Performance of a large-span deep excavation in saturated fine-grained soil adjacent to a historical building: A case study

Abstract

A 14-m deep excavation in fine-grained soil below the groundwater level with 50,000 m2 Area has been carried out in the vicinity of a sensitive historical building. Diaphragm walls combined with either tie-back anchors, a buttress wall or a moment-resisting frame were used to protect the structures. A comprehensive monitoring system was developed to evaluate the groundwater situation, deformations and the stresses. the lessons learned from the project are presented and the different retaining systems have been evaluated. The results of monitoring showed that the use of a tie-back diaphragm wall caused a 20 % decrease in horizontal deformation of the wall compared to the moment-resisting frame. Back analysis based on the results of inclinometers showed that the predictions of a generalized soil-hardening model was more compatible with the monitored data than the small-strain hardening model. Data from the piezometers installed between the layers showed that it was not easy to ensure sealing of the interlayer clayey lenses as a bottom plug. This meant that the diaphragm walls should penetrate into suitably thick clay layers. The strain gauges in the structural elements were highly sensitive to variations in temperature, making it necessary to perform temperature analysis on the retaining structures.