Shear Strength Of Expansive Soil Research Articles

Study on Cynodon dactylon root system affecting dry–wet cracking behavior and shear strength characteristics of expansive soil

Expansive soil exhibits remarkable characteristics of water absorption expansion and water loss shrinkage, rendering it susceptible to cracking under the alternating dry–wet environments of nature. The generation and development of cracks in expansive soil can result in catastrophic engineering accidents such as landslides. Vegetation protection is an important approach to stabilizing expansive soil slopes and fulfilling ecological protection requirements. In this study, through indoor experiments and theoretical analysis methods, the effects of Cynodon dactylon roots on the crack development and shear strength of expansive soil subjected to dry–wet cycles were analyzed, and the relationship between the crack development and shear strength decay in root-doped expansive soil was explored. Furthermore, the mechanism of vegetative root system action was elucidated. The results show that the Cynodon dactylon root system exerts a significant inhibitory effect on crack development in expansive soil. The crack indexes of root-doped expansive soil exhibit significant phase characteristics during the process of dry–wet cycles. The crack-blocking and reinforcing effect of the root system becomes pronounced as the root-to-soil mass ratio increases and the root diameter decreased. Moreover, the process of crack development in expansive soil is accompanied by a decrease in soil shear strength. The quantitative relationship between crack development and shear strength decay can serve as a basis for predicting the stability of slope soil. Overall, the results highlight the potential of vegetation-based approaches in protecting slopes with expansive soils and have practical implications for ecological protection and engineering design in areas with expansive soils.

A Systematic Study to Strengthen the Sub Grade of the Pavement by Stabilization of Expansive Soil with Molasses and Jute Fibre

Abstract: Expansive soils, commonly referred to as Black cotton soils (BC), possess undesirable engineering properties such as low bearing capacity and high compressibility. To address these challenges, various stabilizers have been used to enhance the strength of expansive soil, including jute fiber and molasses. This thesis focuses on investigating the effects of incorporating jute fiber as a stabilizer and molasses as an additive to improve the properties of expansive soil. The objectives of this study are to enhance the shear strength of expansive soil by blending jute fiber and molasses mixtures. Jute fibers of different lengths (1cm, 2cm, 3cm, and 4cm) and various percentages (0.5%, 1%, 1.5%, and 2%) are used as stabilizers. Molasses is employed as an additional stabilizer with varying percentages (5%, 8%, 12%, and 15%). Laboratory investigations reveal that the addition of 12% molasses and 1.5% jute fiber significantly reduces the liquid limit, plastic limit, and plasticity index of the expansive soil, while simultaneously increasing the maximum dry density and California Bearing Ratio (CBR). Furthermore, cyclic load test results demonstrate a 62% improvement in the load carrying capacity of the treated expansive soil subgrade flexible pavement compared to untreated expansive soil flexible pavement. Utilizing construction wastes like molasses offers an alternative to reduce road construction costs, especially in rural areas of developing countries. Additionally, jute fiber provides effective reinforcement for expansive soils. These findings highlight the potential of jute fiber and molasses as sustainable and cost-effective stabilizers for enhancing the performance of expansive soils in construction projects

An updated binary medium constitutive model of frozen rubber reinforced expansive soil under confining pressure

Rubber reinforcement can effectively improve the swelling characteristics and shear strength of expansive soil. However, rubber-reinforced expansive soil has a more complex structure and mechanical properties, especially in a frozen state, and existing models have not been applied to fully characterize its shear deformation characteristics. In this paper, the updated binary medium model of rubber-reinforced expansive soil is proposed based on the theory of the binary medium model and the homogenization theory of heterogeneous material. The deformation and damage mechanism of frozen rubber-reinforced expansive soil is discussed by using the concept of the binary medium model at the microscopic level, and the updated binary medium model is verified by the triaxial tests of frozen rubber-reinforced expansive soil under confining pressure conditions. The main results obtained: (1) Based on the theoretical framework of rock and soil failure mechanics and the concept of updated binary medium model, saturated frozen rubber-reinforced expansive soil can be abstracted into cementing elements (ice-rubber-soil skeleton) with strong cementation properties, elastic friction elements (rubber) and elastic–plastic friction elements (ice-soil broken skeleton) without cementation properties. (2) The stress–strain curve of frozen rubber-reinforced expansive soil can be divided into three stages: linear elastic stage (ε < 1.33%), elastic–plastic stage (1.33 % < ε < 4.17%) and strain softening stage (ε > 4.17%), which can be interpreted by the conversion between the cementing elements and the friction elements in the updated binary medium model.(3) The measured values of stress and strain of rubber-reinforced expansive soil match the calculated values of the model (R2 = 0.92), and the peak point strain deviation and stress deviation of the model and test values are 9% and 3%, respectively, indicating that the updated binary medium model can better simulate the stress–strain relationship of rubber-reinforced expansive soil. (4) The fitting degrees of the unary medium model and the binary medium model are 0.74 and 0.36, respectively. Compared with the updated binary medium model, there are fewer parameters in the equations, the binary medium model species lacks rubber as an elastic material, and the unary medium model lacks elastoplastic and elastic materials, so it is not suitable for simulating the stress-strain relationship of frozen rubber-reinforced expansive soil.

Suitability of Enset Fiber with Coffee Husk Ash as Soil Stabilizer

Expansive soil is a problematic soil due to swelling and shrinkage behavior during moisture variation. Damage to shallow foundations like pavement and footings of residential houses occurred due to these soils. Different scholars deal with stabilizing expansive soils using different mechanisms. This study also evaluated the suitability of Enset fiber with coffee husk ash materials to improve the expansive property of soils found in Jimma town. Different geotechnical parameters were determined for virgin soil and coffee husk ash with virgin soil. After treating the natural soil with varying percentages of coffee husk ash (5%, 10%, 15%, and 20%), the optimum levels of coffee husk ash were determined. Different laboratory tests such as CBR value, compaction test, and Atterberg limits were determined using the optimum coffee husk ash with varying percentages of enset fiber (0.3%, 0.6%, 0.9%, and 1.2%). The study reveals that the addition of coffee husk ash to enset fiber significantly increases the shear strength of expansive soils. With the addition of 15% of coffee husk ash and 0.9% of enset fiber, all tested geotechnical parameters improved the expansive soils to be used as subgrade materials. The soil changed from highly swelled material to poorly swelled material. Therefore, it can be concluded that the reuse of agricultural waste of coffee husk ash with enset fiber is applicable for expansive soil stabilization since it can improve the engineering strength of expansive soils and it is an economic and environmentally friendly material.

Influence of Swelling on Shear Strength of Expansive Soil and Slope Stability

Rainfall is the main factor leading to the landslide of expansive soil slope. To deeply understand the instability mechanism of expansive soil slope under rainfall conditions, it is necessary to clarify the strength attenuation mechanism of expansive soil caused by water absorption and swelling. Therefore, the improved constant volume direct shear test was used in this study to compare with the conventional test, focusing on the variation of effective shear strength parameters with dry density (volume). The micromechanism of expansive soil strength attenuation is further studied, and the influence of expansive soil on slope stability is analyzed by numerical calculation. The results show that the improved direct shear apparatus and method can keep the volume of expansive soil specimens unchanged before and after shear and obtain the real effective shear strength parameter of soil. Under the same conditions, the shear strength parameter of the improved direct shear test is lower than that of the conventional direct shear test. The rapid thickening of the lamellar structure of montmorillonite in expansive soil will lead to the fragmentation and dispersion of clay particles, which is one of the fundamental reasons for the strength difference between expansive soil and ordinary clay. In slope stability analysis, the effect of swelling on the shear strength of slope cannot be ignored and should be considered in engineering design.

Estimation of the unsaturated shear strength of expansive soils in relation to capillary water-retention curve

The hydromechanical behavior of expansive soils is one of the challenging topics in geotechnical engineering. Direct measurements of unsaturated shear strength in the laboratory are complicated and time-consuming. This work introduces a novel model to estimate the contribution of suction to the shear strength of expansive soils. Non-linear relationships in the space of suction and shear strength can be clearly observed, which indicates that the friction angle (ϕb) changes with the evolution of suction. Capillary saturation has been used to upscale suction from pore-scale stress to macroscopic stress using the capillary part of soil-water retention curve. Experimental results indicate that the relationships between capillary suction stress and shear strength show linear properties. However, the friction angle (ϕs) contributed by capillary suction stress to shear strength is not equal to the internal friction angle (ϕ) of saturated soils. The proposed model uses the shear strength value measured at any specific unsaturated state to obtain the evolution of friction angle (ϕs). Results show that the effect of different reference points on computed strength can be ignored. The proposed model is successfully validated with historical data of various kinds of expansive soils from literature.

Enhancing the Swelling Characteristics and Shear Strength of Expansive Soil Using Ferric Chloride Solution

Enhancing the Swelling Characteristics and Shear Strength of Expansive Soil Using Ferric Chloride Solution

Effect of Synthetic Geotextile on Stabilization of Expansive Subgrades: Experimental Study

Structures constructed on expansive soils experience higher upward pressure due to their swelling characteristics. Various conventional treatment methods developed to counteract swell–shrink characteristics of expansive soil are deemed time consuming and not feasible for use in pavement. Geotextiles (GTs) have been used as a filtration and separation medium; however, their effect on swell pressure and shear strength of expansive soil has not been well explored. This study aimed to address these issues by using GT to control swelling behavior, drain moisture content, and provide support at the soil interface. Swell pressure and shear strength were quantified by constant volume swell pressure and direct shear and unconfined compressive strength tests, respectively. The influence of single-layer, double-layer, and triple-layer GTs at varying depths was studied. The higher tensile strength of the GT layer restrained the swell pressure mobilized by resisting internal soil movements and facilitating in-plane drainage conditions. Additionally, soil–geotextile interfacial interactions were observed to contribute to improvement in shear strength. Comprehensive statistical analysis using one-way analysis of variance (ANOVA) was carried out on swell and strength properties. The present study ascertained the use of GT for the dual function (i.e., strength and swell control) of stabilizing expansive subgrades.

SHEAR STRENGTH OF UNSATURATED EXPANSIVE SOILS FROM QUEENSLAND NATURAL SLOPES

Expansive soils exhibit significant changes in their swell and shrink behaviour upon variation of moisture content. The majority of soils in Queensland are expansive; consequently, failures in natural slopes with expansive characteristics are commonly reported under climate-induced soil moisture variations. In order to understand the failure mechanism of such soil slopes, it is vital to analyse slope stability under unsaturated conditions. The current study employed undisturbed soil samples from natural slopes in Queensland and determined their basic soil properties, including the soil-water characteristic curve (SWCC), and unsaturated shear strength to facilitate the analysis of rainfall-induced slope failure. A series of conventional direct shear tests were conducted for different moisture contents under various vertical stresses. The test results were analysed to obtain the variation of the apparent cohesion and the effective friction angle of the soil with moisture content and suction. The study presents an empirical equation to predict the cohesive component in the shear strength of unsaturated expansive soils as an exponential function of suction. The formulation originated from multiple linear regression analyses for data sets obtained from shear tests using undisturbed soils with varying moisture contents. The empirical equations can realistically predict the reduction in soil cohesion due to wetting (R2 = 0.8666). The study provides an alternative to the quantitative estimation of unsaturated shear strength of expansive soils.

Micro-mechanical performance evaluation of expansive soil biotreated with indigenous bacteria using MICP method

This study explored the effect of indigenous bacteria present in the soil to stabilized swelling behavior and improving the mechanical property of expansive soil. The objective of the research is to investigate the effectiveness of the biostimulation microbial induced calcite precipitation (MICP) for controlling the swelling-shrinkage behavior and improving shear strength of expansive soil. An attempt was made to develop an effective procedure to culture the indigenous bacteria for treating clays with varying plasticity and improve their engineering behavior. The detailed procedure has been investigated to effectively apply the MICP technique in clay soil, considering its low permeable nature. The applicability of biostimulation to clayey soils in minimizing their swelling potential and improving the strength is assessed. Both macroscale and microscale studies were conducted on untreated and biostimulated soils to observe changes in plasticity, strength, swelling, mineralogical, chemical characteristics. The present method has shown an effective alternative to improve the road pavement subgrade without affecting the eco-system of natural soil. The method investigated the effective way of providing the enrichment and cementation solution in clayey soil, which is the major concern in current literature. The study confirms that the calcite content has been increased with biostimulated MICP treatment up to 205% in the treated specimens and which future increased the unconfined compressive strength and split tensile strength. A reduction in the swelling pressure and swell strain is also observed. The results show that a cost-effect and eco-friendly method can be deployed for stabilizing the road pavement subgrades. The statistical assessment using multivariate analysis and hierarchical clustering dendrogram has been carried out to investigate the effect of the MICP treatment protocol on different soil and engineering parameters.

Study on Mechanical Properties of the Expansive Soil Treated with Iron Tailings Sand

Aiming at researching shear strength parameters of expansive soil modified by industrial waste iron tailings sand, the enhancement of expansive soil is explored from macroscopic and microscopic aspects. After characterization and testing by various means, the results show that expansive soil modified by iron tailings sand will increase the maximum dry density of the improved soil and reduce its optimal moisture content, which is beneficial in tuning the moisture content at the construction site. In addition, iron tailings sand can improve the shear strength of expansive soils. The influence of iron tailings sand on cohesion increases first, then decreases, and reaches the peak value at 30%, while the effect on internal friction angle exhibits a continuously increasing trend. Furthermore, according to mercury intrusion tests and microangle analysis, the addition of iron tailings sand can reduce the tiny pores and enhance the occlusal force of the soil. Simultaneously, it increases the number of large pores, maximizing the macroscopic strengthening of iron tailings sand towards the expansive soil.

Experimental study on the ultrasonic nonlinear damage characteristics of expansive soil during constant amplitude dry-wet cycles

Dry-wet cycles can cause fatigue damage to expansive soil, and various control parameters of the dry-wet cycles (initial moisture content, number of dry-wet cycles, cycle amplitude, etc.) can affect the development of soil damage. Therefore, it is important to study the fatigue damage characteristics of expansive soil under dry-wet cycles of constant amplitude. This paper considers expansive soil from Baise in Guangxi, China, as the research object. Based on tests of the P-wave velocity and low-stress shear strength of expansive soil under 0-6 constant amplitude dry-wet cycles, the attenuation laws for the P-wave velocity were analysed, the damage variable of expansive soil was characterized by P-wave velocity, and the rationality of this damage variable was verified by measuring the low-stress shear strength values of expansive soil specimens. Based on the experimental P-wave velocity results, a nonlinear empirical model of fatigue damage for expansive soil was constructed. The results illustrate that the P-wave velocity of an expansive soil sample decreases nonlinearly with an increasing number of dry-wet cycles and that the damage degree increases nonlinearly with an increasing number of cycles. The P-wave velocity can be successfully used to define a representative damage variable for expansive soil.

Physical and Mechanical Characteristics of Shallow Expansive Soil due to Freeze-Thaw Effect with Water Supplement

Shear strength of shallow expansive soil varies along with the depth under the freeze-thaw effect. This work investigates shear strength characteristics of shallow expansive soil by simulating the actual freeze boundary conditions of seasonal frozen areas with water supplement. An integrated approach incorporating the freeze-thaw test and direct shear test was adopted. Firstly, unidirectional freezing tests for expansive soil columns under three different freezing temperature gradients were carried out. Secondly, direct shear tests under low vertical stress were performed on the standard samples, which were prepared by using cutting rings cut the thawed expansive soil columns into nine segments along with the depth. Temperature, water content, and dry density at different depths were also investigated after the freeze-thaw process. The test results showed that, after the freeze-thaw process, the shear strength of expansive soil columns showed significant differences along with the depth and highly correlated with water content, specifically the higher water content and the lower shear strength. The minimum shear strength in the expansive soil columns occurred at the soil layer below the frozen and unfrozen zones interface. The expansive soil column’s shear strength changed most under the moderate freezing temperature gradient corresponding to the most considerable shear strength reduction. Moreover, the significant decrease in cohesion was the main reason for the shear strength reduction of expansive soil after the freeze-thaw process. These results indicate significant depth variability in shear strength of expansive soil under the freeze-thaw effect.

Experimental study on the engineering properties of expansive soil treated with Al13

This paper investigates the stabilization of expansive soil with hydroxy-aluminium (Al13) with Al/soil ratios of 0.10, 0.14, 0.18, 0.22 and 0.26 mmol/g. A series of laboratory tests were conducted to study the effects of Al13 on the mechanical properties of expansive soil, including Atterberg limits, grain size distribution, swell percent, swell pressure and unconsolidated-undrained (UU) triaxial strength. The results revealed that Al13 reduced the plasticity index, clay content and swelling potential and enhanced the shear strength of expansive soil. The minerals and micro-structural changes in the soil samples were also determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the stabilized soil showed a remarkable flocculated-agglomerated structure characterized by the densification of particle associations. The consistency of the changes in mechanical properties and micro-morphology indicated that expansive soil can be effectively improved with the use of Al13. Additionally, the optimum dosage of polynuclear hydroxy-Al (PHA) solution for stabilizing expansive soil was 0.18 mmol/g under the given properties of expansive soil and PHA utilized in this study.

Experimental Study on Shear Behavior of Expansive Soil Modified by Gravel Sand

Using the strain-controlled direct shear equipment, some direct shear experiments were carried out on the soil samples of Nanyang expansive soil with different gravel ratios under the specific water content, and the shear strength, cohesion and internal friction angle of the expansive soil samples were studied. The experimental results show that the shear strength of the expansive soil samples increases with the increase of vertical pressure. As the proportion of gravel sand increases, the shear strength of expansive soil samples increases to varying degrees. The shear strength of expansive soil increases significantly when the proportion of gravel sand is in the range of 10%~40%, and the shear strength of remolded soil is the highest when the gravel sand content is 10% under the lower vertical pressure. Under the higher vertical pressure, the shear strength of the remolded soil is the largest when the gravel content is 20%, and the shear strength of expansive soil is close to that of pure expansive soil when the proportion of gravel sand is 50%. The cohesive force of the sample increases first and then decreases sharply with the increase of the proportion of gravel sand, and is maximum when the content of gravel sand is 10%. The internal friction angle increases first and then decreases slowly with the increase of the proportion of gravel sand, and is maximum when the gravel sand content is 40%. The results show that gravel sand can effectively enhance the shear strength index of expansive soil, which can be used as a good engineering application material for improving expansive soil.

Surface Crack Development Rules and Shear Strength of Compacted Expansive Soil Due to Dry–Wet Cycles

Expansive soil is a typical multi-crack soil, and the stability of expansive soil slope is significantly affected by cracks. In this study, pores (particles) and crack image analysis system (PCAS), a crack image processing software was used for the dynamic and quantitative measurement of the development of surface cracks in expansive soils with different compaction degree under the condition of dry–wet cycles. Furthermore, the shear strength of expansive soil with different degree of crack development was also tested. The test results showed that the greater the compaction degree, the smaller the cracking degree. The cohesion decreased with the increase of dry–wet cycles; however, the internal friction angle was less affected. For the same number of cycles, cohesion increased with the increase of the compaction degree. The relationship between the cohesion and the crack parameters including the number of crack joints, number of cracks, total length of cracks, and average width of cracks exhibited similar trends. This indicates that cohesion has some relevance with these crack parameters. The crack rate and fractal dimension exhibited linear relationship with cohesion. The research results provide an important basis for the application of crack parameters to calculate the strength parameter of expansive soil in engineering field.

Development and application of an instrument for simulating wetting-drying cycles of expansive soils under loads

Alternating rainfall and evaporation in nature severely impact the shear strength of expansive soils. This study presents an instrument for simulating the effect of wetting-drying cycles on the strength of expansive soils under different loads, and its testing error is verified. With this instrument, direct shear tests were performed on samples experiencing 0–6 cycles under vertical loads of 0 kPa, 5 kPa, 15 kPa, and 30 kPa. The results found that this instrument provides a new method for evaluating the effects of wetting-drying cycles on soils, and this method represents actual engineering conditions more accurately than do preexisting methods. It accurately controls the water content within 1% while simulating the specified loads at different soil depths. Cohesion is significantly affected by wetting-drying cycles, while the friction angle is not as sensitive to these cycles. Decrease in shear strength can be attributed to the fissures in soils caused by wetting-drying cycles. The existence of vertical loads effectively restricts shrinkage fissuring and cohesion attenuation, consequently inhibiting the attenuation of shear strength.

The Influences of Freeze-Thaw Cycles on the Shear Strength of Expansive Soil Treated with Ionic Soil Stabilizer

A study of the shear strength of expansive soil treated with ionic soil stabilizer during freeze-thaw cycles is presented. The shear strength of treated expansive soil is greater than that of untreated expansive soil at room temperature, and it is evident that the moisture content plays a leading role in this result. After a freeze-thaw cycle the shear strength changes little for untreated soil, but decreases gradually after ionic soil stabilizer treatment. Shear strength reaches the lowest values after seven freeze-thaw cycles. Finally, the influence of freeze-thaw cycles on the porosity of expansive soil is analyzed using scanning electron microscopy, which shows that the porosity of both treated and untreated soil increases with the number of freeze-thaw cycles, although porosity of the treated sample changes little.

Shear Strength of Medium Plastic Expansive Soil Reinforced with Polyester Fibers

Abstract This Expansive soils are very problematic as they are prone to substantial settlements, heave, and possess low bearing capacity. These soils cover more than 20% of the land cover of India and cause obstructions in the development of road networks, railways, and various other construction activities. They make soil stabilization essential. An investigation was carried out to determine the effect of various proportions of randomly-oriented polyester fibers on the shear strength of expansive soil. The unconfined compressive strength of reinforced soil was determined by incorporating four fiber contents, i.e., 0.25%, 0.50%, 0.75%, and 1%, with varying aspect ratios. The effect of various aspect ratios of 20, 40, and 60 were studied in the present work. The stress-strain relationship for different aspect ratios and fiber contents is also presented in the study. The optimum quantity of fibers was found to be 0.75% of the total weight of the soil. A maximum enhancement in the strength of the soil was achieved with fibers with an aspect ratio of 40. The effect of the aspect ratio is significant with a fiber content of 0.50 to 0.75%. The peak strength of untreated soil is found at strain levels of 6-8%, whereas it increases to 10-12% in reinforced soil. A statistical analysis was also performed to develop a regression equation to predict the improvement in the strength of the medium plastic expansive soil used in the study.

Characterization of the Undrained Shear Strength of Expansive Soils of High Water Content

In recent years, engineering constructions increase rapidly in western and central areas of China, where expansive soil widely distributes. Since expansive soil is sensitive to water content, the characterization of its shear strength should be carefully conducted. For simplicity and ease of use, the Mohr-Coulomb criterion is often adopted to describe the shear strength of expansive soil. In this paper, the physical meaning of the cohesion and frictional strength of expansive soil are explained, and the variations of the strength parameters with water content are investigated. By fitting to the experimental results from direct shear test and triaxial tests, the changing characteristics of cohesion and friction angle with water content are obtained.