New Design Method for Space-Varying Rigidity Pile Group with Equal Settlement

Abstract

At present the design method of high-rise building and super high-rise building is based on static equilibrium method. The settlement of foundation should be checked according to the code after the quantity of super-long piles is determined. If theoretical value of settlement has satisfied the design requirement, the design is completed. In Calculation and Study of Settlement of High-rise Building’s Super-long Pile-box (Raft) Foundation, semi-theory and semi-experience solid pier and elastic mechanics are mainly used to calculate the sedimentation value of pile groups. Domestic and foreign experts and code compilation commonly pay attention to the first method, for the method proposed by H.G. Poulis is difficult to get accurate calculation parameters. Otherwise for the settlement calculation of super-long pile-box (raft) foundation (>50m), the value get by theoretical calculation is much higher, even up to ten times of the observed settlement date (for example, for a super long bored pile which is 52.2m long and has piled raft foundation, sedimentation value is 24.5mm, which is got by theoretical calculation based on Shanghai codes, but the measured settlements is 6.9mm and the sedimentation rate is 0.013mm/d before it tended to be stable. Sedimentation value is 22.4mm for another piled-raft foundation which is 59.00m long, but the measured settlements is 2.93mm and the sedimentation rate is 0.0096mm/d before it tended to be stable). The reason for the large error lies in that the composite stiffness of foundation and shoring structures of foundation pit are not considered. According to the distribution of foundation stress, foundation stress and strain analysis, the composite stiffness of foundation play decisive role in foundation settlement, a new design method can be got for pile group with space-varying rigidity and equal settlement. The brief introduction is as follows.