The study of the effects of supercritical CO2 (ScCO2) under high temperature and high pressure on the mechanical properties and fracturing potential of shale holds significant implications for advancing our understanding of enhanced shale gas extraction and reservoir exploration and development. This study examines the influence of three fluids, i.e. ScCO2, deionized water (DW), and ScCO2+DW, on the mechanical properties and fracturability of shale at immersion pressures of 15 MPa and 45 MPa, with a constant temperature of 100 C. The key findings are as follows: (1) Uniaxial compressive strength (UCS) of shale decreased by 10.72%, 11.95%, and 23.67% at 15 MPa, and by 42.40%, 46.84%, and 51.65% at 45 MPa after immersion in ScCO2, DW, and ScCO2+DW, respectively, with the most pronounced effect observed in ScCO2+DW; (2) Microstructural analysis revealed that while ScCO2 and DW do not significantly alter the microstructure, immersion in ScCO2+DW results in a more complex surface morphology; (3) Acoustic emission (AE) analysis indicates a reduction in stress for crack damage, with a decreased fractal dimension of AE signals in different fluids. AE energy is primarily generated during the unstable crack propagation stage; (4) A quantitative method employing a multi-factor approach combined with the brittleness index (BI) effectively characterizes shale fracturability. Evaluation results show that ScCO2+DW has a more significant effect on shale fracturability, with fracturability indices of 0.833% and 1.180% following soaking at 15 MPa and 45 MPa, respectively. Higher immersion pressure correlates positively with increased shale fracturability. (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/).

This research examines the relationship between excavations and tunnel responses, emphasizing the influence of geometric factors on tunnel heave. Utilizing an exponential correlation between heave and unloading ratio, the study investigates into stress changes with increasing excavation depth. Maintaining a constant axial horizontal distance proves crucial for stable tunnel responses. FLAC3D numerical modeling highlights increased stress-strength ratios near excavations, impacting the tunnel crown. Water ingress induces soil consolidation, leading to additional deformations, while adverse excavation conditions can cause leaks, dislocations, and cracks in the tunnel lining. The study also analyzes rock behavior under diverse loading and excavation conditions, revealing stress point relationships with the yield surface in principal stress space.

Despite several parameters having been identified as having an impact on the undrained monotonic response of granular soils, the impact of the overconsolidation ratio (OCR) is still a contentious issue. One of the significant reasons for the inconsistencies in the undrained behavior is the method by which the stresses are applied--specifically, the effective preconsolidation and confining pressures. To address this, two separate series of triaxial compression tests were realized in order to examine and compare the influence of the OCR (OCR = 1, 2, 4, and 8) on the mechanical response of Chlef River (Algeria) sand, considering the way the stress state was applied. During the first series, the OCR was accomplished by consolidating the specimens to an effective preconsolidation pressure (sigma p ' = 100, 200, 400, and 800 kPa) and subsequently unloading them to a constant desired effective confining pressure of 100 kPa. In the second series, all specimens were consolidated to a maximum effective preconsolidation pressure of sigma p ' = 800 kPa (constant effective preconsolidation pressure) and then unloaded to different effective confining pressures (sigma c ' = 800, 400, 200, and 100 kPa), using two different sample preparation techniques--dry funnel pluviation and moist tamping. The test results revealed a suitable increase in the shear strength with an increase in OCR in the first series, with the opposite trend observed in the pore water pressure. For the second series, an increase in the OCR parameter resulted in a minimized shear strength and pore water pressure (although the trend in pore water pressure evolution did not really reflect the behavior of the deviator stress for this series). In addition, certain parameters, such as normalized behaviors, the brittleness index, ratio of excess pore water pressure to deviator stress at the critical state, and flow potential, appear to be reliable predictors for clarifying and, consequently, explaining the studied behaviors.

Directional-dependent properties of the soil, like shear strength, stiffness and hydraulic conductivity, are known as anisotropy in soils. Shape and size of the soil particles and void distribution as microstructure characteristics and external factors such as stress history, environmental and geological conditions, and present stress condition can be the causes of the anisotropy in soils. In this paper, the behaviour of soil has been studied in stress-strain plain under monotonic anisotropic loading to investigate the effect of induced anisotropy on brittleness index of soil sample. The brittleness index of the soil is defined as the difference between the ultimate and peak shear strength divided by the peak shear strength of the soil. The two major parameters describing induced anisotropy or anisotropic loading are intermediate principal stress (b) and principal stress direction (alpha) which are representative of the difference between intermediate, maximum and minimum principal stresses and the rotation angle of the principal stresses' axis, respectively. This paper only takes the effect of intermediate principal stress with the values of 0.25, 0.5, 0.75. In addition, the soil is in the unsaturated state with the saturation degree of 80% using the constant water (C.W.) method.