Studies On Displacement Interaction Factor Solution And Application To Composite Foundation With Hybrid Piles

Pile foundation is widely used in civil engineering, but the study on the load-settlement question of pile group foundations under vertical load is not perfect, due to the complicated characters of the interaction between pile-pile, pile-soil, pile-cap, and cap-soil. It is not perfect for the calculation speed and precision of pile group settlement now. In this paper, the displacement interaction factor approach was deduced based on the integral equation theory, and through the parametric analysis and comparison with the experimental result, a systemic research on the behaviors of composite piled foundations and composite foundations with hybrid piles such as load-settlement characters and load sharing characteristics between piles and soil etc was made.The main research work of this paper consists of the following parts:1. Solution of the pile-pile interaction factor with Fredholm's integral equation method. The basic solution corresponding to the circle load in elastic half space was obtained with Mindlin's solution, and the analysis model was set up using the fictious pile method. Compared with present solutions, the results show that the theory in this paper is more reasonable and the stiffening effect of pile group can be considered. Parametric analyses were made on the pile-pile interaction and some conclusions were valuable for engineering practices.2. Solution of pile group with floating cap with the approach of interaction factor for displacement. Based on the principle of superposition, the pile group with floating cap was calculated with the approach of interaction factor. The method can be used to solve problems of different pile lengths, radiuses and stiffnesses. The validity of the present method and program are verified by comparisons with the results obtained using other methods by present theory of elasticity. Also, the strengthening effects of intervening piles on the behavior of pile foundation were discussed. Then, for cases of same or different pile lengths in pile groups with floating cap, the effects of pile stiffness, pile slenderness and pile spacing on pile group equivalent stiffness and load distribution were studied.3. Solution of piled raft foundations with displacement interaction factor approach. Based on the interaction factor of pile-pile the interaction factors of pile-soil and soil-soil were put forward. Based on the basic solution corresponding to the circle load, by the method of fictious piles the second kind Fredholm's integral equation was deduced to solve the interaction factor of pile-soil. The displacement interaction factor approach for pile groups with floating cap were extended to piled raft foundations considering the bearing capacity of the soil below the cap. Comparisons with present literatures verified the reliability of the present method and program.4. Solution of composite foundation with hybrid piles with displacement interaction factor approach. By simulating the cushion with the Winkler spring the cushion of composite foundations was considered. Based on the solution of piled raft foundations with displacement interaction factor approach the model for calculating the composite foundation with hybrid piles was established. The load sharing between piles and soil and the settlement characteristics of the composite foundation were analysed. A wide parametric analysis was made to investigate effects of the cushion thickness, Young's modulus, pile length, pile spacing, and pile stiffness, and soil Poisson's ratio on the equivalent stiffness and load distribution of the composite foundation.5. Solution of pile group with floating cap in layered soil with displacement interaction approach. With the transfer matrix method the second kind Fredholm's integral equation was deduced to solve the interaction factor of pile-pile in layered soil. Based on the fictious pile method, the interaction factor approach for the pile group with floating cap in layered soil was obtained. Comparisons with the present literatures verified the accuracy of the present method and program. In the parametric analysis, the effects of the pile stiffness, pile slenderness and pile spacing on the equivalent stiffness and load distribution of pile group characteristics were investigated.