Experience from short-and long-term performance of deep excavations in soft sensitive clays

Abstract

Design of excavations and permanent underground structures requires accurate predictions of e.g. deformations and earth pressures for both the short-and long-term. As excavation depths increase and/or the proximity to adjacent infrastructure decreases, there is a need to improve and develop existing design methods and validate numerical models. The first part of this paper revisits the measurement data from a previous excavation, the Göta Tunnel in Gothenburg, Sweden, in order to benchmark a contemporary constitutive soil model, called Creep-SCLAY1S. This study looks into time series including e.g. final dewatering of the excavation, followed by the development of pore water pressures, earth pressures and deformations over time (until 2 years after excavation). The model predictions are in general in good agreement with the measurement data up to final dewatering. However, installation effects due to drilling are believed to have caused continued deformations which are difficult to capture in the numerical model. Part two of the paper presents details of a recently instrumented excavation in soft clay in Central Gothenburg. The measurement data comprises e.g. pore water pressures, deformations as well as vertical and horizontal earth pressures at three locations under the permanent structure. Continued long-term measurements are planned and the existing and future data are believed to provide valuable insights on the development of the stress state and earth pressures under permanent structures in soft clay.