Frictional Effect of Helical Pile Installation in Uniform Clays

The application of helical piles offshore has been attractive due to its 'quiet' installation and retrieving potential, which makes it more environmentally friendly and economical. In this paper, single large plate helical piles in uniform clays are studied for offshore applications. The torsional installation of the helical piles is simulated using three-dimensional large deformation finite element (LDFE) analysis with Coupled Eulerian Largrangian (CEL) method in ABAQUS. The effects of interface friction between the helical pile and the clay are studied on the required torque and crowd force during torsional installations. It is found that the friction coefficient has minimal influence on the installation crowd force but has a greater influence on the installation torque required. The increased installation torque due to frictional effect can be formulated as a linear function of the friction coefficient at a given normalized penetration depth. The soil flow mechanism around the helical plate is revealed to explain the frictional effects. To provide more insight, complementary small strain analysis is conducted studying helix end effects modelled as a strip footing. The effects of plate embedment depth (H) and the soil undrained shear strength (su) on helical pile installation responses are also studied. In flat plate end bearing capacity study, the horizontal plate end bearing factor (Nc) is similar to that of vertical plate end bearing factor with embedment ratio of H/t <= 20. The horizontal plate end bearing factor is independent of the plate embedment depth with embedment ratio of H/t >=20.