3D finite elements analysis of vertically loaded composite piled raft

In recent years, a new type of foundation named composite piled raft foundation (also called long-short composite piled raft) has been developed. Where designing shallow foundations would mean unacceptable settlement, or other environmental risks exist which could impair the structure in the future, composite piled raft foundations could be used. Finite element method was applied to study the behavior of this type of foundation subjected to vertical loading. In order to determine an optimal pile arrangement pattern which yields the minimum settlement, various pile arrangements under different vertical stress levels were investigated. Results show that with increasing the vertical stress on the raft, the effectiveness of the arrangements of short and long piles become more visible. In addition, a new factor named "composite piled raft efficiency" (CPRE) has been defined which determines the efficiency of long-short piles arrangement in a composite piled raft foundation. This factor will increase when short piles take more axial stresses and long piles take less axial stresses. In addition, it is found that the changes in settlements for different long-short piles arrangement are in a well agreement with changes in values of CPRE ratio. Thus, CPRE ratio can be used as a factor to determine the efficiency of piles arrangements in composite piled raft foundation from the view point of reducing raft settlements.