Pile Foundation and Soil Response to Deep Excavation

Abstract

Construction of deep excavation in densely populated area is not a trivial thing. The execution could induce disturbance to the soil and adjacent buildings. Many researches have analysed building responses to deep excavation or tunnelling projects. But the studies were mostly limited to buildings with shallow foundations. The importance of understanding the behaviour of piled buildings is significant, especially in the analysis of buildings displacement. It is commonly found that deep excavation pits are situated close to piled buildings, especially in densely populated cities with soft subsurface. Even the buildings are founded on piles, there are no guarantees that the buildings are not affected by deep excavation activities. Currently, a metro extension project in Amsterdam is being built. It passes the historic centre of the city and the buildings are founded on pile foundations. The project involved numerous amounts of measurements. Based on the measurement results, it has been found that due to the project, the buildings settle more than the foundation layer, but less than the surface settlement. It is suspected that the settlement of the buildings is influenced by the behaviour of the pile foundation. This research is conducted to investigate and explain pile behaviour during the execution of deep excavation project. The focus of the study is at Ceintuurbaan station. The construction stages are modelled in 3-dimensional finite element analysis, in order to include the diaphragm wall installation phases. Before analysing the pile behaviour, back analysis of soil displacement is performed. After reasonable agreement in the soil displacement has been achieved, the pile behaviour has been analysed in more detail. It is found that a reasonable agreement between measurement and simulation results can be obtained. Based on the analysis results, it is evident that the settlement of the building is influenced by several factors, including stress changes in the soil, neutral plane position, and the settlement of the soil adjacent to the pile. These factors are related interactively during each construction stage. The load on the pile also plays important role. Pile with higher load will experience larger settlement compared to pile with smaller load. Based on the monitoring data and the 3D simulation results, the importance of each construction stage is demonstrated. Based on the analysis of monitoring data at Ceintuurbaan Station, it is shown that preliminary works could induce 31-59% of soil and building settlement. In the analysis of soil-structure interaction, it is important to take into account each construction stages and it should not only focus on the excavation stages.