Deformation characteristics and control factors of the surrounding rock in the deep buried soft rock roadway under the influence of mining

In view of the phenomenon that deep buried soft rock roadway is arranged outside the range of mining but large deformation still occurs under repeated mining disturbance, the field investigation, stress field analysis and numerical simulation tests are adopted. On the basis of previous studies, a coupled stress calculation model for the stress field of roadway excavation and the stress field of coal seam mining was established. After substituting the data of the research object, it was found that the stress increase or decrease caused by the gob of the adjacent C5 coal seam was below 15%. It is believed that the simple change of stress will generally not cause the overall failure of the support or the large deformation of the roadway, and the mechanical strength of the surrounding rock will be reduced after repeated disturbances, causing the transition from elastoplastic deformation to loose deformation. FLAC3D was used to simulate the inversion of coal-measure strata and the process of controlled deformation of surrounding rock in the early stage of roadway and uneven deformation in the later stage under repeated disturbance of mining.The causes of continuous floor heave and the failure of spray coating, bolt and anchor cable are analyzed. According to the analysis, the optimal state of primary support and the optimal time for the secondary support of the research object are proposed. It is believed that the shotcrete should be preferentially sprayed after excavation to allow the roadway to fully deform in the elastoplastic range to release the surrounding rock stress,and then strong support should be carried out to achieve the optimal state of primary support, and the best time for secondary support is considered to be after the upper section is mined out and before the lower section is mined. The key factor of the failure is the lack of coordination between the stiffness of the jetting layer and surrounding rock caused by the small construction process and the thickness of the jetting layer. It is considered that the key factor to control floor heave is to support the floor to form a complete support structure and avoid the release of stress from the floor. It is also considered that the timing of the support, the bolt length of the anchor rod and the installation quality are the key factors of bolt and cable failure.