Strength Of Clay Research Articles

Study of Ion Adsorption and Shear Strength of Red Clay under Leaching Action

To study the soil-water effect of red clay, a leaching test is conducted by loading red clay into a soil column and collecting the leaching waste liquid periodically for analysis of the ion content and conductivity changes in the leaching waste liquid. After leaching and filtering, the soil is removed from the column and reconstituted as a straight-shear specimen for a straight-shear test. Ca2+, Mg2+, and SO42− ions increased and then stabilized in water samples as leaching time increased, while Na+, Cl−, and NO3− declined and then stabilized. Due to their presence in the leaching solution, Ca2+, Mg2+, and SO42− ions are initially adsorbed by the soil and then saturated by adsorption. In contrast, Na+, Cl−, and NO3− precipitate out of the soil due to the dissolution and ion exchange of the soil sample, thereby weakening their effects. Consequently, these ions appear to vary in various ways. The relationship between ion content in solution and conductivity has also been discovere, and the conductivity varies with the total ion charge in the solution. The angle of internal friction decreases as the leaching time increases, but the cohesion of the soil increases.

Influence of palm fiber on strength and crack characteristics of red clay

Red clay is widespread in southern China, exhibiting undesirable properties of softening upon contact with water and cracking after losing water. Using red clay as roadbed filler frequently results in a series of geotechnical hazards such as foundation settlement and slope instability. Consequently, it is necessary to improve the engineering properties of red clay. Using natural plant fibers offers improved environmental sustainability and greater economic advantages compared to traditional methods involving lime and cement. In this study, palm fibers were used to improve the properties of red clay. The aim was to quantitatively analyze the influence of palm fiber content and length on the unconfined compressive strength (UCS) of red clay, study the capacity of palm fibers to inhibit soil desiccation cracking, and explore the underlying mechanisms by conducting UCS and desiccation tests. The results show that the UCS and residual strength of red clay can be significantly enhanced by palm fiber, and the soil damage form will be changed from brittle damage to ductile damage. Particularly noteworthy, the content of 0.45% palm fiber with a length of 20 mm increased the UCS by 43.4%. Palm fiber also effectively inhibited soil desiccation cracking, the content of 0.3% palm fiber with a length of 20 mm reduced the crack ratio by 54.4%. This study presents a novel approach for improving red clay, offering valuable insights for the use of palm fiber-improved red clay in road construction and slope protection projects.

Strength and stiffness prediction models of expansive clays blended with sawdust ash

Strength and stiffness characteristics are major concern for selecting any geomaterial. However, laboratory testing of these characteristics is time associated, laborious, and high cost. So, there is a need of intelligence tools to estimate the strength and stiffness of geomaterial. The impact of sawdust ash on the stiffness and strength properties of combined expanding clays is discussed in this research. The combined expansive clays underwent tests for California bearing ratio (CBR), unconfined compressive strength (UCS), optimal moisture content, maximum dry density, plasticity characteristics (liquid limit and plastic limit), and differential free swell (DFSI). According to test results, adding more sawdust to the blended clays improves their performance. This study also investigates the artificial neural network (ANN) model that considers six input variables to forecast the CBR and UCS of blended clays. The findings demonstrate that the ANN model performs more accurately for the CBR and UCS models. This clever method may help manage the under- or overestimation of additive dosage and reduce project costs.

Enhancement of Clay Compressibility and Strength Using Nano Magnesium Oxide

In order to satisfy the requirements of environmentally friendly construction projects and minimize greenhouse gas emissions, it was necessary to focus on utilizing nanomaterials instead of conventional materials to enhance clay soils; nano Magnesium Oxide was suggested for this study. The compression and unconfined compressive strength tests were achieved to assess the compressibility behavior and strength of silty clay treated using nano magnesium oxide. Additionally, an investigation into the alteration of the clay microstructure was conducted using field emission scanning electron microscopy (FE-SEM) tests. The silty clay utilized in this research is characterized by a compression index 0.23 and an undrained shear strength of 53 kPa. The soil was treated by adding different percentages of nano-MgO (0.4%, 0.5%, 0.6%, and 0.8%), and the curing period was seven days. The treated soil samples were prepared based on the optimal water content and maximal dry density of the natural soil. The results indicate that utilization of nano Magnesium Oxide leads to a reduction in both values of the index of compression (Cc) and recompression index (Cr), in addition to a decrease in the value of the coefficient of compressibility (av). Also, the test finding for unconfined compressive strength demonstrates a noticeable increase in strength as the percentage of nano-MgO increases, accompanied by a reduction in failure strain. Adding 0.6% (the optimum percentage) of nano Magnesium oxide enhances the strength by about 114% and decreases the value of the compression index by about 36% compared with natural soil.

Strength and compaction behavior of copper slag stabilized soil

Soil is a unique material. This paper helps in identifying the usage of industrial by-product copper slag as a stabilizing agent. The properties of the soils may affect roads built on unstable subgrade with substantial plasticity. Weak sub-grade soils undergo volume changes as a result of variations in the moisture content, which leads to pavement problems such as cracking, settlement, and heaving. It is important to stabilize these weak sub-grade soils in order to prevent its swelling, strength improvement and performance enhancement. The main aim of this research is to study the effect of copper slag (CS) with clay by performing one of the soil stabilization techniques. In this paper, strength and compaction behavior of kaolin clay (KC) stabilized with CS is studied. For strength characteristics, unconfined compressive strength (UCS) and split tensile strength (STS) tests are carried out. Similarly, for compaction characteristics, modified proctor compaction tests are carried out. Total 7 mixes are prepared using different proportions of CS and KC. The first five mixes are of CS and KC with varying content of CS from 0 to 50 % with an increment of 10% in the mix. The remaining two mixes were of 100% CS and 100%KC each. From the test results, it is observed that the inclusion of CS in KC significantly affected its compaction and strength characteristics.

Strength and compaction characteristics of kaolin clay blended with industrial wastes

The long-term stability of the construction over soil depends significantly on the strength of the ground. Swelling and shrinkage characteristics of expansive fine-grained soil causes volumetric changes followed by distress and damage to the structures resting on it. One of the most popular and cost-effective methods of improving soil is adding admixtures. Utilization of industrial wastes in soil stabilization is a cost effective and environment friendly solution. In this study, two types of industrial wastes, copper slag and pond ash, are used with the aim of improving the strength and compaction characteristics of subgrade. So, the work is focused on evaluating the compaction and strength characteristics of Kaolin clay (KC) blended with Copper Slag (CS) and Pond Ash (PA). For the compaction characteristics, modified proctor compaction tests were conducted and to study the strength characteristics, Unconfined compressive strength (UCS) and split tensile strength (STS) tests were conducted. In Total, 14 different mix combinations were used in this study. From the test results, it has been observed that blending KC with PA and CS not only improved its compaction characteristics but strength too.

Experimental Study on the Effect of Moisture Content on Shear Strength of Unsaturated Silty Clay

Experimental Study on the Effect of Moisture Content on Shear Strength of Unsaturated Silty Clay

Deformation characteristics of the shear band of silty clay–concrete interface under the influence of freeze–thaw

Direct shear tests of the silty clay–concrete interface under different moisture contents and freeze–thaw (F–T) cycles were conducted to study the mechanical and deformation characteristics of the silty clay–concrete interface under the action of F–T cycles. The change rule of shear band thickness under F–T cycles were analyzed based on particle image velocimetry technology. The microstructure changes of the damaged specimens were observed combined with scanning electron microscopy. Experimental results show that the shear strength of the silty clay–concrete interface is negatively correlated with the F–T cycles and moisture content. The moisture content increases from 12.7% to 20.7%, and the shear strength of the shear band decreases by 7.6%, 7.5%, 7.5%, 12.3%, and 10.5% after 9 F–T cycles, respectively. The shear strength of the shear band decreases obviously after 3 F–T cycles, and tends to be stable after 7 F–T cycles. The successive F–T cycles increases the thickness of the shear band until it stabilizes after 3 F–T cycles. The length and width of cracks inside the specimen increase as the number of F–T cycles rises. The orientation of particles in the shear band is weakened, but the orientation of particles in the shear band is always stronger than that outside the shear band. The change in soil particle and pore content is the most obvious in 3 F–T cycles, and it is the reason for the change in shear band.

Ground improvement techniques applied to very soft clays: state of knowledge and recent advances

Soft ground improvement techniques have evolved substantially in Brazil in recent years. However, their application in soft and very soft clays requires a good understanding of the fundamentals of ground improvement techniques suited to the problem as well as the actual field behavior when implemented on a real scale. This paper describes some of the most widely used ground improvement techniques in the context of very soft clays in Brazil. The techniques described in the paper use prefabricated vertical drains (PVD) such as vacuum preloading; or combine PVD and rigid inclusion, such as CPR grouting; or are purely column-like elements such as piled embankments (including those executed with the deep mixing technique, DSM); or combine column-like elements with the drainage function, such as stone columns and geosynthetic encased columns; or use cementitious binders such as shallow soil mixing. The paper reference condition is a soft clay foundation in which no strengthening is implemented, such as, an embankment with basal reinforcement or soft clay with vertical prefabricated drains, or the use of vacuum preloading to speed up the consolidation rate. The applications of the ground improvement techniques are illustrated by case histories, numerical analyses, or physical models. Different types of measurements are used to evaluate the performance of each technique, including settlements, horizontal displacements, excess pore pressures, embankment applied stresses, stress concentration factors, and clay strength following the ground treatment. The settlement improvement factor β, the ratio between the settlements for untreated and treated conditions, is shown to be a suitable parameter to assess the degree of improvement imposed in the soft foundation by ranking the various methods in increased order of strengthening effect.

Enhancing the Life Cycle of the Jack up Structure by Applying Alternative Foundation Methodologies in Geotechnical Engineering

A jack-up structure is a bottom-mounted floating unit having an adjustable hull and movable legs. Particular jack-up structures are more susceptible to hazards under environmental loads during their operation and life cycle in the ocean. Authors' attempts here to enhance its life cycle and sustainability in shallow to deep waters by correctly accessing soil behaviour and predicting its load carrying capacity. Here the numerical analysis of the substructure has been attempted. Simulation of load-deformation behavior under axial compression has been carried out for advancing research. The entire study has been carried out using three-dimensional finite element-based software Plaxis 3D A.E. 2017. The geometrical variation of substructure spud can have an inverted spud at the centre bottom from 120 0 to 180 0 has been studied for knowing behaviour under axial compression, axial tension, and lateral forces. The simulated numerical model is used to develop empirical expressions for axial capacities estimation. The numerical analysis results indicate that spud can have an inverted angle of cone 130 0 is most beneficial under the static combined vertical, moment, and horizontal loading (3D loading) in marine clay. The axial load carrying capacities in compression, tension, and lateral loading follow the same sequence in ascending order from 180 0 ,175 0 , 150 0 , 130 0 and highest in 120 0 . Stiffness and undrained shear strength of soft clay contribute more than the diameter of the spud and embedment depth in compression and tension.

Deformation Characteristics of Lime Stabilized Clay Soil Using Finite Element Method

Clay soil provides a poor working platform due to its plastic characteristics that could affect a structure’s safety and other common structure failure including excessive foundation settlement, the production of cracks in the superstructure and other structural element failure. Thus, there is a challenge for clay soil to be a support for a foundation. The objective of this study is to compile a set data from past research studies that include the parameters of untreated and treated clay soil properties as to be used in the PLAXIS 2D generate its deformation over no load and 100 kPa stress as well as increasing its shear strength and reduce the excessive settlement. Accordingly, the suitable lime content to improve clay strength can be determined. The numerical analysis is done by running the parameters collected from previous studies in PLAXIS 2D in order to generate the final deform soil. The soil with lime content 0%, 3%, 6%, and 9% deformed under both without and with loading of 100 kPa. The result that can be observed from the deformed soil, the treated clay behaved well under loading compared to the untreated. From the result, the amount of lime content did affect the properties of the soil by showing the settlement of each soil and the deformation pattern.

DSS tests on marine clays for offshore windfarm foundation design

This technical note presents results of a series of monotonic and cyclic DSS laboratory tests performed on five intact marine clays offshore China. The laboratory program aimed to determine the cyclic shear strength and soil deformation properties for offshore foundation design. Various cyclic contour diagrams are provided, including cyclic shear strength and average and cyclic shear strains for different number of cycles. Results of the five clays are discussed and compared with an existing database on static and cyclic strengths of clays. In general, the test data fits well with the database and OCR plays an important role in the cyclic behaviour of the marine clays. The provided cyclic strength parameters for the tested clays can be used as references for similar clays offshore. The purpose of this study is to provide a realistic reference for research and practice offshore China where very few cyclic test results are available for offshore wind energy industry.

Developing bearing capacity model for geogrid-reinforced stone columns improved soft clay utilizing MARS-EBS hybrid method

Because of the complicated geometry and a lack of knowledge about the parameters that impact it, estimating the ultimate bearing capacity (qrs) of a geogrid-reinforced sandy bed on vertical stone columns in soft clay is challenging. In practical applications, developing an accurate prediction model can be beneficial due to the difficulty and expense of estimating qrs. The objective of this study is to develop a model for predicting the bearing capacity of geogrid-reinforced stone columns using Multivariate Adaptive Regression Splines (MARS) and Escaping Bird Search optimization algorithm (EBS). In order to accomplish this, 219 constructed experimental samples were used. Feature selection based on the Neighborhood Component Analysis (NCA) method showed that due to the strong correlation between undrained shear strength of unreinforced clay (qu) and the ratio of stone columns distance to foundation diameter (s/D) variables, only qu should be included in the modeling. A developed model for estimating the bearing capacity was found to have coefficients of determination (R2) of 0.997 for training, 0.993 for testing, and 0.995 for total data. This study confirms that the undrained shear strength of unreinforced clay (qu) is the most essential input parameter for assessing bearing capacity, while the the ratio of sandy bed thickness to foundation diameter (t/D) is the least essential input parameter. In addition, the parametric analysis shows that increasing all input parameters increases bearing capacity.

Capacity of spudcan foundation on dense sand overlying clay under combined loading

The evaluation of spudcan foundation capacity under combined vertical, horizontal and moment loading is critical for the site-specific assessment of jack-up rigs. However, the investigation on the behavior of a spudcan on the surface of a sand layer overlying clay under combined loading is limited. This paper reports the results from a series of finite element analyses conducted to explore the failure envelope of spudcan on dense sand overlying clay before punch-through, considering the effects of the preload level on spudcan, the thickness ratio and the relative density of sand, and the underlying clay strength through parametric study. The numerical results provide insights that when the sand layer is sufficiently thick, the failure envelope expands with the increase of vertical load level, leading to higher horizontal and moment capacities; however, for the spudcan on a relatively thin sand layer, the horizontal and moment capacity may decline with rising vertical load level, resulting in eccentricity and shrinkage of the failure envelope. New design formulas for the failure envelope are proposed covering a comprehensive range of soil parameters and layer geometries of practical interest, which facilitates their general application in the site-specific assessment of the jack-up platforms.

Use of the Dynamic Cone Penetrometer in Compacted Clay–Sand Layers

The ASTM D6951 suggests a test method using the dynamic cone penetrometer (DCP) for the assessment of shallow pavement strength. This study is dedicated to evaluating a similar test method to be used for fine-grained clay–sand mixtures, which are commonly used to construct liners and fluid barriers. The liner layers include clay, which is water-sensitive. The shear strength of the liners depends mainly on the composition and proportions of the mixtures adopted. A series of tests were conducted in the laboratory for compacted clay–sand mixtures, including 5% and 10% bentonite material. The responses to advancing a dynamic probe into compacted material at three various moisture conditions—namely, the optimum, dry of optimum, and wet of optimum water contents—are investigated. The penetration profiles are compared for the two clay content levels selected and for three moisture state conditions. The clay–sand liners support vehicles and vibratory compactors during construction and when waste material is placed. The shear strengths of the mixtures are evaluated in the laboratory using direct shear tests. From the results obtained in this investigation, general guidelines and recommendations are presented to help with the efficient assessment of liners consisting of clay–sand mixtures. A cheap and quick approach to assess the density and shear strength of landfill liners or clay–sand layers can be achieved using a hand-held dynamic cone penetrometer. The state of moisture during compaction was found to influence the DCP results. The compaction of layers in a wet of optimum state is not expected to be an ideal alternative.

Effects of Strain-Softening and Strain-Rate Dependence on the Anchor Dragging Simulation of Clay through Large Deformation Finite Element Analysis

Large-deformation finite element (LDFE) analysis with the coupled Eulerian–Lagrangian (CEL) technique for large-deformation soil functions without twisting or distorting the mesh. However, the model does not consider the strain-softening and strain-rate dependence of clay-based soils. The undrained shear strength of clay is sensitive to the strain rate. In addition, the strain-softening effect of soil strength reduction accompanied by large-scale shear deformation should be considered. In this study, anchor dragging simulations were performed for large-deformation analysis considering strain-softening and strain-rate dependence. Furthermore, a shear strength equation expressing the strain-softening and strain-rate dependence of the Tresca constitutive model was developed based on VUMAT, an ABAQUS/Explicit subroutine. The equation was designed so that it could be linked to the LDFE/CEL model. The model was verified by performing comparative analysis with the Mohr–Coulomb (M–C) perfect-plasticity model. The newly constructed Tresca base strain-softening and strain-rate-dependence VUMAT algorithm in the LDFE/CEL model analysis confirmed the effects of strain-softening and strain-rate dependence. The proposed model enabled a highly realistic simulation of the actual phenomenon than the M–C model. Finally, a parametric study on strain-softening and strain-rate dependence was conducted, and the behavior of clay due to the anchor drag phenomenon was revealed.

Changes in the Strength of High-Plasticity Clays After Stabilization: an Experimental Study

Changes in the Strength of High-Plasticity Clays After Stabilization: an Experimental Study

Numerical Simulation of Stiffened Granular Pile

Abstract: Granular piles are suitable for increasing soft clay's strength and consolidation properties. Stone columns offer a practical, affordable solution for enhancing the earth and are crucial for stabilizing the soil. In order to carry higher shear stresses and prevent settlement, stone columns behaved as stiff elements, which enhanced the deformability and strength characteristics of the soft type of soil. The usage of granular piles has been shown to improve slope stability, increase bearing capacity, decrease differential and total settlements, decrease sand liquefaction, and lengthen settlement times. The present study studied the effect of stiffening on the granular pile using PLAXIS 2D. Mohr-Coulomb failure criterion was considered for the stone column, expansive soil, and granular material used for stiffening. The present study results are validated with the experimental results and are in good agreement. Numerical results show that stiffening in granular piles increases the load settlement response and stress transformation to a depth of granular pile and reduces the bulging

Triaxial Experimental Study of Zinc Contaminated Red Clay under Different Temperature Conditions

Temperature is one of the important factors affecting the mechanical properties of geotechnical soils, and its role in engineering construction in China cannot be underestimated. In order to study the effects of temperature and zinc contamination concentration on the mechanical properties of Guilin local red clay, a temperature-controlled triaxial shear test was conducted on Guilin red clay under three variables of temperature, zinc contamination concentration and surrounding pressure. The test findings revealed that there are significant differences in the effects of temperature, zinc contamination concentration and surrounding pressure on the mechanical properties of Guilin red clay. The stress–strain curves of the red clay at various temperatures, contamination concentrations and envelope pressures are of the strain-hardening type, and the deformation modulus showed a tendency to increase rapidly with increasing strain, then decrease rapidly, and finally, decrease slowly. With the increase of temperature, the cohesion of Zn-contaminated red clay increases, while the angle of internal friction increases and then decreases, both of which increase the shear strength of red clay. As the concentration of Zn contamination grows, the shear strength of the red clay increases, while the internal friction angle increases and then decreases, and the shear strength of the soil increases and then decreases. The shear strength of the Zn-contaminated red clay improved as the surrounding pressure increased.

Impacts of Clay Content and Type on Shear Strength and Splash Erosion of Clay–Sand Mixtures

Soil characteristics, especially clay content and clay type, have significant impacts on splash erosion. This investigation was conducted to determine the effects of clay content and clay type (zeolite, phlogopite, bentonite, and kaolinite) on the shear strength and splash erosion of clay–sand mixtures compared with a clay soil under controlled conditions. Clay–sand mixtures were prepared by mixing 15, 30, and 45 kg 100 kg−1 of the selected clays with pure sand and a clay soil; these mixtures were pre-treated with three levels of wetting and drying (W&D) cycles, and then shear strength was measured. The splash erosion rate was measured at three levels of water status: air-dry, plastic limit (PL), and liquid limit (LL). The highest values of splash erosion were observed in the samples without the W&D cycle, and after applying the W&D cycles, splash erosion decreased. Moreover, splash erosion was higher in the air-dry and LL groups. Splash erosion decreased with increased clay content because of the structure development in the mixtures. In general, as clay content increased, splash erosion was reduced and shear strength was significantly increased. From the highest to lowest mean of cohesion, the results showed the following order: bentonite > kaolinite > phlogopite > clay soil > zeolite. However, splash erosion showed the following order for the studied clays: zeolite > clay soil > phlogopite > kaolinite > bentonite. Nonlinear power models, best-fitted relations between splash erosion and shear strength, and the shear strength could explain about 30–33% of the splash erosion variability in this study.