Discrete- and Finite-Element Analysis on the Tunneling Safety of Pipe Jacking Machine in Coal Rock Formation

Abstract

During pipe jacking in unstable coal rock formation, it is difficult to ensure the stability of the workface and the structural safety of the equipment. To solve the problem, this paper establishes a numerical model for the rock-breaking and slag discharge of pipe jacking machine (PJM) with different tunneling parameters, and numerically analyzes the variations in the flow rate and speed of slags, and the stress and deformation of cutterhead, at different cutterhead speeds (1.0-4.0r/min) and jacking speeds (0.5-4.0mm/s). Based on the simulation results, the authors discussed how different tunneling parameters affect the tunneling safety. The simulation results highlight the importance of the matching between cutterhead speed and jacking speed to tunneling safety. As the jacking speed increased, the load of the cutterhead increased significantly, which may cause the cutter to wear. At the jacking speed of 4.0mm/s, the equivalent stress and deformation of cutterhead peaked at 397.43MPa, and 10.73mm, respectively. Excessive jacking speed may result in accidents, such as deformation and structural fracture of cutterhead, posing a serious threat to the structural safety of cutterhead. As the cutterhead speed increased from 1.0r/min to 4.0r/min, the mean axial speed of slags dropped by 68%, and the slag flow rate declined by 76%, due to the rapid discharge of slags from the cabin. In this case, the slag volume in the cabin cannot provide sufficient support to the workface rock, and the risk of collapse soars during the tunneling in unstable formation. In addition, an excessive cutterhead speed increased tunneling energy consumption and aggravated the wear of the cutterhead. The research results promote the setting of control parameters for the safe pipe jacking in unstable coal rock formation.