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 novel approach to enhance wellbore stability was put forth, based on the wellbore rock properties and instability mechanism of the hydrate reservoir, given the issue of wellbore instability when using water-based drilling fluids (WBDFs) in drilling operations, in weakly cemented muddy fine silt reservoirs of natural gas hydrates in the South China Sea. Three main strategies were used to increase the stability of reservoirs: enhancing the underwater connection between sandstone particles and clay minerals, preventing clay hydration from spreading and expanding, and strengthening the stability of hydration skeleton structure. An appropriate drilling fluid system was built with soil phase containing wellbore stabilizer. Sulfonic acid groups and electrostatic interaction were introduced based on the characteristics of underwater adhesion of mussels. Through the process of free radical polymerization, a zwitterionic polymer containing catechol groups named DAAT was prepared for application in natural gas hydrate reservoir drilling. DAAT is composed of tannic acid (TA), dimethyl diallyl chloride ammonium chloride (DMDAAC), 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and acrylamide (AM). Experimental results from mechanical property testing reveal an adhesion force of up to 4206 nN between SiO2 and 5 wt % DAAT, demonstrating its ability to bind quartz sand particles effectively. The compressive strength and cohesion of the cores treated with DAAT increased by 58.33 wt % and 53.26 wt %, respectively, at -10 degrees C, compared with pure ice particle cores. This demonstrates DAAT can significantly enhance the compressive strength and cohesion of the core. Furthermore, the adhesion force between DAAT and hydrate particles reaches up to 344.4 mN/m, significantly improving the structural stability between hydrate particles. It demonstrates excellent adhesive properties to hydrate particles. In addition to adsorbing clay minerals, rocks, and hydrate particles, DAAT also forms hydrogen bonds with argillaceous fine silt particles with its low temperature cohesiveness characteristic. As a result, it improves the cohesion between core particles, and enhances the adhesion between hydrates and rocks, thereby enhancing the stability of hydrate reservoirs. In summary, DAAT is characterized by a simple preparation process, cost-effectiveness, and environmental friendliness. It is an innovative and practical material for enhancing wellbore stability in WBDFs for natural gas hydrate exploration in the South China Sea.

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.

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.

Fracture toughness and cohesive fracturing properties of two classes of sandy-clay soils, (A) with fine and (B) coarse grains and stabilized with low (2%) and high (10%) cement (as soil stabilizer), were investigated using a chevron-notched semicircular bend (CN-SCB) sample under static and cyclic loads. The samples with coarser grains and higher amounts of cement stabilizer showed higher KIc compared to the soils containing low cement and fine grains. A noticeable reduction in KIc was also observed under cyclic loading compared to the monotonic loading. Load-crack opening displacement (COD) graphs obtained during cyclic loading showed high plastic deformation accumulation before the final fracture. The cycles required for the fatigue crack growth of the Class A soil were noticeably (three to six times) higher than the Class B. The FRANC2D nonlinear simulations, cohesive fracture analyses, and maximum stress theory were utilized for estimating the critical crack length and the onset of cohesive unstable crack propagation.

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.

The accumulation or landfill of lithium slag will contaminate the surrounding soil and water quality with residual sulfides and harmful elements, causing serious environmental hazards. This study aims to use Lithium slag (LS) as a sustainable alternative for silica flour (SF) in high-temperature cementing and examines the effects of this substitution on the microstructural and mechanical properties of cement pastes. The results show that an appropriate amount of LS can reduce the permeability of oil well cement and increase its high temperature compressive strength. Compared with pure paste (RS), the compressive strength of the sample replaced by 30 % LS increased by 87.8 % and the permeability decreased by 57.1 % after 28 days of high temperature curing. From the phase point of view, the samples supplemented with LS can form Xonotlite and Katoite with dense structure and high temperature stability. These hydration products can reduce the matrix porosity and permeability, increase the matrix density, and effectively improve the compressive strength of the cement pastes. In addition, the environmental effect analysis showed that the leaching toxicity and radioactivity of the sample did not exceed the standard requirements. This study provides a new direction for the sustainable utilization of LS resources, which not only combats the environmental pollution caused by LS accumulation, but also reduces the cost of cementing materials.