Design, construction and performance of micro-piles as compared to bored piles

• Main Author: Han, Yung Fung.
• Other Authors: School of Civil and Structural Engineering
• Format: Theses and Dissertations
• Language: English
• Published: 2008
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical
• Online Access: http://hdl.handle.net/10356/12256
• Institution: Nanyang Technological University

Micro-piles are drilled shafts of diameter typically 150 to 250 mm. In Singapore, micro-piles are used as substitutes for driven piles and bored piles in bouldery soils and shallow bedrock, for underpinning existing pile-caps to increase their capacity, as retaining walls for braced excavation in weathered rock, and for construction in confined spaces. The allowable load of micro-piles is typically 50 to 130 tonnes in rock and 35 to 50 tonnes in soil. In load tests, this working capacity was found to derive almost entirely from shaft resistance. The design of micro-piles in residual soils and rocks of Singapore is based on methods adopted for bored piles, but the construction methods for micro-piles, some with post-grouting and mostly without, are different from those for bored piles. Micro-piles in hard rock were found to have relatively high shaft resistance and the settlements of these piles are usually smaller than of those in residual soil. This result was consistently achieved without the use of pressure or post grouting of the micro-piles in hard rock. In a comparison of the load transfer response of two micro-piles and a bored pile installed in similar weathered Jurong Formation, which had been designed by the same method, the rate of mobilization of shaft resistance was found to be about the same for micro-piles and bored piles.