Experimental analysis of parameters affecting the lateral resistance of micropile groups embedded in sandy soil

• A higher L/D ratio due to leads to higher interaction, and embedment depth. • Higher density improves the interlocking and interaction of soil and micropile. • The penetration of grout into the sand resulted in higher mechanical strength. Micropiles are small-diameter structural elements used for improving bearing capacity support, particularly in situations where conventional piling methods are impractical or impossible. Micropiles are subjected to both vertical (axial compression) and lateral loads (bending resistance). The behavior of micropiles under lateral loads is influenced by various factors, including their diameter, depth, flexural stiffness, confining conditions, and the properties of the surrounding soil, particularly the soil's relative density (D r ). Despite extensive research on the performance of micropiles in clayey soil, fewer studies have been conducted on the performance of micropiles in sandy soil considering various densities and micropile lengths. Hence, in the present research, the behavior of different groups of micropiles (2*1, 2*2, and 2*1*2) in a sandy soil bed with varying relative densities (30%, 50%, 70%, and 90%) is investigated. The micropiles had length-to-diameter (L/D) ratios of 15, 20, and 25, and the distances between them were 2D, 3D, and 4D. To obtain mechanical strength, after inserting micropile into the soil, grout was injected into the sections and reinforced with a pressure of 10 bars after using a plastic hammer to insert a bar into the soil. Then, the micropiles were subjected to a hydraulic jack to obtain their lateral strength. According to the findings, in loose and medium-density sand, the ultimate lateral resistances of micropile groups are at their highest at 2D spacing. In dense sand, the maximal lateral resistance is observed at a 4D spacing. Furthermore, a lower number of micropiles led to decreased lateral strength, with the highest lateral strength observed at a D r =90%. In addition, the study revealed that higher L/D ratios due to higher interaction, embedment, and effective length enhance strength and reduce displacement by up to 50%. It is observed that the stress rate in the relative density of 90% increased by about 192.3% compared to the relative density of 50% for fixed L/D. Microstructural analysis shows grout coats the sand grains, forming a cementitious bridge between particles. Furthermore, it was observed that the grout fills the voids and binds the grains together, leading to a denser and more cohesive soil structure.