Plant root systems serve as a natural reinforcing material, significantly improving soil stability. Furthermore, the tensile strength of soil is crucial in mitigating the formation of cracks. Consequently, this study aims to investigate the influence of plant roots on the tensile strength of soil. For this investigation, Amorpha fruticose was selected due to its large root diameter and the ease of root extraction. Indoor tensile tests were conducted on individual roots and root-soil complexes under three varying factors. The results indicate a power law relationship between root diameter and tensile strength. Increased root content and dry density notably enhance the tensile strength of the root-soil complex while roots mitigate damage associated with soil brittleness. When root content increases from 0 to 10, the maximum enhancement in tensile strength of the root-soil complex reaches 42.3 kPa. The tensile strength of the root-soil complex at a dry density of 1.7 g/cm3 is four to five times greater than that of the complex at a dry density of 1.4 g/cm3. Moreover, as moisture content increases, the tensile strength of the root-soil complex initially rises before declining, with an increase range of 7.7-35.8 kPa. These findings provide a scientific basis for understanding the role of vegetation roots in soil tensile strength and for guiding slope reinforcement strategies.

In this paper, the EC-5 water sensor and the MPS-6 water potential sensor were used to measure water content and suction, respectively, to investigate the evolution of soil-water retention properties of compacted loess samples prepared at different dry densities and subjected to different numbers of wetting-drying cycles. The water retention data were integrated with a detailed microstructural investigation, including morphological analysis (by scanning electron microscopy) and pore size distribution determination (by nuclear magnetic resonance). The microstructural information obtained shed light on the double porosity nature of compacted loess, allowing the identification of the effects of compaction dry density and wetting-drying cycles at both intra- and inter-aggregate levels. The information obtained at the microstructural scale was used to provide a solid physical basis for the development of a simplified version of the water retention model presented in Della Vecchia et al. (Int J Numer Anal Meth Geomech 39: 702-723, 2015). The model, adapted for engineering application to compacted loess, requires only five parameters to capture the water retention properties of samples characterized by different compaction dry densities and subjected to different numbers of wetting-drying cycles. The comparison between numerical simulations and experimental results, both original and from the literature, shows that only one set of parameters is needed to reproduce the effects of dry density variation, while the variation of only one parameter allows the reproduction of the effects of wetting and drying cycles. With respect to the approaches presented in the literature, where ad hoc calibrations are often used to fit density and wetting-drying cycle effects, the model presented here shows a good compromise between simplicity and predictive capabilities, making it suitable for practical engineering applications.

The disintegration of expansive stiff clay will cause irreversible damage and deterioration of mechanical properties of the soil. The latest studies show that the disintegration is related to the swelling capacity of soil. In this study, a series of hydration disintegration tests and swelling pressure tests were performed on compacted Nanning expansive stiff clay samples with different initial water contents and dry densities. The observed disintegration process of all samples could be divided into initial, rapid and residual disintegration stages, among which the rapid stage dominated the whole process. By introducing relevant indicators to quantify the disintegration process, it was found that at a given dry density, the average disintegration rate of the sample decreased with increasing initial water content; while at a given water content, it decreased with increasing initial dry density. Such phenomena coincided well with the obtained evolution of swelling pressure at different initial water contents and dry densities. Based on these findings, the expansion-disintegration interaction mechanism of expansive stiff clay was finally analyzed from the perspectives of microstructure and hydration cracking. The initial conditions of the compacted samples determine the volume of inter-aggregates pores and thus the water transfer rate in soils, which affects the formation of hydration cracks. The cracking is induced by tension failure due to the expansion gradient formed during the hydration of sample, destructing the soil integrity to facilitate the disintegration. The disintegration, in turn provides preferential water infiltration channels to accelerate further soil expansion and hydration cracking. Such interactions proceeded until the completion of sample disintegration.

Introduction Gas migration in low-permeability buffer materials is a crucial aspect of nuclear waste disposal. This study focuses on Gaomiaozi bentonite to investigate its behavior under various conditions.Methods We developed a coupled hydro-mechanical model that incorporates damage mechanisms in bentonite under flexible boundary conditions. Utilizing the elastic theory of porous media, gas pressure was integrated into the soil's constitutive equation. The model accounted for damage effects on the elastic modulus and permeability, with damage variables defined by the Galileo and Coulomb-Mohr criteria. We conducted numerical simulations of the seepage and stress fields using COMSOL and MATLAB. Gas breakthrough tests were also performed on bentonite samples under controlled conditions.Results The permeability obtained from gas breakthrough tests and numerical simulations was within a 10% error margin. The experimentally measured gas breakthrough pressure aligned closely with the predicted values, validating the model's applicability.Discussion Analysis revealed that increased dry density under flexible boundaries reduced the damage area and influenced gas breakthrough pressure. Specifically, at dry densities of 1.4 g/cm(3), 1.6 g/cm(3), and 1.7 g/cm(3), the corresponding gas breakthrough pressures were 5.0 MPa, 6.0 MPa, and 6.5 MPa, respectively. At a dry density of 1.8 g/cm(3) and an injection pressure of 10.0 MPa, no continuous seepage channels formed, indicating no gas breakthrough. This phenomenon is attributed to the greater tensile and compressive strengths associated with higher dry densities, which render the material less susceptible to damage from external forces.

The heterogeneous constitution of municipal solid waste and problems associated with the prediction of the stability of landfills require an in-situ assessment of mechanical properties. Dynamic cone penetration (DCP) tests were conducted in-situ in seven test pits in a municipal landfill in south-western Johannesburg, and samples excavated from each test pit were used to determine other laboratory geotechnical properties. The composition of pits involves plastics, textiles, leather, metal, glass, soils, gravel, debris, wood and garden cuts, paper, cardboards and organics. The dynamic cone penetration index (DCPI) results from seven test pits revealed that the DCPI of half of the pits was in the range of 0-10 mm/blow, while the others were in the range of 10-20 mm/blow. The in-situ density of the municipal solid waste (MSW) indicates a predominantly loose to medium-density in-situ compaction state. Fibrous content and construction debris are the two dominant waste compositions. DCPI was found to decrease with a ratio of fibrous to construction debris greater than 1.0. Relationships between DCPI and products of specific gravity (Gs) and dry density from laboratory and in-situ tests are moderately correlated with coefficients of determination (r2) of 0.61 and 0.71, respectively.

Tensile strength is a crucial mechanical property that governs the initiation and propagation of soil tensile cracks. With the global prevalence of warming effects and extreme climatic events, the recurrent freeze-thaw (F-T) cycles intensify the complex evolutions of soil pore structure and tensile strength in regions with widespread seasonal freezing or permafrost active layers. This study investigates the combined influence of F-T cycles and desiccation on the tensile strength of clayey soils. Specimens with varying compaction water contents (14.5%, 16.5%, and 18.5%) and dry densities (1.5 Mg/m3, 1.6 Mg/m3, and 1.7 Mg/m3) were prepared and subjected to cyclic F-T actions. A direct tensile test apparatus was utilized to measure tensile strength (6t) along the desiccation path. Additionally, the changes in void ratio (e) and suction (s) during F-T cycles were analyzed to understand the mechanism behind the changes in 6t. Experimental results reveal that as the number of F-T cycles (N) increases, water content (w) declines at a decreasing rate and eventually stabilizes. With increasing N, the tensile displacement at failure and 6t show a pattern of initially decreasing and subsequently rising, with the inflection point typically around 1.5%-2.0% lower than the compaction water content (w0). Under a few F-T cycles, soils compacted at the optimum water content and on the wet side exhibit higher void ratio and lower suction and 6t compared with dry-side compacted soils. However, this trend reverses with further increasing N. In addition, 6t increases as compaction dry density (pd0) rises within all water content ranges, primarily attributed to the significant interparticle cohesion controlled by a dense pore structure. The variation of 6t under F-T and associated desiccation is linked with the microstructural evolution characterized by aggregates, interaggregate pores and water-bridges. It is recommended to compact soils both on the dry side of the optimum water content and at the maximum dry density to enhance the freeze-thaw resistance of earth-works in seasonally frozen regions.

Using traditional materials to improve the permeability of silty soils can cause irreversible damage to the environment. Therefore, it is necessary to develop environmentally friendly biopolymers, such as xanthan gum (XG), to replace traditional materials to improve resistance to water erosion by reducing the permeability coefficient. In this study, a series of permeability tests and scanning electron microscope (SEM) tests were conducted on xanthan gum-improved silty soil (XGS). The variations in the permeability coefficient of XG-improved silty soil and the effects of initial dry density, XG-soil ratio, and curing age on the permeability were investigated. Test results show that the permeability coefficient of XGS decreased with the increase of initial dry density, XG-soil ratio, and curing age. With increasing the initial dry density, soil particles compressed against each other, decreasing the actual water flow crossing area, which leads to a decrease in the permeability coefficient. With the increase of the XG-soil ratio, the fill-blocking effect of xanthan gum with hydrogel connections becomes more and more obvious, which leads to a reduction in the permeability coefficient. Xanthan gum hydration takes time, and a lot of crystals are produced in XGS as the curing age increases; these crystals fill larger pores, resulting in the permeability coefficient decrease. At last, a model was developed to predict the permeability coefficient of XG-improved silty soil by using the initial dry density, XG-soil ratio, and curing age. The model can be used to rapidly predict the permeability coefficient of the improved silty soil under different conditions. This research can provide a scientific basis for the safe and scientific application of xanthan gum in seepage damage control and prevention projects.

In the cold region, frost heave damage in water conveyance channels constructed on expansive soil poses a significant threat to project sustainability. This study aims to investigate the evolution and physical mechanisms of frost heave inhibition by soilbags for expansive soils with varying water contents and dry densities. Standard calibration tests for sample preparation and frost heave deformation tests were conducted on expansive soils with and without soilbag constraints. The test results demonstrate a direct correlation between the compaction height of the sample and its dry density, enabling precise control of the dry density by adjusting the compaction height. Regardless of the presence of soilbag constraints, the relationship between frost heave deformation and time can be divided into three stages: cold shrinkage, rapid freezing and freezing stability. The frost heave of the expansive soil was significantly reduced under the restraint of the bag for samples with the same initial state, indicating that the soilbag can effectively inhibit the frost heave of the expansive soil. Moreover, as water content and dry density increased, the frost heave rate of the samples exhibited a significant increase. The frost heave inhibition rate of the soilbag increased significantly with the increase of dry density, but it did not increase notably with increasing water content. The intrinsic mechanism of soilbag inhibiting frost heave of expansive soil is revealed using the theory of segregation potential and the principle of reinforcement constraint. A conceptual model of the skeleton structure of frozen expansive soil under the influence of soilbag constraints is proposed, based on the pore diameter distribution curve obtained through mercury intrusion porosimetry. This model better explains the variations in the evolution of frost heave inhibition rates of soilbags under different water contents and dry densities.

The study focused on investigating the influence of dry density and load level on the wetting creep deformation of soil-rock mixture. A total of 9 groups of compression creep tests were conducted on the soil-rock mixture under a dry-wet cycle. The results revealed that the wetting creep deformation of the soil-rock mixture increased with higher load levels and decreased significantly with increasing dry density. However, as the dry density further increased, the decrease in wetting creep deformation became less pronounced. The relationship between wetting creep deformation and the logarithm of the number of dry-wet cycles followed a linear development pattern for the soil-rock mixture under the dry-wet cycle conditions. The initial wetting strain and wetting creep rate were found to have power function distribution relationships with the load level and dry density. Based on these findings, an empirical model for the dry-wet cycle creep behavior of the soil-rock mixture was proposed. This model takes into consideration different dry densities and load levels, providing a framework for predicting and understanding the creep deformation of the soil-rock mixture under such conditions.

Soil stabilization is critical in construction, impacting the stability and longevity of infrastructure. Traditional materials such as cement, lime and fly ash have long been used for this purpose. Previous research has demonstrated the effectiveness of cement and lime for stabilizing clayey soils. This study builds on that foundation by investigating the innovative use of sugarcane bagasse ash (BA), an agricultural by-product, as a sustainable alternative for soil improvement. BA and lime were added to clayey soil in varying proportions (0%, 4%, 8% and 12% by dry weight) to assess their impact. Geotechnical tests, including Proctor compaction, unconfined compressive strength (UCS) and California Bearing Ratio (CBR) tests, were performed on both unstabilized and stabilized soil samples, with each test repeated three times for accuracy. The results showed that adding BA and varying lime contents significantly improved the soil's maximum dry density (MDD) and UCS, with specific mixtures yielding peak values. The UCS of the stabilized soil increased by 300% to 400% compared to unstabilized soil, while CBR values improved by 61.32% in soaked conditions and 50% in unsoaked conditions. These enhancements suggest that BA and lime mixtures can effectively improve the performance of clayey soils in construction, potentially reducing dependence on conventional materials. The chemical interaction between lime and BA likely contributes to this improvement through pozzolanic reactions, forming cementitious compounds that enhance soil strength and stability. Of all the combinations, the combination of 8% BA and 12% lime provided the greatest improvements in MDD, optimum moisture content (OMC), CBR and UCS. This research not only addresses environmental concerns regarding waste disposal but also aims to optimize soil properties, contributing to safer, more durable infrastructure while promoting sustainability.