Experimental study of the performance of a 32 m deep excavation in the suburbs of Paris

Abstract

Fort d'Issy-Vanves-Clamart metro station is a 32 m deep excavation part of the new subway line 15 of the Grand Paris Express project. The performance of the support system is assessed through a wide monitoring program covering wall displacements, wall bending moments, strut loads, ground surface settlements, and earth pressure. Classical instrumentation was set up in redundancy to consolidate field measurements (several inclinometers, strain gauges with temperature sensors). Advanced devices were used to provide accurate measurement data, in particular fiber optic was installed along the retaining wall with total pressure and pore-water pressure cells placed at the soil/wall interface at 4 in-depth locations. In addition, measurements data were provided for different excavation levels in order to assess the support system behavior as excavation progressed. The present paper aims at providing a full description of a deep excavation behavior through a complete monitoring system. Bending moments captured with fiber optic are more accurate than those derived from inclinometers. An analysis methodology is proposed to address the temperature effect on strut loads measurements in order to separate the thermal expansion contribution on the strut loading from the excavation process contribution. The stress redistribution behind the wall was observed with the lateral earth pressure increase of top cells while excavating deep levels. The comprehensive field measurements provided in this paper can supply further back analysis to improve numerical modelling prediction.