Effect of Surcharge Pressure on Pile Static Axial Load Test Results

This paper presents the effect of surcharge support pressure on pile load–settlement response during static load testing. A three-dimensional nonlinear finite-element model is developed to investigate the loading sequences of an axial compressive static load test, using surcharge loads as the reaction system. Results of a static load test at a construction site for which the geotechnical data are available were used for verification of the numerical model. The results show that the surcharge pressure on supports has little impact on the ultimate capacity of the pile, as the shaft skin friction is slightly influenced by the surcharge and the effect on the tip resistance is negligibly small. The initial stiffness of the pile, however, might be considerably affected by the surcharge pressure distributed around the pile shaft. The influence on stiffness increases with increase in the pile diameter. The effect of surcharge pressure is more pronounced for piles embedded in frictional soils compared with cohesive soils. Comparing the results with those available in the literature for pile testing using the reaction pile system shows that the pile stiffness is 15 to 25% less affected in the surcharge reaction system.