Transversely isotropic rocks (TIRs) are widespread in geological formations, and understanding their mechanical behavior is crucial for geotechnical and geoengineering applications. This study presents the development of a novel analog material that reproduces the directional mechanical properties of TIRs. The material is composed of quartz sand, mica flakes, and gelatin in adjustable proportions, allowing control over strength and stiffness anisotropy. Uniaxial compressive strength (UCS) and direct shear tests were conducted to evaluate mechanical responses across different anisotropy angles. Results show that the analog material replicates key features of natural TIRs, including directional variations in strength and fracture modes. In UCS tests, the anisotropy angle (beta) governs the transition between tensile and shear failure. In direct shear tests, the orientation angle (alpha) significantly affects shear strength. Higher gelatin concentrations increase cohesion and Young's modulus without changing the internal friction angle, while mica content reduces overall strength and stiffness. Comparisons with published data on sedimentary and metamorphic rocks confirm the mechanical representativeness of the material. Its simplicity, tunability, and reproducibility make it a useful tool for scaled physical modeling of anisotropic rock behavior in the laboratory. This approach supports the experimental investigation of deformation and failure mechanisms in layered rock masses under controlled conditions.

This paper aims to investigate the tunnelling stability of underwater slurry pressure balance (SPB) shields and the formation and evolution mechanisms of ground collapse following face instability. A laboratory SPB shield machine was employed to simulate the entire tunnelling process. Multi-faceted monitoring revealed the responses of soil pressure, pore water pressure, and surface subsidence during both stable and unstable phases. The morphological evolution characteristics of surface collapse pits were analyzed using three-dimensional scanning technology. The experimental results indicate that: (1) The key to stable tunnelling is balancing the pressure in the slurry chamber with the tunnelling speed, which ensures the formation of a filter cake in front of the cutterhead. (2) The torque of the cutterhead, soil pressure, and surface subsidence respond significantly and synchronously when the tunnel face becomes unstable, while the soil and water pressures are relatively less noticeable. (3) Excavation disturbance results in a gentler angle of repose and a wider range of collapse in the longitudinal direction of the collapsed pit. (4) A formula for predicting the duration of collapse is proposed, which effectively integrates the evolution patterns of the collapse pit and has been well-validated through comparison with the experimental results. This study provides a reference for the safe construction of tunnel engineering in saturated sand.

Flow instability impacts negatively on hydraulic structures. Changes in water pressure or the periodic impact of water flows cause structural damage to channels. The rapid increase in water depth leads to overflows or sprays, which erode soil adjacent to channels. In this study, flow instability was examined through the basis of theories and experiments. The theoretical discriminants for flow instability were inferred by Vedernikov number and the effect of slopes on the Froude number was considered. A rectangular cross- channel was selected for the experiments. The experimental results were compared with theories, it was shown that when the flow conditions were on the margin of instability, the discriminant established by this study is able to accurately determine the occurrence of instability. Through this new discriminant, the discrepancy which appears in traditional method can be avoided. The presented results are ideal for channel design and offer new approaches for flow instability prevention.

Climate change increases the frequency of extreme weather events, intensifying shallow flow-type landslides, soil erosion in mountainous regions, and slope failures in coastal areas. Vegetation and biopolymers are explored for ecological slope protection; however, these approaches often face limitations such as extended growth cycles and inconsistent reinforcement. This study investigates the potential of filamentous fungi and wheat bran for stabilizing loose sand. Triaxial shear tests, disintegration tests, and leachate analyses are conducted to evaluate the mechanical performance, durability, and environmental safety of fungus-treated sand. Results show that the mycelium enhances soil strength, reduces deformation, and lowers excess pore water pressure, with a more pronounced effect under undrained than drained conditions. Mycelium adheres to particle surfaces, forming a durable bond that increases cohesion and shifts the slope of the critical state line, significantly enhancing the mechanical stability of fungus-treated sand. The resulting strength parameters are comparable to those of soils reinforced with plant roots. Fungus-treated sand remains stable after 14 days of water immersion following triaxial shear tests, with no environmental risk from leachate. These findings demonstrated that fungal mycelium provides an effective and eco-friendly solution for stabilizing loose sand, mitigating shallow landslides, and reinforcing coastlines.

This paper presents an experimental investigation into the interaction mechanism between aqueous foam and unsaturated granite residual soil during conditioning. Contact filter paper tests and undrained shear tests were used to analyze foam's effects on soil water retention and shear behavior, while surface tension tests, capillary rise tests, and microscopic observations examined the role of soil particles in foam stability. The findings demonstrate that foam-conditioned granite residual soils exhibit three distinct saturation- dependent phases (soil-only, transition, and soil-foam mixture) governed by foam's gas-liquid biphasic nature, with foam injection effectively reducing matric suction in unsaturated conditions. Increasing foam injection ratio reduces shear stress while enhancing pore water pressure, with vertical displacement transitioning from contractive to expansive behavior at low shearing rate. Effective cohesion stress varies with gravimetric water content via a rational function, while other effective cohesion stress and friction angles with respect to foam injection ratio, shearing rate, and gravimetric water content obey exponential relationships. The probability distribution function, cumulative distribution function, and decay pattern of bubbles in foam-only systems and soil-foam mixtures all exhibit exponential relationships with elapsed time. Furthermore, a new water-meniscus interaction model was established to characterize rupture and stabilization mechanisms of foam in unsaturated granite residual soils, with particular emphasis on capillary-dominated behavior. Saturation-dependent particle contact modes were identified for foam-conditioned unsaturated granite residual soils, offering valuable guidance for enhancing soil conditioning protocols in earth pressure balance shield tunneling operations.

The widespread utilisation of vacuum-assisted prefabricated vertical drains (PVD) for managing clayey soft ground has led to the development of numerous consolidation models. However, these models have limitations when describing the filtration behaviour of soil under high water content conditions, without the formation of a particle network. To effectively address this issue, in this work, based on the compressional rheology theory, a two-dimensional axisymmetric model incorporating the compressive yield stress Py(phi) and a hindered setting factor r(phi) was developed to couple the filtration and consolidation of soil under vacuum preloading. A novel approach for determining the unified phi-Py-r relationships was introduced. The equation governing such fluid/solid and solid/solid interactions was solved using the alternative direction implicit (ADI) method, and the numerical solutions were validated against the 1-D filtration cases, 3-D laboratory model tests, and large-scale field trials. Further parametric analysis suggests that the radius of the representative unit and r(phi) exclusively affect the dewatering rate of the clayey slurry, while the gel point and Py(phi) influence both the dewatering rate and the final deformation.

Soils are generally considered anisotropic with respect to hydraulic conductivity, while the evolution of anisotropy condition is unknown for bare and vegetated soils. Therefore, the main goal of this study is to compare the anisotropic hydraulic conductivity of as-compacted, bare, and vegetated specimens. Accordingly, a series of 54 hydraulic conductivity tests were conducted in a custom-made cube triaxial permeameter. The as-compacted specimens were revealed isotropic because the loosely packed preparation procedure resulted in a dominant flocculent structure. However, a fivefold increase in the anisotropy ratio of bare specimens was measured along the isotropic loading path because of the induced surficial degradation zone formed by irrigation and desiccation processes as evident in preliminary observations and crack network analysis. The variations in anisotropy ratio vs. void ratio function of vegetated soil generally fall below the corresponding function of the bare soil. The function was revealed to have a crossed nature, varying from sub-isotropic to super-isotropic states, corresponding to the lower and upper bounds of 0.3 and 3, respectively. It was postulated that vegetation impacts the flow differently by reducing the potential of desiccation cracks, creating preferential flow through the propagation of primary roots and clogging flow channels by secondary roots.

Thermal damage mechanisms are crucial in reservoir stimulation for enhanced geothermal system (EGS). This study investigates the thermal damage mechanisms in granite samples from the Gonghe Basin, Qinghai, China. The granite samples were heated to 400 degrees C and then cooled in air, water, or liquid nitrogen. The physical and mechanical properties of the thermally treated granite were evaluated, and microstructural changes were analyzed using a scanning electron microscope (SEM) and computed tomography (CT). The results indicate that cooling with water and liquid nitrogen significantly enhances permeability and brittleness while reducing P-wave velocity, strength, and Young's modulus. Specifically, liquid nitrogen cooling increased granite permeability by a factor of 5.24 compared to the untreated samples, while reducing compressive strength by 13.6%. After thermal treatment, the failure mode of the granite shifted from axial splitting to a combination of shear and tension. Microstructural analysis revealed that liquid nitrogen-cooled samples exhibited greater fracture complexity than those cooled with water or air. Additionally, acoustic emission (AE) monitoring during damage evolution showed that liquid nitrogen cooling led to higher cumulative AE energy and a lower maximum AE energy rate, with numerous AE signals detected during both stable and unstable crack growth. The results suggest that liquid nitrogen induces a stronger thermal shock, leading to more significant thermal damage and promoting the development of a complex fracture network during EGS reservoir stimulation. This enhances both the heat exchange area and the permeability of the deep hot dry rock (HDR) in EGS reservoirs. The insights from this study contribute to a deeper understanding of thermal damage characteristics induced by different cooling media and provide valuable guidance for optimizing deep geothermal energy extraction. (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 license (http://creativecommons.org/licenses/by/4.0/).

Significant movement of in-situ retaining walls is usually assumed to begin with bulk excavation. However, an increasing number of case studies show that lowering the pore water pressures inside a diaphragm wall-type basement enclosure prior to bulk excavation can cause wall movements in the order of some centimeters. This paper describes the results of a laboratory-scale experiment carried out to explore mechanisms of in situ retaining wall movement associated with dewatering inside the enclosure prior to bulk excavation. Dewatering reduces the pore water pressures inside the enclosure more than outside, resulting in the wall moving as an unpropped cantilever supported only by the soil. Lateral effective stresses in the shallow soil behind the wall are reduced, while lateral effective stresses in front of the wall increase. Although the associated lateral movement was small in the laboratory experiment, the movement could be proportionately larger in the field with a less stiff soil and a potentially greater dewatered depth. The implementation of a staged dewatering system, coupled with the potential for phased excavation and propping strategies, can effectively mitigate dewatering-induced wall and soil movements. This approach allows for enhanced stiffness of the wall support system, which can be dynamically adjusted based on real-time displacement monitoring data when necessary.

Recent years have witnessed a burgeoning interest in sustainable, eco-friendly, and cost-effective construction materials for civil engineering projects. Soilcrete, an innovative blend of soil and cement, has gained significant acclaim for its versatility and effectiveness. It serves not only as grout for soil stabilization in corrosive environments like landfills and coastal regions but also as a reliable material for constructing structural elements. Understanding the mechanical properties of soilcrete is crucial, yet traditional laboratory tests are prohibitively expensive, time-consuming, and often imprecise. Machine learning (ML) algorithms present a superior alternative, offering efficiency and accuracy. This research focuses on the application of the adaptive neuro-fuzzy inference system (ANFIS) algorithm to predict the uniaxial compressive strength (UCS) of soilcrete. A total of 300 soilcrete specimens, crafted from two types of soil (clay and limestone) and enhanced with metakaolin as a pozzolanic additive, were meticulously prepared and tested. The dataset was divided, with 80% used for training and 20% for testing the model. Eight parameters were identified as key determinants of soilcrete's UCS: soil type, metakaolin content, superplasticizer content, shrinkage, water-to-binder ratio, binder type, ultrasonic velocity, and density. The analysis demonstrated that the ANFIS algorithm could predict the UCS of soilcrete with remarkable accuracy. By combining laboratory results with ANFIS model predictions, the study identified the optimal conditions for maximizing soilcrete's UCS: 11% metakaolin content, a 0.45 water-to-binder ratio, and 1% superplasticizer content.