Ultimate capacity of battered micropiles under oblique pullout loads

Abstract

To understand the influence of load inclination and pile batter on ultimate pullout capacity, an experimental study was carried out on single, free head vertical (0°) and battered (±15°, ±30°) model micropiles under central in-plane pullout loads of different inclinations. Auger drilled, centrally reinforced, and grouted micropiles of 20 mm diameter and 600 mm length (L/D = 30) were casted and tested in uniform sand bed. Load–displacement curves were plotted for average displacements in horizontal and vertical directions. Ultimate pullout capacity for each load inclination was determined from load–displacement curves using double tangent interaction method. Test results indicate that ultimate pullout capacity of vertical and battered micropiles decreases as load inclination increases with the micropile axis. Vertical micropiles have more pullout capacity than ±15° battered micropiles at all inclinations of load. Whereas 30° negative battered micropiles beyond 5° of load inclinations have more pullout capacity than vertical micropiles. In general, negative batter micropiles offer more pullout capacity than positive battered micropiles at corresponding load inclinations and axial pullout capacity of the micropile decreases slightly as a result of increase in batter angle.