Reserch On Settlement Calculation Method And Differential Settlement Control Of Composite Pile Foundation

In conventional pile foundation design theory, piles work at the elastic range and upper loads are fully shared by piles. But in composite pile foundation theory, piles work at the nonlinear range and the bearing capacity of piles and soils between piles are fully utilized, so the pile number decreases clearly, at the same time the settlement and differential settlement are larger than those of common pile foundation.The paper puts the emphasis on importing the nonlinear model of foundation soil in the pile-soil interaction and analyses the main working state of single pile in composite pile foundation. The finite element program with interface element simulates single pile's nonlinear working state, which shows the inevitability and essentiality of penetrated settlement in composite pile foundation. At the same time the influences of soil parameters in Duncan nonlinear model, the pile and interface element properties on pile working states are discussed.The distributions of additional stress of common pile foundation and composite pile foundation are simulated by finite element program. The settlement of composite pile foundation is divided into two parts: the compress of soil between piles and soil under pile bottom. On the base of present simplified calculation method, a new method of calculating the settlement of composite pile foundation is presented. It is Modified Simplified Stress Method. In this method, the distribution of additional stress of soil between piles is simplified as a rectangle and that of soil under pile bottom is simplified as a triangle, at the same time the calculating method for soil's modulus of deformation is offered. Then the simplified stress is applied to the settlement calculation. The calculated settlements of several practical composite pile foundation engineerings are contrasted with the observed results and other settlement calculation method's results. The comparisons show that the calculated value by the method not only corresponds with the practical results, but also the method owes clear physical concept, simplified calculation and certain precision, and it is convenient to be applicated in the practical engineering.The paper puts forward the main measures of controlling the differential settlement of piled raft foundation by increasing the rigid of raft and modifying foundation rigid. Through the numerical simulations and analyses of rectangular and circular raft pile foundation, we can draw a conclusion that locating piles in a central area and rigid adjusted method of single pile are two effective ways to reduce the differential settlement of piled raft foundation.The comparison of numerical simulation and measured results of one oil storage tank engineering verifies that rigid adjusted method of single pile is a very good method in controlling differential settlement of piled raft foundation. By the adjusted pile length and pile layout, thedifferential settlement is reduced furthermore, even the differential settlement is completely eliminated, then the raft works at the best situation and the aim of differential settlement control comes into being.