Waste red layers have the potential to be used as supplementary cementitious materials after calcination, but frequent and long-term dry-wet cycling leads to deterioration of their properties, limiting their large-scale application. In this study, the feasibility of using calcined red layers as cement replacement materials under dry-wet cycling conditions was analyzed. The damage evolution and performance degradation of calcined red layer-cement composites (RCC) were systematically evaluated via the digital image correlation (DIC) technique, scanning electron microscopy (SEM) analysis and damage evolution mode. The results show that the calcined red layer replacement ratio and number of dry-wet cycles affect the hydration and pozzolanic reactions of the materials and subsequently affect their mechanical properties. Based on the experimental data, a multiple regression model was developed to quantify the combined effects of the number of dry-wet cycles and the replacement ratio of the calcined red layer on the uniaxial compressive strength. As the number of dry-wet cycles increases, microcracks propagate, the porosity increases, and damage accumulation intensifies. In particular, at a high substitution ratio, the material properties deteriorate further. The global strain evolution process of a material can be accurately tracked via DIC technology. The damage degree index is defined based on strain distribution law, and a damage evolution model was constructed. At lower dry-wet cycles, the hydration reaction has a compensatory effect on damage. The pozzolanic reaction of the calcined red layer resulted in an increase in the number of dry-wet cycles. The RCC samples with high replacement ratios show significant damage accumulation with fast damage growth rates at lower stress levels. The model reveals the nonlinear effects of dry-wet cycling and the calcined red layer replacement ratio on damage accumulation in RCC. The study findings establish a scientific foundation for the resource utilization of abandoned red layers and serve as a significant reference for the durability design of materials in practical engineering applications.

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/).

Aiming at mitigating the high risks associated with conventional explosive blasting, this study developed a safe directional fracturing technique, i.e. instantaneous expansion with a single fracture (IESF), using a coal-based solid waste expanding agent. First, the mechanism of directional fracturing blasting by the IESF was analyzed, and the criterion of directional crack initiation was established. On this basis, laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF. The results indicate that the IESF presents an excellent directional fracturing effect, with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces. Moreover, during concrete fracturing tests, the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the non-fracturing direction, respectively. Finally, the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine. The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation, achieving an average cutting rate and maximum roadway deformation of 94% and 197 mm, respectively. These on-site test results verified its excellent directional rock fracturing performance. The IESF technique, which is safe, efficient, and green, has considerable application prospects in the field of rock mechanics and engineering. (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/).

Polyurethane foam, when used as a compressible layer in deep soft rock tunnels, offers a feasible solution to reduce the support pressure on the secondary lining. The foam spraying method using sprayed polyurethane material is convenient for engineering applications; however, the compressive behaviour and feasibility of sprayed polyurethane material as a compressible layer remain unclear. To address this gap, this study conducts uniaxial compression tests and scanning electron microscope (SEM) tests to investigate the compressive behaviour of the rigid foams fabricated from a self-developed polyurethane spray material. A peridynamics model for the composite lining with a polyurethane compressible layer is then established. After validating the proposed method by comparison with two tests, a parametric study is carried out to investigate the damage evolution of the composite lining with a polyurethane compressible layer under various combinations of large deformations and compressible layer parameters. The results indicate that the polyurethane compressible layer effectively reduces the radial deformation and damage index of the secondary lining while increasing the damage susceptibility of the primary lining. The thickness of the polyurethane compressible layer significantly influences the prevention effect of large deformation-induced damage to the secondary lining within the density range of 50-100 kg/m3. In accordance with the experimental and simulation results, a simple, yet reasonable and convenient approach for determining the key parameters of the polyurethane compressible layer is proposed, along with a classification scheme for the parameters of the polyurethane compressible layer. (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/).

The freeze-thaw damage of cementitious coarse grained fillings (CCGFs) significantly affects the firmness, stability, and durability of high-speed railway subgrades. It is favorable to employ geopolymer binders to improve the engineering performance of coarse grained fillings (CGFs), further ensure the safety of high-speed railway subgrades in cold regions due to their excellent mechanical and environmental-friendly performances. This study conducted a series of freeze-thaw and mechanical tests on geopolymer stabilized coarse grained fillings (GSCGFs). The influence of gradation, compaction degree, and freeze-thaw cycles on the integrity, strength, and stiffness of GSCGFs was investigated. The evolution law of their freeze-thaw damage was discussed quantitatively based on an improved damage factor. The results show that the mass loss rate of Group B GSCGFs with a fine-grained particle content of less than 15% was lower than that of Group A GSCGFs with a fine particle content between 15% and 30% overall. When other conditions remain unchanged, the mass loss rate of GSCGFs decreased with the increase of compaction degree but increased nonlinearly with the freeze-thaw cycles. The strength and stiffness of GSCGFs decrease nonlinearly with the freeze-thaw cycles and presented a first fast and then slow-down change trend, their stiffness evolution at different compaction degrees revealed a big difference due to the weakening bite effect and enhancing overhead structure among rock blocks. The strength reduction of Group A GSCGFs was less than that of Group B under the high compaction degree. The stiffness deterioration of Group A GSCGFs was about twice that of Group B. There seemed to be no absolute correlation that the strength of GSCGFs was positively correlated with their stiffness. By building an exponential relationship between the compressive strength of GSCGFs and the freeze-thaw cycles that followed the findings of previous several studies, an improved exponential damage evaluation model was proposed to represent the performance degradation of GSCGFs. The outcomes of this study can provide theoretical support for understanding the physical and mechanical behaviors of GSCGFs and applying them in engineering practices.

The coupling effects of rainfall, earthquake, and complex topographic and geological conditions complicate the dynamic responses and disasters of slope-tunnel systems. For this, the large-scale shaking table tests were carried out to explore the dynamic responses of steep bedding slope-tunnel system under the coupling effect of rainfall and earthquake. Results show that the slope surface and elevation amplification effect exhibit pronounced nonlinear change caused by the tunnel and weak interlayers. When seismic wave propagates to tunnels, the weak interlayers and rock intersecting areas present complex wave field distribution characteristics. The dynamic responses of the slope are influenced by the frequency, amplitude, and direction of seismic waves. The acceleration amplification coefficient initially rises and then falls as increasing seismic frequency, peaking at 20 Hz. Additionally, the seismic damage process of slope is categorized into elastic (2-3 m/s2), elastoplastic (4-5 m/s2) and plastic damage stages (>= 6.5 m/s2). In elastic stage, MPGA (ratio of acceleration amplification factor) increases with increasing seismic intensity, without obvious strain distribution change. In plastic stage, MPGA begins to gradually plummet, and the strain is mainly distributed in the damaged area. The modes of seismic damage in the slope-tunnel system are mainly of tensile failure of the weak interlayer, cracking failure of tunnel lining, formation of persistent cracks on the slope crest and waist, development and outward shearing of the sliding mass, and buckling failure at the slope foot under extrusion of the upper rock body. This study can serve as a reference for predicting the failure modes of tunnel-slope system in strong seismic regions. (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/).

The digging mechanism is the component of garlic harvesters that consumes the most energy. Consequently, there are theoretical gaps in the design of resistance reduction. These gaps are due to the complexity of the interaction dynamics between the shovel and the soil, and the insufficient understanding of the evolution patterns of soil damage. To address these challenges, this study develops a finite element model of the shovel-soil system using damage mechanics to characterize nonlinear interaction mechanisms under operational loading conditions. The methodology integrates three critical phases: (1) soil damage evolution analysis was employed to identify key damage parameters for model calibration; (2) systematic finite element simulations were used to evaluate the effects of system variables-entry angle, shovel blade bevel angle, forward speed, and vibration frequency-on forward resistance; (3) orthogonal experimental optimization of these parameters was carried out. Key results include the following: (i) A nonlinear relationship was identified between variables (entry angle, forward speed, and vibration frequency) and resistance reduction. Furthermore, the threshold for optimal performance was determined. The optimal parameters were identified as an entry angle of 20 degrees, a forward speed of 0.39 m/s, and a frequency of 2.6 Hz. (ii) Validation through soil bin experiments, demonstrating strong agreement between simulated and measured load-displacement responses, confirming the predictive accuracy of the model. The research presented in this paper may offer insights into the principles of low-resistance designs for underground fruit harvesting.

Localized rock failures, like cracks or shear bands, demand specific attention in modeling for solids and structures. This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged. In such scenarios, as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area, internal variables that signify these microstructural changes should be established within this zone. Thus, localized deformation characteristics of rocks are studied here by the preset angle shear experiment. A method based on shear displacement and shear stress differences is proposed to identify the compaction, yielding, and residual points for enhancing the model's effectiveness and minimizing subjective influences. Next, a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band. Incorporating damage theory and an elasto-plastic model, a proposed damage model is introduced to replicate shear stressdisplacement responses and localized damage evolution in intact rocks experiencing shear failure. Subsequently, a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern. Thereafter, an innovative damage model is proposed to effectively encompass diverse rock material behaviors, including elasticity, plasticity, and softening behaviors. Ultimately, the effects of the preset angles, temperature, normal stresses and the residual shear strength are carefully discussed. This discovery enhances rock research in the proposed damage model, particularly regarding shear failure mode. (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/

Three-dimensional printing (3DP) offers valuable insight into the characterization of natural rocks and the verification of theoretical models due to its high reproducibility and accurate replication of complex defects such as cracks and pores. In this study, 3DP gypsum samples with different printing directions were subjected to a series of uniaxial compression tests with in situ micro-computed tomography (micro-CT) scanning to quantitatively investigate their mechanical anisotropic properties and damage evolution characteristics. Based on the two-dimensional (2D) CT images obtained at different scanning steps, a novel void ratio variable was derived using the mean value and variance of CT intensity. Additionally, a constitutive model was formulated incorporating the proposed damage variable, utilizing the void ratio variable. The crack evolution and crack morphology of 3DP gypsum samples were obtained and analyzed using the 3D models reconstructed from the CT images. The results indicate that 3DP gypsum samples exhibit mechanical anisotropic characteristics similar to those found in naturally sedimentary rocks. The mechanical anisotropy is attributed to the bedding planes formed between adjacent layers and pillar-like structures along the printing direction formed by CaSO4$2H2O crystals of needle-like morphology. The mean gray intensity of the voids has a positive linear relationship with the threshold value, while the CT variance and void ratio have concave and convex relationships, respectively. The constitutive model can effectively match the stress-strain curves obtained from uniaxial compression experiments. This study provides comprehensive explanations of the failure modes and anisotropic mechanisms of 3DP gypsum samples, which is important for characterizing and understanding the failure mechanism and microstructural evolution of 3DP rocks when modeling natural rock behavior. (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/).

In deep-buried long tunnels, train derailment accidents pose a serious threat to the stability of the tunnel lining structures and the safety of personnel along the line. To address the impact damage to the secondary lining caused by high-speed train derailments, a three-dimensional nonlinear dynamic analysis model of the Electric Multiple Unit (EMU) - lining - soil system was established. The advantages of this model include: it fully considers the complex streamlined design of the EMU front end, the nonlinearity of lining materials, and the M-C elastic structural model of the soil, allowing for accurate simulation of the contact and deformation between the EMU and the lining. The results indicate that the first 30 ms of the collision process are extremely intense, primarily involving the first three train vehicles. Among these, the head vehicle experiences the greatest reduction in kinetic energy and plastic dissipated energy, resulting in the most severe plastic deformation of the vehicle body. The impact load exhibits a distinct multi-peak characteristic, mainly composed of lateral impact force components. The area of displacement change in the lining expands continuously along the direction of the train, with peak displacements stabilizing after 30 ms. The lining primarily suffers from tensile failure, with multiple tensile cracks appearing in areas distant from the collision, while compressive damage is mainly concentrated at the point of direct impact. As the collision angle increases, the range of compressive damage along the longitudinal direction becomes narrower. The ratio of tensile damage area to compressive damage area is mainly influenced by the collision angle. In the design of tunnel structures for impact resistance, special attention should be paid to the lateral impact resistance and tensile failure capacity of the tunnel structure.