Hollow bar micropiles (HBMP) have been popular for some time due to their fast installation and efficient load transfer mechanism. In the construction of HBMP, it is common practice to use a diameter ratio of drill bit/ hollow bar (Db/Dh) between 2 and 2.5. However, increasing the drill bit diameter should increase the micropile diameter and hence may enhance its performance and increase its capacity for a minimal increase in cost. In this study, a field testing program was conducted on six single HBMP with two different (Db/Dh) ratios installed in sand to investigate their performance. The ratio Db/Dh was increased from 2.25 to 3 by increasing the drill bit diameter for the same size hollow bar. The micropile length was 6 m, with 0.25 m free standing above ground. The micropiles were subjected to compression and tension load tests. The results demonstrated that increasing Db/Dh to 3 improved the micropiles performance and increased their compression and uplift capacities: the stiffness increased by 38% and 32% in compression and uplift, while the capacity increased by 17% and 22.5%, respectively. The compressive load–displacement response of micropiles was slightly stiffer than the uplift response and their ultimate compressive capacity was slightly higher than their uplift capacity.
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The authors would like to acknowledge the support of HC MATCON for providing the materials, installing the micropiles and setting the reaction frames, and NSERC for partially funding the project. The authors would also like to thank the Libyan Ministry of Education for providing a scholarship for the first author. The authors would like to acknowledge the effort of Dr. Wenbing Wu from China University of Geosciences for his help during the testing program.
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Abdlrahem, M.A., El Naggar, M.H. Evaluation of Axial Performance of Hollow Bar Micropiles Constructed with Different Drill Bit to Hollow Bar Diameter Ratio. Geotech Geol Eng (2021). https://doi.org/10.1007/s10706-021-01718-x
- Hollow bar micropiles
- Field load tests
- Axial capacity
- Uplift capacity
- Micropile stiffness