Compacted Clay Samples Research Articles

Experimental investigation of the effect of landfill leachate on the mechanical and cracking behavior of polypropylene fiber-reinforced compacted clay liner.

This paper aims to investigate the effect of leachate on the geotechnical parameters and the cracking behavior of compacted clay liners (CCLs) containing different percentages of polypropylene fibers. Accordingly, 200 compacted clay samples were reinforced with different percentages of fiber contents (FC) (i.e., 0, 0.5, 0.75, and 1%) and prepared with water or leachate to conduct different laboratory tests. First, the physical properties of the clay were determined. Then, the shear strength parameters (i.e., cohesion and friction angle), unconfined compressive strength, and the hydraulic permeability were determined subjected to water or leachate. Notably, the cracking behavior was modeled using visual images of the samples. The leachate increased desiccation cracks in the natural soil from 0.425 to nearly 1.111%. However, the addition of 0.5% (in the case of water) and 1% (in the case of leachate) fiber to the soil reduced the surface desiccation cracks in clay liners to about 0.185 and 0.352%, respectively. In both water- or leachate-prepared samples, the addition of fibers significantly increased the cohesion and friction angle. The shear strengths of the unreinforced leachate-prepared samples were lower than those of the water-prepared samples. The shear strength and unconfined compressive strength of all specimens increased with increasing fiber percentage. The presence of fibers in all samples caused more ductile behavior. The required amount of energy to achieve the maximum strength in the samples increased with increasing FC. By increasing the percentage of fibers, the permeability of the natural soil and the leachate-prepared samples increased. However, the highest permeability was observed in the leachate-prepared samples containing 1% fibers of 8.3 × 10-10m/s, which is less than 10-9m/s (maximum allowable permeability for clay liners). Finally, the obtained results were satisfactorily confirmed by scanning electron microscopy (SEM) analysis.

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.

Evaluation of the Penetration Behavior of Viscous Fluids into Porous Media in the Context of Volume Determination

Abstract The current study addresses the penetration of viscous fluids into compacted clay samples in the context of volume determination. The volume of compacted clay samples was measured with established methods (paraffin-coated clod method, pycnometer method) and uncoated immersion weighing (IW) with three different fluids (silicone oil, paraffin oil, and canola oil). The suitability of the methods was evaluated statistically. The amount of penetrated liquid into the sample was tracked over time and analyzed. Experimental data were fitted with a modified Washburn’s equation considering different pore sizes in the sample. The fitting yielded very good matches. IW was found to generate the most accurate (i.e., smallest error measurements) and reproducible results for volume determination among the established methods. Thereby, paraffin and silicone oil performed best for IW. The penetration of liquids into the sample was found to be negligibly small for those two liquids in the relevant time range for conducting an IW.

The mechanical behaviour of compacted Lambeth-group clays with and without fibre reinforcement

This study investigated the effect of fibre reinforcement on the large strain behaviour of compacted clay samples tested using large triaxial test equipment. A novel specimen preparation method was proposed where peds of clay are compacted to closely simulate the in-situ compaction. A large number of 100 × 200 mm triaxial tests and one-dimensional compression tests were performed using reinforced and unreinforced samples. The behaviour of unreinforced samples was observed to be similar to highly fissured clays; ped compaction generated a random fissure pattern due to the contact between peds. The addition of fibres to the compacted samples created fissures with higher mobility at lower friction than those in the unreinforced samples; hence, the state boundary surface of reinforced clay was below that of the unreinforced clay. With the addition of fibres, the failure mechanism changed from the formation of a shear plane to barrelling, demonstrating that the fibres transferred stresses further away from the shear plane, producing a more homogeneous stress distribution. The preparation method proposed here produced a fissure pattern in the clay that introduced transitional behaviour, which was drastically reduced with addition of the fibres, allowing better normalisation and the definition of a unique boundary surface.

The elastic properties and anisotropy of artificial compacted clay samples

Clay minerals are a major component of hydrocarbon reservoir rocks, and they are known to play important roles in the physical and elastic properties of rocks. However, it is difficult to directly measure these properties of single-crystal clays due to their small particle size. Therefore, we have constructed three sets of artificial clay samples with different compaction stresses to investigate the effect of the compaction stress and clay mineralogy on their elastic properties and anisotropy. All of the dry samples are measured by the pulse-transmission method. The results indicate that the compaction stress and clay mineralogy have a significant influence on the physical and elastic properties of the clay samples. The microstructures of clay samples indicate that the clay platelets are aligned almost perpendicularly to the direction of compaction stress, and the ultrasonic velocity analysis validates the assumption of transverse isotropy of our clay samples. The velocities increase with the compaction stress, especially at low stress, which corresponds to the rapid porosity reduction at low stress levels. Velocity anisotropy parameters increase with increasing of compaction stress due to the increase of texture sharpness for clay minerals during the compaction process. The elastic moduli of the clay samples display a significant stress sensitivity and a strong directional dependence, with the Young’s moduli increasing and the Poisson’s ratios decreasing with the compaction stress. A simple theoretical template is used to quantify the orientation distribution functions (ODFs) of clay platelets, and the generalized Legendre coefficients of ODF increase with the increase of compaction stress, especially at low stress. Further, the compressional-wave (P-wave) and shear-wave anisotropy increase with the ODF coefficients [Formula: see text] and [Formula: see text], especially P-wave anisotropy.

Numerical efficiency assessment of the lattice Boltzmann model for digital nano-porous rock applications

Abstract Study of transport properties of low permeable sedimentary clay formations is of growing interest in exploration of non-conventional resources, and for long term radioactive waste repositories where these formations play the role of a natural shield which prevents the spreading of radioactive materials in the environment. Recent advances in imaging techniques allow to obtain 3D volume of compacted clay sample with pixel size of order of few nano-meters which enables us to explore transport properties of these media by means of numerical simulation. In our study, the Lattice Boltzmann Model (LBM) is applied to simulate fluid flow inside the 3D image of a compacted illite sample to explore its transport properties. The impact of different image segmentation methods applied to treat the raw data on the numerical results is addressed. Because of the nano-metric pore size, various physical phenomena may influence fluid flow. In this study, we consider the influence of gas slippage effect (the Klinkenberg effect) on the permeability. The numerically obtained results are compared with experimental data obtained for a reconstructed compacted illite sample. If the original geometry is not strongly modified by the applied image segmentation method, the numerically calculated Klinkenberg factor follows well existing trends and provides predictions close to the experimental values.

Water Mobility within Compacted Clay Samples: Multi-Scale Analysis Exploiting 1H NMR Pulsed Gradient Spin Echo and Magnetic Resonance Imaging of Water Density Profiles.

1H NMR pulsed gradient spin echo attenuation and water density profile analysis by magnetic resonance imaging are both used to determine the mobility of water molecules confined within a porous network of compacted kaolinite clay sample (total porosity of ∼50%). These two complementary experimental procedures efficiently probe molecular diffusion within time scales varying between milliseconds and few hours, filling the gap between the time scale of diffusion dynamics measured by traditional quasi elastic neutron scattering and through-diffusion methods. Furthermore, magnetic resonance imaging is a nondestructive investigation tool that is able to assess the effect of the local structure on the macroscopic mobility of the diffusing probe.

Laboratory investigation on the behaviour of an overconsolidated expansive clay in intact and compacted states

Abstract Natural climatic phenomena and human activity frequently cause disorders in the masses of fine-grained soils characterized by very significant volume variation as soon as the conditions of their equilibrium are modified. A better description of the behaviour of fine-grained soils can be seen with respect to drying-wetting cycles. This paper presents a series of laboratory test results obtained on a heavily overconsolidated expansive clay, for which significant damages frequently appear in road and motorway infrastructures, in urban public utilities, as well as in civil and industrial low-rise structures. The effects of compaction and drying-wetting cycles on the mechanical parameters of this clay are analyzed to establish a predictive model of the soil movement following the in-situ water table variation. Comparative analysis between the deformability and strength characteristics of the clay in intact and compacted states are then presented. Tests results show that the values of the geotechnical parameters derived from these tests are depending on some experimental aspects such as the compaction energy, drying time, initial deformability and soil saturation. In all cases, the behaviour of intact and compacted clay samples is governed by the same laws of compressibility and consolidation, shrinkage and swelling as well as shear and failure.

Experimental Study on the Over-Consolidation Stress History of Subgrade Compacted Clay

To study the over-consolidation stress history of clay in a high-filled embankment during hierarchical compaction, indoor compaction and one-dimensional consolidation tests are performed on roadbed backfill clay. Two homemade compaction devices are used to drill into standard heavy compacted clay to prepare compacted clay samples and subsequently investigate the influence of compaction work, compaction impulse, water content, and compaction degree on over-consolidation stress history. Results provide an experimental basis to determine the parameters of an over-consolidated constitutive model. Experimental results show that compacted clays with the same compaction degree and water content can differ in stress history, and that this stress history increases as the compaction impulse per unit area builds up. Under the conditions of the same compaction work and over-consolidated formation, the compacted clay achieves the maximum compaction degree and stress history if water content is at the optimal level. If the water content deviates from the optimal level, the stress history of the compacted clay decreases, and it is more significantly affected by the compaction degree with increased water content.

The influence of saturation on the cracking process in compacted desiccating clays

Tensile failure in unsaturated cohesive soils during desiccation is important for the design of geotechnical applications such as capping systems of landfills and sealing material of dikes. This study presents the results of different initial parameters of compacted clay samples such as gravimetric water content, dry density and degree of saturation. These parameters are varied systematically for each test to find the correlation between those parameters and the tensile failure. The tensile failure for all tests occurred by a comparable constant change of the degree of saturation. The soil specific saturation ratio Sr,s is defined as the quotient of saturation changes ΔSr to initial saturation Sr,0 . This parameter related to the total suction shows an equal course for all results. All in all, the course of the soil specific saturation ratio Sr,s is independent of all initial parameters. These results provide a physical and hydraulic-mechanical description for modelling the desiccation process. To demonstrate the initiation and progress of tensile failure, the experimental results are modelled with a Discrete Element Method (DEM) approach.

Predicting of Permeability Coefficient for Compacted Clay

Permeability coefficients of three compacted clay samples are measured by using Transient Water Release and Imbitions Method which is shortly named as TRIM. The curve between permeability coefficient and suction is obtained, the results of tests show that the permeability coefficient decreases in nonlinear trend along with the increasing of suction. Based on Brooks Corey model and Mualem model which is shortly named as BCM model, an analytical method is put forward to calculate the permeability coefficient of compacted clay. The results of using BCM model and TRIM are compared, which show that the permeability coefficient obtained with two kinds of methods match well when the suction is greater than the inlet value.

Hydraulic conductivity and removal rate of compacted clays permeated with landfill leachate

Compacted clay soils are widely used as a barrier to protect environment from leachate migration. The suitability of clay soil for liner material, depends on resistibility to increase in hydraulic conductivity and contaminant transport. In this article, the influence of compaction energy and permeated leachate properties on the hydraulic conductivity were investigated. Natural attenuation capacities of clays compacted both standard and modified compaction methods were also evaluated. With this purpose, a series of laboratory tests were conducted with soil and real leachate samples obtained from Şile-Kömürcüoda Organized Landfill Site. DI and real leachate samples were percolated through the laboratory-scale column reactors that were filled with compacted clay samples prepared according to Standard and Modified Proctor method. During percolation, the hydraulic conductivity and natural attenuation capacity of the clay liner were determined by hydraulic conductivity calculation and chemical oxygen demand (COD), suspenden solids (SS), total Kjeldahl nitrogen (TKN), total phosphorus (TP) monitoring, respectively. According to the hydraulic conductivity measurements using leachate, it is shown that hydraulic conductivity decreased in both compacted clay prepared by Standard and Modified Proctor methods, possibly associated with biological and chemical clogging mechanisms. It is thought that clogging formed due to biofilm growth and/or suspended solids accumulation between the particles of the clay soil. When the variations of the COD, SS, TKN, and TP were examined, it was observed that the removal efficiency of the clay compacted by the modified compaction method was greater than the one compacted by the standard compaction method, especially for SS.

Simulation of Reactive Diffusion in Clays By a Continuous-Time Markovian Particle-Tracking Scheme

Clay minerals and clay rocks are considered as efficient components of engineered and natural barriers in many high-level radioactive waste disposal programs worldwide because of their low permeabilities and high sorption capabilities. In this paper we present an approach for modeling solute diffusive transport in saturated clay minerals at the structure map scale based on an extension of the Kolmogorov–Dmitriev theory of stochastic branching processes. The proposed modeling framework allows a simple description of (i) the dual-porosity behavior typical of some compacted clay structures, where diffusion occurs both in the interlayers and in the pore space between clay particles, and (ii) the chemical interactions between the dissolved ions and the solid matrix surfaces (both at nonequilibrium and equilibrium conditions). Furthermore, the Markovian nature of the modeling approach lends itself to a continuous-time particle-tracking scheme of resolution of the model equations, which, in general, easily allows us to deal with the complex geometrical structures of the porous media. Finally, in order to account for the uncertainty in the geometrical properties of the clay samples within the proposed modeling framework, the structure map is represented as a stochastic network of interconnected, one-dimensional interlayers with different lengths and orientations. The combined methods are demonstrated on a two-dimensional literature case study of diffusion through a compacted clay sample, and the resulting average diffusion coefficients are in general agreement with those obtained by a different simulation-based technique found in the literature. Then, the methods are applied to model the diffusion of the weakly sorbing cation Na+, providing results in accordance with physical intuition.

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

The aim of the present work was to quantify accessible porosities for iodide and for a water tracer (HTO) on water-saturated compacted clay samples (illite, montmorillonite and MX-80 bentonite) and to relate these macroscopic values to the forms of water in these porosities (surface/bulk water, external/internal water). Low field proton NMR was used to characterise and quantify the forms of water. This enabled the three different populations (structural OH, external surface and internal surface water) to be differentiated on hydrated clays by considering the difference in proton mobility. An accurate description of the water forms within the different populations did not appear possible when water molecules of these populations were in contact because of the occurrence of rapid exchange reactions. For this reason, it was not possible to use the low resolution NMR method to quantify external surface and bulk water in fully water-saturated compacted clay media at room temperature. This latter information could however be estimated when analysing the samples at –25 °C. At this temperature, a distinction based on the difference in mobility could be made since surface water remained in a semi-liquid state whereas bulk water froze. In parallel, accessible porosities for anions and HTO were determined by an isotopic dilution method using capillaries to confine the materials. HTO was shown to probe the whole pore volume (i.e. the space made of surface and bulk water). When the surface water volume was mainly composed of interlayer water (case of montmorillonite and bentonite), iodide was shown to be located in the pore space made of bulk water. When the interlayer water was not present (case of illite), the results showed that iodide could access a small fraction of the surface water volume localised at the external surface of the clay particles.

Utilization of red mud as a stabilization material for the preparation of clay liners

Red mud is a waste material generated by the Bayer Process widely used to produce alumina from bauxite throughout the world. Approximately, 35% to 40% per ton of bauxite treated using the Bayer Process ends up as red mud waste. Because of storing issues, the waste negatively affects the environment. To solve this problem, it is essential to investigate different uses for red mud waste. The potential use of red mud for the preparation of stabilization material is presented in this study. This study examines the effects of red mud on the unconfined compressive strength, hydraulic conductivity, and swelling percentage of compacted clay liners as a hydraulic barrier. The test results show that compacted clay samples containing red mud and cement–red mud additives have a high compressive strength and decreased the hydraulic conductivity and swelling percentage as compared to natural clay samples. Consequently, it is concluded that red mud and cement–red mud materials can be successfully used for the stabilization of clay liners in geotechnical applications.

Quantifying the effect of membrane potential in chemical osmosis across bentonite membranes by virtual short-circuiting

Clay liners are charged membranes and show semipermeable behavior regarding the flow of fluids, electrical charge, chemicals and heat. At zero gradients of temperature and hydrostatic pressure, a salt concentration gradient across a compacted clay sample induces not only an osmotic flux of water and diffusion of salt across the membrane but also an electrical potential gradient, defined as membrane potential. Laboratory experiments were performed on commercially available bentonite samples in a rigid-wall permeameter connected to two electrically insulated fluid reservoirs filled with NaCl solutions of different concentrations and equipped with Ag/AgCl electrodes to measure the electrical potential gradient. The effect of membrane potential could be cancelled out by short-circuiting the clay with the so-called virtual shortcut. The potential gradient across the sample is brought to zero with a negative feedback circuit. It was observed that the water flux and the diffusion of Cl − were hindered by the occurrence of a membrane potential, indicating that an electroosmotic counterflow is induced. Flow parameters were calculated with modified coupled flow equations of irreversible thermodynamics. They were in excellent agreement with values reported in the literature. Comparing the method of short-circuiting with a study elsewhere, where the electrodes were physically short-circuited, it was shown that the virtual shortcut is more appropriate because physically short-circuiting induces additional effects that are attributed to the fluxes.

Fiber Reinforcement for Waste Containment Soil Liners

The hydraulic properties of compacted clay liners can be adversely affected by desiccation cracking. Previous studies evaluated the use of soil additives (such as lime, cement, and sand) for crack reduction. Initial results indicated that soil shrinkage was reduced. However, in many cases, the additives resulted in an increased hydraulic conductivity and decrease in soil plasticity. As a result, there is an increasing interest in the use of fiber reinforcement, which has shown successful results in concrete and other material applications. The present investigation focused on the impact of fiber reinforcement on the development of desiccation cracks in compacted clay samples, as well as the impact of the fiber additives on soil workability, compaction characteristics and hydraulic conductivity. The results of this study indicate that, for the soils of this investigation, the optimum fiber content necessary to achieve maximum crack reduction and maximum dry density, while maintaining acceptable hydraulic c...

The positive effects of silica fume on the permeability, swelling pressure and compressive strength of natural clay liners

Clays are essential materials to reduce the hydraulic conductivity of natural clay liners in landfill sites. Impermeable compacted clay liners are needed the landfill to be designed. It is known that clays with high plasticity absorb water several times as much as their weights. The clay liners subjected to water pressure in landfills generate high permeability in time and instability problems in their body due to their expansive capacity. Though the compacted clay liners possess many advantages such as low permeability and large capacity of attenuation, they have high shrinkage and high expansive potential causing instability problem. The aim of this study is to examine the effects of silica fume on permeability, swelling pressure and compressive strength of the compacted clay liners as a hydraulic barrier. The test results showed that the compacted clay samples with silica fume exhibit quite low permeability, swelling pressure and significantly high compressive strength as compared to raw clay samples. Thus, silica fume appears to be promising for construction material of liners subjected to leachate in solid waste containment systems.

A reexamination of the permeability index of clays: Reply

The permeability of water through a compacted clay sample depends on the amount of micropores and macropores present. The bulk of the water permeates through the macropores. As consolidation progresses, the macropores become smaller and smaller, decreasing the permeability (Griffiths and Joshi 1989). The flow of water through the micropores in fine-grained soil is relatively restricted because most of these pores are occupied by the adsorbed water held in the diffuse double layer around the clay platelets. This bound water not only decreases the pore space but also imparts a shearing resistance to the permeating water. The large macropores are relatively less affected by the existence of the diffuse double layer. However, as consolidation progresses these become smaller and the double layer around the clay ,! particles tends to affect the'permedbility appreciably. It is probably for this reason that the e--k plo4 is usually curvelinear. Thus, the permeability of clays is largely a function of pore size and pore-size distribution, which are related to the grain-size distribution, particle size, and degree of dispersion. This means that if two clays have the same void ratio, the clay with a higher amount of macropores may have a higher permeability. It must further be noted that the authors have plotted the coefficient of permeability on a log scale, therefore any error in its prediction will exponentially magnify or diminish its value. Data reported by the authors, discussers, and others indicate that empirical equations to obtain the coefficient of permeability may possibly be developed. However, such equations should also consider a parameter that includes the effect of the pore geometry and its change with consolidation pressure (Griffiths and Joshi 1989). Such equations may then predict the coefficient of permeability with a fair degree of accuracy.

Effective Cohesion for Compacted Clay

When an unsupported chunk of compacted clay is placed in water, it will generally completely slake apart. However, if the sample is compacted over optimum and after the sample is allowed to cure, it may not slake apart. For the unsupported compacted clay sample, the horizontal total stress is zero, and if the sample is sheared at a very slow rate to enable the dissipation of negative pore pressures, then the effective cohesion can be determined. The effective cohesion for compacted silty clay varied from 8 psf (0.4 kPa) for one day of curing to 45 psf (2.2 kPa) for 21 days of curing. Curing allows for the development of bonds, yielding reduced swelling and higher effective cohesion. The effective shear strength envelope for the compacted silty clay at high normal stresses can be described by the linear relationship defined by the angle Φ′=28° and c′=265 psf (12.7 kPa). But in the low normal effective stress range, the strength envelope is curved with a significantly lower effective cohesion intercept.