土压平衡盾构不满舱施工遇到的问题及对策

中国土压平衡盾构采用不满舱施工非常普遍,因此施工过程中经常出现一些问题。通过对开挖面压力平衡状态的分析,结合工程实例对开挖面的整体稳定、渣土排出异常、开挖面部分坍塌、壁后注浆窜浆等现象进行讨论,解释其发生的主要原理。提出渣土泥浆化的概念、判断标准,明确其与喷涌的差异,并讨论不满舱施工时窜浆发生过程,给出判断窜浆发生的主要条件,明确发生局部渗透破坏的条件。研究结果表明:即使风化岩等高渗性地层开挖面整体稳定性计算满足不满舱施工的强度要求,也会出现局部渗透破坏甚至开挖面坍塌;不满舱施工开挖面局部渗透破坏等引起的超挖量大、窜浆引起盾尾充填效果差均导致地表沉降过大。基于上述问题产生的原理提出相应措施以维持土舱内压力与地层中土水压力的平衡,研究结果能够为土压平衡盾构施工提供一定技术支撑。

Problems and Measures of Earth Pressure Balance Shield During Construction with the Unfilled Chamber

During low-pressure construction in the earth pressure balance (EPB) shield in China, problems often occur in the construction process due to the unfilled chamber. Based on an analysis of the pressure balance state of the excavation face, combined with engineering examples, problems, such as the abnormal discharge of soil in the high-permeability stratum, unstable failure of the excavation face, grout leakage, and excessive surface settlement, were studied to clarify the main principles of their occurrence. The concept of the judgment standard of chamber soil sliming was proposed, and the difference between sliming and spewing was clarified. Even if the stability calculation of the excavation surface of the high-permeability strata, such as weathered rock, met the strength requirements of the overall stability of the surface, partial seepage failure was considered to occur and gradually develop into the collapse of the excavation face. In addition, the conditions for partial seepage failure were examined. Furthermore, the process of backfill grouting leakage during construction with a unfilled chamber was investigated, and the main conditions for determining the occurrence of grout leakage were determined. The significant over-excavation of the stratum due to seepage failure and the poor grouting effect due to grout leakage are expected to lead to excessive surface settlement. Based on the principles of the above-mentioned problems, corresponding measures were proposed to maintain the balance between the chamber pressure and the earth and water pressures in the stratum. The findings of this study may provide technical support for EPB shield construction in China.