عنوان مقاله [English]
Combined piled-raft foundations (CPRF), is an innovative idea proposed since the 1970s. Adding piles to raft foundations contributes to settlement reduction and an increase in the bearing capacity of the raft. Generally speaking, CPRF helps in considerably reducing the number of piles and pile lengths, improving serviceability in both total and differential settlements, and minimizing tilt and instability probabilities. Reduction in the number and length of piles also contributes to considerable saving in construction cost. The applicability of the construction of piled-raft foundations on soft clay has been under greater attention in recent years. Lack of sufficient stiffness
for soil and, thus, excessive settlement, allowing mobilization of pile loads, is a major concern in this regard. This paper presents a numerical investigation into the effects of geometrical variations of piled-raft components on soft clay, as a parametric study.
A 3D FEM numerical model is developed using ABAQUS. The model was calibrated by comparing physical and numerical modeling of other researchers. An elaborate parametric study was then conducted to evaluate the effect of various parameters on CPRF applicability on soft clay. In this study, attention was focused on the drained (long-term) response of a piled-raft resting on a soft clay layer, so the clay was idealized using drained shear strength parameters, c and phi Thus, consolidation effects were neglected. In all analyses vertical
uniform loading was applied to the top of the raft surface. The results indicate that pile arrangements under the raft play an important role in piled-raft performance. An increase in pile length and diameter results in
settlement reduction and an increase in the pile contribution ratio. An increase in raft thickness reduces differential settlements, but has no considerable effect on the pile and/or raft bearing ratio.
Overall, the construction of pile-rafts on soft clay is promising, as long as the total settlement of the structure is not imposing restrictions, such as the common 20 mm allowable settlement. But, instead, if the allowable settlements are in the range of 100 to 150 mm, for example, in the case of rigid steel tanks, the method will be applicable, with considerable cost and co tanks, the method will be applicable, with considerable cost and construction time savings.