Lateral Performance of Single and Grouped of Hollow Bar Micropiles in Cohesionless Soil

Hollow bar micropiles (HBMP) offer high structural capacity through the hollow steel bar and the grout and are increasingly used to support a variety of structures subjected to lateral loads. However, their performance under lateral loading is largely unexplored. Therefore, there is a need to evaluate the lateral capacity and performance of single and groups of HBMPs. In this study, six 6 single micropiles were constructed in cohesionless soil utilizing hollow bars with 51 mm OD and 33 mm ID and were subjected to monotonic and cyclic lateral load tests. Four 4 micropiles were installed with a 152 mm diameter drill bit and two micropiles were installed with a 115 mm diameter drill bit to examine the effect of drill bit size on HBMP lateral capacity. In addition, a square group of four micropiles was installed and subjected to monotonic lateral loading. The total length of the micropiles was 6 m with an embedded length of 5.75 m. The load test results are presented and discussed. In addition, the lateral response of the micropiles was analyzed utilizing the commercially available program LPile and the results were compared to the experimental results. The results indicated that increasing the drill bit diameter improved the lateral capacity by about 32% resulted in substantially stiffer performance. The cyclic load test results were used to establish the degradation behavior of the HBMP as the number of load cycles increased. The results on the numerical modeling indicated that the properties of the soil along the top eight to nine micropile diameters govern the HBMP performance under lateral loading.