An investigation on the bearing capacity of piled raft foundations experimentally and comparison with modified hyperbolic model results

Abstract

Because of non-linear and settlement dependent behavior of soil and effect of the interactions, understanding the behavior of piles and raft and the load sharing mechanism in piled rafts is a key issue. Recently, researchers have introduced few normalized hyperbolic models according to numerical analysis to estimate the load-sharing ratio of piles in piled raft foundations. These models are based on experimental results and considering different interaction effects between pile-raft-soil, raft, and pile dimensions and the amount of settlement. The aim of this research is to investigate the behavior of piled raft foundation and to estimate the load-sharing ratio of piles experimentally. So, various tests have been conducted on piled rafts, group piles, and unpiled rafts under vertical loading by changing the number and length of piles and density of bed sand. For this purpose, an innovative combined loading system, instrumented by measuring devices, is designed and constructed; then the load-sharing ratio of piles from the total load with a novel method is estimated by measuring soil pressure underneath the raft at any settlement. According to the results, bearing capacity of piled raft foundation in analogous conditions is more than unpiled raft and twice group piles approximately. Also increasing the number of piles in piled rafts and group piles increases bearing capacity and reduces raft settlement. The load sharing ratio of piles shows downward trend by increasing settlement and it increases with increasing the number of piles in the same conditions. In this study, the ultimate bearing capacity of group piles which have been experimentally obtained is compared with the ultimate criterion of the hyperbolic model proposed by other researchers. Then, the model is modified by mathematical analysis methods indicating good agreement between experimental and analytical results.

Keywords

• piled raft foundation
• pile group
• unpiled raft
• load sharing ratio
• hyperbolic model