The Soil Parameters Effects on the Optimum Face Pressure of Mechanized Tunnels in Cohesive Soils

Estimating the pressure required to support the tunnel face is one of the most important factors regarding safe and optimal excavation using mechanized tunnel boring machines in urban areas. Applying a pressure more or less than the balance to the face would cause collapse and blow out in the tunnel face respectively. This pressure depends on several factors such as soil type and its engineering specifications, TBM type, underground water conditions, excavation method, amount of surcharge and tunnel section area. In this paper, the influence of soil elasticity modulus, cohesion and friction angle on the optimum amount of face pressure in cohesive soil were studied in different underground water conditions. For this purpose, a 3D finite element model was used employing the ABAQUS software (Ver. 6.14). The main construction aspects and all main elements of mechanised excavation were modelled: TBM shield, concrete tunnel lining, over-excavation, tail gap grouting and progressive hardening of the cement based grout. More than 130 3D models were analyzed and optimum pressure in the tunnel face was determined through measurement the amount of induced average displacement in the tunnel face. In the other word, for various elasticity modulus, cohesion, and internal friction angle different values of face pressure were applied in tunnel face and corresponding tunnel face average displacement were measured for each state.