Influence of consolidation settlement on the stability of inclined TBM tunnels in a coal mine

The Xinjie Coalfields in China plan to construct two inclined mine access tunnels using a tunnel boring machine. These tunnels will be supported by a segmented concrete liner and will penetrate 50 m of Quaternary silty clay before they enter the sedimentary bedrock hosting the coal seams. Dewatering associated with future coal mining activities are expected to reduce the pore pressures within the silty clay resulting in approximately 0.3 m of consolidation-induced settlement that may affect the mine tunnels. Consolidation settlement of thick soil deposits has damaged shafts at other coal mines in China and thus it was important to evaluate the impact of consolidation settlement on the planned tunnels, which will be the first inclined tunnels excavated by TBM in a coal mine in China. The consolidation deformation ratio obtained from 1-D consolidation tests on core samples of the silty clay was used to estimate the consolidation settlement. By regarding the inclined mine tunnel as a cantilever beam, a method is proposed to analyse the influence of consolidation settlement on the stability of the tunnel. An equivalent continuous model was used to study the mechanical behaviour of the segmented liner. Using the proposed new method, the consolidation settlements are predicted to not adversely affect the inclined tunnels because the lateral stiffness of the tunnel liner is relatively soft. The bending of the tunnel liner caused by the ground settlement does not induce high stresses in the liner.