A new equation to determine the load percentage carried by cap in piled raft systems

Piled raft foundations are an effective and economical system in case of high-rise buildings and are a suitable alternative to conventional deep foundations. In this type of foundation, raft is in direct contact with the soil and hence it carries a significant portion of load. Regarding to the design of piled raft foundation, one of the uncertain issues is to determine the proportion of load sharing of the raft and piles. In this paper, Finite element analyses were carried out by developing three-dimensional models in ABAQUSE and with considering interaction effects for a piled raft foundation, the effective factors and their impact on load percentage carried by raft are investigated. In addition, a new equation for determining the load percentage carried by cap in granular soil is proposed for a group of piles for an alignment of less than 9×9 piles. The developed model is validated with available experimental results. The results of numerical analysis show that the distance of the piles from each other, the diameter of the piles, the internal friction angle of the soil and the number of piles in the pile group are among the most important and effective parameters in determining the load percentage carried by cap. In the current study, from the numerical analysis, it has been concluded that, the load percentage carried by cap, is 15% to 42%.