科研之友
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摘要
Based on the principles of soil mechanics, a theoretical calculation method for computing the reverse torque of Earth Pressure Balanced shield driving in soft ground was derived by considering lots of relative factors, including the resistant moments induced by soft soil around shield body, the gravity of shield and segments left in shield, and the reaction force of jack thrust. The theoretical calculation method was verified through a case history of a metro tunnel section in Hangzhou soft ground. The reverse torques calculated by the proposed method are approximately 18.9 to 16 times of the measured cutting torques, which implies that the inherent reverse torque of shield can effectively prevent the shield from rolling during the advancing process. In the start stage, although the theoretical calculated reverse torques were still larger than the measured torques, they have low safe factors. A simple but effective method was proposed to prevent shield from rolling in the start stage in the improved ground. Its effectiveness was verified successfully in actual engineering practice. Due to the viscous of soft soils, slight rolling angles of shield body were observed when the cutter head was rotating in one single direction during the advancing process. The rolling angles can be effectively eliminated by adjusting the cutter head in the opposite direction.
