A laboratory study of blast densification of saturated sand

Laboratory tests have been conducted to investigate the potential of millisecond delays in blast-densification of saturated cohesionless sand. A large liquefaction tank was used to prepare and contain the sand. Commercially available blasting caps were used as the explosive. Cone penetration tests and sand surface elevation changes were measured. In addition to lowering the peak body wave ground motions, densification with millisecond delays was shown to be comparable to densification by a single large blast with a total charge weight equal to the sum of the delays. Increases in cone penetration resistance were measured 10–40 cm (4–16 in.) from the charges. A gradual increase in point resistance was observed with time after each blast. The increase in penetration resistance may be attributed to gradual improvement of intergranular bonds and dissipation of explosion created gases.