Numerical investigation of the performance of micropiled rafts in sand

The micropiled raft (MPR) offers an efficient foundation system that combines the advantages of micropiles and piled rafts that can be used as primary foundation system or to enhance an existing raft foundation. In this paper, a calibrated and verified finite element model (FEM) with centrifuge tests was used to carry out a numerical investigation on the performance of MPR in sand. A total of 78 different cases were analyzed in this study to assess the behavior of MPR in sand taking into account a number of factors that may influence its behavior such as: the number of micropiles (MPs), the spacing to micropile diameter (S/Dmp), the raft thickness, type of loading and soil density. The outcomes of this investigation should help in understanding the effect of these factors on the MPR axial stiffness, including; differential settlement; load sharing between the MPs and the raft; and the raft bending moment. Moreover, the ability of the PDR method to evaluate the axial stiffness of a MPR for the preliminary design stage is examined. It was found that the MPR system has the ability to increase the tolerable bearing pressure by 190% compared to an isolated raft system. In addition, an adjustment factor (ωPR) for PDR method was introduced to account for the raft flexibility.