Influence of Load Obliquity on Pullout Capacity of Micropile in Sand

Abstract

An experimental study was undertaken to understand the influence of load obliquity on ultimate pullout capacity of pile. Twenty, single free-head vertical piles in the form of micropiles of 20 mm diameter and 600 mm lengths were drilled using an auger and grouted under gravity in uniform sand bed. Ample cured micropiles were tested at 0°, 5°, 10°, 15°, 20°, 30°, 45°, 60°, 75° and 90° load inclinations with respect to axis of micropile i.e. vertical. Ultimate pullout capacity at each load inclination was determined from load-displacement curves using double tangent intersection method. It is found that ultimate oblique pullout capacity as well as vertical pullout capacity of micropile decreases as load inclination increases with axis of micropile. To understand the relationship between the two components of oblique pullout load an interaction diagram has been derived from test results which show that horizontal load significantly affects vertical pullout capacity than vice versa. Test results of similar studies on micropiles have been presented through a polar diagram. An attempt has also been made to assess the applicability of existing theories to estimate the ultimate pullout capacity of micropiles under oblique loads.