Geotechnical Aspects of Underground Construction in Soft Ground

The development of tunnelling projects for new transportation systems in many urban areas is an inevitable trend because of the increasing shortage of over ground space in the built environment. A critical problem in tunnel construction is the induced ground deformations that may cause serious damage to surrounding structures. Therefore, realistic prediction of tunnelling-induced ground movements is very important to ensure operational safety for surrounding buildings. Finite element analysis is among the common methods that has been used widely for prediction of ground movements caused by tunnel excavation. However, one of the common drawbacks of finite element analysis in tunnelling is the obtained settlement curves are often wider than those in practice especially for shallow tunnels. This paper proposes a modification to the original gap method to take into account the deformation mechanism of sand soil around the tunnel boundary. A series of finite element analyses using different tunnel excavation simulation approaches, including the gap method and the modified gap method, have been carried out to back-analyse surface settlement caused by tunnelling in sand in line Number 1 Ben Thanh - Suoi Tien in Ho Chi Minh city, Vietnam. The field measurements are used to evaluate the performance of each approach. It was found that the modified gap method proposed in this paper provided closer prediction to the measured soil settlement.