软土地区土压平衡盾构反扭矩分析

Analysis of reverse torque of EPB shield tunneling in soft ground

基于土力学基本原理,综合考虑覆土、盾构自重及未脱开管片自重、千斤顶反力因素等产生的阻滞力矩,推导出在软土地层中盾构施工反扭矩理论计算方法。通过杭州软土地区盾构地铁区间实例分析,发现理论计算反扭矩为实测切削扭矩18.9到16.0倍,表明在盾构切削施工过程中,反扭矩足够保证盾构正常掘进而不会有产生侧翻的可能。在盾构始发掘进时,虽然理论计算反扭矩大于实测切削扭矩,但是安全系数较小。提出一种简单有效防止侧翻的措施并应用于实践。由于软黏土的黏滞特性,在刀盘切削扭矩作用下盾构体轻微回转,通过反向调整切削方向可以消除盾构回转角。

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.