Numerical Study on the Applicability of the Pipe-Jacking Method for the Main Gate of an Underground Coal Mining in Weak Rock Mass

Ulaankhuu Batsaikhan,Hideki Shimada,Takashi Sasaoka,Akihiro Hamanaka,Hiroto Hashikawa

doi:10.3390/app12031719

Abstract

The typical reinforcements and supports used in the main gate of underground coal mining (particularly in the weak to very weak rock strata), such as rock/cable bolts, steel sets, and grouting materials, often allow the mine to remain serviceable in the long run, but in complicated geotechnical and geological conditions, they are insufficient. Low rock strength leads to instability and exhibits serious ground control issues. The pipe-jacking method with a precast concrete pipe support can be one of the more appropriate options for significantly improving geotechnical concerns. This paper aims to study the applicability of pipe-jacking technology in underground coal mining based on a series of numerical analyses employing a three-dimensional FEM (3D-σ software, Geoscience Research Laboratory Co Ltd, Kanagawa, Japan). In the numerical analyses, we study the crown deformation and failure proximity using different inclination angles for the tunnel, different highwall slopes, and two different shapes for the pipe. It is important to note that a precast concrete pipe is effective as a primary support system and can improve the stability of the main gate efficiently.

Highlights

The increasing demand for coal due to global economic growth and the depletion of coal resources from favorable geological sites force engineers to re-evaluate the safety of underground mining and to create more effective tunneling methods and better supporting procedures
In order to evaluate the stability of the roadways, (a) the failure proximity and (b) the crown deformation, which represents the ground behavior, displacement, and fracturing, were considered under some specific conditions
Numerous displacement measurements have been taken during the extension of the main roadway which had been done from December 2015 to February 2016, the measurement results by extensometer-01, which was installed at around a depth of 13 m and a distance of 60 m from the entrance of the main gate, was selected to compare the actual field deformation and the numerical analysis results

Summary

Introduction

The increasing demand for coal due to global economic growth and the depletion of coal resources from favorable geological sites force engineers to re-evaluate the safety of underground mining and to create more effective tunneling methods and better supporting procedures. Ground control in weak rock is always an interesting challenge for researchers. Designing good supports for tunnels created in weak rocks is a complex problem [1] due to the low quality of the rock mass and the possibility of large deformations. Rocks with an estimated uniaxial compressive strength [2] of less than 25 MPa can be classified as weak, very weak, and extremely weak. Weak rocks that have low strength and high expansibility result in large deformations and severe fractures in the surrounding rock, which lead to instability

Objectives

Results

Conclusion