Numerical Analysis of Existing Foundations Underpinned by Micropiles: Fid-Bau Portal

Numerical Analysis of Existing Foundations Underpinned by Micropiles

Han, Jie

AbstractMicropiles of small diameter have been used in practice to increase load capacities of existing foundations on soft soil, which may resist additional loads from the vertical expansion of structures. Load transfer from the existing foundation to the micropiles is an important mechanism to consider when designing an existing foundation underpinned by micropiles. However, this mechanism has not been well investigated or understood. This paper presents a numerical study on an existing foundation underpinned by micropiles using three-dimensional (3D) finite-difference software. Verification of the numerical model was first achieved by comparing the results of the numerical model to those obtained from the full-scale loading test. In this verification, the numerical model was used to simulate an existing footing initially constructed on a natural soil to support a structure and later subjected to additional loads under two different conditions. Under the first condition, micropiles were installed without connection with the existing foundation. The existing foundation was subjected to initial loads, and then the micropiles were connected to the existing foundation for additional loads. Under the second condition, the foundation was first subjected to initial loads. Micropiles were installed and then connected to the foundation for additional loads. These two conditions were investigated further in a parametric study to understand the behavior of micropiles in the underpinned foundation under additional loading, including the load transfer between the existing foundation and the micropiles. This parametric study revealed that the installation sequence of micropiles had obvious effects on the vertical displacement of the footing, the percent load on the micropile, and the skin friction along the micropile. This study also revealed that the initial pressure ratio for underpinning and the length of micropiles had more effects on the behavior of the existing foundation underpinned by micropiles than the modulus of micropiles.