The behavior of micropiled raft foundations subjected to combined vertical and lateral loading: numerical study

Abstract

The micropiled raft offers a foundation system that combines the advantages of the conventional piled raft and the efficient installation of micropiles. In this paper, a comprehensive numerical analysis was conducted on the behavior of micropiled rafts under combined vertical and lateral loading using finite element modeling. A numerical model calibrated against full-scale axial and lateral field tests is used to conduct the analysis. The soil profile was soft clay soil underlain by a layer of dense sand. Numerous cases were analyzed to assess the lateral performance of micropiled rafts while considering several factors that may affect the performance, such as micropiles spacing, raft thickness, the magnitude of vertical loading, micropiles length, and their arrangement. The difference between the lateral performance of a primary micropiled raft and that of an existing raft enhanced by underpinning micropiles was also investigated. The lateral load capacity of the micropiled raft, the bending moment, and the shear force along the micropiles depth were estimated. Moreover, the load-sharing ratio between the micropiles and the raft was assessed. Based on the parametric study results, significant guidelines for choosing suitable micropiled raft configurations for initial design purposes were provided.

Important Guidelines On The Finite Element Modelling Of Micropiles

“…The easiest method for simulating the radial stress increase due to pile installation is using an increased Ks value (where Ks is the coefficient of lateral earth pressure). This method was used by a number of researchers who investigated the behaviour of micropiles under axial and lateral loads [5]- [9], [12], [13]. In PLAXIS, this method involves two steps.…”

“…However, this approach is inadequate for micropile problems involving cement grout injection under high pressures, possibly exceeding 1000 kPa. In the literature, few researchers, who did numerical studies on micropiles, tried to consider the numerical consequences of the micropile installation process by increasing the coefficient of lateral earth pressure (Ks) of the soil to account for the increase of radial stresses around the pile [5]- [9]. As an initial phase of a comprehensive research study on different approaches used for FE simulation of micropile installation and loading, the present paper aims to highlight some guidelines on the finite element modelling of pressure-grouted micropiles.…”