Study on the Disturbed Mechanical Behavior and Energy Evolution Characteristics of Deep Roof Rock Considering Spatio-Temporal Effects
ObjectiveDeep mines are characterized by significant high geostress and high seepage pressure, which are prone to roof falling, gas outbursts, and other disasters under the strong engineering disturbance during coal mining. The strong engineering disturbance in deep coal seams has a significant spat...
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| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Editorial Department of Journal of Sichuan University (Engineering Science Edition)
2024-01-01
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| Series: | 工程科学与技术 |
| Subjects: | |
| Online Access: | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202400487 |
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| Summary: | ObjectiveDeep mines are characterized by significant high geostress and high seepage pressure, which are prone to roof falling, gas outbursts, and other disasters under the strong engineering disturbance during coal mining. The strong engineering disturbance in deep coal seams has a significant spatio-temporal effect, In the spatial dimension, it is manifested as the cyclic disturbance of longitudinal multi-stage adjacent coal seam mining and the unloading disturbance of working face advancement, and in the time dimension,it is manifested as the historical record of disturbance stress formed by longitudinal adjacent coal seam mining and the disturbance influence of the target coal seam mining. Therefore, coal seam mining disturbance directly determines the mechanical response characteristics of the engineering rock mass,and the reconstruction of the authentic mining disturbance stress path that takes into account the spatio-temporal effect of engineering disturbance is a core challenge in conducting indoor research on disturbed mechanical.MethodsThis paper taking the roof rock of deep high-outburst and low-permeable coal seam as the research object, comprehensively considering the stress evolution process of longitudinal adjacent coal seam mining disturbance and lateral working face mining disturbance, a generalized model of the mining disturbance stress path considering spatio-temporal effect was established. This model generalizes the disturbance stress path generated by the multi-working face mining of coal seam group in the longitudinal dimension as a cyclic loading and unloading process, the increase of the disturbance stress concentration factor caused by the reduction of the distance between the coal seams is reflected in the stress path as the increase of the peak stress of cyclic loading and unloading. The unloading disturbance stress generated by the mining process of target coal seam in the lateral dimension is generalized as an increase in axial compression and a decrease in confining pressure, and the difference in stress path of different disturbance areas is achieved by changing the amplitude of the confining pressure reduction. Based on the disturbance stress path model and fully consider the environmental characteristics of high geostress and high seepage pressure in deep coal seams, the disturbance stress field-seepage field coupled mechanical experiments under different disturbance conditions were conducted by using roof rock taking from coal seams at a depth below 1000m. The strength and deformation characteristics of roof rocks in each disturbance area under different confining pressure (10MPa, 20MPa and 30MPa) and seepage pressure (2MPa, 4MPa and 6MPa) conditions are comprehensively clarified, and the energy evolution of deep roof rocks under the influence of cyclic loading disturbance and excavation unloading disturbance load were analyzed.Results and Discussions The results show that the roof rock damage accumulates and deepens due to the mining disturbance of adjacent multi-faces, and the smaller the layer spacing of adjacent coal seams, the stronger the interlayer disturbance effect. The results of cyclic loading and unloading experiments show that directly proportional to the number of cycles,and the larger the confining pressure, the faster the strain growth rate. The elastic modulus and poisson's ratio change periodically with the evolution of loading and unloading process, and seepage pressure is negatively correlated with elastic modulus and positively correlated with poisson's ratio. With the increase of the loading stress level, the elastic modulus decreases, and area of the hysteresis loop shows an obvious positive correlation with the loading stress level. Additionally, the elastic modulus of the unloading stage is greater than that of the loading stage. The yield stage weakening under the influence of lateral working face mining disturbance, with peak strength decreased significantly and post-peak axial stress decreases rapidly. The closer the roof rock is to the already excavated roadway, the stronger the unloading disturbance, resulting in a more pronounced reduction in peak strength. While increased confining pressure improves the strength of roof rock in original rock stress zone, its influence on excavation disturbance zone, and excavation fragmentation zone remains limited. Seepage pressure significantly suppresses the peak strength of the roof rock and leads to a notable volumetric dilatancy in rock under high seepage pressure conditions. In terms of energy evolution, during the cyclic loading and unloading disturbance stage, the elastic energy and dissipated energy of the roof rock gradually increase. Seepage pressure significantly increases its dissipation energy density, promoting the development of micro-crack development, while increased depth of occurrence results in a higher proportion of elastic energy. During the unloading disturbance stage, the total energy of the roof rock affected by excavation shows a decreasing trend, and the stability of the original rock stress zone is higher, while the disturbance area is more prone to instability and failure. Excavation unloading reduces the energy threshold for crack development, confining pressure increases the energy storage limit, and seepage pressure enhances energy dissipation.ConclusionsThe above research shows that longitudinal adjacent coal seam mining disturbance and lateral working face mining disturbance significantly affects the peak strength of the roof rock. The results can provide useful guidance for disaster prevention and roadway support design optimization in the mining process of deep gas-bearing coal seam. |
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| ISSN: | 2096-3246 |