The Bearing Capacity And Settlement Of Long-short Pile Composite Foundation In Loess Area

The long-short pile composite foundation is becoming more and more popular indeep and thick soft soil area along the river and sea. Recently, long-short pile compositefoundation has been used in loess area and attained good economic and social benefits.Whereas, there is number of documents about long-short pile composite foundation inloess area.Based on analysis of already existing kind of means to calculate the settlement ofcomposite foundation, discusses the advantages and disadvantages and the scope ofapplication of them; Besides, these calculation methods are made in an engineeringinstance, and modified stress is proved to be useful with the practical example.Then, the behavior of the long-short pile composite foundation in loess area issimulated and analysed. The numerical analysis is taken by using ABAQUS FEM andthree-dimensional elastic-plastic model. The author also calculates and analyzes theeffects of some important parameters to bearing capacity and settlement of thecomposite foundation, such as the module and thickness of the cushion. The results ofthe numerical analysis indicate that:1.The skin friction of long piles is related to the cap’s load of the compositefoundation: when there is load on the cap, the negative skin friction is smaller and theposition of the neutral point is higher; Otherwise, the negative skin friction is larger andthe neutral point is lower. When the loess is not collapsible, the skin friction’s absolutevalue increases with load level; The positive skin friction increases and the neutral pointupward as the load level increases after collapsed.2. Draws a conclusion Based on the analysis of cushion’s module and thickness onload–sharing and settlement of composite foundation that: the recommended module is 20MPa~50MPa and the thickness should be selected between0.2m~0.4m based on therequirement of settlement and the load level of superstructure.3. As the auxiliary pile,short piles’primary role is to eliminate the collapsibility ofcollapsible layer and is not sensitive to external factors (such as the upper structure load)and the others of the composite foundation.Finally, the results of analysis is expected to provide a good reference for thedesigning and construction of long-short pile composite foundation in loess area.