Study on the Rock Mass Caving and Surface Subsidence Mechanism Based on an In Situ Geological Investigation and Numerical Analysis

Fengyu Ren,Shaohua Li,Dongjie Zhang,Miao Yu,Jianli Cao

doi:10.1155/2018/6054145

Abstract

To deeply understand the mechanism of the rock mass caving and associated surface subsidence during sublevel caving mining, the Xiaowanggou iron mine was selected as an engineering project case study. The study area was analyzed by means of an in situ geological investigation and numerical simulation. First, a borehole television (BHTV) system and a GPS monitoring system were used to monitor the caving process of the roof rock mass and the development of the surface subsidence; the monitoring time was thirteen months. Then, a numerical simulation was used to analyze the damage evolution of the rock mass. Research shows the following:(1)in situ geological monitoring results indicate that the caving process of the roof rock mass presents intermittent characteristics, where slow caving and sudden caving are conducted alternatively and the arched-caving trend is more pronounced with continuous mining. The surface subsidence, horizontal displacement, and horizontal deformation of the hanging wall are higher than that of the footwall, and the subsidence center gradually deflects to the hanging wall in the late stage of the +45m sublevel mining.(2)Numerical simulation results indicate that the extension and penetration of the shear and tensile cracks along the joints and intact rock bridges are the main factors causing the rock mass caving and the existence of the stress arch and its evolution process is the fundamental reason for the intermittent caving of the rock mass. The rapid development of damage to the hanging wall (the damage angle reduced) is the main cause of the deflection of the subsidence center affected by joints and the mining size.(3)In the future of mining, large-scale subsidence will occur on the surface of the hanging wall.

Highlights

There are a large number of iron ore resources in the northeastern part of China, and the total reserves of these resources account for two-fifths of the national gross proved reserves
Due to the influence of geological conditions, orebody distribution characteristics, and mining technology, most of these underground iron mines are mined by the sublevel caving method [1,2,3], which is characterized by extraction on a large scale and high production efficiency with low mining cost
To control the dangerous situation, it is of great importance to study the mechanism of the rock mass caving and associated surface subsidence

Summary

Introduction

There are a large number of iron ore resources in the northeastern part of China, and the total reserves of these resources account for two-fifths of the national gross proved reserves. The caving process propagates upwards to the surface; significant surface subsidence appears and even large-scale collapse pits are formed [9]. As a result, this poses a serious threat to buildings, haulage roads, rivers, industrial facilities, and farmland [10,11,12]. The strike length is approximately 350m and the average thickness is 100m It is a typically inclined metal mine, the deep mining area extends from 190 m below the surface to over 340 m, and the surrounding rock is mainly mixed granite

Results

Discussion

Conclusion