Montmorillonite Content of Expansive Soils and Its Relationship with Swelling and Consistency Properties

This study focuses on the advancements of characterization of unsaturated expansive soils which would allow better prediction of its swelling and mechanical behaviours. The paper has been divided into three parts. Firstly, a novel model is developed by considering two micro-soil parameters, soil-specific surface area and internal pore size distribution, to predict the natural swelling in expansive clayey soils. The model was validated by comparing the predictions with experimental results for eight soils. Secondly, the paper deals with the diffused-double-layer (DDL) theory-related electrostatic forces from individual clay minerals of expansive soils and their influence on soil swelling. A DDL-based model was also developed, which was validated for swell prediction for fourteen expansive soils. A good correlation was observed for both models when the results were compared with experimental results. Finally, the paper demonstrated the use of vapour pressure technique to control suction beyond 5 MPa for performing suction-controlled repeated load triaxial (RLT) test at high suction state. This novel technique mitigates the limitation of axis-translation technique for maintaining suction till the air-entry-value (AEV) of the ceramic disk. These new models and unsaturated laboratory testing techniques would aid in better characterization of expansive soils in their unsaturated state. This would also provide accurate prediction of swell and stiffness behaviours of soils, thereby reducing the uncertainties in the design of civil infrastructure built on expansive soils.KeywordsUnsaturated soilsSwellingExpansive soilsResilient modulusHigh-suction state

This study evaluates the effects of microbial processes in improving the swelling and shrinking properties of expansive soil. Elemental microanalysis, X-ray diffraction, Fourier-transform infrared spectroscopy and soil swelling-shrinkage tests were conducted to explore the changes in composition, content and structure of the mineral aggregate of expansive soil in bio-mediated treatment process, as well as the effects of microbial-induced mineral phase transformations on the swelling and shrinking characteristics of the soil. The experimental results indicate that cations Si⁴⁺, Al³⁺, K⁺, and Mg²⁺ in the microbial-soil reaction liquid continuously leached out over time. Notably, the concentration of K⁺ exhibited an initial increase followed by a decrease, reaching a peak at 14 days. The Si-O, Al-O and -OH bonds within montmorillonite crystals were also affected. It was suggested that K⁺ ions entered the interlayers of montmorillonite crystals, disrupting their structures. After 14 days of microbial activity, an illite-smectite mixed-layer peak appeared at 2<italic>θ</italic> = 9.882° in the expansive soil samples, and an illite peak was observed at 2<italic>θ</italic> = 48.07° after 28 days. Calculations using the K-value method proved a decrease in montmorillonite content and an increase in illite content. The free swelling rate and load swelling rate of the expansive soil decreased by 69.01% and 24.04%, respectively; the linear shrinkage rate and volumetric shrinkage rate decreased by 32.9% and 30.98%, respectively. The study reveals that <italic>Paenibacillus mucilaginosus</italic> effectively promotes the transformation of montmorillonite to illite and improves the swelling and shrinking properties of expansive soil, which provides a novel approach towards modifying some engineering properties of soils.

Expansive soils have a high tendency for volume change in case of fluctuations in moisture content, potentially causing significant damage to light structures, particularly road pavements. This paper investigates the influence of waste paper sludge () as an alternative sustainable stabilizer on the volume change behavior of expansive road subgrade soils of different origins. For this purpose, was added to the expansive soils at ratios of 3%, 6%, 9%, 12%, and 15% by dry weight of the soils. A series of Atterberg’s limit, swelling, shrinkage, compaction, and consolidation tests were performed on pure soils and soil specimens with to attain a comprehensive understanding of the role that plays in the volume change behavior of expansive soils. The experimental test results showed that the addition of led to a considerable decrease in the plasticity and swell-shrink potentials of subgrade soils. The consolidation settlement of expansive road subgrades was also reduced to some extent with . Moreover, the statistical analysis of the test data indicated a significant relationship among different swelling-shrinkage parameters. The experimental results presented here suggest that the may be a cost-effective, environmentally friendly, and sustainable stabilizer to reduce the volume change sensitivity of expansive road subgrade soils.

Many researchers have been interested in studying the effect of adding local natural materials or construction waste on the properties of poor subgrade soil. However, changes in size and strength of expansive soils can cause extensive damage to the geotechnical infrastructure. This damage is often repeatable and latent in the long term, and is a critical issue in highway subgrade engineering. This paper examines the effect of adding both Fine Silica Sand (FSS) and Granite Cutting Powder Waste (GPW) materials on the welling characteristics of expansive soils. Atterberg limits, free swell index, and rate of swell of the mixtures were used as a key to assess properties of a group of expansive soil samples after adding different percentages of the mentioned materials. The rates of additions were 10%, 20%, 30%, 40%, 50%, 60 and 70% of the weight of the soil samples. The test results showed that FSS and GPW significantly affect the expansive soil properties. However, adding 70% of both FSS and GPW reduced the swelling index from 58.3% to 6.6% and from 58.3% to 11% after 7 days of curing, respectively. This study suggests that the Fine Silica Sand and Granite Powder Waste can be used as stabilizers for expansive highly plastic soils.

Utilization of fly ash with and without secondary additives for stabilizing expansive soils: A review

Expansive soil is one among the problematic soils that has a high potential for shrinking when it is dried and swelling due to change of moisture content. Expansive soils (clays) popularly known as black cotton soils in India. Due to alternate swell-shrink behavior of expansive soils causes, distress in the foundation structures such as buildings, pavements of earth retaining walls etc. Understanding the behavior of expansive soil and adopting the appropriate control measures have been great task for the geotechnical engineers. Extensive research is going on to find the solutions for black cotton Soils. In this study, Nylon Fiber has been used in the form of fibers. The effect of the stabilisation was evaluated through carrying out standard laboratory tests. The tests included the standard compaction test, unconfined compressive strength (UCS) test, California Bearing Ratio (CBR) test. The main motive of this research is to investigate the optimal combination of Nano-Silica and Nylon Fiber with clay soil. The engineering properties such as liquid limit, plastic limit, maximum dry density and unconfined compressive Strength (UCS) are analyzed with virgin soil, the soil with Nano-Silica and combination of soil with Nano- Silica and Nylon Fiber. Three different combinations of Nano-Silica at different percentages 2%, 4% &amp; 6% are used in integration with Nylon Fiber is used in different percentages such as 2.0%, 3.0% and 4%. From these experiments, it has been analyzed that with the increase of Nylon Fiber content in addition to Nano-Silica, the UCS increases and maximum value of UCS is obtained at 6% of Nano-Silica with 2.5% of Nylon Fiber. The intermixing of Nylon Fiber with the soil acts as a reinforcing material in binding the soil particles and the ‘bridge effect’ of fiber reinforcement in soil impedes the further development of tension cracks. Key Words: Compaction test, CBR, UCS, Nano Silica, Nylon Fiber

Expansive soils pose significant geotechnical challenges due to their time-dependent swelling behaviour, which can cause severe infrastructure damage. The ability to predict swell potential accurately is vital for effective designs and risk mitigation. This study combines constitutive modelling with machine learning to enhance the predictive capability of swell behaviour in expansive clays. The constitutive swell model introduced by Liu et al. was evaluated by experimental one-dimensional swell tests, demonstrating its ability to accurately predict time-dependent swelling behaviour under varying surcharge pressures (SPs). A data-driven decision tree (DT) framework was created to relate key swelling parameters of Liu et al. model to fundamental soil index properties such as moisture content, SP, and plasticity index to improve predictive accuracy. Based on these measurable index properties, the model successfully captured the final swell potential of clay samples. Independent validation using literature datasets demonstrated high accuracy, with R2 &amp;gt; 0.97 for predicting final swell potential. The proposed DT framework provides geotechnical engineers with a practical tool to assess final swell potential based on fundamental soil index properties, aiding in better infrastructure design and mitigating the risks associated with shrink-swell behaviour.

The reversible shrink–swell behavior of expansive soil imposes a serious challenge that threatens the overlying structures’ safety and durability. Traditional chemical additives such as lime and cement still exhibit satisfying performance over their counterparts in terms of swelling potential reduction. Nevertheless, significant concerns are associated with these chemicals, in addition to their environmental impact. This paper proposes a novel application of the closed-cell one-component hydrophobic polyurethane foam (HPUF) to stabilize the swelling soil. An extensive experimental study was performed to assess the efficiency of HPUF in mitigating both the swelling and shrinkage response of high montmorillonite content expansive soil. Expansive soil was injected/mixed with different weight ratios of the proposed stabilizer, and the optimum mixing design and injection percentage of the foam resin were identified to be ranged from 10% to 15%. The shrink–swell behaviors of both injected and noninjected samples were compared. Results of this comparison confirmed that HPUF could competently reduce both the swelling potential and the shrinkage cracking of the reactive expansive soil, even after several wet-shrink cycles.

Effect of industrial waste on the behaviour of expansive soil

Prediction of the free swell index of the expansive soil using artificial neural network has been presented in this paper. Input parameters for the artificial neural network model were plasticity index and shrinkage index, while the output was the free swell index. Artificial neural network algorithm used a back propagation model. Training of the artificial neural network model was conducted on the data collected from literature, and the weights and biases were obtained which described the relation among the input variables and the output free swell index. Further, the sensitivity analysis was performed, and the parameters affecting the free swell index of the expansive soil were identified. The sensitivity analysis results indicated that the plasticity index (63.97 %) followed by shrinkage index (36.03 %) was affecting the free swell index in this order. The study shows that the prediction accuracy of the free swell index of the expansive soil using artificial neural network model was quite good.

Freeze-thaw effects can significantly alter the volume of expansive soil due to the water-phase change and soil expansion. The montmorillonite content was an important factor influencing the expansibility of expansive soil. This paper investigated the micropore structure characteristics of expansive soil under freeze-thaw cycles with various montmorillonite contents. In addition, the micropore evolution of expansive soils and relationship between the unfrozen water content and temperature were also examined via X-ray diffraction (XRD) and nuclear magnetic resonance (NMR). The results indicated that: (1) the montmorillonite content affected the pore size distribution of expansive soil, and with increasing montmorillonite content, the relaxation time (T2) distribution curves changed from single-peak into double-peaks; (2) after multiple freeze-thaw cycles, the macropores in expansive soil increased and mesopore pores decreased; (3) considering the freezing point and capillary adsorption, the soil freezing characteristic curve (SFCC) could be divided into four stages, namely, unfrozen water, free water, freezing-capillary water, freezing-hydroscopic water; (4) the montmorillonite content only affected the unfrozen water content from 0°C to −5°C, while at temperatures lower than −5°C, the effect of the montmorillonite content on the unfrozen water content was negligible.

The mechanical behaviour of soil is quite complicated and depends on many factors. Expansive soils are those clayey materials which exhibit significant volume changes caused by changes in the subsoil moisture. This has been a subject of research for many years, and the advent of the numerical technique of finite element has given added impetus to these effects. A constitutive law is developed and implemented in a finite element program. The finite element technique is used to compute displacements and stresses developed in structures and soil along time of activity of the swelling. The main objective of this work is to verify the produced unified model for the swelling and shrinkage behaviour of expansive soil. To see the performance of the soil in dryness process, the computation of the heave and stress is continued after the assumed time of wetting period. The values of the heave of soil reduce after reaching a peak value. The reductions of the values of heave are different from layer to layer depending on the rate of loss of water. The main conclusions driven from the various aspects of this study are consistent with the literature findings.

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.

The development of heave and swelling pressure in the natural calcareous expansive soils in the Eastern Province of Saudi Arabia causes major damage to structures constructed on or in them. The behaviour of expansive soil depends on the predominant type of clay minerals present, the cementing agents that bind these clay minerals and other physical and chemical properties. This paper presents the problems and the geotechnical and physicochemical properties of the calcareous expansive soil deposits in the Eastern Province of Saudi Arabia. X-ray, thermal and chemical analyses and scanning electron microscopy were used to estimate the type and quantity of clay and non-clay minerals and fabric of the investigated soil. The swelling potential was determined using a conventional oedometer test. A field test conducted for measurement of heave was compared with heave estimated from laboratory- tests, Results showed that the investigated soil had moderate to very high swelling potential and the heave estimated from the suction method was very close to the value measured from the field test.

In the southwest of China, there are widely distributed expansive soils. However, to save costs and manage the speed of construction, these shallow expansive soils are often filled with subgrade materials. Therefore, it is necessary to clearly understand the mechanical behaviors of unmodified shallow expansive soils. Current research on the mechanical behaviors of shallow expansive soils is mainly focused on shear and compressive strengths but rarely on the tensile strength since general tests are costly, time consuming, and difficult to conduct. Therefore, uniaxial tensile, unconfined compression and direct shear tests were carried out to study the mechanical behavior of shallow unsaturated expansive soils under different saturation degrees, and the tests analyzed the change mechanism of its mechanical behavior. The following were found: (1) with an increase in saturation degree, the uniaxial tensile strength, unconfined compressive strength, shear strength, cohesive force, and internal friction angle first increased and then decreased; (2) when the saturation degree increased from 18.7% to the saturation degree corresponding to the peak, the uniaxial tensile strength, unconfined compressive strength, cohesive force, and internal friction angle increased by about 11 times, 3.24 times, 2.34 times, and 0.52 times, respectively; (3) when the saturation degree increased from the saturation degree corresponding to the peak to 80.3%, they decreases by about 42%, 51.4%, 36%, and 50%, respectively; (4) with the increase in dry density, the saturation degree corresponding to the peak of uniaxial tensile strength gradually increased, while the saturation degree corresponding to the peak of unconfined compressive and shear strength did not significantly change.