Long-Term Performance of a Deep Excavation in Silty Clay in Xi'an-A Case Study

The long-term deformation of a 17.5 m deep excavation constructed with the bottom-up technique in silty clay in Xi'an was monitored in this study. The retaining wall was built with one or two rows of contiguous bored concrete piles and tie-back prestressing tendons. The monitoring of settlement and lateral deflection at the top of the retaining structure, and the settlement of the ground surface and of the adjacent building lasted for more than 4 years. After the final depth was reached, the excavation was surveyed for more than 3.1 years. It was observed that the deformation of the excavation increased with the increase in the excavation depth, and a significant increase in displacement was recorded after the excavation reached the final depth. The averaged time-dependent rates of the deflection of the retaining wall, and the settlement of the ground surface and of the adjacent building when the excavation remained partially unfilled were around 0.23-0.25 mm/month in this study. The time-dependent behavior of the excavation could lead to excessive deformation and cause severe safety risks to the retaining system. The recorded data, together with a comparison with cases reported in the open literature, are presented in this paper.