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.