Behavior of Piled Raft Foundation in Calcareous Cemented Sand

Abstract

The calcareous cemented sand exists in many places around the world where in last two decades there was a huge development. During such huge development, the foundation design was a major challenge. This research aims to introduce the piled raft foundation as a competitor solution for this challenge. To achieve this goal, a research plan consist of four stage was planned by the author. These stages are investigating the characteristic behavior of calcareous cemented sand, selecting a presentable constitutive law for the calcareous cemented sand, utilizing pile load test result to calibrate the constitutive law parameters, and analysis a case history dealing with conventional piled foundation using the piled raft concept respectively. Investigating the characteristic behavior of calcareous cemented sand reveals a cohesion intercept because of existence of carbonates as bonding agent at points of contact between the particles and interlocking between the particles. Also, investigating the characteristic behavior of calcareous cemented sand shows increased stiffness with depth, small difference between the peak friction angle and residual friction angel, and unloading reloading stiffness is higher than the loading stiffness. Based on this characteristic behavior of calcareous cemented sand, double hardening soil model has been utilized as a suitable constitutive law to represent the stress strain behavior of calcareous cemented sand. In light of available published triaxial tests on calcareous cemented sand, the parameters of double hardening soil model were estimated. Moreover, calibration of these parameters was conducted via back calculation of real pile load tests in calcareous cemented sand. In the end of this research, a conventional case history dealing with pile foundation was redesigned applying the piled raft concept, where raft, pile, and soil mutual interactions were introduced using a 3D finite elements analysis. The soil was modeled by the double hardening model, the raft was utilized using plate element, and the piles were modeled using embedded pile model.