Blast densification: Multi-instrumented case history

A comprehensive blast densification field study was conducted at a test site in South Carolina to densify a loose soil layer at a depth between z=8-13 m. The study included extensive laboratory and field characterizations and four carefully monitored blast events. Results revealed that densification is not an instantaneous phenomenon; underlying time-dependent processes involve resedimentation, drainage of excess pore pressure as the granular skeleton deforms and the effective stress recovers, and secondary settlement effects, which do not involve excess pore pressure dissipation. The degree of densification decreased in successive blasting events, and the soil gradually evolved toward an asymptotical terminal density associated with blast densification. The blasting sequence and detonation delays appeared to have a minor effect on shear-induced movements. The increase in penetration resistance manifested 2 years after four blasting-drainage events. Instead, surface settlement using standard surveying techniques, subsurface deformation assessment, and subsurface pore fluid pressure monitoring provided valuable, real-time indicators of the soil response to the blasting events.