Numerical simulation of spatiotemporal distributions of stresses in vicinity of normal fault due to mining within hanging wall

Abstract

One main reason for mining earthquakes and fault rockbursts is the fault movement induced by mining. In the previous numerical simulation, monitored nodes are few so that a full understanding of the overall mechanical status on the fault is difficult. Moreover, in the past simulation for the stress distribution of the coal seam, the vertical stress (abutment pressure) is focused on, but not for the other stresses. To study stress distributions of the fault and coal seam in the vicinity of the fault, a numerical model of hanging wall mining was built in FLAC3D. In the model, thirteen rock strata and one normal fault with a dip of 45° were included. Spatiotemporal distributions of the fault and coal seam in the vicinity of the fault were obtained during the mining process. Twenty two nodes on the fault in the hanging wall were monitored to obtain the overall mechanical status on the fault. The following numerical results were obtained. As the working face advances, there are one compressing zone and one or more loosening zones on the fault. The compressing zone on the fault is safe. As the working face advances, the normal stress in loosening zones which are above and below the compressing zone becomes low, and the maximum size of upper loosening zones is about 78m. Fault segments in upper loosening zones become dangerous when the coal wall of the working face is close to the fault. As the working face advances, peaks of vertical, horizontal and shear stresses of the coal seam in the vicinity of the coal wall of the working face in the hanging wall are 7.5 m−10.5 m, 10.5 m−15.5 m and 11.5 m−12.5 m ahead of the coal wall of the working face, respectively. As the working face advances, three kinds of maximum stresses of coal seam in the footwall increase or show an increasing trend. As the horizontal distance between the fault and the coal wall of the working face decrease from 40 m to 20 m, changes in sizes of regions of vertical, horizontal and shear stresses of the coal seam, which are affected by the fault apparently in the hanging wall, are negligible, and sizes of these regions close to the fault are 3.5 m, 10.5 m and 3.5 m, respectively.

Keywords

• fault stress
• stressed zone
• destressed zone
• hanging wall mining
• rock burst