Design and measurement of piled-raft foundations

Piled-raft foundations for multi-storey buildings have been employed widely in Shanghai since the 1990s. However, there has been a lack of long-term studies on load distribution, and few improvements have been made to foundation design over the years. The goal of this paper is to extensively analyse long-term data on three multistorey residential buildings with piled-raft foundations to propose an improved design method that has the potential to reduce construction costs. One six-storey building was monitored between 1999 and 2011, and two other six-storey buildings between 1991 and 1995. Parameters analysed over time in this study include pile-raft tests, measured data for load distribution on top of the pile group, ground pressure distribution and the settlement of the buildings. Pile spacing was found to be the key parameter for load sharing between the piles and the soil. The proposed design model accounts for observed load sharing between the piles and the soil and divides the settlement prediction into three steps for a more accurate representation of how settlement proceeds as buildings with piled-raft foundations age. By using the proposed method, safety factors can be calculated more efficiently, which it is expected will lead to reduced construction costs.