Elasto-plastic Three Dimensional Analysis of Shielded Tunnels, with Special Application on Greater Cairo Metro

Abstract

The Egyptian tunneling activities have augmented in the last two decades for several purposes such as construction of subways, sewers and road tunnels. The preponderance of the Egyptian tunnels are constructed through soft soils under high ground water pressures in which tunneling can trigger substantial ground deformations. The prevailing subsurface conditions limited the construction methods to full face tunneling machines; otherwise tunneling cannot be proceeding. The Bentonite Slurry Shields proved to be very successful m many mega Egyptian tunneling projects.

The objects of the present study is to introduce a sophisticated three­ dimensional numerical model of the Bentonite Slurry Tunneling Machine by adapting the main factors affecting the pressurized Bentonite Slurry Tunneling such as unloading forces due to excavation, ground constitutive nonlinearity, interface condition, engineering properties of shield, rate of advance, machine overcutting, face pressure, yielding zones, the tail grouting and the hardening characteristics of the grout material. Soil constitutive behavior is represented using the hyperbolic elastoplastic model to account for the effect of the stress level, stress path and the confining pressure. Shield and tunnel lining elements are represented by elastic elements considering the different stiffness of the liner and the shield