An analytical and applied blasting approach to facilitate rock-socketed bored pile excavation

Abstract

Conventional bored piling excavation technique in a rock formation is a time-consuming and costly operation due to excavation speed. Blasting can be a useful method for the reduction of rock strength before bored pile excavation by breaking the rock in an area as large as the bored pile diameter. In this way, the drawbacks of pile driving operation can be minimized in terms of project time and cost. In this study, the usability of blasting was investigated in order to increase the speed of conventional bored piling excavation. For this aim, an analytical method based on the airy stress function was established to determine the fragmentation zone that provides sufficient fragmentation to facilitate the bored pile excavation operation in a motorway cut and cover tunnel project. In the model, the detonation pressure, the tensile strength of rock, explosive properties, and drill hole diameter were taken into consideration. The developed model was tested by three different blasting designs and a non-blasting excavation to verify its applicability for the bored pile excavation in the site. As a result, the suggested blasting method can be used in rock-socketed bored pile driving studies to obtain a fragmentation zone as much as pile diameter in order to increase excavation speed and reduce cost and to provide expected excavation performance. This study introduced a first in the literature that the blasting technique was used as the first stage of bored pile excavation. In addition, the developed method can be applied by revising according to different rock conditions and it can be used as a basic pre-design approach.