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Swelling-shrinkage deformation of expansive soils is the primary governing factor for development of the crack network, which is intimately associated with the bearing capacity and the structural integrity of the soil body. To suppress the swelling-shrinkage characteristic, sintered red mud was utilized as a curing agent to stabilized expansive soil, and the physical property testing phase consisted of compaction tests, Atterberg limit tests and pH tests to derive patterns on the physical and mechanical properties of the expansive soil influenced by the incorporation of red mud. The principal engineering property tests include unconfined compressive tests, one-dimensional swell tests, desiccation-induced crack study and micro-structure analysis by scanning microscopy techniques. The test findings demonstrate that even red mud would somewhat weaken the strength, but restrict the plasticity and successfully prevent swelling-shrinkage deformation of expansive soils. Such an effect is positively correlated with the red mud content. When the content reaches 20%, the crack ratio reduction exceeds 40%, the swelling deformation are reduced by about 20%, and the unconfined compressive strength higher than 500 kPa with dry density of 1.6 g/cm3. The stabilization of expansive soils with red mud effectively increases the structural integrity of the soil layers and the safety of constructions to offer guidance for environmentally friendly construction in expansive soil areas. [ABSTRACT FROM AUTHOR]

This study addresses the critical role of shaft friction of pile in the interaction with expansive soil under varying moisture content. A simplified estimation method is proposed, capturing the non-linear correlation between the interface relative displacement between the soil and pile and unit skin friction and during water infiltration. The approach integrates soil-pile displacement, interface shear strength parameters, and soil matric suction fluctuations. Tests on Nanyang expansive soil include a laboratory model with water infiltration, constant volume swelling, direct shear for interface shear strength, and a filter paper method for SWCC determination. Initial water content of 21% shows an increases swelling pressure more than 24% and 27%. Increasing soil water content reduces soil matric suction. Due to lower soil matric suction, cohesion, friction, and soil interface shear strength decreased. After the passage of the infiltration duration (specifically, 200 hours), ground heave peaks at 10.7 mm, potentially affecting pile axial forces. As matric suction diminishes, the pile's shaft friction reduces, transferring more weight to the pile base, leading to settlements. Experimental data validate the proposed shaft friction estimation method. The approach aligns with previous studies and laboratory models, providing a comprehensive understanding of soil-pile interaction in changing moisture conditions. [ABSTRACT FROM AUTHOR]

This paper introduces a rational method to analyze the inverted T-section strip footing resting on expansive soil. A computer program called SFOEES using the suggested analysis procedure was created to obtain the solution. The program SFOEES involves two major problems that are solved independently for simplicity. Firstly, estimating the distorted soil surface by solving Mitchell's suction diffusion equation using the FDM in 2D and using Wray's model to predict the soil movements. Secondly, analysis of the strip footing-distorted soil surface interaction using the FEM and the Vlasov model. The program's accuracy has been checked through comparison of its results with others' results and shown to be valid. The program was also used to investigate the behavior of the inverted T-section strip footings of different stiffnesses resting on expansive soil and subjected to columns' loads of a lightweight structure consisting of a 3-story. It is concluded that the case of edge heave is considered the critical case for the distortion criteria and the maximum positive bending moment whereas, with regard to the negative bending moment, the case of edge shrinkage is considered the critical case. [ABSTRACT FROM AUTHOR]

The moisture and thermal characteristics of expansive soil slopes have a significant impact on the strength and overall stability of the soil. In this study, the medium-strength expansive soil vegetated slope in Baise, Guangxi, was taken as the research object. Through the combination of numerical simulation and measured meteorological data, the impact of moisture and heat characteristics on slope stability was then analyzed, and optimal geometric parameters conducive to the stability of vegetated slopes were proposed based on these findings. The research results indicate that under long-term climatic conditions, solar net radiation has the most sensitive effect on the evaporation of slope soil. During the evaporation process, vegetation transpiration dominates in the vegetation-covered layer, while below the depth of the vegetation cover layer, soil evaporation itself plays a dominant role. Under the conditions of evaporation-rainfall-evaporation, slopes with a smaller permeability coefficient in the vegetation cover layer have significantly higher safety factors than slopes with a larger permeability coefficient and bare slopes. A steep vegetated slope with a slope gradient of 50° can maintain slope stability with proper handling of its height. The research findings have reference value for the design and construction of vegetated slopes with expansive soil. [ABSTRACT FROM AUTHOR]

The formation of shrinkage cracks is a natural phenomenon in expansive soils. The development of these cracks affects both the physical and mechanical properties of the soil. This paper proposes new procedures for predicting and detecting the formation of crack patterns in expansive soils, based on customized Convolution Neural Network (CNN) and transfer learning. A total of four different deep learning models are developed to detect the soil crack pattern by changing the convolution layers and hyper-parameters in the analysis. The novelty of the proposed detection methods lies in the use of customized CNN models in shrinkage crack detection for expansive soils. The customized CNN models are constructed by varying the number of convolution layers and the hyperparameters. The results show that the proposed CNN models provide very accurate results and are capable of detecting the presence of cracks in the soil with great accuracy. The best results are from one of the customized CNN models namely the Customized CNN Model 2 which consists of five convolution layers, three activation layers, one pooling layer, two fully connected layers, and a softmax layer. The results from this model are compared with other well-known approaches from the literature and are shown to provide improved results. Overall, the proposed deep learning methods developed in this paper produce excellent results in terms of the accurate detection of shrinkage soil cracks and can also be applied to other types of soil cracks. [ABSTRACT FROM AUTHOR]

This study aims to evaluate experimentally the potential of expansive soil stabilization using different additives: zeolitic tuff (ZT), lime, and a combination of lime and ZT. Four different percentages of ZT (10%, 20%, 25%, and 30%), three percentages of lime (2%, 4%, and 6%), and variable percentages of their combinations were used to stabilize the soil for pavement subbase application. Atterberg limits, pH, compaction, linear shrinkage, swelling, unconfined compressive strength (UCS), and California bearing ratio (CBR) tests were performed on treated and untreated soil specimens at different curing times. Results showed that ZT additives effectively reduced the plasticity, linear shrinkage, and swell potential in addition to increase the maximum dry unit weight, UCS, and CBR. The results of this study were supported by a microstructural analysis using scanning electron microscopy (SEM) associated with the energy-dispersive X-ray spectroscopy (SEM/EDX) technique. It was determined that the UCS and CBR values for the 4% lime stabilized soil increased by 22% and 70%, respectively, after the addition of 25% ZT. Based on evaluation of the results, an optimum mixture of 25% ZT and 4% lime stabilized soil can be used in pavement subbase applications as it achieved the minimum strength target. [ABSTRACT FROM AUTHOR]

The influence of pozzolanic materials on calcium-based soil stabilization technique has recently attracted researchers' attention as such materials may catalyze the occurrence of pozzolanic reactions due to their high SiO2 and AL2O3 content. In this study, the effect of adding natural zeolite, which is a common pozzolanic material, on soil stabilized with cement kiln dust (CKD) is investigated. The optimal CKD content was determined by conducting tests on soil treated with percentages of CKD (0%, 2%, 4%, 6%, 8%, 10%, and 12%), and then, the optimal CKD treatment was applied on soil replaced by different zeolite percentages (1%, 3%, 5%, 10%, and 15%). Atterberg limits, swelling, California bearing ratio and unconfined compression tests were performed on all samples to evaluate the performance of additives in stabilization. Unconfined compression test samples were cured for 0, 7, 14 and 28 days to study the effect of time. Addition of CKD resulted in reduction of soil swelling and a significant increase in the long-term strength to an optimum of 10% that resulted in 3-folds of strength value higher than the based soil. Addition of 15% natural zeolite to the optimized CKD stabilized soil, caused 21% increase of strength higher than that with CKD optimized soil, however the swelling is only slightly reduced. [ABSTRACT FROM AUTHOR]

Expansive soil is considered to be an unfavorable soil due to its swelling-shrinking behavior. In order to improve the properties of expansive soil, the addition of steel slag powder (SSP) has been used to improve expansive soil that has been mixed with the cement. In this study, a series of cylindrical improved expansive soil specimens were prepared, which were improved either by the addition of cement, cement SSP, or cement SSP sodium hydroxide (NaOH). All of the specimens were prepared with an optimum water content and then subjected to a maximum of 12 closed-system freeze-thaw (F–T) cycles. The specimens were subjected to different curing times and temperatures (−5°C,−10°C and −15°C) during the tests. After each freeze-thaw (F–T) cycle, the volume of each specimen was measured and an unconfined compression strength (UCS) test was performed. The results have shown that as the temperature of the F–T cycle decreased, the volume expansion rate increased with the increase of the length of the F–T cycle. As the curing time increased, the effect of the F–T cycles on the volume change rate of the specimens reduced and the UCS increased. The first F–T cycle had the greatest influence on the volume of the specimen as well as the UCS of the improved expansive soil. After the improved expansive soils had undergone more than eight F–T cycles, the volume change rate of the specimen tended to stabilize. The maximum F–T volume change rate of the improved soil was 1.93%. When the curing age was 60d and 90d, the strength of the specimen with cement SSP sodium hydroxide was 377.3 kPa and 294.7 kPa higher than the specimen with cement only (ES specimen), and its strength degradation rate was 18.737% and 9.97% lower than the ES specimen. The results have shown that the addition of SSP and cement improved the expansive soil; moreover, NaOH inhibited the degradation of the soil during an F–T cycle. [ABSTRACT FROM AUTHOR]

The impact of periodic freezing-thawing cycling on the stress-relaxation behavior of expansive soil, which was discovered during the construction of the Harbin-Jiamusi high-speed railway, was investigated in this paper. The laboratory tests associated with this study involved X-ray diffraction (XRD), thermal analysis, and direct shear testing. Test results indicate that shear stress decreases gradually in line with the number of freeze-thaw (F-T) cycling (NFT). When the NFT exceeds 7, F-T cycling no longer has any observably significant influence on the shear stress. The relaxation rate decreases during the first F-T cycle, after which almost no appreciable effect from F-T cycling is visible. It is concluded that, during the relaxation process, the shear stress decreases gradually and tends towards a stable value. A three stage process for the stress relaxation of soil samples affected by F-T cycling was observed: instantaneous relaxation; attenuated relaxation; and steady relaxation. Based on the experimental results, a disturbed state concept (DSC)-based stress-relaxation model for expansive soil exposed to freeze-thaw cycling was proposed. Close agreement between the experimental data and results predicted according to the model confirms the model's validity. [ABSTRACT FROM AUTHOR]

Expansive soil swells, softens, and disintegrates when absorbing water, whereas it shrinks when losing water. Understanding the swelling characteristics of a shield tunnel in expansive soil is important. However, most in-site experiences on the swelling characteristics of a tunnel are obtained from the NATM tunnels constructed in swelling rock using drill and blast method; most laboratory experiments or theoretical analyses on the swelling characteristics of a shield tunnel in expansive soil are under certain hypotheses which have not been verified in actual situation. To solve the problems, the Slender West Lake tunnel was selected as the background, laboratory and in-site experiments were performed to understand the swelling characteristics of a shield tunnel in expansive clay. Four experimental sections were constructed in the actual tunnel. The measuring gauges were pre-installed in the segments in factory and the segments were installed in-site to observe the actual earth pressure and temperature during construction. The influences of expansive soil to the distributions and variations of earth pressure, bending moment, and temperature were analyzed. The increasing earth pressure was divided into three stages. Large earth pressure was detected at the top, bottom, left, and right sides of the tunnel. The earth pressure at the left and right sides was larger than that at the top and bottom. Large negative bending moment was detected at the top and bottom of the tunnel, whereas large positive bending moment was detected at the left and right sides of the tunnel. The minimum bending moment appeared at 45° oblique. The largest negative bending moment was larger than the largest positive bending moment. Based on the observations, a load mode of swelling pressure for a beam-spring model was suggested. It can be referred by the similar tunnels. [ABSTRACT FROM AUTHOR]

The piles in expansive soils would experience uplift force on the shaft of the piles due to the swelling of the soils. For a given soil, the magnitude of interface shear stress (uplift force) on pile depends on the interface friction between the pile material and the soil, normal stress acting on the pile surface and the magnitude of swelling, which in turn creates the relative movement at the interface between the soil and the pile material. The hyperbolic representation of stress strain curves has been found to be a convenient and useful means of representing the non-linearity of the stress strain curves of soils and forms an important part of the stress strain relationship. In this paper a simplified hyperbolic model is proposed to evaluate the pile uplift in expansive soil. The hyperbolic model is developed based on the model pile uplift tests, interface shear tests and consolidation test results. The interface shear stress is also evaluated using a program PIES (Axial response of Pile In Expansive Soils). Both the analytical studies gave a good correlation of interface shear stress profile obtained by laboratory studies. Finally a design procedure is proposed to evaluate the uplift force along the shaft of pile in expansive soils. [ABSTRACT FROM AUTHOR]

Expansive clays exhibit a high potential for the volume change behavior when the soil moisture changes. The estimated annual cost of the damage to the facilities built on expansive clay in the United States exceeds 9 billion dollars. Because of the physicochemical nature of the expansive clay, the use of chemical agents to improve their engineering properties is common. This research investigated the effects of chemical agents on an expansive soil from Texas through a laboratory injection method. The agents used in this study included lime, potassium based agents, and a group of ionic agents. Swelling tests, chemical tests, and soil suction tests were used to evaluate the stabilizing effects of those chemical agents. The testing results indicated that potassium based stabilizer, is an effective stabilizing agent to control the swelling potential of the expansive clay. It can also be injected in the field to build a moisture barrier. The chemical tests on the injected Texas clay showed that the stabilizing mechanism of the ionic agents is possibly through the cations' exchange and the increase of the cations' concentrations in the soil pore water. [ABSTRACT FROM AUTHOR]