Ultimate pullout capacity of the granular pile anchors by laboratory model tests

The use of granular piles (GP) and their application in weak and soft soils for ground improvement are well understood. GPs improve the performance of the ground by reinforcement, densification and drainage and are utilized predominantly for increasing bearing capacity, reducing settlements and accelerating consolidation of the ground.

Experiments are carried out on granular piles to enhance their ability and to extend their utility to resist uplift or pullout forces by placing a geogrid or a nominally reinforced concrete pad to which a reinforcing rod or a cable is attached which is then connected to the footing or another pad on the surface. Such granular piles are termed Granular Pile Anchors (GPA).

Laboratory models have been designed and experiments carried out on GPA in two different soils for different L/d ratios. Results are presented as load – displacement responses for different L/d ratios. Typical failure patterns and exhumed post failure profiles of GPA in both the soils are presented. The ultimate pullout load and tip displacements increase while top displacements decrease with increase in L/d ratio. A new form of failure, a combination of pile and anchor type failure is identified in the experiments for GPA with shorter lengths (L/d < 7.5). GPA with longer lengths (L > 7.5) appears to fail by bulging.