Non-destructive control methodology for micropiles based on low strain dynamic load test

Micropiles are widely used since their creation in the 1950s in Italy by Dr. F. Lizzy [1]. This foundation technique has been highly developed; nevertheless, such growth does not come with a development of specific “proof” load tests. Actually, among the control techniques that can be used in micropiles, the uplift load test is the most widely used. The static load test is easy to perform and interpret, however this test cannot be made systematized. In this paper a methodology to control the ability of the micropile to safely carry the design load in service based on a simple low strain dynamic load test (LSDT) is developed and adapted to the specific conditions of the site. LSDT test consist in the application of a simple low energy impact that allows determine the small-strain elastic stiffness of the micropile-soil system. The objective is to test in a relatively simple, economical and systematic way vertical micropiles. The calibration and for subsequent validation of the testing method and its protocol have been carried out from a large amount of static and dynamic test performed on 18 real scale micropiles made in an experimental site. The results show that the proposed methodology allows determining the micropile bearing capacity under service loads. This methodology is easy to carry out and has an immediate interpretation; also it is particularly adapted to the reals conditions of micropiles site constructions.