查看更多>>摘要：? 2021This paper focuses on analyzing the mechanical properties, permeability and energy characteristics of limestone from coal measures strata of through-coal seam (TCS) tunnel in the context of the Taoziya tunnel as the engineering background. The improved MTS815 Flex test GT rock mechanics system and acoustic emission (AE) technology were utilized for the triaxial compression with permeability test of limestone from coal measures strata of TCS tunnel. The results indicate that gas pressure and confining pressure significantly affect the mechanical properties and permeability of limestone from coal measures strata of TCS tunnel. The gas pressure promotes the development and propagation of cracks, whereas increasing confining pressure strengthens the resistance of limestone samples to crack propagation. When limestone samples transition from the initial compaction stage to the unstable cracks propagation stage, the possibility of gas leakage during tunneling in the coal measures strata should be recognized, and the stability of surrounding rock should focus on the failure stage. In the process of progressive failure of limestone samples, AE events with larger amplitude are distributed near the main macroscopic fracture zone, and the distribution of AE events closely corresponds to the macroscopic failure mode of limestone samples. Exponential functions can be used to describe the trend of initial permeability ki, peak permeability kp and residual permeability kr decreasing with effective confining pressure σe. The closure and propagation of microcracks are the fundamental reason for the corresponding relationship between the stress variation process, AE characteristics and permeability of limestone samples. Finally, the energy characteristics of limestone under triaxial compression were analyzed based on the stress-strain curves of limestone. This study may give fresh insights and necessary references to ensure the safe construction and development of TCS tunnels.
查看更多>>摘要：? 2022 Elsevier B.V.Excavation of the galleries for the geological disposal of radioactive waste can induce an excavation damaged zone (EDZ), which can have consequences on the long-term safety of the repository. In this study, intact Callovo-Oxfordian (COx) claystone taken from the Meuse/Haute-Marne Underground Research Laboratory in France was artificially fractured in different directions, and the hydro-mechanical behaviour was investigated by performing high pressure oedometer test and hydraulic conductivity test. Comparison between the fractured and intact COx samples allows identification of the effects of fracture in terms of swelling, compression, hydraulic conductivity and creep. It appears that the presence of fracture decreases the swelling strain and this phenomenon depends on the infiltration path and the orientation of fracture. In particular, the infiltration path affects the global swelling rate of fractured claystone. The self-sealing of fracture is mainly attributed to the swelling of COx claystone grains in the fracture zone. Lower compression coefficient a, higher compression index Cc* and higher secondary consolidation coefficient Cα are observed for the fractured claystone, indicating a higher compressibility and creep than the intact one. The compression and creep behaviours depend on both the orientation of fracture and the stress level. Comparison of hydraulic conductivities between fractured and intact claystone indicates that the hydraulic conductivity can be partially recovered due to the collapse of macro-pores in the filled fracture zone. This is also confirmed by analysing the evolution of consolidation coefficients cv with stress. Beyond a stress level about 16 MPa, the fracture effect can be neglected, but the compressibility increases further due to grain breakage. Interestingly, this stress is close to the in-situ stress before excavation.
NSTL
Elsevier