To investigate the influence of normal stress on the seepage and damage characteristics of sandstone during dynamic constant-amplitude cyclic direct shear, red sandstone samples were subjected to dynamic constant-amplitude cyclic direct shear tests under normal stresses of 10, 15, 20 and 25 MPa. During the loading process, acoustic emission (AE) signals were simultaneously recorded, and the permeability of the sandstone was measured in real time. After testing, the fracture surfaces of the sandstone samples were scanned using a 3D scanner. The test results indicate that the permeability evolution of sandstone during direct shear exhibits distinct stage characteristics, which can be described as “gradual decrease→slow decrease→slight recovery→exponential increase.” Throughout the loading process, the permeability of samples subjected to high normal stress consistently remains lower than that of samples under low normal stress. As the normal stress increases, the initiation of AE activity in the samples is delayed. However, the Felicity effect occurs earlier and more prominently, indicating a greater extent of damage. Higher normal stress facilitates a transition in the fracture mode of sandstone from tension-dominated to shear-dominated. At the microscopic level, increased normal stress promotes the development of transgranular cracks, leading to straighter crack propagation paths. Simultaneously, crack propagation is restricted near the main shear plane, ultimately resulting in macroscopically flatter fracture surfaces with lower roughness.

How can the essential requirements of retention, hydraulic conductivity, and clogging for geotextile filters be simultaneously satisfied? Coordinating the assessment of their seepage stability performance is crucial. To achieve this, sixteen soil-geotextile column hydraulic gradient ratio tests were conducted using four typical geotextiles. The seepage stability was evaluated based on hydraulic conductivity, stable hydraulic gradient ratio, and the washout of soil fines observed during the tests. Additionally, both the grain size of the soil and the constriction size of the geotextile were treated as random variables. Utilizing soil-water interaction theory, a retention assessment approach was proposed based on the probability of ineffective retention. The performance limits of retention were determined using data from eighty-five experimentally assessed soil-geotextile columns. Furthermore, a hydraulic conductivity assessment approach was developed, considering the partial clogging of the geotextile due to the formation of a bridging structure. The results indicate that the proposed design criterion surpasses previously published criteria in effectively distinguishing between clogging or blinding in ineffective and effective systems. It was found that polypropylene long-filament geotextiles with a high mass per unit area are particularly well-suited for use as filters.

To investigate the mesoscopic crack evolution behavior and the dominant mechanisms during the failure process of sandstone, an integrated approach combining acoustic emission moment tensor inversion with RA-AF parameter analysis was employed to quantitatively characterize the types, spatiotemporal distribution, and stress response characteristics of microcracks. Based on moment tensor theory and incorporating sensor coupling coefficients calibrated through pencil-lead break experiments, microcracks were classified into five categories—shear cracks, tensile-shear mixed-mode cracks, compressive-shear mixed-mode cracks, tensile cracks, and compressive cracks—using the crack tensile angle criterion. Furthermore, an RA-AF empirical model was established to support the analysis. The results indicate the following: (1) Under various loading paths, microcracks resulting from sandstone failure are predominantly shear cracks. The number of each of the five microcrack types exhibits a positive correlation with stress level, with shear cracks showing the most significant increase. (2) As stress increases, microcracks initiate, propagate, and gradually coalesce, forming a fracture zone that corresponds to the macroscopic failure surface. (3) RA-AF analysis reveals that shear cracks account for more than 50% of all microcracks in sandstone, which aligns with findings from moment tensor inversion. (4) Waveforms generated by tensile cracks exhibit abrupt characteristics, with concentrated signal energy in the frequency domain, whereas waveforms associated with shear cracks display oscillatory behavior, featuring dispersed frequency-domain energy and higher amplitude. This distinction provides a physical mechanism that explains the heterogeneity observed in RA-AF parameters. (5) Moment tensor inversion is well-suited for theory-driven, detailed analysis of crack mechanisms, while RA-AF analysis is more appropriate for rapid identification of crack types in engineering practice. This study elucidates the dominant micromechanical mechanism of shear failure in sandstone and the co-evolutionary behavior of multiple crack types, thereby providing a theoretical foundation for rock fracture prediction.

To identify the distribution differences between fractures and interlayer gravels within glutenite cores, accurately evaluate spatial heterogeneity, and enhance hydrocarbon recovery efficiency, this study employed elastic ultrasonic wave velocity—a parameter highly sensitive to variations in the internal rock structure—to measure wave velocities in 18 outcrop cores collected from the Shawan Sag in the Junggar Basin. A non-destructive evaluation method for heterogeneity was established based on stratified elastic wave velocity measurements. Fifteen samples were utilized as test cores for heterogeneity assessment using this method, while the remaining three served as validation cores, with their velocity distributions compared for verification. The results demonstrate that: (1) the proposed method effectively identifies heterogeneity characteristics, such as gravel distribution and pore-fracture networks in glutenite, enabling an accurate assessment of spatial heterogeneity; (2) the method offers several advantages over conventional heterogeneity evaluation techniques, including non-destructiveness, high sensitivity, rapid measurement, and cost-effectiveness; and (3) consistent heterogeneity evaluation results were obtained between the test and validation cores. Therefore, this method can serve as a valuable reference for heterogeneity assessment in glutenite reservoirs.

On 15 August 1950, an M_s8.6 earthquake struck the Medog—Zayu region in the Eastern Himalayan syntaxis, with a maximum intensity of XII and an area with intensity≥VIII of about 2.19×10⁵ km². This mainshock-dominated event released seismic energy in a highly concentrated manner and triggered extensive landslides and related geological hazards. To systematically reveal the spatial distribution and the river-blocking patterns of coseismic landslides, we integrate multi-temporal historical imagery since 1961, archival records and field investigations to analyse the intensity distribution. For the high-intensity zone (X–XII) from Milin Wolong to downstream of Duden in the Namcha Barwa region, a coseismic landslide inventory is constructed for the first time, resulting in a dataset of 920 landslides. Quantitative analysis reveals that landslides predominantly occurred at 2 000–4 000 m elevation, on 20°–50° slopes, and within 4 km of active faults. The landslide distribution is strongly controlled by the main central thrust fault, the Motuo fault, and the Apalong fault. Based on statistical analysis and morphological characteristics, we delineate four types of earthquake-induced landslide-damming patterns: seated landslides, high-altitude remote hazards, whole gully-scale landslides and multi-landslide clusters, typified by the Gengbangla, Zelongnong Gully, the Jamaqiming Gully, and Zhaqu—Xirang landslide groups, respectively. The maximum duration of river blockage reached 15–16 hours. The unique geomorphic and tectonic environment of the Eastern Himalayan Syntaxis provides favorable conditions for the occurrence and evolution of high-altitude remote geological hazards. As the region is currently in a seismically active phase, it is critical to enhance research on the failure mechanisms and early warning of under extreme earthquake conditions, thereby improving disaster preparedness, resilience, and emergency response capabilities in the region.

In response to the engineering challenges associated with limited construction scale and slow development speed in high-impurity salt mines oil storage, this study proposes a novel technical approach that utilizes sediment voids to expand oil storage capacity. Laboratory experiments and theoretical analyses were conducted on sediment particles from the Yunying salt mine in Hubei Province. A evaluation system encompassing sediment characterization and sediment void storage capacity was established. The mechanism of oil injection and production under the fluid-solid coupling of oil/brine and sediment was systematically studied. The sediment void clogging risk during oil injection and production was explored. The migration rule of oil and brine in sediment voids were elucidated. The results indicate that Yunying sediments possess a void ratio exceeding 40% with favourable connectivity in total, meeting the requirements for oil storage. Multiple oil injection and production cycles demonstrate low flow resistance and a linear mass-time correlation. Dominant flow channels are established only during the initial injection, stabilizing thereafter. The oil-brine interface exhibits fingering phenomena without abnormal pressure or rate fluctuations. Transient clogging events occur randomly, presenting an overall low risk. The oil injection pressure increases stepwise as the oil-brine interface descends. The hydrophilic properties of the sediments improve brine injection and oil production efficiency through capillary forces. These findings provide scientific support for the construction of high-impurity salt mines oil storage facilities.

Significant limitations and hysteresis are presented in dynamic prediction methods driven by on-site monitored displacement data for tunnel surrounding rock deformation. By comprehensively utilizing the physical information contained in tunnel construction project documents and the mathematical information from displacement time-series curves, a modelling method based on the dynamic Bayesian network (DBN) was developed using the concept of physical information machine learning (PIML) to achieve dynamic predictions of surrounding rock deformation. Through discretization processing and reconstruction of displacement time-series curves, a static sample database was established by combining physical information data with ultimate displacement data, while a dynamic sample database was created by integrating physical information data with displacement time-series curve data. Based on the characteristics of the static samples, the K2-score algorithm was improved to construct a static Bayesian network (BN) model for ultimate displacement prediction. Utilizing the static BN model and the characteristics of the dynamic samples, physical-data dual-drive modelling methods for the Markov DBN were derived by incorporating prior information, including the constraints of steady-state random processes and Markov process constraints. By integrating prior information for constraint-enhanced optimization, the optimized Markov DBN model was established. Five-fold cross-validation tests revealed that the prediction capability of the Markov DBN model decreased rapidly over time and that the network transition direction significantly affected this capability. In contrast, the prediction ability of the optimized Markov DBN model remained robust over time, was unaffected by the network transition direction, and significantly exceeded that of the Markov DBN model, as the optimized model enhanced constraint connections between target nodes and influencing factor nodes throughout the entire timeframe. Through engineering case analysis, it was concluded that before and during the early stages of tunnel construction, the optimized Markov DBN model could effectively predict displacement time-series curves, overcoming the limitations and hysteresis inherent in traditional methods. Furthermore, during construction, self-updating of the optimized Markov DBN model and dynamic predictions of surrounding rock deformation could be achieved by inputting the on-site monitored displacement data.

Rock masses often exhibit significant size effects under uniaxial compression, yet the underlying mesoscopic controlling mechanisms and sensitivity to crack parameters remain poorly understood. In this study, we conducted uniaxial compression and acoustic emission (AE) monitoring experiments on granite specimens of various laboratory scales. By incorporating constraints from X-ray diffraction (XRD) mineral composition and AE-guided micro-crack data, we established a numerical model with a pre-existing micro-crack network using the PFC platform. The results indicate that the uniaxial compressive strength, failure mode, and crack propagation of the specimens demonstrate pronounced size dependence: peak strength decreases with increasing specimen size, and the failure mode transitions from splitting to shearing. In a homogeneous mineral matrix model (without pre-existing micro-cracks), the strength is nearly independent of specimen size, suggesting that pre-existing micro-cracks are the primary factor controlling the size effect. Furthermore, crack length has a significantly greater impact on strength degradation than crack number, with smaller specimens being more sensitive to variations in crack parameters. The established model effectively reproduces the experimental results regarding stress-strain behavior, AE event sequences, AF-RA crack classification, and failure patterns, thereby validating the reliability of the multi-scale numerical approach. These findings provide theoretical support for addressing the strength size effect and enhancing the safety design of engineering rock masses under complex geological conditions.

When constructing tunnels in rheological strata, the creep of the surrounding rock increases the load on the supporting structure over time. Additionally, environmental influences may cause creep phenomena in the supporting structure, resulting in a complex interaction mechanism between the tunnel's surrounding rock and support due to the coupling effects of both. This article proposes an analytical method for circular tunnels based on the theory of complex functions and Laplace transform. Unlike previous analytical solutions, the approach presented here incorporates the rheological properties of the surrounding rock, non-hydrostatic stress fields, and the creep characteristics of supporting structures. The Kelvin-Voigt model was employed to simulate the rheological properties of both the surrounding rock and the supporting structures. Displacement and stress solutions were derived from the displacement coordination equation and the stress boundary conditions of the surrounding rock and support structures. The accuracy of the analytical solution was verified through numerical simulations, followed by a parameter analysis. The main conclusions drawn from this study are as follows: (1) For simple mechanical models, the analytical method proposed in this paper is faster, simpler, and retains a degree of accuracy superior to that of numerical simulations; (2) When accounting for the creep characteristics of the supporting structure, the deformation of the surrounding rock is greater compared to existing analytical results, the contact pressure between the surrounding rock and the supporting structure is reduced, and the creep of the supporting structure diminishes its bearing capacity and deformation constraint. A higher creep rate in the supporting structure correlates with a faster rate of deformation in the surrounding rock, a lower creep modulus, and increased deformation of the surrounding rock; (3) In the context of non-hydrostatic stress fields, the coupling effects of creep between the tunnel and the supporting structure can exacerbate tunnel issues such as arch uplift or inward compression of tunnel sidewalls, thereby compromising the safety of the supporting structure. Considering these factors is crucial for the design and construction of tunnels in complex environments; (4) Engineering applications demonstrate that the analytical method proposed in this paper effectively predicts the trends in tunnel surrounding rock deformation and support structure stress, showcasing its potential for practical engineering applications.

Coral sand deposits in the islands and reefs of the South China Sea are vulnerable to seismic liquefaction. Shear wave velocity provides a rapid and non-destructive method for assessing liquefaction potential; however, existing criteria, primarily developed for quartz sands, exhibit limited applicability to coral sands. This study aims to establish a specific relationship between shear wave velocity and cyclic resistance ratio for coral sand. A series of cyclic undrained triaxial tests and bender element tests were conducted using a GDS dynamic triaxial system on saturated coral sand from the South China Sea and comparable quartz sand. Systematic measurements of cyclic resistance and shear wave velocity were obtained for both materials, leading to the development of a quantitative model relating shear wave velocity to cyclic resistance for coral sand. The validity and engineering applicability of the proposed model were further validated through a case study of typical liquefaction sites, resulting in an empirical equation for the critical shear wave velocity of coral sand. The results indicate a strong correlation between shear wave velocity and cyclic resistance ratio in coral sand, with coral sand exhibiting significantly higher shear wave velocity than quartz sand at equivalent cyclic resistance ratio levels, thereby confirming their intrinsic mechanical differences. The proposed model effectively characterizes the liquefaction resistance of coral sand under varying seismic intensities and can accurately delineate liquefied layers in case analyses. This research provides a valuable reference for seismic safety assessments and foundation design in coral sand sites, such as islands and ports in the South China Sea.