Study of soil disturbance effect on bearing capacity of helical pile by experimental modelling in FCV

Abstract

Helical piles as deep foundations are a traditional solution for supporting structures such as residential construction, communication tower installations, static or seismic structural retrofitting and reconstruction. Two mechanisms of failure during helical pile loading occurred depending on pile geometry and soil strength as individual or cylindrical failure. Commonly, soil disturbance effects during pile driving by torque mechanism are not considered in conventional static analysis methods for determine bearing capacity of the helical pile toe or helices plates, while this disturbance can influence the bearing resistance of the pile. Present study considered the behaviour of three models of instrumented helical piles in two densities of Babolsar Sand by the frustum confining vessel developed at Amirkabir University of Technology (FCV-AUT) as the physical modelling apparatus. Bearing capacity of the pile toe and helices plates in addition to axial capacity of the pile are measured and controlled during pile compression load test. Two static analysis methods are used in order to verify the experimental results and deriving the coefficient of bearing capacity for promotion of the conventional static analysis to predict axial capacity of helical piles with more accuracy. The axial capacities of 21 full-scale helical piles are predicted by the new approach and compared with measured capacity from static pile load test. The results of comparison have shown that using the new approach errors in helical pile capacity estimation have been lowered almost 43%. Therefore, it can be realised as an alternative in static analysis of helical pile design.