Effect of Overburden Pressure and Soil Parameters on Tunnel-Induced Ground Settlement

Abstract

AbstractWith the continuous improvement of urban transportation systems, the requirement of the tunnel has increased day by day due to the scarcity of surface space and restricted movements. Mechanized excavation by tunnel boring machine is being extensively used in metro, railway and road tunnels due to comparatively less hazards and relatively faster excavation speed. Therefore, it is essential to have an innovative, cost-effective and safe design of tunnel with appropriate consideration of design methodology and site constraints like existing buildings and other structures. In the design of a tunnel, it is very important to have a proper estimation of ground settlement that is induced due to tunneling. The variation in ground settlement due to varying characteristics of subsurface deposits and tunnel depth, which cause variation of overburden pressure, needs to be addressed properly for tunnel design. Therefore, with this in view, a parametric study has been made for a 6.3 m diameter circular tunnel structure having different depths of 9.7 m, 10.6 m, 12.8 m and 13.6 m, encountering varying soil layers of clayey silt, sandy silt and silty sand. A set of numerical models have been developed to compare the results obtained from an analytical method as well as field data recorded at the project site. The results of the study reveal that ground settlement gradually decreases with an increase of overburden pressure, and thereby, the depth of the tunnel. It is observed that about 9–29% reduction in ground settlement value occurs when overburden pressure, as well as the depth of the tunnel, increases by 10–41%. Also, with the change of soil layer from silty sand to clayey silt, the ground settlement reduces significantly from 14% to 25%, even when the depth of the tunnel remains the same. The findings of the present study may be helpful to the researchers and practicing engineers in the design of tunnels under different subsoil conditions.KeywordsGround settlementSoil parametersTunnel depthOverburden