Numerical simulation of load tests on hollow-bar micropiles considering grouting method

The bearing capacity and bond diameter of hollow-bar micropiles are higher than those of conventional solid-bar micropiles, as is well documented by full-scale testing. The limitations in existing codes for the design of hollow-bar micropiles have also been qualitatively addressed. However, despite the increased use of hollow-bar micropiles, the effect of the grouting method on their performance has not been confirmed and numerical modelling of their behaviour has not been reported. No quantitative value for an increase in the bond strength and bond diameter of hollow-bar micropiles compared with conventional micropiles has been presented. In the current study, finite-element modelling of full-scale loading tests on hollow-bar micropiles in coarse-grained and fine-grained soil was used to evaluate their design parameters and the effect of grouting method. An increase in the bond diameter and bond strength of the hollow-bar micropiles was determined from the results of 21 full-scale loading tests and numerical simulations. An equation to predict the bond diameter of a hollow-bar micropile was developed. The results show that the bond diameter in fine-grained and gravelly soil was 1.5 and 2 times larger than the drill bit diameter. The bond strength was 10-30% higher than current recommendations for hollow-bar micropiles.

Automated summary

In this study, numerical modeling was used to evaluate the design parameters and the effect of grouting method on hollow-bar micropiles. The results showed an increase in bond diameter and bond strength compared to current recommendations for hollow-bar micropiles. An equation to predict the bond diameter of hollow-bar micropiles was also developed.