Analysis of Shield Excavation Face Failure and Tunneling Control with Two Parameters in Sandy Cobble Strata

Abstract:

To explore the failure process of excavation face and setting of support force during shield tunneling， a three-dimensional engineering discrete element method（EDEM） analysis is conducted for the excavation face failure case in sandy cobble strata of Chengdu Metro. The limit support pressure and excavation face stability are analyzed under the conditions of different support force distributions. Based on the tunneling data observed in the excavation face failure case， the suggested values of two parameters during shield tunneling is proposed for stability of excavation face considering the overall mechanical performance of shield machine. The results show that the failure position of the excavation face is related to the support force distribution. The soil arching effect occurs within 0.75 D above the shield as the excavation face is in the limit state. The failure zone gradually develops to ground surface as the support force decreases to 0.1 P₀. The chamber pressure should be kept less than the static earth pressure with a low rotation speed of cutter head during tunneling， which is supposed to reserve enough cutter head torque for possible large size boulders and chamber pressure control.

Key words:shield tunneling construction;excavation face stability;limit support force;cutter head torque;chamber pressure