Fibre-Reinforced Grout for Micropile Construction

Abstract

Hollow bar micropiles (HBMP) are increasingly used to support heavy structures owing to their ability to carry considerable axial loads. However, their lateral capacity is relatively small due to their small flexural strength, which could limit their application for structures subjected to large lateral loads. Enhancing the micropile flexural strength by utilizing fibre-reinforced grout in its construction can thus improve its lateral performance. This study investigates the use of four types of fibers in grout mixture with different dosages to enhance the strength of grout used for micropile construction. Plastic, basalt, steel and micro-steel fibers were applied with dosages of 1%, 1.5% and 2%. Based on the obtained results, steel fibers were selected for further investigation. Nine model micropiles 1000 mm long and 76 mm in diameter were casted and tested in a laboratory environment with two different types of steel fibers. The micropiles were subjected to pure bending tests and the moment – curvature curves were extracted. The moment – curvature results indicated that the micropiles moment capacity increased and their post-cracking behaviour improved by adding steel fibers to the grout mix. As part of a large-scale study of lateral performance of single and grouped micropiles installed in cohesionless soil, one micropile was constructed with 1% micro-steel fiber to investigate its effect on its lateral performance. The lateral load test results indicated that the lateral capacity of the reinforced micropile improved by 10% over that of the non-reinforced micropile.