The Simplify Method For Analyzing Piled Rafts Foundations

Piled raft foundations, which is extensively used, is an important foundation pattern of high rise buildings. The researches on the interaction characteristics of piled raft foundations and the soil have been being paid close attention to by academic and engineering circles. Though a lot of achievements in the field have been obtained in recent thirty years, many problems remain unsolved for their complex nature. With the rapid development of computer, it is possible to realize further the interaction mechanism by theoretical analysis and to try to find out reasonable, practical and effective analytical methods of piled raft foundations. Along with the high speed developing of country economic, more and more skyscrapers are built in coastal area. Hundreds and thousands piles are necessary to support bigger and bigger structural loads. Traditional the finite element methods and the boundary element methods need to divide piles into a great number of elements, which can cause the enormous pile-soil stiffness arrays. So the piled raft foundations which have many piles can not be analyzed by these methods in a little time. The paper focus on the simple method for analyzing nonlinear interaction of large scale piled raftsThe main work of this paper includes: first, attention is confined to the displacement behavior and computation methods of single piles, the approach is presented for the analysis of non-linear responses of vertically loaded single pile; second, pile group settlement analysis by pile-pile interaction factors can save a lot of computing time. However, the traditional interaction factors method that Polous developed can't consider "reinforcing effect" and "shadowing effect" of pile groups. Thus, pile group computed settlement is more than measured settlement. This paper give an simplified approach which considers "reinforcing effect". Moreover , "shadowing effect" of pile groups can be considered by modifying the soil shear modulus between two piles. Comparisons show that the simplified approach can give more reasonable interaction factors with those from measured results; Finally ,the paper puts forward a simple method for analyzing the nonlinear interaction of large piled rafts. This paper describes the method to estimate parameters including soil modulus and Poisson's ratio, and develops a technique of back-analyze soil modulus from appropriate interpretation of field pile load tests. The simple method applies the single pile load test's results to the settlement of piled rafts .The raft is modeled as a thin plate and the piles are modeled as the interacting nonlinear springs. The single pile load test's Q-S curves can be matched by the hyperbola function. The non-linear characteristic of the piles can be modeled by the hyperbola function. The interaction between piles is analyzed by interaction factors, "restraint" action between piles is considered in this paper, the interaction factors between pile-pile and pile-soil are matched by the multinomial regression. The interaction between soil elements can be analyzed by elastic semi-space or finite layer theory. Compared with the results of the full piled raft analysis and the model pile groups, the approximate method can not only save a large amount of computing time but give the reasonable results.With the listed above analysis, the paper successfully solve the problem that the nonlinear settlement of large scale piled rafts can not be analyzed appropriately. Moreover, the simple method applies the single pile load test's results to the settlement of piled rafts, which can achieve more appropriate results. It should be useful for projects.