Failure Depth of a Floor of a Fully Mechanized Working Face When Passing a Collapse Column

Jinlong Cai,Min Tu,Wensong Xu

doi:10.1155/2018/9406839

Jinlong Cai, Min Tu + Show 1 more

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https://doi.org/10.1155/2018/9406839

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Abstract

The stress change law of a collapse column and the failure depth of a coal seam floor before and after mining when the fully mechanized coal mining face passes through the collapse column are investigated. Here, we present the constructed program in FISH language, render the damage variable in FLAC3D to establish the numerical model, and complete the numerical calculation. The 10–115 working faces that pass the collapse column at a coal mine in Tuanbai are identified as the research object. The floor failure is numerically simulated to assess the damage. The following results were obtained: the failure depth of the full floor is stabilized at 14.6 m; the maximum failure depth of the floor near the collapse column is 18.2 m; and the stress concentration coefficient is 1.27 times greater than that of normal mining. The calculated depth failure of the floor of the working face without structural defects is 14.6–14.7 m based on the Hoek–Brown criterion. With the collapse column, the failure depth of the floor is 16.8–17.8 m. According to the water injection test, the maximum failure depth of the floor is 18 m. The three derived values agree well with one another.

Highlights

In northern China, collapse columns are widely distributed in the Permian–Carboniferous coalfields
When the compaction and cementation of the fillings in the collapse columns are poor, the columns may be activated and transformed into Ordovician limestone water inrush channels under the action of mining and other external factors, which can lead to water disasters
Wang et al [7,8,9,10] explained the burst of water inrush from the floor based on cusp catastrophe theory by using mathematical mechanics

Summary

Introduction

In northern China, collapse columns are widely distributed in the Permian–Carboniferous coalfields. Many scholars have studied the stress distributions of collapse columns and their surrounding rocks and the related failure depth of floors. Wang and Park [15] explained the failure and water inrush mechanisms of a coal floor in a goaf area by conducting simulation analysis in FLAC3D. Xu et al [18] and Liu et al [19] derived the constitutive relations of fractured rock masses from the reciprocal theorem and established the damage evolution equation and the probability model with a strength criterion by employing fracture mechanics Both authors verified the applicability of the water inrush law of collapse columns through theoretical analysis and numerical simulation. Collapse columns may indicate a water drench phenomenon, which implies water inrush, and can complicate the hydrogeological conditions of the mine

Realization of the Damage Theory in FLAC3D

Numerical Simulation and Prediction

Analysis of the Vertical Stress

Theoretical Calculation

Findings

Conclusions