Jie Hu

The excavation compensation method (ECM) is used in deep tunneling to manage large deformations by applying high-prestressed active support immediately after excavation. Under asymmetric in-situ stresses, tunnel convergence becomes non-uniform, causing negative Poisson’s ratio (NPR) cables to carry different axial forces even when the same pre-pretension is applied. To capture this circumferentially varying rock-support response, an equivalent compensation pressure along the tunnel perimeter is introduced and assumed to follow a first-harmonic (cosine-type) angular distribution. Based on this representation, analytical solutions are derived within a plane-strain, linear-elasticity framework for the equilibrium convergence displacement and the corresponding bolt axial forces, with the surrounding rock idealized as homogeneous and isotropic. The results show that the proposed first-harmonic distribution provides a rational estimate of cable force variation and enables practical design calculations for NPR-cable pretension and spacing. The analytical predictions are validated against field monitoring data from Changning Tunnel, demonstrating applicability for pretension design and post-excavation deformation assessment. These findings provide analytical guidance for designing NPR-cable pretension and allowable deformation in the ECM-based support design.

Groundwater is a key factor influencing rockburst in underground engineering. Identifying how water alters precursory signals is essential for reliable prediction and mitigation. Using a self-developed true triaxial rockburst system integrated with high-speed camera (HSC) and acoustic emission (AE) monitoring, we investigated water effects on sandstone rockburst processes, failure modes and AE evolution, clarified microscopic water-induced weakening mechanisms, and developed a multi-parameter coupled AE precursor model incorporating critical slowing down (CSD) and Ib value theory. Results show saturated sandstone exhibits significantly reduced rockburst strength, ejected fragment mass and peak AE energy compared to dry samples, with a distinct AE energy “quiet period” prior to instability. Among the investigated indicators, the Ib value and Variance (Var) provided clearer precursor responses in the present tests. Based on Var based warning, the precursor time for saturated sandstone occurred at 475 s, which was 45.7% earlier than that for dry sandstone. The proposed AE multi-parameter integrated early warning framework is preliminary and requires further validation; within this dataset, it indicated that the warning interval for saturated sandstone was advanced by 2.15% compared with dry conditions. These findings offer effective AE-based indicators for rockburst early warning and support water-assisted risk control in deep underground engineering.

Shale, a sedimentary rock with significant heterogeneity and well‐developed bedding structures, exhibits complex mechanical behaviors and failure mechanisms. In this study, the Discrete Element Method (DEM) is employed to develop a Weibull distribution‐based parameter assignment approach for simulating heterogeneous shale specimens under uniaxial compression. The mechanical responses and fracture evolution are systematically analyzed, and a novel damage constitutive relation is proposed that accounts for both material heterogeneity and bedding structure effects. The results show that: (1) the stress‐strain curves consist of three stages: linear elasticity, nonlinear crack propagation, and brittle failure. The peak strength follows a power–law relationship with the homogeneity index ( m ), and at higher homogeneity levels ( m ≥ 8), enhanced stress uniformity delays post‐peak stress reduction. At a 90° bedding angle, the mechanical response transitions to bedding‐plane‐dominated ductile deformation, with reduced sensitivity to homogeneity. (2) The failure mechanisms are governed by dual control effects: at bedding‐dominated angles (60°–90°), tensile fracturing along bedding planes predominates and is weakly affected by homogeneity, while at co‐controlled angles (0°–45°), failure patterns evolve with increasing m , progressing through V‐shaped, inverted V‐shaped, and oblique L‐shaped fractures. (3) Stress‐strain curve fitting using the proposed damage constitutive relation demonstrates strong consistency with simulation results for m > 2. These findings provide a quantitative framework for assessing damage thresholds in shale with varying homogeneity and bedding angles, offering valuable guidance for shale‐related engineering projects.

This paper addresses evaluating the evolution of stress inside the casing‐cement sheath‐formation system during the cement injection, setting, completion, and production stages of hydrocarbon recovery. This full‐life‐cycle analysis of cement sheath integrity gives rise to assessment of potential failure mode (i.e., tensile mode, shear mode, and microannulus) in different stages, and the prevention measures can be proposed accordingly. Considering the loading history, two regimes should be distinguished. Before the accomplishment of cementation, as the cement slurry can merely withstand its hydraulic pressure, the in situ stress and the wellbore pressure are withstood by the rock and the casing, respectively. Once the cementation process is completed, the stress increment (e.g., hydraulic fracturing pressure) is withstood by the casing‐cement sheath‐formation system. The autogenous shrinkage of cement adversely affects the resistance of the system to all types of failure, whereas a moderate swelling of cement is favorable to the cement sheath integrity. In addition, the cement sheath integrity is strongly influenced by the depth: the failure is encountered more easily at the shallow layer. Both the hydraulic fracturing pressure in the completion stage and the increase in casing temperature in the production stage may lead to tensile circumferential stress, and the hydraulic fracturing is the most critical stage for the integrity of cement sheath.