Design Aspects of Deep Excavations in Soft Clays Focusing on Retaining System
The West Link (Västlanken) railway tunnel in Gothenburg is characterized by wide and deep excavations in soft clays. This paper focus on the excavation in the central station area of the E02 contract. The excavation, around 15m deep and 50m wide, follows a bottom-up methodology within the 100m deep Gothenburg soft clay. The retaining system, with diaphragm walls supported by temporary steel struts at the top and concrete cross-walls below planned final excavation level, represents one of the main design challenges. This paper addresses the design analysis using FEM software PLAXIS, where a 2D equivalent model of the cross-wall, simulated as a trussbeam element, is compared against a 3D model with volumetric cross-walls panels with interfaces between panels. The NGI-ADP soil constitutive model is used in order to capture the anisotropic behaviour of the clay and the soil-structure interaction with the diaphragm walls. The horizontal stability of the cross-walls, due to asymmetrical loads during longitudinal excavation sequence is also evaluated.