Study On The Piled Raft Foundation Leveling Design Of Variable Stiffness

The piled raft foundation leveling design of variable stiffness is always an important subject in geotechnical field in recent decades. Many scientists has done a lot of theoretical analysis and made some model tests and field tests about the piled raft foundation research work.Based on this, many design methods are acquired. Although people have a preliminary understanding about these design methods,they haven't taken these design methods widely to apply to the actual design work. Therefore, the further research made on leveling design of variable stiffness has great practical value.The piled raft foundation leveling design of variable stiffness is a design method which changes piled stiffness of distribution by adjusting pile length, pile spacing, pile diameter, etc and makes reduce differential settlement and the internal force of the caps as the target to make the settlements of building tend to uniformand and the internal force of the caps reduce.This paper mainly gets by constantly adjusting piled length of the piled raft foundation to realize the optimizational design which could make the settlement value of the piled raft foundation and the internal force of the raft be relatively small. The main contents of this paper are as follows:l.The Matlab language is used to program to the process of computing the settlement value of piled foundation using Mindlin stress formula,and then to get the settlement value of pile foundation. The settlement value getting by the program and the one obtained by the hand calculates are similar which verifies this program applicable; 2.The program is used to calculate the settlement value of the grouped piles under the average piled reaction on the model test in which the length of all piles is equal. Then the piled settlement value obtained by the program and the average piled reaction are used to determine the initial piled stiffness.3. Assuming that the piles under the raft are spring, the piled stiffness is equal to the spring stiffness.Then piled raft foundation is analysised by the finite element method for getting the reaction of the piled top through the software of ABAQUS. In this process, the role of the soil under the raft isn't considered.The model of the finite element is made up of a raft, spring and foundation. The reaction of the piled top obtained is defferent with the average piled counterforce under preliminary assumption. And then under the action of the new reaction of the piled top, the reaction and the displacement are regained.The caleulation is finished until the displacement by software and the one by program calculation close. Comparing the final settlement of pile foundation value with experimental results,it is founded that the error is in the allowed range.4.The piled length around the center of the raft is adjusted.Then the settlement value of the piled foundation and the internal force are recalculated.It is compared with the settlement value of the piled foundation and the internal force when the piled length is equal.The results is that which meets the general rules.Through the above analysis and comparison,it is founded that the calculation method of the piled raft foundation leveling design of variable stiffness is feasible.