饱和土中考虑衬砌界面排水的浅埋盾构隧道开挖影响分析

盾构隧道施工引起的环境土工效应分析一直是隧道及地下建筑工程领域中研究的热点问题。由于目前该领域较少考虑饱和土质以及隧道衬砌与土体间界面排水工况所带来的影响,尤其是较少针对隧道施工长期变形影响以及衬砌应力进行解析分析。由此基于隧道开挖椭圆化变形模式,考虑衬砌界面完全排水以及完全不排水两种工况,提出了饱和土中浅埋隧道开挖引起的地层长短期变形和隧道衬砌应力计算方法。结果表明:椭圆化变形模式对地层短期变形和长期变形的影响均较明显,在此条件下得到的位移曲线与实测值吻合较好。在计算衬砌内力时,衬砌轴力和弯矩整体关于90°/270°轴即隧道竖轴线严格对称,其中轴力沿圆周呈上大圆下小圆的倒“8”字形分布;而弯矩沿圆周呈上下圆基本一致的“8”字形分布,其中下圆稍大。土质和界面排水条件显著影响衬砌内力值的大小,其中饱和土长期排水工况下衬砌内力值一般大于不排水工况解,且其与饱和土短期不排水解相比差距明显。分析成果可为正确预估饱和土浅埋盾构开挖变形提供一定的理论依据。

Excavation influences induced by shallow shield tunnel in saturated soil considering drainage at ground-liner interface

The excavation impact analysis of geo-environmental effects caused by shield tunnel in saturated soil has been a hot issue in the researches of tunnel and underground structure engineering. However, the current researches give little investigations on the impacts of saturated soil as well as the interface drainage process between tunnel liner and surrounding soils. Particularly the long-term deformation influences and the liner stress are not investigated. Considering the two conditions of no drainage or full drainage at the ground-liner interface, a method for soil displacements and liner stresses affected by tunneling is proposed based on the oval deformation mode. It is observed that the oval deformation mode yields significant impacts on both the short-term and long-term ground displacements. The soil deformation curves are in good agreement with the measured values. It can be concluded that when calculating the stress of liner, the axial force and bending moment of liner are strictly symmetrical to axis 90º/270 º or tunnel vertical axes. The type of axial force is somewhat “8”- shaped circumference, with the above circle obviously larger than the below one. The type of bending movement is also “8”-shaped, with the below circle a little larger than the above one. The soil and interface drainage conditions significantly affect the value of internal force of liner. The internal force of liner under long-term and full drainage conditions in saturated soil, which is larger than that under the long-term condition without drainage, is quite different compared to that under the short-term condition without interface drainage. The analysis results may provide a theoretical basis for correct prediction of the shallow shield excavation deformation in saturated soils.