Nonlinear three-dimensional modeling of bentonite slurry tunneling

Abstract

The Egyptian tunneling activities have been augmented in the last two decades for several purposes such as the construction of subways, sewers, and road tunnels. The preponderance of the Egyptian tunnels is constructed through soft alluvial soils under high groundwater 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 successful in many Egyptian tunneling projects. In the present study, a three-dimensional finite element model is developed to update the different sophisticated measures employed in the Bentonite Slurry technique to minimize the ground displacements associated with tunneling operation. The proposed numerical model is used to evaluate two case studies of tunnel projects constructed in Cairo namely, Greater Cairo Metro and the intersection of Al-Azhar Twin Road Tunnels and the CWO sewer at Port Said Street. The latter case study is a typical three-dimensional problem; otherwise, the output will be unrealistic. The results of the numerical modeling of the two case studies are then compared with the field measurements compiled during tunneling activities in order to verify the results of the proposed numerical model.