Effect of the face support pressure on tunnelling-induced ground movement

This paper studies the influence of the tunnel face support on tunnelling-induced ground movements via numerical methods. An advanced 3D FEM numerical model is used which realistically simulates the main characteristics of an EPB tunnel excavation procedure (i.e., the steering gap between the shield and the surrounding soil, the segmental lining, grout pressure and its consolidation characteristics, the rate of excavation advance). The Simulia Abaqus FEM code is used to perform coupled hydro-mechanical analyses which can account for the effect of the groundwater. The results suggest a strong interplay between the applied face pressure, ground strength and the anticipated surface settlement. In general, an increased ground strength (favorable geotechnical conditions) limits the anticipated surface settlements even under relatively low face pressures (i.e., 50% of the horizontal total geostatic stress), while examining excavation through poor geotechnical conditions reveals an increased sensitivity of the ground settlement on the magnitude of the applied face pressure. Overall, the results reveal a strong relation between face stability conditions and surface settlement, with face stability being a necessary but not a sufficient condition for surface settlement minimization.