layer, the well casing was positioned and the in-well casing leachate level was reduced to the well casing bottom, and the leachate level recovery was observed so that the steady leachate level of this layer could be measured 24 h later; (2) the perched leachate level height on each intermediate cover layer were not consistent; (3) the low-permeability intermediate cover layers were the main course of the formation of the multi-layer perched leachate levels.

Low-permeability slurry trench cut-off walls are commonly constructed as barriers for containment of subsurface point source pollution or as part of seepage control systems on contaminated sites. Scholars made achievements on design methods for first-type inlet boundary scenarios, but there are still lacking on third-type inlet method, as the choice of inlet boundary conditions is still controversial. A method to estimate wall thickness in slurry wall design in such boundary condition is proposed based on previous design method for first-type inlet. An error analysis is performed to investigate the impact of this assumption by comparing the results obtained by the proposed method to those from an analytical solution. For breakthrough criterion C* of less than 0.1, which covers common practical situations, the relative error is not greater than 15%, demonstrating that the proposed method is suitable for design. An example is also presented to illustrate the procedure of implementing the proposed method for slurry wall design.

To use high dense compacted bentonite or bentonite-sand mixture material are accepted as engineered barriers for high level nuclear waste disposal waste. The bentonite as engineered barrier is initially in unsaturated condition before pore water coming from natural host rock. The bentonite subjected to thermo-hydro-mechanical actions by natural geological situation and the canisters of high-level radioactive disposal waste. This study conducted out the creep test for compacted bentonite, and the developed relative humidity circulation triaxial apparatus. Two different initial water contents were prepared to make the specimens at constant dry density. As parameter for this creep test, the stress ratio was defined using specified unconfined compressive strength. All specimens were applied without confining pressure. The vapor transfers due to changing of relative humidity induced some hydration efforts that were controlled using vapor pressure technique. Performing the creep test in this study is of couple hydro-mechanical and is applied to identification for two efforts (i.e. strain due to hydration and stain by deviator compression stress). Investigation of creep behavior that accumulated strains associated to couple thermo-mechanical actions are measured at constant deviator compression stress.

Carboxymethyle cellulose (CMC) is considered to enhance the chemical compatibility of bentonite in terms of hydraulic conductivity. In this study, a series of modified fluid loss (MFL) tests is conducted to investigate the hydraulic conductivity (k) of CMC-treated bentonite when exposed to heavy metal contaminant and landfill leachate. CMC content in bentonite is set at 0% (i.e., untreated bentontie) and 10% (i.e., CMC-treated). Lead-zinc nitrate mixture is selected as representative heavy metal contaminants; and calcium chloride is also used for comparison. Total metal concentrations of the chemical liquid ranged from 0 to 20 mmol/L. The result indicated that minimal change in k of CMC-bentonite is found from the MFL test; whereas the k value of untreated bentonite significantly increased with increased Pb-Zn and Ca concentration. The k value of untreated bentonite is approximately 20 times higher than that of CMC-treated bentonite for a given void ratio. In addition, it is found that the impact of landfill leachate on the hydraulic conductivity is insignificant for CMC-treated bentonite. The k of CMC-treated bentonite considerably lower than that of untreated bentonite when exposed to the leachate.

This paper addresses the reactive magnesia (MgO) activated ground granulated blast furnace slag (GGBS) blends with bentonite (GMB)as the cutoff wall mixture, compared with Portland Cement with bentonite (CB) for enhancing durability performance. A range of tests have been conducted to investigate the durability of the two batches cutoff wall (GMB and CB) as subjected to sodium sulfated and Pb-Zn solution, including unconfined compressive strength (UCS), hydraulic conductivity, and microstructure analyses with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of curing age, GMB and CB content, and soaking solution type on the durability are also addressed. The UCS of GMB mixture is lower 73.6% and 11.2% than the CB reference after curing 28-days and 90-days. The hydraulic conductivity of GMB is much lower than the cutoff wall commonly accepted limits of 10−6–10−7 cm/s, regardless of soaking in sodium sulfated and Pb-Zn solution. The microstructural analyses show the hydrotalcite-like phases (Ht) could be formed during the hydration of GMB, and C-S-H could be founded in GMB and CB mixture. The characteristic H-O-H bond stretching is noticed around 3460 and 3620 cm−1, followed by shallow wide transmittances, which indicates the presence of Portlandite (Ca(OH)2) and brucite (Mg(OH)2). The brucite and Ht are confirmed in the SEM images of GMB mixture.

This paper focuses on the experimental research on swelling properties gas migration in a compacted bentonite-sand plug. The aim is to investigate the swelling behaviour, gas breakthrough pressure as well as its sealing efficiency. Results show that bentonite-sand swelling is incomplete from 4 MPa gas pressure, so that gas breakthrough occurs at very low pressures (on the order of 1 MPa). Gas permeability of the bentonite-sand plug is affected by the variation in the confining pressure, so that tightness to gas can be achieved at a certain coupled hydro-mechanical condition. Specially, when the confining pressure is equal to 7 MPa and the water saturation degree is 86–91%, gas permeability can decrease to 10−20 m2.

Over the past 30 years, geosynthetic clay liners (GCLs) have been demonstrated to be a valuable barrier technology in numerous environmental containment applications. However, past research has also shown that the hydraulic conductivity (k) of GCLs is sensitive to the electrolyte concentration of the permeant liquid. At low effective stresses, a sufficiently high electrolyte concentration has the potential to result in a multiple order of magnitude higher k than the same GCL exhibits to water. To expand the boundaries of GCL functionality, recent research has focused on the use of enhanced (e.g., polymer modified) bentonites (EBs) for improving the resilience of bentonites, and GCLs, subjected to high concentration electrolyte solutions. These EBs have frequently incorporated anionic polymers (e.g. sodium polyacrylate) into the bentonite using a plethora of methods, (e.g. dry mixing, wet mixing, in-situ polymerization.) However, existing standard indicator tests (swell index, fluid loss, modified Atterberg limits) for GCL k may not always be effective for EB-GCLs. A rapid fluid indicator test (FIT) for screening high k versus low k of EB-GCLs and unmodified sodium bentonites, is proposed. Preliminary tests were conducted on granular sodium bentonite and an EB (bentonite polymer composite). Results of the FIT were compared with the swell index and k for these materials over a range of CaCl2 solutions. The results support that a passing FIT generally correlates to low k for the same fluid under low stress conditions.

This paper focuses on gas breakthrough tests through bentonite-argillite interface. The main contribution of our study is to provide insights into the swelling kinetics, gas breakthrough pressure of these materials. During the tests, bentonite/sand plugs and bentonite-argillite plugs are used to perform swelling tests and gas breakthrough tests. Experimental results show that continuous gas passage through fully saturated bentonite/sand is not obtained until 10.5 MPa gas pressure. When a bentonite/sand plug swells inside a smooth metal tube, gas passage occurs at 7–8 MPa, which is similar to the effective swelling pressure of bentonite, as measured by independent swelling experiments. For argillite alone, saturated with water until sealing (water permeability on the order of 10−20–10−21 m2), gas breakthrough may occur at as low a pressure as 0.2 MPa and up to 6 MPa for undisturbed argillite. Finally, also after full water saturation, continuous gas breakthrough through the bentonite-argillite interface is detected at between 7 to 8 MPa gas pressure. It is interpreted that the argillite rock or the bentonite-argillite interface are both preferential pathways for gas migration when all materials become fully saturated.

The hydraulic performance and migration parameters of cementitious mixtures are currently under investigation by an experimental study. The main aim of the research is to investigate the diffusion coefficient and sorption capacity of the mixtures and their interaction with inorganic sulphate solutions at different concentrations, as a function of their composition and curing time. The paper shows and discusses the results related to the hydraulic performance and the sorption capacity as a function of the mixtures composition. Simulations of solute migration through cut-offs made by the different mixtures investigated show the importance of taking into account their sorption capacity to optimize the design.

Geosynthetic clay liners (GCLs) are often used as barriers for landfill liners and cover systems due to the high swelling ability of the bentonite in water that results in low hydraulic conductivity. However, contact with electrolyte solutions and leachate can impede the osmotic swelling of the bentonite and cause an increase in both liquid and contaminant flux through the GCL.In this framework, different modified bentonites (e.g. multiswellable bentonite, dense pre-hydrated GCL, HYPER clay) have been developed to improve their chemical resistance in aggressive environments.The purpose of this paper is to provide an overview of the hydraulic performance of the recently developed chemically modified bentonites subjected to wet and dry cycles.Hydraulic conductivity results of modified bentonites are promising. However, the enhanced performance may still be impaired with aggressive solutions after wet and dry cycles.

Engineered compacted earthen liners are significantly important for the disposal of municipal and industrial solid wastes. Compacted clay liners strain during seasonal wet and dry fluctuations, providing pathways for leachate to contaminate surrounding soil and groundwater. Although geosynthetic clay liners are utilized, GCLs may be infeasible in areas that undergo cyclic wet and dry seasonal or groundwater fluctuations. This study focuses on improving the properties of kaolinite silty-clay by minimizing permeability through induced hydrophobicity. Siloxane, a water repellent material, was mixed with kaolinite soil at concentrations between 0.5% to 20% by weight to determine optimal induced hydrophobicity for retention of mass during cyclic wetting and drying. Hydrophobicity was measured using sessile drop methodology and water drop penetration time. Fine particles are preferentially influenced, resulting in soil gradation differences on the portion passing No. 200 sieve. Resistance to water penetration was improved, resulting in greater adherence between soil particles without inducing any crystalline structural changes. Volume losses and moisture absorption from wetting and drying cycles were reduced in optimally treated siloxanated clay molds, as compared to untreated samples. These experimental results indicate siloxane treated kaolinite clay possess improved engineering characteristics, and have potential to improve the useful lifetime of clay liners.

The swelling characteristics of bentonite is important to evaluate the long-term performance of deep geological repository of nuclear waste. A series of wetting tests on GMZ sodium and calcium bentonite were performed to investigate the swelling characteristics under different conditions. The influences of initial dry density and particle size were studied at different temperature. The test results show that the swelling deformation due to wetting is mainly affected by the dry density and little affected by particle size. The swelling ratio of GMZ bentonite increases with the increase of initial dry density. However, only the swelling ratio of sodium bentonite increases with the rise of temperature. The process of swelling deformation is a single or multi-stage mode depending on the initial dry density. Finally, the sample of the bentonite is subjected to a rapid swelling with the increase of the initial dry density. The swelling property of sodium bentonite is much higher than that of calcium bentonite. All results are very important for the study of swelling properties of GMZ bentonite.

Anisotropic shrinkage of compacted bentonite blocks threatens the security of a buffer barrier in a geological disposal project for high-level radioactive wastes (HLW). In this investigation, fan-shaped buffer blocks on an industrial scale were compacted and exposed to an indoor environment to dry naturally. Digital image correlation (DIC) was used in an attempt to monitor the blocks’ shrinkage deformation in a vertical (z) direction, and dial indicators were used to measure horizontal (r and θ) shrinkage for comparison. Before and after the blocks desiccation, pore size distributions were investigated by mercury intrusion porosimetry (MIP) to analyze the shrinkage behavior in the microstructure, and the micro-fissuring was investigated by X-ray computed tomography (CT) in terms of internal visual structure. The initial evaporation stage on the industrial scale and over compaction of the blocks was not detected. In horizontal directions, isotropic shrinkage strains were observed, which were lesser than 2%. Linear shrinkage strains decreased with the increase of the initial lengths of the measuring lines, indicating that block shrinkage is mainly concentrated on the external part, while the internal part shows poorer shrinkage ability. CT images showed that no obviously micro-fissuring was found in a block before drying it and MIP results demonstrated that both macrostructure and microstructure at a 5 cm depth slightly changed after block desiccation. Vertical shrinkage, monitored by DIC, exhibited a poorer ability compared to the horizontal direction, which had almost equal linear strains though its initial measuring lines lengths were shorter. In future research, more attention should be paid to the lateral shrinkage of buffer blocks.

GCLs are employed in containment applications, where both advection and diffusion need to be evaluated as possible migration mechanisms of contaminants. Permeation column tests were carried out on a GCL using two synthetic multispecies inorganic solutions of different ionic strength and containing equimolar concentration of heavy metals (Pb, Zn, Cu). The hydraulic conductivity (k) of the GCL to inorganic solutions increased by one order of magnitude relative to permeation with water. The solute breakthrough curves were interpreted using the software Pollute®, which allows modeling solute transport in case of variable transport parameters and nonlinear equilibrium sorption. The experimental data were best fitted by assuming effective diffusion coefficients of solute species increasing with time.

The most common soil barriers used to contain waste units consists of fine grained clayey soils. For these soil barriers, the permeability is the parameter of primary concern. This parameter can be determined either directly by performing in situ tests or indirectly through the check of the dry unit weight and water content frequently measured in situ. In fact, the measurement of soil permeability in situ is not an easy task; the permeability test takes long time to perform, and makes difficult any intervention to improve the quality of the soil barrier. Therefore, the simple way to check the permeability of compacted soils in situ is through measuring the dry unit weight and water content. This paper presents a methodology for the study and indirect control of the permeability of soils compacted in situ. According to the quality sought for the soil barrier, this methodology allows laboratory definition of an acceptable zone in terms of the dry unit weight and water content. This zone must be complied with during construction and serves as a criterion for in situ checking of permeability.

This paper focuses on the experimental research of water and gas transport in a compacted bentonite/sand mixture under flexible condition. The main contribution of our study is to provide insights into water and gas transport properties in the compacted bentonite/sand mixture. Experimental results indicate that water tightness can be achieved after full saturation, and the water permeability of the sample is at the magnitude of 10−20 m2. Gas breakthrough tests show that gas migration properties depend on both external stress state and internal fluid pressure. In addition, change of the external stress also has a hysteresis effect on the gas transport properties. At certain stage, the increasing rate of downstream gas pressure continue decreasing even though the gas pressure was increased while the confining pressure was kept constant. During the whole process, gas migration properties were determined by the coupling effects of confining pressure and gas pressure.

Pure clays or sand-clay mixtures with different clay mineral are widely used in liners or vertical barriers of waste landfill, and the pore water was characterized by its high salinity in coastal area. Thus, it is essential to understand the salinity effects on their consolidation behavior. In this study, oedemeter and SEM tests were conducted on four pure clays with different mineralogy. Several aspects of soil behavior, such as compression index, the end of primary consolidation stage and micro-structure, were investigated in view of pore water salinity effect. The results show that higher ionic concentration significantly decreases the compression index Cc and liquid limits (LL) for clays containing montmorillonite. While the period of primary consolidation was shorten under the impact of water salinity. For kaolinite with or without sodium chloride, a similar Cc, LL and the ending time of primary consolidation stage tp were observed. In view of flocculation, the salinity effect on consolidation behavior was interpreted. Increasing in salinity allows a flocculation and particle readjustment at constant water content for montmorillonitic clay. Then, larger inter-particle spaces and effective void ratio increased the permeability and decreased the drainage period, and larger internal frictions decreased the compression index Cc and LL.

This study investigated effects of phosphate dispersant on lead (typical heavy metal) sorption capacity of the sand/Ca-bentonite backfill for slurry trench cutoff walls. Several series of batch sorption tests were conducted using backfills consisting of sand and 20% Ca-bentonite with/without dispersant, as well as amended/un-amended Ca-bentonite alone. First, amended/un-amended backfills and amended Ca-bentonite were prepared. Next, aqueous solutions with 0 to 40,000 mg/L Pb concentration were prepared. Finally, the backfills and the Ca-bentonites were mixed with the solution in liquids to solid ratio of 10 and shaken for 24 h. The mixture was then centrifuged, and the supernatant was separated and analyzed for Pb concentration. The results show that the relationship between the amount of sorption and equilibrium concentration of Pb was well quantified by Langmuir and Freundlich isotherm models. Phosphate dispersant significantly increased Pb sorption capacity of both the sand/Ca-bentonite backfill and Ca-bentonite. The sorption process of the Pb onto the backfills or Ca-bentonites was found to be favorable. Overall, phosphate dispersant is shown to be a promising additive to sand/Ca-bentontie backfill in slurry trench cutoff wall construction for effective containment of Pb-laden groundwater.

Developing a sound theoretical description for the evolution of unsaturated hydraulic conductivity of compacted bentonite during re-saturation has remained a challenge because of the complex microstructure effects influenced by physico-chemical phenomena. This paper proposes a new relationship for the unsaturated hydraulic conductivity of compacted bentonite based on Kozeny-Carman relationship. A new relationship is also proposed for the relative permeability of compacted bentonite that incorporates the effects of microstructure swelling. The application of the new relationship for the case of compacted GMZ bentonite provides well correlated results with the experimental data reported in the literature.

The swelling deformation tests of Tsukinuno bentonite and its sand-mixtures were performed in distilled water and NaCl solution with different concentration. The results showed the swelling strain decreased with the increase in the vertical pressure, the salt concentration, and the sand content in the mixtures. The swelling properties of the bentonite can be characterized by a unique fractal em-pe relation, where the effective stress pe incorporating with osmotic suction was applied to take the effect of salinity into consideration. And the coefficient K, as the physical constant of bentonite can be estimated by diffuse double layer (DDL) model in the case of distilled water. The applicability of the fractal em-pe relation has been confirmed by comparing the predicted results with swelling deformation tests on Tsukinuno bentonites in various salt solution concentrations.

Because of high deformability even after construction, soil-bentonite (SB) cutoff walls, which are constructed by blending slurry and powder bentonite with in situ soil, are occasionally conjunct with soil-cement (SC) walls or cement stabilized soil having relatively high strength in the case that both strength and barrier performance is partly required. In this study, barrier performance of SBs containing cement at different proportions was experimentally evaluated using a flexible-wall permeameter. Specifically, SCs made with cement proportions of 100, 300, 500 kg/m3 were crushed after certain periods of curing time and used as a parent material of SBs. Experimental results demonstrate that hydraulic conductivity of SB containing cement can sufficiently decrease with time when bentonite is blended three hours after cement addition, while barrier performance of SB is insufficiently high when bentonite is added after 7-day and 28-day curing. Thus, a bentonite powder content of 100 kg/m3, which is a conventional proportion for construction of SB walls, is insufficient when cement stabilized soil exists in the ground.

Bentonite is frequently used as a liner material at the waste disposal site because of its high swelling ability, high contaminant adsorption capacity and low hydraulic conductivity. It acts as a barrier material by preventing and minimising the ingress of pollutant to contaminate the ground water resource. Metals present in the landfill leachates may shrink the thickness of the diffuse double layer (DDL) of bentonite, which in turn reduce its effectiveness as a liner material. Therefore, it is very essential to investigate the behaviour of bentonite in the existence of the different pollutant present in the leachate. Consolidation is one of the important behavior of bentonite, which is required to be investigated for settlement analysis of landfill liner. This study was performed to investigate the influence of copper (Cu2+) and zinc (Zn2+) solutions of various concentrations, on the consolidation behaviour of bentonite. Various consolidation parameters, such as compression index (Cc), coefficient of consolidation (cv), volume change (mv), time requires for the completion of 90% of consolidation (t90), were studied in the presence of heavy metals of concentration of 0, 500 and 1000 mg/L. The results indicated that with the increase in concentration of heavy metals the Cc, mv, and t90 of the bentonite decreases; whereas, cv increases. The study concluded that the presence of the heavy metals in the lechate increases the rate of consolidation of the compacted bentonite. The outcomes of this investigation may provide a general suggestion for evaluating the liner performance in the presence of different kinds of pollutants present in the lechate.

The chemical compatibility of backfills for soil-bentonite vertical cut-off walls is examined in this paper. The use of soil-bentonite cut-off walls as hydraulic barriers for waste containment facilities is on the rise. Their low hydraulic conductivity to water is attributed to the bentonite in the soil-bentonite backfills, which is composed primarily of smectite mineral. However, there have been concerns as to the compatibility of soil-bentonite backfills, since bentonite is very sensitive to chemical effects and this can lead to an increase in hydraulic conductivity. Thus, Fujian standard sand was employed for simulating a sandy soil layer, and Hebei Bentonite and Jiangning Clay were served as additives for studying the chemical compatibility of sand-bentonite backfills. The present study focuses on the influences of the stress level on the hydraulic conductivity, bound water content and effective porosity of soil-bentonite backfills under the situation of calcium chloride solutions with various concentrations.

Thermal expansion coefficient (TEC) of clay is an important parameter for evaluating the crack formation in landfill barriers during heating and cooling. To investigate the influences of soil fabric on the TEC of clay, saturated reconstituted, intact and recompacted loess were tested using a thermo-controlled invar oedometer. The linear TEC of each specimen was measured through thermal volume changes during cooling. Results showed that the linear TEC of the reconstituted specimen was almost three times larger than those of the intact and recompacted specimens. On the other hand, the void ratio has an insignificant effect on the linear TEC of reconstituted specimen. These observed differences in the linear TECs of reconstituted, intact and recompacted specimens are likely attributed to different distributions of clay particles in soil specimens (with 28% clay content). In the intact and recompacted specimens, most of clay particles formed silt-size aggregates which were less sensitive to temperature changes than clay particles founded in the reconstituted specimen.

Multi-layered cover system (MLCS) is constructed upon hazardous landfills that has reached its full potential. Soil erosion is a primary stressor of surface soils used in MLCS, which ultimately results in exposure of lower layers. The effect of compaction state is crucial to assess erosion potential of compacted surface soil used MLCS. The erosion potential needs to be studied as a function of initial compaction state, soil type and flow rate, under high intensity rainfall conditions. For this purpose, a well-established pin hole test was used to evaluate the erosion potential of soil. A total of 324 pin-hole tests on four loamy soils were conducted and the individual effect of initial moisture content, soil density and flow rate was discussed. It is observed that compaction process in top surface of MLCS can be done at wet of optimum moisture content (OMC) with highest maximum dry density (MDD) to minimize risk of erosion related failure. The compaction state of (OMC+5, 1.05MDD) is suitable for top surface design as it showcases significantly lower erosion rates than the permissible erosion rate for cover systems.

This paper presents the results of a numerical investigation of the transport of a volatile organic compound (VOC) through a composite liner system comprising a geomembrane (GM) overlying and in intimate contact with a geosynthetic clay liner (GCL), which is commonly used as an engineered barrier for containment of solid waste. The simulations were performed using the established CST2 model (i.e., Consolidation and Solute Transport 2). The results are presented in the form of VOC mass flux, cumulative VOC mass outflow, and distribution of VOC concentration within the GCL. Consolidation of the 10-mm-thick GCL is shown to result in a decrease in the thickness, void ratio, and effective diffusion coefficient of 41%, 49%, and 72%, respectively, such that the steady-state TCE mass flux and cumulative TCE mass outflow at the bottom of the GCL decreased by 47% and 43%, respectively, relative to results for traditional diffusive simulations that ignore the effect of consolidation. Thus, despite the thinness of the GCL, the effect of consolidation on the transport properties of the GCL can result in a significant decrease in VOC transport through a composite GM/GCL liner system.

The performance of highway subgrade is affected not only by soil type but also by other parameters such as water and temperature. Distribution and variation of temperature in subgrade affect the stability of highway subgrade in seasonal frozen area. In seasonal frozen areas, water accumulation in highway subgrade can cause frost heave and thaw settlement, which will finally affect the function of road structures. Due to its waterproof performance, geosynthetic clay liner (GCL) is mainly used in engineering practice as an effective material for sealing, isolation and leakage prevention. So it may be introduced into highway subgrade to provide possible moisture and temperature adjustment. Through water and heat coupling analysis of two kinds of subgrade models, following conclusions can be drawn. GCL can effectively prevent rainfall infiltration and adjust moisture field of subgrade. GCL in the subgrade can significantly decrease the maximum freezing depth and thereby reduce the frost damage risk of the highway subgrade in Seasonal frozen soil area.

Geosynthetic clay liners (GCLs) are an important part of composite hydraulic barriers in environmental projects, with recent applications in harsh conditions such as in Antarctica. To assure an adequate hydraulic performance of the GCL, the bentonite of the GCL needs to be well-hydrated. However, the sub-zero temperatures attained in Antarctica freeze the water inside the bentonite, and as a result, the hydration process stops with potential consequences on the hydraulic performance of the GCL. To predict the impact of freezing on GCL performance, it is essential to obtain the unsaturated freeze property functions (UFPFs) for the bentonite. The freezing characteristic curve (FCC), which relates the unfrozen water content with freezing temperatures, is the first of the UFPFs, and can be obtained experimentally or by prediction methods. This paper reviews the concepts leading to the determination of the FCC, its relationship with the other UFPFs and its importance for predicting GCL performance in cold regions.

A coupled of discrete-continuum numerical model was established for the two-stage Mechanically Stabilized Earth (TS-MSE) wall on soft ground based on centrifugal test. In the numerical model, the wall and soft ground were simulated using Particle Flow Code (PFC) and Fast Lagrangian Code (FLAC), respectively. The deformations of the TS-MSE wall on soft ground were analyzed under working loading. Then, the failure mechanism of the wall was further investigated. It was found that the numerical results were in good agreement with the measured results in the centrifugal test and that the TS-MSE wall can well adapt to the soft ground under the working loading. The TS-MSE wall on the soft ground generally suffers the deep seated failure mode, and the deep seated failure surface is composed of a Rankine failure surface in the unreinforced zone and an arc failure surface in the foundation. The strength of the reinforcements was gradually reduced to investigate the internal failure mechanism of the TS-MSE wall on the soft ground, and the internal failure mechanism of the wall exhibited that the reinforcements were fractured from the bottom to the top of the wall in sequence following the failure surface in the foundation, forming a Rankine failure surface passing through the end of the connection element at the bottom layer.

Loss of bentonite from geosynthetic clay liners (GCLs), installed as a component of a composite liner beneath an exposed geomembrane (GM) on the side-slopes of landfills and exposed to thermal cycling, has become a topic of some importance recently as it raises questions on the long-term durability of modern landfill lining products. Laboratory drip testing was used to evaluate the resilience of four GCLs containing polymer-modified powdered bentonite against down-slope bentonite erosion. Onset erosion features were observed only after 60–140 drip cycles. In all probability the polymer-modified bentonite can be expected to self-heal if no further erosion takes place at these initial stages. A detailed assessment of the drip test and comparison with known field test results, indicates that the drip rate and duration of the laboratory test conducted at ≈22 °C is equivalent to in-field conditions where daytime temperatures of the GM/GCL may reach 65 to 75 °C. Thus, meaningful accelerated testing of polymer-modified powdered bentonite GCL products is possible. The results need to be validated with in-field tests under local conditions because recoverable service-lives of GCL products ultimately depend on the in-field conditions where these materials are deployed.

Internal shear strength of geosynthetic clay liner (GCL) is of vital importance for the stability of waste containment facilities where GCLs are widely used as hydraulic barriers. This paper presents an experimental investigation of the internal shear strength of hydrated needle-punched geosynthetic clay liners (NP GCLs) under monotonic loading. A new dynamic direct shear apparatus with the capability to cover a large range of normal stress and displacement rate is developed. Series of direct shear tests on NP GCL for different normal stress levels and displacement rates are performed. The failure mechanism of hydrated GCL is explored through inspection of tested specimens and analysis of test results. The intrinsic relationship between peak/residual shear strength of NP GCL and displacement rate is also studied. Experimental results indicated that displacement rate has obvious effect on the peak shear strength of NP GCL, while the influence of displacement rate on residual shear strength is of little significance for the same normal stress level.

A series of laboratory model loading tests were performed on strip foundations supported on unreinforced and geotextile-reinforced transparent soils. Fused silica sand and white oil were carefully mixed to prepare the transparent soil. The transparent soils were reinforced with geotextiles with the spacing of 0.25B and 0.5B, the length of 1B to 7B, and the depth of 0.5B, 1B and 1.5B (B is the width of the foundation). The deformations of the soils and geotextiles were monitored using a digital camera and a laser transmitter. The results show that for the soils with reinforcements of 0.5B spacing, the deformations of the geotextiles show that each peak point observed in the curves of the bearing capacity improvement versus foundation settlement is related to the failure of one layer of reinforcement, which indicates the progressive failure of different layers of reinforcements. However, for the soils with reinforcement of 0.25B spacing, failure of layers of reinforcements occurs from bottom to top. Moreover, most of the foundations show brittle failure behavior. It also reveals that the bearing capacity of reinforced soil foundation does not always increase with the increase in length of reinforcements when suitable reinforcement spacing is chosen.

A study was conducted to determine the effect of freeze-thaw cycling concurrent with municipal solid waste (MSW) landfill leachate on the hydraulic conductivity of a geosynthetic clay liner (GCL). The GCL was hydrated with MSW landfill leachate and subsequently subjected to 5, 10, 15 and 20 freeze-thaw cycles. After the prescribed numbers of freeze-thaw cycles was met, the hydraulic conductivity of the GCL was tested in a flexible wall permeameter. Hydraulic conductivity of GCL experienced freeze-thaw cycles was slightly higher than those without frozen, with the hydraulic conductivity increased with increasing of number of freeze-thaw cycles. The increase in the hydraulic conductivity of GCL could be a result of the contraction of double-layer, resulting from the increases in the concentrations of cations in the pore water (i.e., MSW landfill leachate) induced by freeze.

Experiments were conducted to evaluate the compatibility of bentonite-polymer (B-P) GCLs to Coal Combustion Product (CCP) leachates. The B-P GCLs were manufactured by dry-mixing polymer and sodium bentonite (NaB). Six synthetic leachates were selected based on database of coal ash leachates. Hydration characteristics (i.e., free swell index) and hydraulic conductivity of B-P GCLs were investigated using deionized water and synthetic leachates. The hydraulic conductivity of B-P GCL with low polymer loading (1.2%) is strongly affected by the ionic strength of leachates and controlled by swelling of bentonite. However, the hydraulic conductivity of B-P GCL with high polymer loading (≥5.1%) is controlled primarily by hydrogel blockage in the pore space. Polymer hydrogel forms reticular structure and bonds free water when hydrated with DI water. However, under 20 mM CaCl2, the reticular structure of polymer hydrogel is inhibited by self-entanglement due to divalent cations and high ionic strength.

Experiments were conducted to evaluate the hydraulic conductivity of geosynthetic clay liners (GCLs) to bauxite liquor from aluminum refining. Tests were conducted with a GCL containing conventional sodium-bentonite (Na-B) and one GCLs containing a bentonite-polymer composite. B-P has polymer loading of 6.8%. Hydraulic conductivity tests were conducted on the GCLs with bauxite liquor in flexible-wall permeameters following procedures in ASTM D6766. The bauxite liquor used in the experiments has pH 13 and ionic strength = 700 mM. Hydraulic conductivity of the Na-B GCL increased to approximately 10−7 m/s during permeation, whereas the B-P GCL maintained low hydraulic conductivity (~ 4.3 × 10−12 m/s). Suppression of bentonite swelling by the bauxite liquor is the primary factor responsible for the higher hydraulic conductivity of the Na-B GCL. Low hydraulic conductivity of the B-P GCL to bauxite liquor is attributed to polymer clogging intergranular pores controlling flow of bauxite liquor through the GCL. The findings indicate that B-P GCLs with sufficient polymer loading can be used effectively in composite liners for disposal facilities containing bauxite liquor.

Geosynthetic clay liners (GCLs) are increasingly used in mining applications, their hydraulic performance need to be further assessed. In this study, the fluid loss (FL) tests of three bentonites from different GCLs were conducted under different mining leachates. The results suggest that the FL values in mining leachates greatly increased compared to those in water. The greater ionic strength of the leachates led to much higher fluid loss. The triaxial hydraulic conductivity tests using mining leachates as permeant solutions were also performed, the hydraulic conductivity (k) value increased with the increased ionic strength of the mining leachates. The relationship between fluid loss and hydraulic conductivity was also established. The k calculated from the FL test (kFL) is in good agreement with that from triaxial hydraulic conductivity test (kTri). Therefore, the FL test could be considered as a quick method to evaluate the hydraulic conductivity under the studied mining leachates. This study would provide useful reference to the mining application of GCLs.

Since decades the use of nonwoven geotextile filters is a common application in geo-environmental engineering. The main functions of the filter are to prevent the movement of the base soil fine particles allowing the liquid to flow as freely as possible. Geotextiles are easy to transport and install, their main advantage is to help to minimize clogging effect of drainage and the proper selection of geotextile filter layers is essential to ensure durability of drainage systems. However, the design of a geosynthetics filter is a very complex process because of the large number of parameters involved. In this paper the current geotextile filter design criteria: retention, permeability and anti-clogging were showed. What is more, laboratory tests of water permeability normal to the plane of worn nonwoven geotextile samples taken from Białobrzegi earthfill dam after more than 20 years of exploitation were presented. Therefore the factors affecting the geotextile filters clogging were illustrated. The results show a marked influence of clogging on hydraulic properties of tested nonwoven geotextiles and allowed to verify the effectiveness of applied geofilters in earthfill dam.

The installation process may cause unwanted changes in the mechanical behaviour of the geosynthetics. In this work, some geosynthetics used in the base liner system of landfills (a combination of a geotextile, a geomembrane and a geosynthetic clay liner) were submitted to mechanical damage under repeated loading tests (procedure adapted from EN ISO 10722), being monitored the changes occurred in their short-term behaviour. The mechanical damage under repeated loading tests consisted in placing the geosynthetics between a flexible base (granite residual soil with a relative density of 80%) and an aggregate and submitting them to cyclic dynamic loading. The geosynthetics were damaged with a natural aggregate (gravel 14/20), a recycled ceramic aggregate and corundum (synthetic aggregate used in EN ISO 10722). The damage suffered by the geosynthetics was evaluated by monitoring changes in their tensile, tearing (only for the geomembrane) and static puncture properties.

The installation procedures (which may cause mechanical damage) and abrasion may provoke unwanted changes in the properties of the geosynthetics, affecting their performance. This work evaluated the resistance of two geotextiles (with different structures) against two degradation mechanisms: mechanical damage under repeated loading and abrasion. The geotextiles were (1) exposed in isolation to each degradation mechanism and (2) exposed consecutively to both degradation mechanisms. The damage suffered by the geotextiles (in the degradation tests) was evaluated by monitoring changes in their tensile and static puncture behaviour. Based on the changes occurred in tensile and puncture strength, reduction factors were determined. The reduction factors obtained in the successive exposure to mechanical damage under repeated loading and abrasion were compared with the reduction factors determined by the traditional methodology for the combined effect of those degradation mechanisms.

The filtration performance of woven geotextiles is a constant issue in water proof and flood prevention site. Woven geotextiles have been characterized by a two-dimensional single-pore model and linear change laws of characteristic pore size and percent open area (POA) with increasing of tensile strain have been applied by people before. However, percent open area (POA) which is decided by the ratio of pores area and geotextiles area is proved to be non-linear as tensile strain increases. In this paper, change laws of percent open area (POA) and characteristic pore size in uniaxial tension test are explored by using imagine analysis. Considering the effect of “pore size deformation coefficient” and “textile shrinkage coefficient”, “multi-pore model” of woven geotextiles is come up with in this paper in order to improve change laws of percent open area (POA) and characteristic pore size in uniaxial tension test.

The objective of this paper is to evaluate the hydraulic conductivity of a commercially-available geosynthetic clay liner (GCL) by Flexible-wall permeameter. The GCLs are produced by the same factory, but the content of bentonite is different. And hydraulic conductivity (HC) tests are performed on GCL specimens with different HC results (i.e., 10−9 cm/s and 10−6 cm/s). After 18 days, specimens were complete saturated under backpressure 20 kPa. The results of these tests indicate that there is a decrease in hydraulic conductivity of the GCL may be expected due to the consolidation of GCL. Measured hydraulic conductivities of GCL specimens with high HC permeated with distilled water under 20 kPa stress conditions that there is a slightly decrease and the HC keep in one order of magnitude, whereas measured hydraulic conductivities of low HC GCL specimens tested under similar conditions the HC keep in one order of magnitude. The test results show that similar hydraulic conductivity values are obtained for GCL specimens after complete saturated. In addition, the flow rate decreases with the time of test. The research findings may be of interest to researchers and engineers who design liners for landfills and other liquid containment facilities.

Geogrids are used to reinforce the MSW slope in some landfills, but the interactions between MSW and the geogrid reinforcement are not clear at present. Xingfeng landfill used geogrids to strengthen the MSW slope during the project of vertical expansion. To observe the behavior of the reinforced MSW slope, systematic field monitoring was carried out. The vertical earth pressures in the reinforced MSW and the tensile strains of the geogrid reinforcement were measured by earth pressure cells and flexible strain sensors, respectively. The distribution of the vertical earth pressures and the reinforcement strains was nonlinear along the length of reinforcement. The vertical earth pressures were adjusted to not equal the theoretical values due to the deformation of the geogrid reinforcement, indicating the interactions between MSW and geogrid reinforcement were relatively effective. However, due to the geogrid reinforcement is relatively short and doesn’t traverse the potential slip surface, the risks of slide still cannot be ignored for this reinforced MSW slope.

Woven geotextiles are typically subjected to complex unequal biaxial tensile strains in filtration applications. Analytical solutions have been proposed to predict the per cent open area (POA) and analytical pore size of woven slit-film geotextiles under certain biaxial tensile strains. The influence of unequal biaxial tensile strains on pore size characteristics of one woven slit-film polypropylene geotextiles was evaluated by image analysis. The ratios of warp to weft strains are set to be 2:1, 3:1 and 4:1, respectively. Comparisons of experiments and predicted results suggest that POA and pore size increase with the biaxial tensile strain. The increasing trend of POA and O95 can be predicted by the analytical solutions.