Ensuring the stability of the surrounding rock mass is of great importance during the construction of a large underground powerhouse. The presence of unfavorable structural planes within the rock mass, such as faults, can lead to substantial deformation and subsequent collapse. A series of in situ experiments and discrete element numerical simulations have been conducted to gain insight into the progressive failure behavior and deformation response of rocks in relation to controlled collapse scenarios involving gently inclined faults. First, the unloading damage evolution process of the surrounding rock mass is characterized by microscopic analysis using microseismic (MS) data. Second, the moment tensor inversion method is used to elucidate the temporal distribution of MS event fracture types in the surrounding rock mass. During the development stage of the collapse, numerous tensile fracture events occur, while a few shear fractures corresponding to structural plane dislocation precede their occurrence. The use of the digital panoramic borehole camera, acoustic wave test, and numerical simulation revealed that gently inclined faults and deep cracks at a certain depth from the cavern periphery are the primary factors contributing to rock collapse. These results provide a valuable case study that can help anticipate and mitigate fault-slip collapse incidents while providing practical insights for underground cave excavation. (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/).

It is important to study the effects of the mechanical properties and failure characteristics of defective frozen soil under coupled compression-shear loading for engineering construction safety and disaster prevention. In this study, the particle flow code was used to establish the distinct element method (DEM) model of a split-Hopkinson pressure bar experiment on frozen soil. The failure processes of frozen soils with different tilting angles and holes were simulated using the DEM model to investigate the influence of the tilting angle and hole deviation (deviation from the geometric center of the frozen soil specimen) on the impact mechanical properties and failure characteristics of frozen soil specimens under coupled compression-shear loading. The results of numerical simulation indicated that when the tilting angle and impact strain rate were 0 degrees and 100 s(-1), the axial peak stress of frozen soil specimen with a hole was smaller than that without a hole, the hole deviation had a minor influence on the axial peak stress. When the strain rate was 100 s(-1,) the axial and shear peak stresses of the frozen soil specimen without a hole increased and decreased, respectively, with increasing tilting angle, and the number proportion of shear-cracks also increased. When the tilting angle and strain rate were 60 degrees and 100 s(-1), the fully deviated hole had a minor influence on the impact mechanical properties and failure characteristics of the frozen soil. The impact loading also had a minor influence on the deformation of the hole.

Triggered by continuous heavy rainfall, a catastrophic large-scale high-locality landslide occurred in Hengshanbei mountain slope of Shangxi Village, Longchuan County, Guangdong Province, China, on June 14, 2022, at 12:10 (UTC + 8). The landslide had an estimated volume of about 1.45 x 105 m3 and resulted in severe damage to the region. To investigate the causative mechanisms of this landslide, a comprehensive study was conducted, involving geological and hydrological surveys of the research area, combined with field investigations, satellite imagery, drone photography, data analysis of rainfall and landslide displacement monitoring, and laboratory experiments. The research focused on analyzing the process of landslide formation and development, trigger factors, destruction characteristics, and instability mechanisms. Additionally, the study employed the Mohr-Coulomb strength theory to explain stress variations during the landslide process. Findings indicated that: (1) the slope soil structure was loose with well-developed pores, mainly composed of kaolinite with strong water absorption properties, causing softening and disintegration of the soil when encountering water, resulting in reduced cohesion and internal friction angle, and overall poor soil properties; (2) continuous heavy rainfall infiltrated the slope through soil pores and eroded channels, increasing pore water pressure and reducing effective stress, subsequently reducing anti-sliding force and increasing sliding force; as well as (3) unfavorable terrain conditions, such as high landslide starting point and high-locality, significant height, and steep slope, lead to landslides running farther and being of larger scale. The study further highlighted that the intrinsic properties of the slope soil were the decisive internal cause of the landslide, while continuous heavy rainfall and adverse terrain were external triggering factors. These findings provide essential insights for understanding and preventing similar landslide disasters.

To investigate the effects of the maximum principal stress direction (theta) and cross- shape on the failure characteristics of sandstone, true-triaxial compression experiments were conducted using cubic samples with rectangular, circular, and D-shaped holes. As theta increases from 0 degrees to 60 degrees in the rectangular hole, the left failure location shifts from the left corner to the left sidewall, the left corner, and then the floor, while the right failure location shifts from the right corner to the right sidewall, right roof corner, and then the roof. Furthermore, the initial failure vertical stress first decreases and then increases. In comparison, the failure severity in the rectangular hole decreases for various theta values as 30 degrees > 45 degrees > 60 degrees > 0 degrees. With increasing theta, the fractal dimension (D) of rock slices first increases and then decreases. For the rectangular and D-shaped holes, when theta = 0 degrees, 30 degrees, and 90 degrees, D for the rectangular hole is less than that of the D-shaped hole. When theta = 45 degrees and 60 degrees, D for the rectangular hole is greater than that of the D-shaped hole. Theoretical analysis indicates that the stress concentration at the rectangular and D-shaped corners is greater than the other areas. The failure location rotates with the rotation of theta, and the failure occurs on the side with a high concentration of compressive stress, while the side with the tensile and compressive stresses remains relatively stable. Therefore, the fundamental reason for the rotation of failure location is the rotation of stress concentration, and the external influencing factor is the rotation of theta. (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/).

On December 18, 2023, the Jishishan M(S)6.2 earthquake caused serious damage to Jishixiongguan, China, which is a rammed-earth city wall, and was about 14 km away from the epicenter. There was a large area of collapse and part of the vertical ramming overlap separation phenomenon. Based on the results of earthquake field investigation, the dynamic response of Jishixiongguan under the earthquake was studied by analyzing the maximum displacement, peak acceleration (PA) and stress-strain distribution characteristics of wall measuring points at different locations, and the mechanism of Jishixiongguan failure induced by Jishishan M(S)6.2 earthquake was given. The results show that the plastic zone initially develops from the bottom erosion of the wall and the transverse through crack at the top of the right-end, and it rapidly extends downward along the slope into the interior of the wall, resulting in destructive permanent displacement shortly after the peak ground acceleration (PGA) is reached, the maximum plastic strain and maximum displacement occur at transverse through cracks of the right-wall top. Owing to the wall being constructed against a mountain slope, the amplification effect (AE) of the slope on the displacement of the wall is obvious, and the closer the wall is to the higher parts of the slope, the more significant the AE of the displacement is due to the combined effect of the mountain slope and the wall height. Pre-existing defects in the wall will weaken the AE of the slope and the wall height on the acceleration, however, the transverse through cracks will enhance the AE of the wall height on the acceleration. Stress concentration caused by hollowed-out overhangs and stress discontinuity caused by the transverse through crack is the internal factor of the wall failure, the plastic yield of soil caused by the AE of slope and wall height on displacement is the external factor of large-scale collapse of wall. The research results can provide theoretical guidance for the restoration and reinforcement of ancient sites.

Investigating deformation and failure mechanisms in shafts and roadways due to rock subsidence is crucial for preventing structural failures in underground construction. This study employs FLAC3D software (vision 5.00) to develop a mechanical coupling model representing the geological and structural configuration of a stratum-shaft-roadway system. The model sets maximum subsidence displacements (MSDs) of the horsehead roadway's roof at 0.5 m, 1.0 m, and 1.5 m to simulate secondary soil consolidation from hydrophobic water at the shaft's base. By analyzing Mises stress and plastic zone distributions, this study characterizes stress failure patterns and elucidates instability mechanisms through stress and displacement responses. The results indicate the following: (1) Increasing MSD intensifies tensile stress on overlying strata results in vertical displacement about one-fifth of the MSD at 100 m above the roadway. (2) As subsidence increases, the disturbance range of the overlying rock, shaft failure extent, and number of tensile failure units rise. MSD transitions expand the shaft failure range and evolve tensile failure from sporadic to large-scale uniformity. (3) Shaft failure arises from the combined effects of instability and deformation in the horsehead and connecting roadways, compounded by geological conditions. Excitation-induced disturbances cause bending of thin bedrock, affecting the bedrock-loose layer interface and leading to shaft rupture. (4) Measures including establishing protective coal pillars and enhancing support strength are recommended to prevent shaft damage from mining subsidence and water drainage.

The failure modes of rock after roadway excavation are diverse and complex. A comprehensive investigation of the internal stress field and the rotation behavior of the stress axis in roadways is essential for elucidating the mechanism of roadway failure. This study aimed to examine the spatial relationship between roadways and stress fields. The law of stress axis rotation under three-dimensional (3D) stress has been extensively studied. A stress model of roadways in the spatial stress field was established, and the far-field stress state at different spatial positions of the roadways was analyzed. A mechanical model of roadways under a 3D stress state was established using far-field stress solutions as boundary conditions. The distribution of principal stresses s1, s2and s3 around the roadways and the variation of the stress principal axis were solved. It was found that the stability boundary of the stress principal axis exhibits hysteresis when compared with that of the principal stress magnitudes. A numerical analysis model for spatial roadways was established to validate the distribution of principal stress and the mechanism of principal axis rotation. Research has demonstrated that the stress axis undergoes varying degrees of spatial rotation in different orientations and radial depths. Based on the distribution of principal stress and the rotation law of the stress principal axis, the entire evolution mechanism of the two stress adjustments to form the final failure form after roadway excavation has been revealed. The onsite detection results also corroborate the findings presented in this paper. The results provide a basis for the analysis of the failure mechanism under a 3D stress state. (c) 2024 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 complex mechanical behaviours of steeply inclined and layered surrounding rock in strong and active fault zones result in control measures that cannot adapt to asymmetric squeezing tunnel and are still unsolved. Hence, the Yuntunbao Tunnel was taken as an example to study this issue based on geological survey and indoor and outdoor tests. The results showed that strong geological structures and abundant groundwater undoubtedly deteriorate the mechanical properties of rocks containing many water-sensitive minerals, approximately 45%. The stepwise growth of deformation characteristics before reaching the rock peak strength and the gradient to abrupt failure characteristics after reaching the rock peak strength are determined via triaxial cyclic and static load tests. According to field test results, the unilateral squeezing deformation is severe and greater than 1.5 m, the average extent of the excavation loosening zone is approximately 10 m, and the highest deformation rate reaches 12 cm/d. The gradual and sudden changes in tunnel deformation are demonstrated to be consistent with the postpeak deformation characteristics of layered rock in indoor tests. Moreover, the steel arch exhibits composite failure characteristics of bending and torsion. Finally, reliable and practical controlling measures are suggested, including the optimised three-bench excavation method with reserved core soil, advanced parallel pilot tunnel, long and short rock bolts, and large lock-foot anchor pipe. Compared with tunnel deformation before taking measures, the maximum convergence deformation is reduced from 2.7 to 0.9 m, and the bearing force of the primary support is also reasonable and stable.

Tunnels subjected to active fault dislocation may experience significant damage. This paper establishes a novel methodology and solution procedure for analyzing the mechanical response and failure characteristics of tunnels subjected to active fault dislocation based on an elastic foundation beam model. The proposed methodology includes axial, transverse, and vertical soil-tunnel interaction terms, in addition to geometrical nonlinearity and axial force terms in the governing equation. This approach has a significantly extended application range, effectively addressing the problems encountered in tunnels crossing active faults with diverse crossing angles, dip angles, and fault types. The proposed methodology is verified by comparison to a 3D FEM model with various fault types, experimental tests, and on-site case, and the results are in excellent quantitative and qualitative agreement with the numerical, experimental, and on-site results. When fault displacement is below 0.5 m, disregarding geometric nonlinearity results in calculation errors of approximately 10% to 17% for peak axial force (Nmax), 18% to 22% for peak shear force (Vmax), and 20% to 30% for peak bending moment (Mmax). Finally, the responses caused by different factors, i.e., fault type, fault displacement, tunnel stiffness, and tunnel diameter, are investigated in detail to better understand tunnels crossing active faults. The results show that amongst the various fault types, the Vmax and the Mmax experienced by tunnels subjected to oblique slip-fault dislocation surpass those of other fault types, accompanied by the most extensive failure range. The augmentation of fault displacement, tunnel stiffness, and tunnel diameter precipitates a corresponding escalation in the Nmax, Vmax, Mmax, and failure range. Under oblique-slip fault dislocation, the tunnel undergoes an initial phase of shear failure, followed by tension-bending failure, delineated by distinct fault displacement thresholds of 0.1 m and 0.2 m, respectively. The proposed methodology provides the advantage of reliable stability analysis and design of tunnels crossing active faults.

The blocking of rivers by landslides is common in mountainous areas with deep and narrow valleys. Landslide dams may pose a severe threat to the safety of life and property downstream in the event of a sudden dam failure. The similarities and differences in failure characteristics between the large-scale and small-scale landslide dams are insufficiently understood. Relatively large-scale physical models to study the failure processes are expensive and time-consuming. Relatively small-scale experiments give a better opportunity to explore the failure mechanisms, but the scale effect needs to be considered. In this study, a large-scale test and three small-scale flume tests were conducted to study the failure characteristics of landslide dams with a scale ratio of 10:1. Experimental results showed that the large-scale and small-scale dam tests followed almost the same failure processes, which can be divided into three stages: seepage on the downstream surface, slope failure, and overtopping and erosion. But they differed in some quantitative outcomes such as the failure duration and pore water pressure value. The small-scale dam tests can be used to study the failure processes and mechanisms of landslide dams, but can not be used to predict the specific parameters due to the scale effect.