Abstract
To investigate the compressive strength and permeability of deep mudstone under stress disturbance, a triaxial rheometer is used to conduct seepage experiments on mudstone specimens with different buried depths under triaxial compression and unloading conditions. The experimental results show that the compressive strength of mudstone specimen with a depth of 1000 m is much lower than that of specimen with a depth of 200 m, and the compressive strength of mudstone increases with the increase in confining pressure. Under constant axial pressure and unloading of the confining pressure, the mudstone with a depth of 200 m exhibits brittle failure, and the strain fluctuates in a pointwise manner with the increase in axial stress. In this case, the mudstone with a depth of 1000 m exhibits a transition from brittle failure to ductile failure, and the strain fluctuates linearly with the axial stress. Further, when the volumetric strain change reaches 0.01, it shows an oblique “Z” fluctuation. During the initial stage of unloading of confining pressure, the permeabilities of both the mudstone specimens (with depths of 200 and 1000 m) decrease gradually. As the confining pressure is unloaded, the permeability of mudstone with a depth of 1000 m increases. Until the specimen is completely destroyed, the permeability of mudstone increases rapidly. Overall, this study can serve as a useful reference for analyzing the engineering disasters associated with deep rock mass, tunnel ventilation, and gas storage.
Highlights
During the process of underground mining, roadway excavation and heading face cause the surrounding rock to produce stress disturbance and break the equilibrium state of coal and rock, which is usually manifested as axial loading and confining pressure unloading. is phenomenon is more obvious during the deep mining of coal and rock.Traditionally, the mechanical properties of coal and rock are primarily investigated using experimental triaxial compression test [1,2,3]
In this study, based on the difference between deep and shallow rocks, the compressive strength and permeability characteristics of deep mudstone under confining pressure unloading are investigated through comparative experiments. e results can serve as an effective guide for the analysis of engineering disasters associated with deep rock mass, roadway ventilation, and gas storage
The two deep buried mudstones exhibit significantly different response in the confining pressure unloading stage. e volume strain of mudstone with buried depth of 200 m is negligibly changed during this stage, and the axial stress remains basically constant at its maximum value and fluctuates in a pointwise manner until the confining pressure is unloaded to 6 MPa, which indicates fracture of the specimen, where the volume strain drops rapidly, and the mudstone exhibits extremely strong brittle characteristics. e volume strain (Δε) of the mudstone specimen with buried depth of 1000 m is close to 0.02 at this stage
Summary
During the process of underground mining, roadway excavation and heading face cause the surrounding rock to produce stress disturbance and break the equilibrium state of coal and rock, which is usually manifested as axial loading and confining pressure unloading. is phenomenon is more obvious during the deep mining of coal and rock. The mechanical properties of coal and rock are primarily investigated using experimental triaxial compression test [1,2,3]. E influence of confining pressure and loading-unloading cycles on the mechanical properties of residual rocks was examined through the stress and strain characteristics and acoustic emission monitoring. Several other researchers (Pan and Connell [14], Wang and Du [15], Xie et al [16], and Zhang et al [17]) systematically explored the mechanical or permeability properties of coals under confining pressure unloading through triaxial compression tests. In this study, based on the difference between deep and shallow rocks, the compressive strength and permeability characteristics of deep mudstone under confining pressure unloading are investigated through comparative experiments. In this study, based on the difference between deep and shallow rocks, the compressive strength and permeability characteristics of deep mudstone under confining pressure unloading are investigated through comparative experiments. e results can serve as an effective guide for the analysis of engineering disasters associated with deep rock mass, roadway ventilation, and gas storage
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