Increasing pull-out capacity of granular pile anchors in expansive soils using base geosynthetics

Granular pile anchors are innovative and effective in resisting the uplift pressure exerted on the foundation by a swelling expansive soil. In a granu lar pile anchor, the foundation is anchored at the bottom of the granular p ile to an anchor plate with the help of a mild steel rod. This renders the granular pile tension-resistant and enables it to offer resistance to the u plift force exerted on the foundation by the swelling soil. This resistance to uplift or pull-out load depends mainly upon the shear parameters of the pile-soil interface and the lateral swelling pressure of the soil, which c onfines the pile radially and prevents it from being uplifted. The resistan ce to uplift can be increased by placing a base geosynthetic above the anch or plate so that it forms an integral part of the granular pile anchor. The increase in resistance is due to the friction mobilized between the geosyn thetic and the confining media when the uplift load acts on the pile and th e geosynthetic moves along with the pile. Hence it depends on the friction between the geosynthetic and the confining media and the area and stiffness of the geosynthetic. This paper discusses the effects of these parameters on pull-out load, rate of heave, and relative ground movement near the pile surface.