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

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.

Surface Subsidence Prognosis above an Underground Longwall Excavation and Based on 3D Point Cloud Analysis

“…The 3D point cloud acquired in the initial epoch on 2 February 2017 was selected as the reference cloud in each cloud-to-cloud comparison. Nine C2C analysis were performed by comparing point clouds of each epoch (1)(2)(3)(4)(5)(6)(7)(8)(9) to the reference cloud. The absolute distances between each pair of point cloud along the z-axis are shown in Figures 17-19.…”

“…Obtaining and analyzing these data is the starting point for evaluating the prognostic theories and their rational application. Mining damage is reflected on the surface in the form of subsidence troughs which are that part of the earth's surface that has been transformed under the influence of mining [6][7][8]. A change in shape in the vertical direction (subsidence) is observed between the initial and final state of the surface when equilibrium in the undermined rock mass is reached.…”

Determination of the Ultimate Underground Mining Depth considering the Effect of Granular Rock and the Range of Surface Caving

“…Subsequently, Brown and Ferguson [19] extended Hoek's analysis to consider a sloping ground surface and groundwater pressure in the tension crack and the shear plane. However, the effect of granular rock [20][21][22][23] was neglected to control the surface strata movement.…”

“…Substituting equations (13)- (17) and equations (19) and (20) into equation (18) and rearranging the equation yield…”

Numerical Analysis for the Caving Characteristics of Rock Mass with Inclined Joints in Caving Mining

“…Rafiee et al [21] studied the influence parameters on the cavability of rock mass in block caving mines by using PFC3D software. Ren et al [22] analyzed the damage evolution of a rock mass during caving and the surface subsidence mechanism based on RFPA2D. Eremin et al [23] applied the finite-difference method and the continuum damage mechanics approach to simulate the stress-strain evolution of a rock mass on the underground opening during coal extraction.…”