Compacted Clay Research Articles

A Study on Natural Clay and Moringa Oleifera for Sustainability of Landfill Liners

This project aims to characterize the municipal solid waste leachate, using column study method to evaluate the concentrations of constituents present in landfill leachate. The leachate sample were tested for several physical and chemical parameters. The initial results demonstrated that the characterizations of leachate found to be highest range of contamination. Hence compacted clay liner is used in this treatment. Moringa Oleifera is added with compacted natural clay to retain the constituents in the liner. Compacted natural clay liner shows the removal efficiency of TDS, Sodium and Potassium is 88.44%, 90.6% and 68.46% respectively. Moringa Oleifera with Compacted natural clay liner shows the removal efficiency of TDS, Sodium and Potassium is 90.2%, 98.75% and 81.2% respectively. Result shows Moringa Oleifera with Compacted clay liner has been an effective for the removal of constitutes present in landfill leachate.

Role of Stress History on the Swelling–Shrinkage Behavior of Compacted Scaly Clay

Role of Stress History on the Swelling–Shrinkage Behavior of Compacted Scaly Clay

Effect of suction on the mechanical behaviour of unsaturated compacted clay–sand mixtures

Abstract In this work, a series of unconfined compression tests at different water contents were performed to investigate the mechanical behaviour of clay–sand mixtures compacted in standard Proctor conditions. For studying the effect of water content and suction on unconfined compressive strength (UCS) and on strain secant modulus (E50 modulus) of these mixtures, drying–wetting paths were defined by measuring the soil–water characteristic curves (SWCCs) using osmotic and salt solution techniques and filter paper method. The results highlighted that an increase in sand content of the mixture leads to an increase in the maximum dry densities and a decrease in the optimum water content of the materials. However, at the given state, when clay is mixed with 25% of sand, the UCS and E50 modulus increase to 37% and 70%, respectively, compared to those of clayey samples. But when clay is mixed with 50% of sand, the UCS and E50 modulus decrease to 38% and 46%, respectively, compared to those of clayey samples. The results also indicate that the UCS and E50 increase with a decrease in the water content and an increase in suction, irrespective of the sand content.

Evaluation of Performance of Polyacrylamide-Modified Compacted Clay as a Gas Barrier: Water Retention and Gas Permeability and Diffusion Characteristics

In this paper, the performance of a gas barrier that consisted of polyacrylamide (PAM)-modified compacted clayey soil was experimentally explored. The moisture content and water loss characteristics of the tested soils were adopted as indicative indices of water retention capacity (WRC). The gas permeability (Kp) and gas diffusion coefficient (Dp) of the modified compacted clays were evaluated via gas permeability and gas diffusion tests. The test results showed that the moisture content of the modified compacted clay samples subjected to drying tests increased with increasing polyacrylamide content. Kp and Dp decreased with increasing PAM content. Compared with 0.2% PAM content, the Kp of the sample with 1.0% PAM was reduced by ten times, and the Dp was reduced to ~35%. Compared to the unmodified clay, the liquid limit of the PAM-modified clay increased by 45~55%. Comparison of the liquid limit tests between this study and previous studies revealed that the liquid limit ratio of the zwitterionic polyacrylamide (ZP)-modified soil was much higher than the other material-modified soils. The results of this study are useful to facilitate the application of modified compacted clays as gas barrier materials at industrial contaminated sites.

Effect of Bentonite Content on Hydraulic Conductivity of Sand-Bentonite Mixtures Used in Landfill Liners as an Alternative to Clay Liner in Egypt

Compacted clays are commonly utilized as landfill liners due to their impermeable properties, however, the availability of natural clay soil may be difficult or prohibitively expensive in some regions thanks to the expense of transportation, the local soil availability or regulation. As an alternative hydraulic barrier, a compacted mixture of sand with a low percentage of bentonite (6% to 14%) was used. The purpose of this research is to investigate the applicability of bentonite available in the Egyptian market for controlling the hydraulic conductivity of sand-bentonite mixtures to be used in landfill liners. The study was divided into two phases: first, laboratory tests were conducted to identify the optimum bentonite percentage and bentonite types, using local commercial bentonite products. Then, in two distinct landfill liners layers, full-scale measurements were obtained. The experimental program demonstrated that Bentonite produced and found in the Egyptian market can be utilized in landfill liners with an acceptable quality control procedure to prevent any outcome deviation.

Geotechnical behavior of fly ash-coal ash and bentonite clay composite as a landfill barrier material with special emphasis on desiccation cracks

Compacted clay barriers have been used to retard leakage of contaminated fluids from landfillsites. These liners may shrink, crack, desiccate and lose their integrity if the liner material doesn't have permeability (10−9 m/s), unconfined compressive strength (UCS = 200 kPa) and no desiccation cracks at all as per the CPCB-2001 and USEPA 1989 guidelines. These three parameters form the basis of utilizing any material as a liner material however bentonite clay (BC) due to excessive desiccation cracks upon drying and wetting events can't be used individually. The usual practice to overcome failure, of barrier material the usual practice is to amend BC with sand though being costly and unsustainable. Recently, Fly ash (FA) and Coal ash (CA) byproducts from thermal power plant, have been explored as a substitute of sand in landfill liner material for sustainable practices. The purpose of this study is to investigate and and compare the various composition of B-FA and B-CA in terms of adequate strength, permeability, and shrinkage/desiccation in such a way to meet the CPCB-2001 and USEPA 1989 guidelines. The variation of specific gravity, liquid limit, plastic limit, and DFSI with varying compositions of bentonite was also studied. The present study demonstrates that with the increment of BC permeability was found to decrease and 80CA20B, 80FA20B, 80FA15B5CA combinations were meeting CPCB-2001 permeability criterion. To replicate the field condition the overburdening pressure was varied from 100 to 800 kPa and the permeability was found to be within the prescribed range for the three compositions. In total, 72 UCS, including triplicates for 7, 14 and 28 days, were conducted to see if any pozzolanic reaction was ensuingand its effect on the strength. The maximum UCS was found to be 302 kPa for 80CA20B composition while 277 kPa for 80FA20B. Strength Improvement Factor (SIF) and Mobilized peak strain factor (MPSF) were found to be maximum for the 80CA20B composition for 28 days as 1.54 and 0.44 respectively. The composition 80CA20B demonstrated better desiccation crack resistance behaviour than 80FA20B and 80FA15B5CA. The volumetric shrinkage for 80CA20B, 80FA20B and 80FA15B5CA were 4.6, 10.49 and 4.2%. Further, there were no desiccation cracks observed if the volumetric shrinkage is around 4%. The water retention behavior of all the three compositions was almost same. The microstructure analysis for morphology, compositional characterization, and thermal analysis of the various constituents was also carried out.

Effect of Cashew Nut Shell Ash on Volumetric Shrinkage of Compacted Clay Soil


 Hydraulic conductivity value of a compacted clay soil can rise above the minimum regulatory value during desiccation thereby induces large cracks in an engineered landfill. In the quest to reduce the degree of cracking that will be generated dues to the volumetric shrinkage of the compacted clay soil, which in turn will reduce the amount of leachate that will be percolating into the underground water system, an investigation was performed by treating a clay soil with up to 16% Cashew Nut Shell Ash (CNSA) content using three compactive efforts (Standard proctor (SP), West African standard (WAS) and Modified Proctor (MP)) at -2, 0, 2 and 4% of optimum moisture content (OMC). Samples were extruded from the compaction moulds and placed on the laboratory table to air dry for 30 days at a uniform regulated temperature of 27 ± 2Oc in order to evaluate the suitability of the material for the construction of cover and liner in an engineered landfill. Results indicated that the OMC and maximum dry density (MDD) increased with higher CNSA treatment. Volumetric shrinkage strain (VSS) increased with; higher CNSA, higher molding moisture content and moisture content relative to the optimum. Effect of CNSA on the soil showed that all specimens prepared at 2% dry of optimum to 4% wet of optimum for 4% and 8% soil-CNSA mixtures for the three compactive efforts, met the maximum allowable regulatory VSS criterion of4%, thus making the material suitable for the construction of cover and liner in waste dumping ground.

Screening Additives for Amending Compacted Clay Covers to Enhance Diffusion Barrier Properties and Moisture Retention Performance

The cover systems in contaminated sites have some problems, including desiccation cracks, which would lead to degradation of the barrier performance. This study presented a systemic laboratory experimental investigation on the liquid–plastic limit, moisture retention, hydraulic conductivity (k), and gas diffusion barrier properties of amended compacted clay by attapulgite and diatomite for controlling desiccation cracks and migration of water and volatile organic compounds (VOCs). The results showed that the attapulgite could enhance the moisture retention and liquid limit of amended compacted clay. Diatomite could reduce the gas diffusion coefficient (Dθ) significantly. The compacted clay amended by the dual-additives component of attapulgite and diatomite could enhance the liquid limit, moisture retention percent, gas barrier property, and hydraulic performance compared with the unamended clay. Based on the experimental data obtained, the dosage of additives was targeted to be 5%. The moisture retention percent of dual-additives (attapulgite 4% and diatomite 1%) amended clay increased by 82%, the k decreased by 25%, and the Dθ decreased by 42% compared with unamended clay. Scanning electron microscopy (SEM), BET-specific surface area test method (BET), Mercury Intrusion Porosimetry (MIP), and thermogravimetric analysis (TGA) indicated the enhancement mechanism of additives-amended compacted clay.

An Attempt to Study Foundation Anchoring Conditions in Sedimentary Estuaries Using Integrated Methods

The search for and knowledge of the best conditions for anchoring the foundations of certain structures such as bridges, tunnels and quays in sedimentary estuaries is a challenge, for both scientists in general and engineers in particular. Indeed, wharves are structures that receive a lot of stresses and therefore require anchoring to avoid tilting and to guarantee their stability during service. This work, based on the analysis of data from seismic refraction methods, mechanical soundings and laboratory tests, characterises the terrain of the Wouri estuary in Central Africa. The objective is to determine and present the subsurface layers encountered as well as their characteristics, in order to define the best conditions for anchoring the foundations to ensure the stability of the quays to be built there. The seismic refraction campaign shows that the study area is relatively heterogeneous over the first 25 m, with velocities measured in the range 1520–1750 m/s; modulated in two distinct ranges, between 1520–1580 m/s characteristic of mud and loose sediments (alternating layers of clay, sand, loose silt) and the range 1580–1750 m/s corresponding to the signature of sandy-silty or compact clays. The mechanical tests show sedimentary soils, with alternating layers of sandy clay and clayey sand over the 42 m drilled, loose over the first 30 m in the bank area and over the first 15 m in the canal or dredge area, with a limit pressure of less than 1 MPa. Similarly, the soil samples taken and tested in the laboratory show that the soils are clayey over the first 30 metres, plastic and liquid with respect to their water content, respectively, below and above the liquidity limits, confirming their loose character. The results of seismic refraction, mechanical soundings and laboratory tests show that, in estuarine areas characterised by alternating sandy clay and clayey sand, there are not always hard formations in the first 25 metres of depth but, from a depth of 30 m, the soils become moderately compact and begin to form an anchoring layer sufficient to guarantee the stability of the quays against earth pressure forces.

A Simple Relationship to Estimate Parameters of the Optimum Compaction Point

Compacted clay covers have been the most commonly used materials for hydraulic barrier layers. During their construction, the control of some parameters such as compactive effort and molding water content is required. These last parameters affect the hydraulic conductivity, which is considered as one of the important key parameters for cover design. To reach the target in terms of hydraulic conductivity, the cover must be compacted to a pre-determined dry unit weight that usually corresponds to a certain percentage of the maximum dry unit weight (γdmax). During the prefeasibility stage of a project (before conducting the required tests), γdmax and the optimum water content (wOpt) can be estimated to obtain an early overview of the conditions that can be anticipated. In this regard, a new approach was proposed to estimate these parameters using the liquid limit (wL) and the plastic limit (wP). The proposed equations were developed using data from 56 compacted clay liners and validated using 44 others taken from published data. Results presented in this paper indicate how the proposed equations can successfully estimate parameters of the optimum compacted point.

Analytical solution for solute transport in a triple liner under non-isothermal conditions

Analytical solutions for the transport of contaminant through a 1D triple-layer composite liner system consisting of a geomembrane (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) under non-isothermal conditions are derived using the generalized integral transform technique. The proposed analytical solutions account for the combined effects of molecular diffusion, sorption and thermodiffusion as well as the temperature-dependent distribution coefficient and effective diffusion coefficient. The proposed analytical solutions are successfully validated against the experimental results of thermodiffusion tests and verified against an analytical solution available in the literature and a numerical model based on commercial finite element software. Using the verified analytical solutions, simulations are performed with representative geometry and material properties for a GMB/GCL/CCL liner system. The results indicate that neglecting the effect of non-isothermal condition can underestimate the benzene outflow rate by over 30% when the temperature difference between the surface and bottom of the liner system exceeds 10 K. The temperature-dependent CCL effective diffusion coefficient and CCL distribution coefficient have a significant effect on benzene transport through the GMB/GCL/CCL liner system, whereas the liner thermal conductivity and the temperature-dependent GCL effective diffusion coefficient and GCL distribution coefficient have a negligible effect.

Field Investigation of Effect of Plants on Cracks of Compacted Clay Covers at a Contaminated Site.

Compacted clay covers (CCCs) are effective in restricting the upward migration of volatile organic compound (VOC) and semi-volatile organic compound (SVOC) vapors released mainly from unsaturated contaminated soils and hence mitigate the risks to human health. Desiccation cracking of CCCs would result in numerous preferential channels. VOC or SVOC vapors can prefereially migrate through the cracks and emit into the atmosphere, exposing threats to human health and surrounding environmental acceptors. This study presented results of comprehensive field investigation of desiccation crack distribution in CCCs, where four herbaceous plants were covered at the industrial contaminated site in. The plants included Trefoil, Bermuda grass, Conyza Canadensis, and Paspalum, and the corresponding planting areas were labeled as S1, S2, S3, and S4, respectively. The quantity and geometry parameters of the cracks including crack width, depth, and length, were investigated. The results showed that the cracks of the CCCs were mainly distributed in the areas of S3 (Conyza Canadensis) and S4 (Paspalum), where more cracks were formed when the degree of compaction (DOC) of the CCCs was less than 87%. In addition, the results revealed that: (1) no cracks were found in the area S1 (Trefoil); (2) the quantity, average width, average depth, average length, and maximal length of the cracks in the investigated areas followed S4 (Paspalum) > S3 (Conyza Canadensis) > S2 (Bermuda grass); (3) the maximal crack length in the area S2 (Bermuda grass) was the shortest, which was approximately one-seventh and one-eighth of those in the areas S3 (Conyza Canadensis) and S4 (Paspalum), respectively; and (4) the maximal width and depth of the cracks followed S3 (Conyza Canadensis) > S4 (Paspalum) > S2 (Bermuda grass).

Swelling of Compacted Clay as Affected by Quantity of Water Intake and Soil Structure

Swelling of Compacted Clay as Affected by Quantity of Water Intake and Soil Structure

Effect of biochar on permeability of compacted soil and its microscopic mechanism

Biochar has attracted much attention in the field of geo-environmental engineering as a carbon-neutral alternative for soil amendment. In this study, the effects of biochar dosage, type, and particle size on the permeability and physical properties of compacted silty clay were investigated. And the prediction model of permeability coefficient of biochar-amended soil (BAS) was established. Based on the microscopy test results, the influence mechanism of biochar on the permeability of compacted soil was analyzed. Results revealed that adding different biochar types affected the consistency limits, specific gravity, and compaction curves of soil obviously. As the biochar content increased, the permeability coefficient of compacted BAS initially decreased before increasing. The permeability coefficient of compacted BAS with peanut-shell biochar was much higher than with other biochar types. Additionally, reducing the particle size of biochar can effectively decrease the permeability coefficient of BAS due to the pore-filling effect. Microscopy test results show that the permeability coefficient of BAS is affected by both the most probable pore size and the main-peak area of the pore-size distribution curve. Results suggest that controlling the biochar content at 5% and reducing the particle size of biochar are more beneficial to improve the impermeability of compacted BAS.

X-Ray microtomography of mercury intruded compacted clay: An insight into the geometry of macropores

Soil properties, such as wetting collapse behaviour and permeability, are strongly correlated to the soil microstructure. To date, several techniques including mercury intrusion porosimetry (MIP), can be used to characterize the microstructure of soil, but all techniques have their own limitations. In this study, the features of mercury that penetrated and has been entrapped in the pore network of the specimens through MIP testing were investigated by X-Ray microtomography (X-μCT), in order to give an insight into the geometry of macropores and possible ink-bottle geometry. Two conditions of water content and density were selected for the compacted Maryland clay. The distribution and geometry features of mercury entrapped in the microstructure after MIP were characterized and pore size distributions were also reconstructed. The results suggest that, for the two conditions studied in this paper, macropores were evenly distributed within the specimens, and most of them with a non-spherical shape, and with aspect ratio (ratio between the maximum and minimum thickness along a given segment) smaller than three. Different dominant entrance pore size of macropore was obtained from MIP and X-μCT, due to the specific experimental protocol used in tests and the effect of ink-bottle geometry. Only the large pore bodies with high aspect ratio were imaged in X-μCT, due to the extrusion of mercury during the process of depressurization and subsequent sample preparation for X- μCT. But entire pore space was accessible in MIP. The difference in dominant entrance pore size was more significant for specimens with lower void ratio due to a more pronounced aspect ratio.

Development and Application of a 1D Compaction Model to Understand 65 Years of Subsidence in the San Joaquin Valley

AbstractHigh rates of land subsidence, caused by groundwater overdraft, are resulting in millions of dollars of infrastructure damage in California's San Joaquin Valley (SJV). In recent years, the use of interferometric synthetic aperture radar (InSAR) has enabled us to substantially improve our understanding of this subsidence. However, only very occasionally have the InSAR data been integrated with a physical model of subsurface compaction. Here, we have used InSAR and other data to parameterize and calibrate a 1D compaction model. We applied our model to a study area in the SJV where we had access to the necessary information on hydraulic head to develop model inputs. Our model simulated subsidence in the three aquifer system layers over the period 1952–2017, and is the first 1D compaction model in the SJV to simulate multiple aquifer system layers from the 1950s to 2017. The results from our model suggest that previous studies have significantly underestimated the time constants governing the slow, residual compaction of subsurface clays. We suggest that residual compaction of clays is a process that continues for decades‐to‐centuries, indicating that to significantly reduce subsidence requires some recovery of head, not just a stabilization. We also show how compaction in the lower, confined aquifer has accounted for over 90% of subsidence in the past 20 years. Although our study area is small, our findings are likely representative of the subsiding regions of the SJV, and our methodology can be applied to unconsolidated aquifer systems exhibiting subsidence worldwide.

Structural, volumetric and water retention behaviors of a compacted clay upon saline intrusion and freeze-thaw cycles

This study investigates the evolution of the structural, volumetric and water retention behaviors of a compacted clay during soaking and desiccation considering the influences of freeze-thaw (FT) cycles and saline intrusion. Compacted specimens were subjected to different FT cycles and then submerged in NaCl solution with different concentrations to facilitate the saline intrusion and measure the swelling behaviors. Shrinkage curve and filter paper tests were thereafter performed to reveal the clay's volumetric and water-retention characteristics during desiccation. Mercury intrusion porosimetry and field emission scanning electron microscopy tests were conducted to observe the evolution of the clay's microstructure. Experimental results show that the clay's micropores decrease and macropores increase after FT cycles, which is associated with the migration of water, growth of ice crystals, and development of FT-induced cracks during FT cycles. Similar observations were obtained from specimens after the saline intrusion, which is attributed to the osmotic and osmotically-induced consolidation. FT-induced cracks significantly reduce the clay's swelling and shrinkage potentials. FT cycles result in the shrinkage of micropores which leads to a reduction in the water retention capacity in the low suction range (capillary regime). The salinization suppresses the swelling of the clay and prolongs its primary and secondary swelling stages. The shrinkage potential initially increases and then decreases with increasing saline concentration. Salinization has significant influences on the osmotic suction and thus alters the clay's water-retention curves in terms of total suction. It demonstrates little impact on the clay's water-retention curves in terms of matric suction. • Studied joint effects of FT action and saline intrusion on a compacted clay. • Micropores decrease and macropores increase upon FT cycles and salinization. • Swelling and shrinkage potentials reduce after FT cycles and saline intrusion. • Salinity and FT mainly affect adsorptive and capillary effects, respectively.

Coupled hydromechanical model for evaluating the volume change and fluid permeation behavior of expansive clay smear in a fault upon interaction with CO2

The interaction between clay minerals and CO2 at in-situ conditions of geological carbon sequestration leads to adsorption-induced strain, which increases the mineral's interlayer space. The effect of change in interlayer spacing of minerals on the evolution of macro-permeability, gas storage capacity, gas pore pressure, and stress state of compacted clays is unknown. The present study described a coupled numerical model to investigate the effect of adsorption-induced swelling of smectite-based clay on its gas permeation and mechanical properties upon interaction with CO2. To simulate the interaction of the fill material present in caprock faults with the injected CO2, compacted clay under confined, free and uniaxial confinement conditions are analyzed. It is evident under confined conditions, permeability of the clay filled in fault reduced, and mean compressive stress increased due to gas adsorption-induced strain. On the contrary, the permeability of the clay increased for both free and uniaxial conditions. The magnitude of the swelling stress within the media under uniaxial conditions depends on the degree of expansion caused by the adsorption-induced effect and applied overburden pressure. Overall, the study contributes to a comprehensive approach to evaluate the efficacy of geological formations having faults for long-term storage of CO2 in them.

Volumetric and hydraulic behaviour of compacted natural clay–sand mixtures during wet–dry cycles

Volumetric and hydraulic behaviour of compacted natural clay–sand mixtures during wet–dry cycles

A Numerical Characterisation of Unconfined Strength of Weakly Consolidated Granular Packs and Its Effect on Fluid-Driven Fracture Behaviour

Soft or weakly consolidated sand refers to porous materials composed of particles (or grains) weakly held together to form a solid but that can be easily broken when subjected to stress. These materials do not behave as conventional brittle, linear elastic materials and the transition between these two regimes cannot usually be described using poro-elastic models. Furthermore, conventional geotechnical sampling techniques often result in the destruction of the cementation and recovery of sufficient intact core is, therefore, difficult. This paper studies a numerical model that allows us to introduce weak consolidation in granular packs. The model, based on the LIGGGHTS open source project, simply adds an attractive contribution to particles in contact. This simple model allows us to reproduce key elements of the behaviour of the stress observed in compacted sands and clay, as well as in poorly consolidated sandstones. The paper finishes by inspecting the effect of different consolidation levels in fluid-driven fracture behaviour. Numerical results are compared qualitatively against experimental results on bio-cemented sandstones.