Ultimate capacity of granular pile anchors

The paper presents methods for the estimation of the ultimate pullout capacities of Granular Pile Anchors (GPA) for homogeneous and non-homogeneous (undrained strength increasing linearly with depth) ground conditions as the lesser of the two values obtained considering shear and bulging failure mechanisms. The ultimate pullout capacity and the critical lengths of GPA corresponding to a transition from shear failure to bulging failure are evaluated as functions of various parameters such as the length to diameter ratio, L/d, of GPA, the ratio of the shear modulus to undrained strength, G/cu, of the ground, the undrained shear strength of soil, cu, unit weight, gamma gp, the angle of shearing resistance, phi gp, of the granular pile material, lateral coefficient of earth pressure, K0, etc. The variations of ultimate capacities and critical lengths are presented as functions of several parameters under investigation. The influence of non-homogeneous strength parameter, alpha, on the ultimate capacities and critical length is also investigated. The predictions are validated with limited test results available in literature [Caskey in Uplift capacity of rammed aggregate piers soil reinforcing elements, Thesis, University of Memphis, MS, 2001; Lillis C, Lutenegger AJ, Adams M (2004) Compression and uplift of rammed aggregate piers in clay. Geosupport: ASCE/GEO Geotechnical Special Publication No 14, 497-507]. The paper presents methods to estimate ultimate pullout capacity of granular pile anchors for homogeneous and non-homogeneous ground conditions. The ultimate capacity of GPA increases with increasing undrained shear strength of soil and resistance shifts to deeper depths in GPA unlike the granular piles which are independent of length. Theoretical results are validated with field test results.