Protective coal pillar design for segmental lining-supported TBM mine tunnels using physical model tests

Segmental lining is a new supporting structure for mine tunnels, but the applicability of the existing protective coal pillar design method to this structure is uncertain. In this paper, based on TBM-inclined tunnels in Xinjie Coalmine, China, a 1:35 scale 2D physical model with a 4 m width and 1.8 m height was constructed to simulate the complete engineering process. The effects of coal mining on the safety of segmental linings were assessed to determine the optimal size of the coal pillar under inclined tunnels. The results indicate that a reasonable pillar width can maintain the inclined tunnel and its segmental lining stable under deep mining activities. During the coal excavation process, the tangential force around the lining will gradually increase; the left shoulder, crown, and right shoulder of the lining are the positions where the highest forces are expected, which are two or three times those of other positions; and the maximum displacement of the tunnel in the vertical direction is approximately triple that in the horizontal direction. Mining-induced rock bursts are the key factor in lining instability, especially under excessive amplitudes and high-frequency vibrations, which promote segment cracking. For the Xinjie Coalmine, damage to the tunnel lining can be initiated when the coal pillar width below the pair of tunnels reaches 120 m, and visible cracks appear when the pillar width is below 100 m. Thus, it is recommended that the optimum pillar width for mining should be set at 120 m.