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Coal mines in Pingdingshan mining area, Henan province, China, are commonly mined at a great depth up to 1000 m, and inevitably reside in high temperature, high pressure, high permeability, strong mining disturbance, and strong time effect environment. Support structures of the mines in the area are vulnerable to failure and destruction while roadway stability has been a long-standing issue in the region. Based on the specimens collected from the roof of the return-air rise at Pingdingshan No.1 coal mine, here, we investigated the creep characteristics of sandy mudstone under triaxial conditions and developed a constitutive relationship to predict the creep behavior. Parameter identification and sensitivity analysis were performed to determine the influential factors of creep deformation. We showed that the creep deformation and steady-state creep rate at Pingdingshan coal region grow as axial stress is elevated while descend with increased confining pressure. However, the maximum creep deformation of sandy mudstone increases with a higher confining pressure. Thereby, stress difference, elastic modulus and coefficient of viscosity are the major parameters controlling creep deformation. Hence, it is important to enhance the support strength and mechanical properties of the surrounding rock, to better the roadway stability. In addition, numerical simulation was also conducted for simple excavation geometries to analyze different support structures. On this basis, the "cable bolts steel arch, deep and shallow reinjection, floor pressure relief and local reinforcement" scheme was proposed and field practice showed promising results. The findings in this study can be used to guide the support design for the deep soft rock roadway (DSRR). [ABSTRACT FROM AUTHOR]

In deep mines, since the broken surrounding rocks & high-stress level of a roadway being near a coal seam, the creep characteristics of surrounding rocks should be considered as the main influencing factor in the selection for the roadway's location of the lower coal seam. Both VI15 and VI16-17 coal seams of the Pingdingshan No. 4 Coal Mine, in China, Henan province, are close coal seams with a depth of around 900 m. According to the traditional formula calculation results, when the lower coal seam roadway is staggered 10 m to the upper coal seam goaf, the roadway pressure behaviour is significant, and the support becomes difficult. In this paper, the properties of surrounding rock were tested and the influence of lower coal seam on the stress state of surrounding rock is analysed by numerical simulation, and systematic analysis on the stress and creep characteristics of the surrounding rock of the mining roadway and its effects on the deformation is performed. The results demonstrated that the roadway's locations in the lower coal seam can be initially divided into three zones: the zone with accelerated creep, the transition creep zone and the insignificant creep zone. The authors believed that the roadway layout in an insignificant creep zone can achieve a better supporting effect. Based on the geological conditions of the roadway 23070 of the VI16-17 coal seam of the Pingdingshan No. 4 Coal Mine, combined with the above analysis, a reasonable location of roadway (internal offset of 30 m) was determined using numerical simulation method. The reliability of the research results is verified by field measurement. The above results can provide a reference for selecting the roadway's location under similar conditions. [ABSTRACT FROM AUTHOR]