3D Evaluation of PWP Development Due to Tunnel Excavation in an Over Consolidated Clay

Abstract

The stress relief promoted by the excavation process may induce the reduction of the pore water pressure within the soil when an undrained condition occurs. According to the magnitude of the stress relief and the initial hydrostatic pressure, the pore water pressure reduction may generate suction in the soil, thus increasing the soil shear strength. Effects of the stress relief promoted by a circular tunnel excavation process in stiff clay was investigated by means of a series of 3D numerical analyses. These analyses considered a NATM unsupported excavation advance of a shallow and small diameter tunnel in a saturated soil mass. The results highlight the development of a suction zone in front of the tunnel face where the soil shear strength is increased. The extension of this suction zone and its dissipation rate through time, however, are influenced by the soil massif coefficient of earth pressure at rest, and hydraulic conductivity, respectively.