考虑土体软化的隧道盾构掘进界面稳定性分析

岩土工程中的许多土体有应变软化行为，这种软化行为能导致应变局部化，进而对土体的稳定性有重要影响．首先研究饱和砂土的排水平面应变压缩试验的剪切带的形成，进行数值分析，预测了实验现象．然后，考虑土体应变软化盾构掘进面失稳的影响，对深埋隧道的盾构掘进进行三维数值分析，对比分析渗流条件下应变硬化模型和应变软化模型以及应变软化条件下考虑渗流与未考虑渗流模型之间的区别．分析表明，土体应变软化更容易导致盾构掘进界面失稳，使得开挖面的极限支护压力和地表沉降增大、塑性区扩展比没有应变软化的土体更大．探讨了诸如内摩擦角、黏聚力等土质应变软化参数的变化对盾构掘进界面稳定性的影响，发现内摩擦角软化的影响较大，黏聚力次之．最后，对天津地铁9号线的一段盾构掘进进行了模拟，其结果与工程实测数据相吻合．

Analysis on Stability of Shield Tunneling Face in Soil with Strain-Softening Behavior

Many kinds of soil in geotechnical engineering display strain-softening behavior ,which can result in strain localization and, furthermore, the instability of soil. On the basis of the local strain fields in the specimen obtained from the drained plane strain compression test on saturated sand, the paper first makes a numerical analysis to predict the experimental phenomenon. Then, the strain-softening influence of shield excavation surface instability is consid- ered, three-dimensional numerical simulation for deep shield tunneling is performed, and the strain hardening and sof- tening models in the condition of seepage are compared, so are the seepage and non-seepage models in the condition of strain softening. The analysis shows that, compared with soil without strain-softening behavior, the strain-softening of soil more easily causes the instability of shield tunneling face, increases the limits of face pressure and the settle- ment of the ground, and leads to more expansion of plastic regime. How the change of the values of strain-softening parameters, such as internal friction angle and cohesion, affects the instability of shield tunneling face is discussed, and it is found that internal friction angle has a great influence, followed by cohesion. Finally, the shield tunneling in a section of Tianjin Metro Line 9 is simulated, and the results are consistent with the measured data.