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.

Accurately predicting the dynamic evolution of permeability during CO₂ injection into shale reservoirs is crucial for carbon sequestration and enhanced shale gas recovery. However, traditional permeability models often fail to comprehensively describe the full-range evolution of permeability throughout the entire CO₂ injection process in shale—from the low-pressure gaseous state to the supercritical state. To address this limitation, this study develops a shale permeability evolution model based on a dual-elastic system comprising both the matrix and fractures, determined by component permeability weighting. By incorporating key factors such as mechanical degradation of the matrix, secondary adsorption, and strain hysteresis effects, we establish a governing equation for permeability evolution under multi-effect coupling. Utilizing an overlapping dual-elastic medium structure, we perform parallel cross-coupling numerical solutions, achieving an accurate representation of the nonlinear permeability evolution during full-pressure CO₂ injection. Furthermore, a decoupled analysis of influencing effects reveals that the degradation of mechanical parameters of the matrix material due to CO₂ defines the boundary thresholds for permeability fluctuation ranges. The asynchronous response between mechanical strain and adsorption strain significantly amplifies differences across evolutionary stages, leading to clearly distinguishable phase transitions. Additionally, the strain hysteresis effect prolongs the duration of evolution. Gas adsorption and mechanical responses jointly regulate the transition points between evolutionary stages, with the secondary adsorption-induced swelling strain particularly enhancing phase differentiation throughout the evolution process. This study also provides an in-depth analysis of the fundamental framework of fluid-solid coupled permeability modeling and explores the characteristics of different numerical simulation methods. The findings not only deepen the understanding of shale permeability evolution during CO₂ injection but also offer valuable insights for theoretical modeling and numerical simulation of permeability in geological fluid sequestration.

Ice avalanches are a primary trigger for glacier-related disaster chains in high-mountain regions. Understanding how boundary conditions influence the dynamics and deposition of ice avalanche debris flows is crucial for deciphering the evolution of such disaster chains. This study systematically investigates the motion and depositional behavior of ice avalanche debris flows under varying mass, elevation differences, slope gradients, and toe constraints, utilizing a chute-based experimental setup within a low-temperature laboratory. Key parameters, including flow velocity, basal force, and deposition morphology, are analyzed throughout the debris flow movement. Results indicate that elevation differences and mass govern the dynamic energy transfer within the flows. Specifically, elevation differences control depositional dispersion by regulating peak flow velocity, while mass influences travel duration, resulting in a positive correlation between run-out length and deposit thickness. Furthermore, topographic conditions significantly affect energy dissipation during deposition. An increased slope gradient in the run-out zone reduces basal resistance, thereby expanding the depositional area and enhancing particle scattering at the flow front. A wider slope toe promotes lateral spreading, increasing travel distance and shifting the mass center, which transforms deposit morphology from tongue-shaped to fan-shaped. Finally, theoretical analysis confirms that run-out distance is dictated by the efficiency of kinetic energy transfer among particles and their interaction with the substrate, exhibiting a positive correlation with both particle energy-transfer efficiency and fluctuations in basal stress.

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.

This paper investigates the effect of anisotropic stress states on the small strain stiffness of red mudstone fill material (RMF). A comprehensive experimental program was conducted, including 18 triaxial-bender element tests, 4 isotropic consolidation tests, and 6 stress-controlled loading-unloading tests. The results indicate that the normalized strength is well characterized by the nonlinear strength envelope. Under isotropic stress conditions, the small strain stiffness increases with mean stress, which can be described by a power equation. During conventional triaxial shear, small strain stiffness increases at low axial strains. When the axial strain exceeds 2%, the damage point can be identified, at which point small strain stiffness decreases by more than 25% with further axial strain. A power model has been employed to characterize the small strain stiffness and shear stress at both the damage point and peak point. Unloading at stress states below the damage point results in an increase in small strain stiffness. Conversely, due to irreversible structural disturbance, unloading at stress states above the damage point leads to a progressive reduction in small strain stiffness. The difference in small strain stiffness at various unloading points can exceed 30%. Therefore, the coupled effects of stress history and stress path should be considered for accurate determination of small strain stiffness, as the conventional monotonic model is not applicable in such coupled scenarios.

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.

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.

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.

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.