Ground surface settlement of loose sands densified with explosives

Abstract

This paper presents the results of a blast densification program conducted at a sanitary landfill located in South Carolina, U.S., to densify a liquefiable loose sand layer deposit and thus increase its resistance to liquefaction and flow during a seismic event. Five zones were selected for improvement, and a total of four blasting passes were implemented at each zone. Additionally, preblast CPT soundings were performed to determine the location of the loose sand layer, and thus define the distribution of the explosives. Topographic surveys were conducted along the centerline of the long direction to measure the ground surface settlements before and after each blast event. Measurements of ground surface settlements indicated that, regardless of the initial "apparent" decrease in penetration resistance commonly measured by standard verification tests, blast densification is an effective technique to increase the soil density. At the tested zones, the final relative densities varied from 65% to 91%. At these densities, the improved sand layer is not considered susceptible to liquefaction and flow, and a dilative response will be expected during a seismic event.