Large deformation mechanism and “stress relief-support reinforcement” synergetic control method of soft rock roadway in footwall of deep normal fault

Abstract

The surrounding rock of the soft rock roadway is seriously deformed and damaged under the superposition of mining stress and fault tectonic stress. In this paper, taking the No. 232206 intake roadway in Meihuajing Coal Mine as the engineering background, the deformation and failure law of the surrounding rock of the roadway in different fault protection pillar widths were obtained by numerical simulation method. On this basis, the mechanical model of the roadway under the action of hanging wall overburden migration and fault slip in normal faults was established, and the energy-driven mechanism of large deformation of the surrounding rock of the roadway was revealed. The ratio T of the energy applying on anchoring surrounding rock to the resistant energy of the anchored surrounding rock was defined as the criterion for the deformation of the roadway. Finally, it was calculated according to the actual working conditions on site, and the control method of “stress relief-support reinforcement” was used to support the roadway with the risk of large deformation. The on-site monitoring results show that the control effect of the surrounding rock of the roadway is obvious.

1. Introduction

The coal resources in China are complex and diverse in their distribution. Fault structures are inevitable geological factors in the mining of coal mines and are the main factors threatening the safety of mine extraction [1−4]. The mining roadways and working faces near faults are prone to problems such as rock burst, water inrush, and coal and gas outburst [5−9]. During the mining process along the fault working face on the footwall of a normal fault, the soft rock roadways are affected by the superposition of mining stress and tectonic stress, making the surrounding rocks of the roadways very prone to large deformations [10−12].

Experts and scholars have conducted extensive researches on the impact of fault structures on the stability of roadway surrounding rocks. In terms of the influence of fault activation and movement, KENETI et al [13] investigated the effects of horizontal stress, internal friction angle of the fault, a distance of the working face from the fault, mining thickness, vertical stress, and other factors on fault slip, and then determined the main controlling factors of the mining disturbance-induced fault damage slip. CAO et al [14] studied the impact of the main stress deviation induced by mining activities on the risk of fault activation, the characteristics of the main stress deviation on the fault plane of the roadway roof, and the stability of the roof. Through the process of sorting out the main controlling factors of the disaster of rock burst, TAN et al [15] concluded that the two sides of a fault will produce a relative “rebound” under the sudden unloading effect caused by mining disturbance, which will impact the mining roadway. SAINOKI et al [16, 17] used theoretical analysis, numerical simulation, and data analysis methods to study and concluded that in the “fault-fold” structural area, the roadway is subjected to support pressure, tectonic stress, and disturbance from mining dynamic loads. The superimposed load on the surrounding rocks exceeds its critical stress, thereby inducing an impact phenomenon. Based on the incremental plastic flow theory and the rheological theory, KANG et al [18] established a Burgers, viscoplastic and strain softening (BVS) model by connecting an improved Burgers body, an improved viscoplastic body, and a strain-softening plastic body in series to study soft rock roadways. They concluded that the continuous heave of the floor mudstone drives the dilating bottom coal to squeeze into the roadway space.