Behaviour of Piles with Enlarged Tip in Non-Cohesive Soil. Model Tests and Numerical Simulations

Sammanfattning: Slender piles reduce detrimental vibrations during installation. In order to preserve a high bearing capacity, the pile tip can be enlarged after installation.

This study consists of model tests of conventional piles (unexpanded piles) and piles with enlarged tip (expanded piles). Furthermore, numerical simulations and comparisons with existing design rules are made.

The model tests comprised load tests in dry sand. The effects of varying the overburden pressure, initial density, installation procedure and degree of expansion were examined. During each test the load-displacement response, grouting pressure, changes in soil stresses and soil displacements were measured. In the numerical simulations the load-displacement responses of the unexpanded and expanded piles were obtained and compared with the measured responses.

The model tests showed that the increase in bearing capacity, due to the expansion, was less than proportional to the increase in tip and shaft areas. Furthermore, the load response of the expanded piles showed a temporary decrease in tangential stiffness at a displacement of about 6 mm due to the design of the piles. The numerical simulations considerably overestimated the capacity of the expanded piles when soil properties evaluated from triaxial tests were used. However, in order to match the measured stress increase in the soil due to the expansion, the soil stiffness was reduced. This improved the calculated load response considerably.