Numerical modelling of under-reamed scaled-down piles by water jet driving

Federal University of Rio Grande do Sul, Civil Engineer Department, Osvaldo Aranha Avenue, 99, Porto Alegre, Brazil

^* cesar@ufrgs.br

Abstract

Water jet pile driving technique has been shown to be viable for driving precast piles in highly resistant soil layers. However, the use of this technique drastically reduces the pile load capacity. On the other hand, the use of under-reamed precast piles improves the vertical load capacity. The objective of the present paper is to show the efficiency of the use of under-ream, through the numerical modelling of load tests carried out in laboratory scaled-down models. For numerical modelling, finite element method (FEM) was used. Through numerical analysis, it was possible to identify the distribution of stresses and strains at the toe, shaft, and under-reams. With that it was possible to identify and check the contribution of these in the total vertical compressive load capacity. It was possible to verify that the under-reams contribute to the vertical load capacity varying from 47% to 57% depending on the configuration, number, and distribution of the underreams along the pile. Thus, increasing the final vertical load capacity, if compared to piles without under-ream (uniform shaft). Numerical modelling proved to be a fundamental tool, which made it possible to show the mechanisms involved in the action of under-ream in increasing the vertical load capacity of piles.