FE Simulation of Installation and Loading of Single and Group Pressure-Grouted Micropiles

The most influential effect of installing pressure-grouted micropiles is the increase of the radial stresses in the surrounding soil, which subsequently increases the micropile load capacity. The Increased Ks Approach has been extensively utilized in the literature for simulating this effect within finite element-based software, such as PLAXIS, and has been deemed reasonably suitable. However, this paper aims to outline the principal limitations of this approach and introduce an alternative method—the Cavity Expansion Approach—that can accurately simulate the expansion of micropiles during installation. A case study involving the installation and loading of both single and group micropiles was simulated using FE modelling to assess the efficacy of the proposed method. The findings indicate that the Increased Ks Approach results in an unrealistic stress field around the micropile following installation, with the micropile retaining a straight shape with the drill bit’s initial diameter. Conversely, the Cavity Expansion Approach was found to produce reasonable stress fields, characterized by uneven increases in radial and hoop stresses within a confined zone extending up to a distance of 9 D_mp from the micropile. When implemented using prescribed pressures, the Expansion Approach yields tapered micropiles featuring rough, corrugated surfaces.