Consolidation Effect on the Behavior of Micropiled Rafts Under Combined Loading: Case Study

Abstract

This paper used finite element modeling to evaluate the consolidation effect on the performance of existing rafts underpinned with micropiles under combined vertical and lateral loads. For this purpose, a real-life case study was discussed, in which micropile underpinning was used to stop the continuous tilt of a 13-floor residential building supported by a surface raft. It was found that the building tilted towards the northeast direction because of the consolidation of a deep soft clay layer under the northeast building corner. After discussing the as-built micropiling system, a 3D numerical model, developed using the PLAXIS software, was used to conduct the numerical research. The time-dependent behavior of the raft with and without the consideration of micropiles was assessed. Moreover, the variation of load-sharing ratios with time was investigated. The numerical results emphasize that the underpinning process was effective and reduced the final raft rotation and maximum settlement by 79.9% and 73.9%, respectively, compared to the case of the absence of micropiles. The consolidation process under a steady level of vertical loads enhanced the performance of the micropiled and unmicropiled rafts against upcoming lateral loads. The vertical load-sharing ratio increased during a life span of 20 years by 10.4% due to the consolidation process, but the increase was at a decreasing rate. Comparing all the four directions in which the lateral load was applied, the micropiles carried (57.4–76.6%) of the lateral load.

Important Guidelines On The Finite Element Modelling Of Micropiles

“…Not only do engineers have to consider the installation process in FE modelling, but the interface reduction factor (Rint), used to control the friction behaviour of the soi/grout interface, should be in the range of 0.95 to 1.0 to simulate the very rough corrugated surface condition of pressure-grouted micropiles [5], [6], [11].…”