Consolidation Of Clay Research Articles

Attenuation-type and failure-type curve models on accumulated pore water pressure in saturated normal consolidated clay

Based on dynamic triaxial test results of saturated soft clay, similarities of variations between accumulated pore water pressure and accumulated deformation were analyzed. The Parr’s equation on accumulated deformation was modified to create an attenuation-type curve model on accumulated pore water pressure in saturated normal consolidation clay. In this model, dynamic strength was introduced and a new parameter called equivalent dynamic stress level was added. Besides, based on comparative analysis on variations between failure-type and attenuation-type curves, a failure-type curve model was created on accumulated pore water pressure in saturated normal consolidation clay. Two models can take cycle number, coupling of static and dynamic deviator stress, and consolidation way into consideration. The models are verified by test results. The correlation coefficients are more than 0.98 for optimization of test results based on the two models, and there is good agreement between the optimized and test curves, which shows that the two models are suitable to predict variations of accumulated pore water pressure under different loading cases and consolidation ways. In order to improve prediction accuracy, it is suggested that loading cases and consolidation ways should be consistent with in-situ conditions when dynamic triaxial tests are used to determine the constants in the models.

Consolidation of sensitive clays: a numerical investigation

Consolidation of sensitive clay layers, which have significant compressibility at different stress states, is investigated via a nonlinear one-dimensional consolidation approach with a piecewise linear e ~ log10σ′ model. The behaviour of sensitive clays during consolidation and the limitations of conventional consolidation theory are addressed. It is shown that (1) the sensitive clay layer can be divided by the preconsolidation pressure into two zones, that is, high- and low-compressibility zones. The progressive destruction of particle cementation bonding through the soil layer is shown by the moving front of the interface between these two zones; (2) the excess pore pressure dissipation primarily takes place in the low-compressibility zone, which results in a small settlement during the early stages of consolidation; (3) conventional consolidation theory highly overestimates the settlement and gives a poor prediction of effective stress distribution.

Numerical model of electro-osmotic consolidation in clay

Electro-osmotic consolidation is a unique soil improvement technique. A physics-based model for electro-osmotic consolidation is proposed, in which Biot's consolidation equation is coupled with the electro-osmotic flow and control equation for an electrical field, and the displacement of soil mass and pore-water pressure can be obtained. Furthermore, the non-linear variation of the mechanical and electrical properties of the soil mass during consolidation is incorporated into the model. The numerical solution agrees well with the analytical solution. The developed model can predict the ground displacement and provide useful data for the design of an electro-osmosis treatment system.

Closure to “New Methods for Aquifer Parameters from Slug Test Data” by Sushil K. Singh

Closure to “New Methods for Aquifer Parameters from Slug Test Data” by Sushil K. Singh

Constitutive Model of Saturated Structural Clays Based on SMP Failure Criterion

For normal consolidated or low over consolidated saturated structured clays, a constitutive model of the clay was proposed by introducing a structural parameter d in order to quantitatively describe the change of its deformation and strength based on unified hardening model. Stress-strain and body strain of the clay were predicted by the new model and were measured by K0 consolidated compression and shearing tests. The rationality and feasibility of the new model were proved by comparing the predictive and experimental value. The results show that the model can well describe structural characteristics, deformation and mechanical properties of the saturated structured clays; predictive value of stresses and strains are basically in agreement with experimental ones, and this further proves the rationality and feasibility of the new model.

Elasto-viscoplastic modeling of the consolidation of Sri Lankan peaty clay

The consolidation behavior of Sri Lankan peaty clay is analyzed using an elasto-viscoplastic model. The model can describe the secondary compression behavior as a continuous process and it can also account for the effect of structural degradation on the consolidation analysis. The analysis takes into account all the main features involved in the process of peat consolidation, namely, finite strain, variable permeability, and the secondary compression. The material parameters required for the analysis and the procedures to evaluate them, using both standard laboratory and field tests, are explained. Initially, the model performance is assessed by comparing the predicted and the observed peat consolidation behavior under laboratory conditions. The results indicate that the model is capable of predicting the observed creep settlements and the effect of layer thickness on the settlement analysis of peaty clay. Then, the model is applied to predict the consolidation behavior of peaty clay under different field conditions. In this context, firstly, the one-dimensional field consolidation of peaty clay, brought about by the construction of compacted earth fill, is predicted. Then, the two-dimensional peat foundation response upon embankment loading is simulated. A good agreement is seen in the comparison of the predicted results with the field observations.

Attenuation-Type and Failure-Type Curves of Cyclic Accumulated Deformation Models in Saturated Normal Consolidated Clay

Based on dynamic triaxial test results of saturated soft clay, influence factors and variations on accumulated deformation were analyzed. The Parr’s equation on accumulated deformation was modified to create an attenuation-type curve model on accumulated deformation of saturated normal consolidation clay. In this model, dynamic strength was introduced and a new parameter called equivalent dynamic stress level was added. Besides, based on comparative analysis on variations between failure-type and attenuation-type curves, a failure-type curve model was created on accumulated deformation of saturated normal consolidation clay. The two models can take cycle number, coupling of static and dynamic deviator stress, consolidation way into consideration. The models were verified by test results. The correlation coefficients are more than 0.96 for optimization of test results based on the two models, and there is good agreement between optimized and test curves, which show that the two models are suitable to predict variations of accumulated deformation under different loading cases and consolidation ways. In order to improve prediction accuracy, it is suggested that loading cases and consolidation ways should be consistent with in-situ conditions when dynamic triaxial tests being used to determine the constants in the models.

Geotechnical characterisation and engineering properties of Burswood clay

The Burswood clay is a lightly overconsolidated and sensitive silty clay of high to extremely high plasticity. In two extensive characterisation studies, a wide range of in situ tests were carried out at the Burswood site, including full-flow penetrometer tests (T-bar, ball and plate). In addition, thin-wall tube samples and high-quality Sherbrooke block samples were collected for laboratory testing. The stress–strain–strength, consolidation and compressibility characteristics of Burswood clay were investigated, and the performance of various penetrometers in characterising the soft Burswood clay was assessed. The paper compares values of stiffness and shear strength measured by different in situ and laboratory tests, quantifying the degree of non-linearity of the stress–strain response, the effect of sample disturbance on the measured mechanical properties, the degree of strength anisotropy, and the influence of strain rate on the measured shear strength. In addition, factors relating the net penetration resistance measured by cone, T-bar and ball penetrometers to yield stress, small-strain shear modulus and different measures of undrained shear strength are also provided.

Predictions of coefficient of consolidation from CPTU dissipation tests in Quaternary clays

The coefficient of consolidation (c v or c h) is an important parameter in both geotechnical and geo-environmental engineering, measuring the flow characteristics of soils. In China, conventionally it is obtained from the oedometer test, which is time consuming and of limited accuracy due to inevitable sample disturbance. These difficulties can be overcome by in situ pizeocone dissipation tests which provide continuous measurements of pore water pressure with time. In this paper, existing methods for interpreting coefficient of consolidation in clays from piezocone dissipation tests are briefly reviewed. Piezocone tests were undertaken at different sites in the Jiangsu province of China and piezocone dissipation tests conducted at different penetration depths. Based on the reference c v values determined from the laboratory oedometer tests, comparisons with existing interpretation methods were undertaken. It is shown that the Teh and Houlsby’s interpretation method has a much higher accuracy for determining the coefficient of consolidation of Quaternary clay deposits while the values of c h obtained by the CPTU method are in the range of back-analyzed field values.

STUDY ON EFFECT OF FACTORS ON CRITICAL SHEAR STRESS OF COHESIVE BANK MATERIALS FOR COASTAL EROSION

The aim of this study is to investigate effect of sand-silt-clay content, moisture content, salinity, consolidation, and vegetation density on critical shear stress (tc) of cohesive bank materials for erosion processes of rivers and coastal regions. The authors used the non-vertical submerged jet test apparatus designed by Hanson et al. (2002) and reproduced by Deguchi et al. (2007) to carry out both laboratory and in situ measurements. The laboratory experimental results showed that the tc increased as the rate of clay content, salinity, consolidation, and vegetation density increased. The t c decreased as the moisture content increased. The in situ experimental results of five severely eroded sites of the Soai Rap river banks, southern Hochiminh City were similar to thoses of laboratory experiments. The erodibility (kd) of cohesive bank material can also be determined when the t c is measured.

Fractal Approach on Quantitative Analysis of Micro Pore Structure of Isotropic Consolidated Clay

The micro pore structure of isotropic consolidated clay was studied by using a scanning electron microscope (SEM). A digital imaging technique was applied to analyze the evolution of size, number of pores and their distributions in the process of isotropic consolidation according to the SEM images. Based on the fractal concepts of Koch curve and Sierpinski carpet, the Koch fractal dimension Dk and the Sierpinski fractal dimensionDsof soil pores are obtained from the measured data. The variations of bothDkandDsfollowing the change of micro pore parameters and mechanical properties of clay are investigated. The results show that the porosity and pore size decreases as the consolidation pressure increases, and the range of pore size becomes narrower.Dkreflects the degree of irregularity of the pore-solid interface in soil, and the larger theDkthe more irregular the soil pore profile. The distribution of Dkwas found in agreement with a total normal distribution in soil pore. The magnitude ofDsreflects the variation of porosity of clay under isotropic consolidation. Large fractal corresponds to large consolidation pressure and small porosity.Dsdisplays a significant linear regression relationship with porosity, consolidation pressure, consolidation deformation of clay and an exponential growth relationship with permeability coefficient of clay. Both Dk andDsis sensitive to isotropic consolidation of soil and they may be cited as useful indicators for soil consolidation.

Precisely estimating primary consolidation settlement of homogeneous NC clays with an alternate equation

<p>Estimating primary consolidation of NC clays with conventional 1-D consolidation equation underestimates the settlement value as the effective stress is merely taken at the mid-depth of a compressible layer. For thick compressible stratum, the error cannot be disregarded and is often minimized by dividing the entire stratum into a finite number of sub-layers. Computation with too many sub-layers is rather tedious and time-consuming as the settlement of each layer needs to be calculated separately and to be added up finally to get the settlement of the entire stratum.</p><p>An alternate equation is put forward in the present study wherein the effect of compressible layer thickness is eliminated altogether. The equation proposed herein is, in fact, an extension of classical primary consolidation equation for homogeneous NC clays and is based on the same assumptions. This paper lucidly explains the formulation of the proposed equation and validation of the same with a practical example. Comparison of results shows that the proposed equation subdues the conventional one by precisely computing the consolidation settlement not involving any iteration or time-consuming effort.</p>

Multi-dimensional chemo-osmotic consolidation of clays

A model of chemo-osmotic consolidation of clays in multi-dimensional domains is presented, with volumetric strains induced by both changes in the chemistry and osmotically driven pore water flow considered. Three fully coupled governing equations considering force equilibrium, pore water transport and chemical transport are presented and solved using the transient finite element method. The proposed approach is verified via consideration of chemo-osmotic consolidation of a compacted clay landfill liner and then applied to investigation of a hypothetical case with a local leachate leak in the compacted clay liner. An assessment of the impact of the two-dimensional nature of the system is made. The consolidation process is found to be dominated by osmotic consolidation in the early stages and subsequently by chemical consolidation. It is found that the surface settlement and the leachate concentration in the compacted clay liner may be highly overestimated by a one-dimensional analysis. Moreover, the peak negative excess pore pressure predicted by the two-dimensional solution remains in a shallow region under the leak while in the one-dimensional solution it moves progressively downwards.

Long term behaviour of a retaining wall resting on clayey soil

The magnitude and distribution of lateral earth pressure acting on a retaining wall due to dry cohesionless backfilling material and existence of saturated consolidated clay in the foundation are studied by a series of two-dimensional plane-strain analyses. For the particular wall geometry and soil condition, effects of wall height and elapsed time of consolidation are investigated and discussed. The analysis was carried out using the finite element computer program, CRISP, with some modifications to cope with the objective of the analysis. The behaviour of the concrete retaining wall is represented by a linear elastic model. The backfilling material was assumed to be elasto-plastic with Mohr-Coulomb failure criterion, while the clay foundation is assumed to follow Cam-clay model. The thin layer interface element is used to represent the interface between the wall and the surrounding soil. The results showed that the wall tilted towards the backfilling material during consolidation. Also, it was found that the permeability and Poisson's ratio of the foundation soil are the most important material parameters that influence the behaviour of the retaining wall.

Colloid diffusion coefficients in compacted and consolidated clay barriers: Compaction density and colloid size effects

An experimental methodology applying the nuclear ion beam technique Rutherford Backscattering Spectrometry (RBS) is used to measure colloid diffusion profiles within three different types of clay: consolidated Opalinus clay (Switzerland), Callovo-Oxfordian clay (France) and FEBEX bentonite (Spain) compacted at different densities. The RBS technique is widely applied in materials science and it was selected because it allows the measurement of concentration profiles at short range distances (μm). The effects of colloid size, clay type and clay density were analyzed with negatively charged Au colloids of 2, 20 and 40 nm. Apparent diffusion coefficients ( D a) for gold colloids could be measured and D a values ranged from (10 −18 to 10 −19 m 2/s). The larger diffusion coefficient was measured for 2 nm colloids in the Opalinus clay with D a(Au 2 nm) = (2.1 ± 0.5) × 10 −18 m 2/s. The accessible porosity for colloids is even lower than that measured for anions, since not only anion exclusion but also size exclusion hinders diffusion. For example, 40 nm colloids did not accede at all to bentonite compacted at higher densities.

Superhydrophobic paper coating containing nonconventional clay

Hydrophobic clay fillers have not been widely used in dispersion coatings for linerboard because of the difficulty of dispersing them in water. This work investigated whether hydrophobic clay can be used as filler in barrier dispersion coatings. Hydrophobic clay was compared with conventional clay in terms of coating consolidation, structure, wetting, and barrier performance. All coatings were applied to linerboard sheets made using a laboratory dynamic sheet former. The coated linerboards were examined using scanning electron microscopy and Raman spectroscopy, and were characterized with respect to water absorption, vapor transmission rate, and contact angles. The results show that a coating containing hydrophobic clay provides a superhydrophobic character to paper; i.e., a high water contact angle (150°) and relatively low water absorption. Raman mapping of cross-sections revealed that the latex distribution is uniform in the presence of either conventional clay or hydrophobic clay, and that the distribution of hydrophobic clay tends to be more uniform than conventional clay, which might reflect good mixing and consolidation of hydrophobic clay.

Analysis on Nonlinear Flowing Consolidation of Clay

It exist non-linear flow in soft clay, which is caused by the shear flow situation of bounded-water. In this case, permeability coefficient is a nonlinear function of hydraulic gradient. With the discharge of pore water, the effective stress is increasing, and part of weakly bound-water begins flow, while the porosity and permeability are became lower. By taking into the characteristics of the pore water, it is established a model, which is explained the nonlinear flow of clay, and shown that, with the increasing of and , the consolidation time is obviously increased

Surface settlement of cementitious-based materials determined by oedometer testing

The oedometer test is commonly used in soil mechanics to evaluate consolidation of clays and other compressible soils. A research project was undertaken to evaluate the suitability of such test to assess surface settlement of freshly mixed cementitious-based materials. Three series of concrete-equivalent-mortar (CEM) mixtures made with different cement contents, water-to-cementitious materials ratio (w/cm), silica fume, and viscosity-modifying admixture (VMA) were tested. Validation of test results was performed by casting concrete mixtures in a PVC column having 600-mm height and 200-mm diameter. Test results have shown that CEM settlements determined using the oedometer test as well as concrete settlements determined using the 600-mm PVC column are affected quite similarly by the mixture composition. For example, for given consistency, settlement decreases with the increase in cement content, decrease in w/cm, and incorporation of increased concentrations of silica fume or VMA. Statistical analysis was then performed to propose regression models for predicting maximum settlement of concrete through the determination of CEM characteristics.

Numerical Analysis of One-Dimensional Consolidation in Layered Clay Using Interface Boundary Relations in Terms of Infinitesimal Strain

The interface boundary relations are derived in this study for the numerical analysis of one-dimensional consolidation in multilayered clay profiles. The finite difference solutions are formulated based on Mikasa’s consolidation equation with infinitesimal strains and constant consolidation parameters under the same fundamental assumptions and limitations of the classic Terzaghi equation. Numerical examples are presented for multilayer clay profiles under single and double drainage conditions that validate the predicted excess pore pressures, strains, settlements, and rates of consolidation using interface boundary relations in terms of infinitesimal strains that are equivalent to those expressed in terms of excess pore pressures.

Consolidation of marine clay using electrical vertical drains

Electroosmosis (EO) is the movement of water in a porous medium under the influence of a direct current (dc). In past decades, electro-osmosis has been successfully employed in many soil improvement and other geotechnical engineering projects. Metal electrodes, such as steel, copper and aluminum have been used traditionally to conduct current. The shortcoming of these electrodes is that they corrode easily during an EO treatment, which results in reduced effectiveness and environmental concerns. More recently, conductive polymers are developed to replace metal electrodes in EO treatment. Electrical vertical drainages (EVDs) are one of these products under trial. The goal of this study is to assess the performance of EVDs for soil improvement and to further understand the scientific principle of the EO process, including the voltage drop at the soil-EVD interface, electrical current density, polarity reversal, and changes in soil physico-chemical properties generated by electroosmosis. It is found from the study that after 19 days of EO treatment with a constant applied dc electric field intensity of 133 V/m, the soil's moisture content decreased by 28%, the shear strength and pre-consolidation pressure increased more than 400%. It is also found that the current density required triggering the water flow in the soil tested, the Korean Yulchon marine clay, is 0.7 <TEX>$A/m^2$</TEX>. The project demonstrates that EVDs can serve as both electrodes and drains for soil improvement in short term. However, the EVDs, as tested, are not suitable for polarity reversal in EO treatment and their service life is limited to only 15 days.