A Mechanical Model of the Overlying Rock Masses in Undersea Coal Mining and a Stress-Seepage Coupling Numerical Simulation

Jie Fang,Zhiguo Cao,Lei Tian,Zhijie Wen,Yanyan Cai,Jinhao Wen

doi:10.1155/2018/8161498

Abstract

The water inrush of a working face is the main hidden danger to the safe mining of underwater coal seams. It is known that the development of water-flowing fractured zones in overlying strata is the basic path which causes water inrushes in working faces. In the engineering background of the underwater mining in the Longkou Mining Area, the analysis model and judgment method of crack propagation were created on the basis of the Mohr–Coulomb criterion. Fish language was used to couple the extension model into the FLAC3d software, in order to simulate the mining process of the underwater coal seam, as well as to analyze the initiation evolutionary characteristics and seepage laws of the fractured zones in the overlying strata during the advancing processes of the working face. The results showed that, during the coal seam mining process, the mining fractured zones which had been caused by the compression-shear and tension-shear were mainly concentrated in the overlying strata of the working face. Also, the open-off cut and mining working face were the key sections of the water inrush in the rock mass. The condition of the water disaster was the formation of a water inrush channel. The possible water inrush channels in underwater coal mining are mainly composed of water-flowing fractured zones which are formed during the excavation processes. The numerical simulation results were validated through the practical engineering of field observations on the height of water-flowing fractured zone, which displayed a favorable adaptability.

Highlights

Mining activities under complicated conditions, especially underwater coal mining, have attracted constant attention recently, due to the increasing demand for coal resources
Undersea mining technology represents the highest level of underwater mining. e greatest concern of undersea coal mining is the prevention of the seawater flushing into the undersea coal mines. e undersea coal mine water inrushes are the major factors affecting the safety of undersea mining
According to some of the previous analyses, the water inrushes, which are caused by the development of Advances in Civil Engineering water-flowing fractured zones, and the connections with the overlying aquifers are the main reasons for water inrushes induced by roof caving [5,6,7]. erefore, the examination of the damage height problems of the overlying strata in stopes should be given appropriate attention [8,9,10]

Summary

Introduction

Mining activities under complicated conditions, especially underwater coal mining, have attracted constant attention recently, due to the increasing demand for coal resources. E fractures and failure instabilities of the surrounding rock masses within a mining space, especially the roof areas, are considered to be dynamic processes. Using a physical test system of similar materials, Chen et al [14] analyzed and discussed the laws and mechanisms of roof water inrushes during underwater mining processes. In the engineering backgrounds of certain under-river coal mines, Lai et al [15] used an indoor mechanical characteristic test experiment of roof rock masses, which included physical simulations, numerical simulations, and other means to consider the stress fields and overlying strata rupture instabilities as a dynamic system. Erefore, on this basis, a “three-zone” theory which was composed of a caving zone, water-flowing fractured zone, and overall mobile zone for the overlying strata failure was created and developed in China. In the engineering background of the underwater mining in the Longkou Mining Area, based on the above research, a FLAC3d numerical model was established according to the specific geological conditions. en, through the theoretical analysis of the roof structure mechanical model in this study, the roof movements and seepage laws during the process of the advancing working face were effectively simulated

Criterion of Crack Propagation under Water Pressure

Criterion of the Fracture Propagation

Discussion

Conclusions e conclusions reached in this study were as follows: