富水饱和区盾构隧道施工地表沉降计算方法

随机介质理论在预测隧道开挖引起的地表沉降中应用广泛，但在赋存地下水的地层中，该理论不能完全反映地层变形机理，造成算出的理论结果与实际地表沉降往往存在一定的偏差。为了拓展随机介质理论的应用范围，本文依据地层变形机理，认为在富水地层中隧道开挖引起的沉降原因主要包括开挖扰动导致的地层损失，以及由于地下渗流导致的地层有效应力增加。因而，在传统随机介质理论的基础上，联合地下水渗流理论分别推导了由于隧道开挖扰动和地下渗流作用下的地表沉降理论解，再将两者叠加便得到了隧道在富水地层中的地表沉降值。通过将理论值与数值模拟结果对比，地表沉降曲线较为吻合，证明了所提方法的可靠性。另外，通过与工程案例对比，进一步验证了所提方法的正确性。研究发现，仅考虑隧道扰动或仅考虑地下渗流时，往往会低估隧道在富水地层中造成的沉降，而当两者结合时沉降曲线与数值结果较为接近；隧道开挖后，地表沉降在前期下降速率较快，而后期下降速度变化逐渐缓慢，直至沉降趋于稳定，这主要由于变形机理从地层扰动向渗流诱导转变所致。该研究成果可为隧道在富水地层中开挖时沉降预测和控制提供参考。

THE SURFACE SETTLEMENT CALCULATION CAUSED BY SHIELD TUNNEL CONSTRUCTION IN THE STRATUM WITH GROUNDWATER

The random medium theory is widely used in predicting the surface settlement caused by tunnel excavation, but the theory can not fully reflect the formation deformation mechanism in the stratum with groundwater, resulting in a certain deviation of surface settlement between the theoretical results and the actual results. In order to expand the application scope of random medium theory, based on the formation deformation mechanism, it is considered that the settlement caused by tunnel excavation in water rich formation mainly includes the formation loss caused by excavation disturbance and the increase of formation effective stress caused by underground seepage. Therefore, this paper combined the traditional random medium theory with groundwater seepage theory, and then deduced the theoretical solutions of surface settlement caused by tunnel excavation disturbance and underground seepage respectively, when superposing these two factors, the surface settlement value caused by the tunnel in water rich stratum is obtained. The reliability of the proposed method is proved by comparing the theoretical value with the numerical simulation result, and the surface settlement curves are in good agreement, in addition, the correctness of the proposed method is further verified by comparing with an engineering case. It is found that when only considering tunnel disturbance or underground seepage, the settlement caused by tunnel in water rich stratum is often underestimated, and when the two are combined, the settlement curve is close to the numerical results. After tunnel excavation, the surface settlement decreases rapidly in the early stage, and changes slowly in the later stage until the settlement tends to be stable, which is mainly due to the transformation of deformation mechanism from formation disturbance to seepage induction. The research results can provide reference for the settlement prediction and control of tunnel excavation in water rich stratum.