(1. Key Laboratory of Disaster Prevention and Mitigation in Civil Engineering of Gansu Province，Lanzhou University of Technology，Lanzhou，Gansu 730050，China；2. Western Engineering Research Center of Disaster Mitigation in Civil Engineering of Ministry of Education，Lanzhou University of Technology，Lanzhou，Gansu 730050，China)
Abstract：The research of pile foundation in loess subsoil is insufficient. The first super high-rise building in Longdong was investigated with the concrete strain meters and stress gauges installed on the pile body，and the soil pressure cells placed under the pile cap and pile tip. The software ANSYS was used to analyze the raft settlement of the whole short pile，the whole long pile and the composite pile foundation with long and short piles and to analyze the stress field and settlement variation of soil foundation. The ground soil has the collapsible and non-collapsible loess layers. The non-collapsible loess may become collapsible. The soil layers around the pile has the major effect on the transmission and distribution of the internal pile force. There are several neutral points on the pile body，so the determination of the lower limit of collapsible soil is more complicated. Under the different load levels，the Q-S curves of the piles vary slowly, indicating that the piles are frictional ones. The internal force of pile body develops asynchronously. When the test load reaches up to 8 000 kN，the maximum settlement on the pile top is 8.15 mm and the resistance of the single pile and single pile cap is 4.8% and 2.1% of load on pile top respectively. The measured reaction force at cushion cap of the single pile shapes like an inverted basin and the edge stress is relatively greater. The load carrying properties of pile-soil-cushion cap system are better than the one of single pile foundation. The composite pile foundation with long and short piles makes the full use of the settlement control ability of long pile and the shallow bearing ability of foundation soil to reduce the number of long piles which reduces the cost of pile foundation.
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2017, Vol. 36 
