Numerical Simulation of the Stress Field in Repeated Mining of Coal Seams Based on In Situ Stress Measurement

Donghui Yang,Zhangxuan Ning,Zhaoheng Lv,Bohu Yang,Yongming Li,Hongming Cheng,Qiuhong Wu

doi:10.1155/2021/3588868

Abstract

We established an evaluation index of the rock mass stress state for underground coal mines using the strength-stress ratio based on the measured in situ stress and the generalized Hoek–Brown strength criterion. Three in situ stress states, σcm/σ1m < 1.4 (high), 1.4 < σcm/σ1m < 3.6 (medium), and σcm/σ1m > 3.6 (low), were established based on the value of the unconfined compressive strength (σcm) and the maximum principal stress of the rock mass (σ1m). This index classifies the Burtai mine as a medium-high in situ stress field, which is in agreement with the on-site situation, establishing the reliability of the index. The working face was a three-dimensional geological model based on the log sheets. The initial conditions for the model were determined using the combined measurements of the in situ stress regression model. We performed numerical simulations of the roof stress field distribution under repeated mining. Mining the overlying coal seam leads to significant variation in the value and direction of the main roof, σ1, within the range of the front abutment pressure under the pillar and gob. Along the main roof strike direction, σ1 under the pillar is 1.5 times that under the gob, and the σ1 direction under the pillar is deflected by 5°, which is 30° smaller than that under the gob. This provides a reference for optimized underground coal mining.

Highlights

E strength-stress ratio method was used to establish the evaluation index for the stress state of the mine rock mass based on the in situ stress measurement through Kaiser effect and the generalized Hoek–Brown rock mass strength criterion, and a preliminary engineering verification was carried out
A refined geological model for the stratum occurrence conditions in the Burtai mine was established with 42# coal seam mining combined with the measured in situ stress regression model. e roof stress field of the working face under repeated mining conditions provided a reference for optimizing the mining plan in the Burtai mine and provided the guidelines for mines under similar conditions
Stress increase zones, and stress reduction zones are present on the strike of the working face under the pillar, and the size of the stress increase zone is different under different pillars

Summary

Introduction

E strength-stress ratio method was used to establish the evaluation index for the stress state of the mine rock mass based on the in situ stress measurement through Kaiser effect and the generalized Hoek–Brown rock mass strength criterion, and a preliminary engineering verification was carried out. When σcm/ σ1m > 3.6, local rock mass collapses, or the structural plane becomes unstable because it is difficult to achieve a ninefold stress concentration factor in coal-measure strata, and this corresponds to a low in situ stress state.

Results

Conclusion