FEM Back-Analysis of a Deep Excavation in Hanoi, Vietnam

In Hanoi Old Quarter, buildings tend to develop underground space in order to increase the usable area. The projects have been trending to get deeper and deeper, which challenges the designers as well as the contractors in ensuring the safety not only of deep excavation but also neighbouring existing buildings. A good understanding of diaphragm wall behaviour during basement construction is necessary for future projects. This paper presents a project with 6-basement floors; the excavation depth is about 25 m, built in the Old Quarter with a very high population density (up to 29,500 people/km2). Two soil models including hardening soil model (HSM) and Mohr–Coulomb model (MCM) are adopted in the analyses. The comparison of lateral displacement of diaphragm walls (D-wall) monitored by inclinometers and modelling results is presented. Some conclusions are drawn: the ratio of lateral displacement to excavation depth is around 0.1–0.25% with a maximum value 0.31%. The relationship between the stiffness and the undrained shear strength of the soft clay layer is E = (500–700) Cu (kPa) with hardening soil model.