An analytical model to predict the radial deformation of surrounding rock during shaft construction via shaft boring Machine

During shaft construction using a shaft boring machine (SBM), the extrusion effect caused by the thrusts of the shaft boring machine can lead to excessive radial deformation and local failure of the surrounding rock. To calculate the rock radial deformation, the deformation mechanism of the rock during the SBM driving process was investigated via numerical simulation. Then, a new analytical model was proposed to calculate the radial deformation, and the extrusion effect of the shaft boring machine was innovatively considered using an additional vertical stress in the proposed model. The equation of the vertical additional stress can be derived by the limit equilibrium method, and the radial deformation of the surrounding rock is calculated using cavity expansion theory. The effectiveness of the proposed model was verified by numerical calculation results, and a parametrical discussion was performed to study the impacts of the thrusts of the cutterhead and grippers. The results indicate that the rock radial deformation calculated by the proposed model is more accurate than that calculated by the existing model. The maximum radial deformation of the surrounding rock occurs at the transition interface. The thrusts of the shaft boring machine’s cutterhead and grippers are the major factors affecting the rock radial deformation. The increase in the cutterhead thrusts or the decrease in the gripper thrusts will lead to an increase in rock radial deformation. Therefore, an appropriate combination of the shaft boring machine thrusts is beneficial for restricting the radial deformation of the surrounding rock.