Numerical evaluation of square arrangement of charges in explosive compaction

Abstract

Explosive Compaction (EC) or Blast Densification (BD) is a common deep soil improvement technique where loose, saturated granular soils are compacted with a huge compression force of the explosion. The design of EC is often conducted using empirical equations and/or preliminary explosion tests. The former is based on limited experiments and provides rough estimation, whereas the latter is costly. Recently, the numerical approach has shown advantages in capturing complex condition of such problems and pose itself as a robust alternative. In this study, a numerical method is evaluated as a design tool to optimize EC. A fixed volume of soil is therefore considered to be densified with a specific amount of explosive charges. All charges are located at the same depth and are horizontally placed using square pattern arrangement. An estimation of EC design is achieved using an empirical equation. Subsequently, numerous numerical simulations are performed to achieve the efficient design in terms of the optimum equivalent weight of TNT and arrangement distance. The induced pressure in the soil, as well as the surface displacement, is used as measures of efficiency. Results show that the empirical equations provide a rough or inaccurate design while by use of the numerical approach this range is narrowed. Also, by reaching the optimum distance a more uniform compaction is achieved which reduces the unwanted surface heaving caused by cumulative upward waves. A compaction variation of about 30% was observed due to settlement variation, whereas the compaction variation due to change in explosive weight was approximately 80%. By applying the detonation delay the surface heaving is reduced up to 50%, which improves the EC efficiency.