Study On Ground Settlement During Long-distance EPB Shield Tunneling In Water-rich Sandy Strata

As a technique of tunnel construction, shield tunneling has become the main measure in subway construction of cities in recent year At the same time the main issue considered both in design and construction in urban environments is constrolling ground movement to keep the safety of existing buildings。By analyzing the substantive field observation data about Guang Zhou Metro, the effect that shield digging has on horizontal and vertical land subsidence has been studied. The main work has been done is as follows:1. The ground surface settlement caused by shield tunnelling is dependent on not only the distribution of stratums, ground properties, overburden, underground water, size of tunnel and other objective factors, but also on the GAP and the thrust of excavation face. So close supervision is very important for the control of the ground surface settlement.2. While the shield approaches and crosses the measuring holes, the ground movements of lateral soil behave heaving, moving along the shield tunneling direction and outward the tunnel. Settlement, moving along the shield tunneling direction and inside the tunnel are main deformation characteristics when the shield leaves the measuring holes.3. A 3D numerical model is built with Plaxis to study the settlement of ground surface caused by the construction and operation of a Metro tunnel. the Earth Room Pressure, the fault of shield and soil, the GAP are considered. The results are accordant with site measurement results basically.4. The analysis of the instability of excavation face in sand is done. The limit equilibrium method and the numerical simulation method also are used to analyze the maximum and minimum thrust of excavation face.