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

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.