Mechanism of Support Optimization and Confined Blasting of Thick and Hard Rock with a Wedge-Structure Immediate Roof: A Case Study

Tong Zhao,Changyou Liu,Peilin Gong,Xiaofei Gong,Kaan Yetilmezsoy,Majid Bahramian,Loupasakis Constantinos

doi:10.1155/2021/5586310

Abstract

Based on the occurrence conditions of a thick and hard main roof and wedge-structure immediate roof in the Zhuxianzhuang Coal Mine, the fracture characteristics and instability migration law of a thick and hard roof (THR) were examined via physical simulations. Mining zones were divided with respect to the strata behaviors and roof control difficulty levels, and the principles and methods of zonal control under THR were put forward. This study proposed a coordinated control strategy of using confined blasting in water-filled deep holes, and reasonable support optimization, which could effectively reduce the roof fracture size, increases the supporting intensity and eliminate roof-control disasters. The length of confined blasting blocks and supporting intensity were calculated using a mechanical model for roof control in the strong strata behavior zone and less-strong strata behavior zone. These key parameters were determined as 20–25 m and 1.15–1.28 MPa, respectively, and the mining strategy was successfully applied in working face 880, performing high security and reasonable economical efficiency.

Highlights

In China, coal seams with a thick and hard roof (THR) are more than 1/3 of the total active coal mines [1, 2]; roof accidents have been ranked the highest among coal mining accidents over the last decade for its frequency and fatality [3]
The first fracture and collapse of THR occurred when the working face advanced to 132 m, which indicates that the first weighting distance is set to be 132 m (Figure 3(b))
The THR blocks rapidly subsided and squeezed the gangue after the initial fracture, and strong strata behaviors occurred in the stope

Summary

Introduction

In China, coal seams with a thick and hard roof (THR) are more than 1/3 of the total active coal mines [1, 2]; roof accidents have been ranked the highest among coal mining accidents over the last decade for its frequency and fatality [3]. THR is hard to control owing to its high strength, large thickness, and strong integrity [4]. Strong strata behaviors have been observed during mining, whose fracture instability has potentially led to frequent serious support crushing accidents. THR control has been considered as the main principle for safe and efficient coal mining. With the immediate roof thickness being decreased to 0, THR came in direct contact with the coal seam; the subsidence space, fracture location, and size of the broken blocks differed from those with thick immediate roof, so was the mining response [5]. Under the conditions of a thick and hard main roof and thin or even lacking immediate roof, the precontrol of THR was a prerequisite for roof safety rather than support optimization in the conventional control strategy [6, 7]

Methods

Results

Conclusion