Lime-activated ground granulated blast furnace slag (GGBS) is usually used to treat gypseous soils. However, sulphate-bearing soils often contain other sulphates, e.g., sodium sulphate (Na2SO4), potassium sulphate (K2SO4) and magnesium sulphate (MgSO4). Therefore, in this study, lime-GGBS was used as a curing agent for stabilising four sulphate-bearing soils, which were named as Na-soil, K-soil, Mg-soil, and Ca-soil. Unconfined compressive strength (UCS), swelling, X-ray diffraction, scanning electron microscopy and inductively coupled plasma spectroscopy tests, were conducted to explore the macro- and micro-properties of the lime-GGBS-stabilised soils. The results showed that at 5000 ppm sulphate, stabilised Mg-soil had the lowest swelling and highest UCS. At 20,000 ppm sulphate, stabilised Ca-soil had the lowest swelling, while stabilised Na-soil had the highest UCS. Generally, increasing sulphate concentration decreased swelling for Ca-soil but increased for other three soils, and decreased UCS for Mg-soil but increased for other three soils. This was because less ettringite was generated in the stabilised Ca-soil and the formation of magnesium silicate hydrate (MSH) in the stabilised Mg-soil. Therefore, the sulphate type had a significant impact on the swelling and strength properties of lime-GGBS-stabilised sulphate-bearing soil. It is essential to identify the sulphate type before stabilising the soil on-site.

To study the degree of strength parameter deterioration (DSPD) of Lushi swelling rock in the high slope area under wetting-drying cycles, 114 samples are remodeled. Wetting-drying cycle and triaxial tests are conducted to comprehensively analyze the influence of dry density, wetting-drying cycle path, and number of wetting-drying cycles on the strength deterioration characteristics of Lushi swelling rock. Using the fitting analysis and function superposition methods, the DSPD model of Lushi swelling rock under wetting-drying cycles is established, which considers the previous four influencing factors. The influence of the DSPD of Lushi swelling rock on the stability of high slopes under rainfall seepage and circulation conditions is studied. Lushi swelling rock exhibits significant strength deterioration characteristics under wetting-drying cycles. The overall DSPD for cohesion is higher than that of the internal friction angle. Under rainstorm conditions, strength deterioration leads to a shallower depth of the critical slip surface of the slope and a smaller safety factor. After eight rounds of rainfall seepage and circulation, the safety factor gradually decreases by approximately 14%-28%. This study provides and verifies the DSPD model of Lushi swelling rock under wetting-drying cycles, and the results could provide a basis for disaster prediction and the optimization design of swelling rock slopes.

Conventional in-situ light non-aqueous phase liquid (LNAPL) remediation techniques often face challenges of high costs and limited efficiency, leaving residual hydrocarbons trapped in soil pores. This study investigates the efficiency of an alcohol-in-biopolymer emulsion for enhancing diesel-contaminated soil remediation. The emulsion, formulated with xanthan gum biopolymer, sodium dodecyl sulfate surfactant, and the oil-soluble alcohol 1-pentanol, was evaluated through rheological tests, interfacial tension measurements, and onedimensional sand-column experiments under direct injection and post-waterflooding scenarios. The emulsion exhibited non-Newtonian shear-thinning behavior with high viscosity, ensuring stable propagation and efficient delivery of 1-pentanol to mobilize trapped diesel ganglia. It achieved 100 % diesel recovery within 1.2 PV during direct injection, outperforming shear-thinning polymer-only and polymer-surfactant solutions, which achieved recovery factors of 83.4-92.9 %. Post-waterflooding experiments also demonstrated 100 % diesel recovery within 1.3 PV, regardless of initial diesel saturation. Key mechanisms include reduced interfacial tension, diesel swelling and mobilization induced by 1-pentanol, and uniform displacement facilitated by the emulsion's viscosity. Additionally, the emulsion required lower injection pressures compared to more viscous alternatives, enhancing its injectability into the soil and reducing energy demands. These findings highlight the emulsion's potential to overcome conventional remediation limitations, offering a highly effective and sustainable solution for diesel-contaminated soils and groundwater.

A common physical technique assessed for improving expansive clays is by the addition of natural fibres to the soil. A good understanding of the impact of stabilisation using fibres on the clay soil's constituents, microfabric, and pore structure is, however, required. Mixtures of clay and fibre, regardless of type or extent, can never change the natural composition of the clay. Even the smallest part must still consist of spaces with clay with the original physical properties and mineralogy. This suggests that, although the mixture may show beneficial physical changes over the initial clay soil, its spatial attributes in terms of mineralogical characteristics, remain unchanged. This paper discusses some of the fundamentals that are not always adequately considered or addressed in expansive clay research, aiming to improve the focus of current and future research investigations. These include the process, mechanics, and implications of chemical and physical soil treatment as well as the concept of moisture equilibration.

To overcome the limitations of microscale experimental techniques and molecular dynamics (MD) simulations, a coarse-grained molecular dynamics (CGMD) method was used to simulate the wetting processes of clay aggregates. Based on the evolution of swelling stress, final dry density, water distribution, and clay arrangements under different target water contents and dry densities, a relationship between the swelling behaviors and microstructures was established. The simulated results showed that when the clay-water well depth was 300 kcal/mol, the basal spacing from CGMD was consistent with the X-ray diffraction (XRD) data. The effect of initial dry density on swelling stress was more pronounced than that of water content. The anisotropic swelling characteristics of the aggregates are related to the proportion of horizontally oriented clay mineral layers. The swelling stress was found to depend on the distribution of tactoids at the microscopic level. At lower initial dry density, the distribution of tactoids was mainly controlled by water distribution. With increase in the bound water content, the basal spacing expanded, and the swelling stresses increased. Free water dominated at higher water contents, and the particles were easily rotated, leading to a decrease in the number of large tactoids. At higher dry densities, the distances between the clay mineral layers decreased, and the movement was limited. When bound water enters the interlayers, there is a significant increase in interparticle repulsive forces, resulting in a greater number of small-sized tactoids. Eventually, a well-defined logarithmic relationship was observed between the swelling stress and the total number of tactoids. These findings contribute to a better understanding of coupled macro-micro swelling behaviors of montmorillonite-based materials, filling a study gap in clay-water interactions on a micro scale. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

This experimental study is to find a solution to reduce the amount of waste and at the same time improve the geotechnical properties of fine soils. Compaction, odometer, direct shear tests, and unconfined compression tests were carried out on a clay with a very high degree of plasticity mixed with 0%, 10%, 20%, 30%, and 40% of recycled concrete aggregates (RCA). The addition of concrete aggregates to the clayey soil shows an increase in the maximum dry density and a reduction in the optimum water content. The odometer tests results showed that the increase in the recycled material content leads to a decrease in the compression index, swelling index and creep index. On the other hand, the pre-consolidation stress, the odometric modulus, the consolidation coefficient and the permeability coefficient increase with increasing RCA content. According to the direct shear test, the higher RCA content provided an improvement in shear strength which is accompanied by an increase in the dilatant character. For different curing times and for a content of 10% recycled concrete aggregate, the unconfined compressive strength increased compared to the untreated soil.

Due to economic and demographic growth, there is a rising demand for land reclamation in coastal cities of East and Southeast Asia. Marine clays typically play a critical role in these projects, and the deformation characteristics of marine clays become a crucial problem in terms of the quality of the subsoil conditions. The long-term loading behavior of marine clays has been studied by many researchers. However, relatively few studies have been done on the unloading behavior of these clays after preloading; and thus, the strain rate dependency on the unloading behavior of marine clays remains unclear. The aim of this study was to accumulate experimental data on the unloading behavior of marine clays and to develop a strain rate-based model for improving the accuracy of the predictions of the swelling behavior of marine clays during unloading. The authors conducted a series of constant rate of strain (CRS) consolidation tests from loading to unloading, and long-term unloading oedometer tests on Ariake clay, which is a well-known sensitive marine clay, to observe the swelling behavior during in unloading. The preloading time, corresponding to different strain rates at the end of preloading, was controlled to elucidate the effect of the stress history. Moreover, instead of parameter r ' p (preconsolidation pressure) for the normal consolidation visco-plastic behavior, the authors developed and proposed a new visco-plastic model by introducing the concept of a plastic rebound boundary and a new parameter R for swelling behavior during unloading. Parameter R represents the normalized distance from the current stress state to the plastic rebound boundary in logarithmic effective consolidation stress. Therefore, the visco-plastic model for the behavior in the loading stage was developed into the swelling visco-plastic behavior in the unloading stage for Ariake clay. Comparing the simulation and test results, the simplified visco-plastic swelling model was found to agree well with the test results. (c) 2025 Published by Elsevier B.V. on behalf of Japanese Geotechnical Society. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

With the increasing emphasis on environmental protection and sustainable economic development, recycling industrial by-products for soil improvement has received increasing attention in geotechnical engineering. Lignin fiber, a by-product of the paper industry, has the advantages of good flexibility and dispersion, etc. Given these advantages of lignin fiber, this paper uses lignin fiber to improve expansive soils' strength and swell-shrink characteristics, then carries out a series of experiments to evaluate the effect of the improvement. Soil specimens with 0%, 1%, 2%, and 4% doped lignocellulosic fibers were prepared indoors, and these specimens were subjected to the unconfined compressive strength test, the consolidated undrained triaxial shear test, the unloaded expansion rate test, and the shrinkage test. The mechanism of lignin fiber's action in improving expansive soil was revealed by X-ray diffraction test (XRD) and scanning electron microscope test (SEM). XRD and SEM tests have shown that lignin fibers act as a ''bridge'' lap and fiber web in the soil. The ''bridge'' lap connects the soil particles and enhances the connecting force between the soil particles. The fiber mesh gives the soil a good stress structure and limits the sliding of the soil particles to a certain extent. The value of unconfined compressive strength of expansive soils is maximum under 2% content of lignin fibers with an increase of 54%. Under 4% content of lignin fibers, the expansion soil had the least unloaded expansion rate, which was reduced by 32.8%. Combining all the test results, it was obtained that expansive soil was best modified with 2% lignin fiber content. In conclusion, using lignin fiber as an additive to modified expansive soil is viable and can lead to resource recycling.Graphical AbstractAdequate amount of lignin fiber, in the soil body can play a bridge lap and fiber web role. The bridge lap can connect the soil particles together, enhance the connection between soil particles, so that the soil body to form a stable structure. The fiber web gives the soil body a good stress structure, which can evenly spread the load to other regions of the soil body. The fiber web restricts the sliding of the soil particles to a certain extent, which can enhance the friction of the soil body. However, Excessive lignin fibers tend to collect into clusters within the soil body, separating the soil particles, which tends to form weak surfaces within the soil body, and the presence of weak surfaces affects the overall stability of the soil body.

Sodium hydroxide (NaOH)-sodium silicate-GGBS (ground granulated blast furnace slag) effectively stabilises sulfate-bearing soils by controlling swelling and enhancing strength. However, its dynamic behaviour under cyclic loading remains poorly understood. This study employed GGBS activated by sodium silicate and sodium hydroxide to stabilise sulfate-bearing soils. The dynamic mechanical properties, mineralogy, and microstructure were investigated. The results showed that the permanent strain (epsilon(p)) of sodium hydroxide-sodium silicate-GGBS-stabilised soil, with a ratio of sodium silicate to GGBS ranging from 1:9 to 3:7 after soaking (0.74%-1.3%), was lower than that of soil stabilised with cement after soaking (2.06%). The resilient modulus (E-d) and energy dissipation (W) of sodium hydroxide-sodium silicate-GGBS-stabilised soil did not change as the ratio of sodium silicate to GGBS increased. Compared to cement (E-d = 2.58 MPa, W = 19.96 kJ/m(3)), sulfate-bearing soil stabilised with sodium hydroxide-sodium silicate-GGBS exhibited better E-d (4.84 MPa) and lower W (15.93 kJ/m(3)) at a ratio of sodium silicate to GGBS of 2:8. Ettringite was absent in sodium hydroxide-sodium silicate-GGBS-stabilised soils but dominated pore spaces in cement-stabilised soil after soaking. Microscopic defects caused by soil swelling were observed through microscopic analysis, which had a significant negative impact on the dynamic mechanical properties of sulfate-bearing soils. This affected the application of sulfate-bearing soil in geotechnical engineering.

This study introduces a novel method for stabilising expansive subgrade soils by integrating microbially induced calcite precipitation (MICP) process with a synergistic combination of waste sugarcane bagasse and recycled polyester fibres. This innovative approach aims to enhance strength properties and reduce volume susceptibility. The study demonstrates increases in Unconfined Compressive Strength (UCS), Split Tensile Strength (STS), and California Bearing Ratio (CBR), while substantially decreasing linear shrinkage, swell strains and pressures, indicating improved soil stability. The study also investigates the microstructural and chemical transformations through SEM-EDS, FTIR, and DSC-TGA, further corroborated by 16S metagenomic sequencing to understand microbial dynamics. Optimal stabilisation results were obtained with 0.5% fibre content and a four-day mellowing period, enhancing soil structure and durability by calcite precipitation and leveraging the combined benefits of natural and synthetic fibres. These fibres strengthen the soil structure and facilitate calcite nucleation, ensuring lasting stability, particularly valuable for stabilising expansive subgrade soils.