Numerical modelling of a deep excavation in the overconsolidated soil of Vienna

Abstract

This contribution deals with the numerical modeling of a 33-meter-deep excavation in the overconsolidated soil of Vienna. Diaphragm walls are used as retaining structures, which are integrated into the newly constructed metro station at Matzleinsdorfer Platz. Due to deformation-sensitive buildings in the vicinity of the shaft, a comprehensive deformation monitoring system had to be installed on the site. Numerical 2D- and 3D-models, based on the finite element method, were created and compared with each other. Among other approaches, elastoplastic material models with isotropic hardening (Hardening Soil Model with and without small strain stiffness) were used. The soil stiffness parameters of the Hardening Soil Model have been determined through laboratory and field tests. Due to the low hydraulic permeability of the soil, the study also explores the impact of various drainage conditions (drained, undrained, consolidation) on the deformation behavior of the shaft, resulting in a set of 24 calculation models. The calculated deformations are compared with the in-situ measurements of the actual shaft to validate the used soil stiffness parameters and material models. Following a detailed analysis of the results, a suitable calculation model is selected for further soil parameter and sensitivity studies. In the soil parameter study, the effect of the pre-consolidation pressure of the overconsolidated miocene soil layers on the deformation of the diaphragm walls and excavation base is analyzed by varying the pre-overburden pressure (POP) in the calculation model. Additionally, assuming the soil parameters follow a normal distribution, shear and stiffness parameters are varied based on standard deviations from literature. The sensitivity study further explores the influence of the diaphragm wall thickness and concrete beam prop width on the deformation behavior of the retain walls and the basal heave.