Calculation Of The Pile-soil Stress Ratio Of The Rigid Composite Foundation And Its Engineering Application

With the continuous development of infrastructure construction in China, the scale of high-rise building construction is expanding constantly. For the foundation of the high-rise buildings embedded in the soft soil, the bearing capacity is often insufficient and settlement deformation is quite large. Therefore, the issue of reinforcing the soft soil has been an urgent problem. Due to the good performance for improving the bearing capacity and reducing non-uniform settlement, the rigid pile composite foundation becomes an effective reinforcement method and has been applied widely recently. However, the working mechanism of the rigid pile composite foundation is quite complicated, which involves the interaction among the mattress layer, the pile and the soil. In view of bearing mechanism and the study of the rigid pile composite foundation and the key parameters such as pile-soil stress ratio are still incomplete yet, which remain to be further explored. Therefore, in this paper, according to the loading characteristics of the rigid pile composite foundation of the high-rise buildings, the load transfer mechanism of the rigid pile composite foundation was discussed. Introducing the thought of multi-stage loading and based on the vertical deformation compatibility condition among the mattress layer, the pile and the soil, this paper put forward a kind of the calculation method of stress ratio of pile-soil for the rigid pile composite foundation and conducted an in-situ test experiment. The main work and conclusions are as follows:Firstly, based on the existing research results, the paper discuss es the reinforce mechanism and the failure modes under the vertical load for the rigid pile composite foundation, summarizes the several common calculation expression of the bearing capacity for the rigid pile composite foundation and deeply analyzes the factors influencing the bearing capacity of the rigid pile composite foundation.Secondly, on the basis of understanding the bearing mechanism of the rigid pile composite foundation, by establishing a reasonable mechanical model to analyze the interaction among the mattress layer, the pile and the soil, introducing the thought of multi-stage loading, considering the hyperbolic curve of the lateral frictional resistance versus the pile-soil relative displacement and the characteristics of the soil mechanical parameters varying with deformation of the soil, the Two-Way Pierce model is applied. If only the vertical deformation is considered, based on the vertical deformation compatibility condition among the cushion, the pile and the soil, the calculation method of pile-soil stress ratio is obtained. Combined with a field engineering instance,Finally, the pile-soil stress ratio calculation method is applied on a public apartment high-rise building in Pingtang Town, Xiandao district, Changsha, which uses the rigid pile composite foundation. From the pre-embedded earth pressure cells, the stress data of the pile and the soil are obtained. The results show that the theoretical solution is close to the measured data, provid ing a reference for the relevant design.on the basis of it, the distribution of lateral frictional resistance of the pile and the normal stress of the pile shaft of the rigid pile composite foundation versus the vertical loading is obtained.Through further comparison analysis of parameters, the influence rules are obtained of the cushion thickness, the cushion modulus, the pile and soil modulus, the pile length, replacement rate and internal friction angle on pile-soil stress ratio of the rigid pile composite foundation.