Centrifugal model test on relationship between support pressure of shield tunnel face and ground deformation in water rich sand strata

In this study a centrifugal model test system was developed to explore the relationship between the face support pressure and ground deformation characteristics of shield tunnel in water rich sandy soil. Based on Wuhan Metro Line 8 large shield tunnel project, the influence of face support pressure on the face stability and ground deformation characteristics under different buried depths was investigated. The correlation curve between excavation face support pressure and surface deformation was obtained and the results show that: 1) When the cover of tunnel is shallow (<1.5D, where D is shield diameter), the influence of support pressure on surface deformation decreases with the increase of tunnel depth; when the tunnel is deep (>1.5D), no matter the support pressure is too small or too large, the influence of the excavation face support pressure on the ground deformation is difficult to extend to the surface. 2) When the support pressure is too high, the disturbance to the stratum takes on a "fishtail type", which can be divided into compaction area, uplift area and settlement area induced by the jacking of excavation face as well as the settlement area. The settlement area is within 1D from the surface to the excavation surface, and the uplift area is within 1D-2D. 3) When the support pressure is too small, the main disturbance to the ground is settlement, and the influence range is about 1D in front of the excavation face. Additionally, the influence range will increase as the buried depth decreases. Based on centrifugal model test, the suggestion value of the range of support pressure premised on deformation control for different buried depths is obtained, which aims to provide guidance for the control of support pressure in practical engineering.