Evaluation of Determination Methods for Ultimate Axial Capacity of Micropiles in Ontario soils

ABSTRACT: This paper evaluates different methods to determine the failure load of micropiles in Ontario soils. Micropiles are small-diameter, grouted piles installed with a high amount of steel reinforcement. Since a higher level of uncertainty exists in geotechnical load capacity of micropiles than of conventional piles, designers commonly rely on the confirmation of geotechnical capacity based on the maximum test load achieved during pre-production testing on sacrificial piles in representative soils. This research analyzed 47 full-scale micropile load tests, conducted by Keller Foundations Ltd, to determine the most suitable method for the evaluation of the ultimate geotechnical capacity in Ontario soils. Since most tests terminated before reaching the ultimate capacity, the load-displacement curves were first extrapolated to provide sufficient data for the analysis by various criteria from literature. Results were compared in terms of closeness to the average failure load, variation, and goodness of fit to normality. Based on the study, Fuller and Hoy (1970) and Butler and Hoy (as cited in Fellenius, 1980) provided the best estimation of ultimate load capacity of micropile in Ontario soils.