Comparison of actual ground settlements in tunnelling excavation to model predictions

Abstract

It has been discovered that the underground structures are vulnerable to seismic phenomena mainly due to permanent ground deformations caused by earthquakes rather than the dynamic seismic movement itself. Several models (empirical formulae) have been developed to estimate such deformations. In this paper, measured settlements from the tunnelling excavation for the extension of Line 3 of the Athens Metro (from Egaleo station to Chaidari) are used for the verification and calibration of such formulae. Firstly, some general information is presented concerning the progress of Line 3 so far. Typical buildings, infrastructure and utility grids that can affect the design and construction of the tunnel are examined. Typical geological, hydrogeological and geotechnical conditions along the axis of the excavation, as specified by laboratory tests, are presented as well. According to these conditions, ground settlements are predicted along the tunnel. Secondly, a comparison is made of the actual values of the ground settlements, which come from geotechnical and structured observations, and the estimates provided by the empirical formulae. Some improvements are proposed for this formulae through the RS2 software program (Phase 2 v.9.0) by Rocsience. The improved model is then used to estimate strains that could be induced by future earthquakes.