Blast-Induced Liquefaction for Full-Scale Foundation Testing

This paper describes a pilot test program that was carried out to determine the appropriate charge weight, delay, and pattern required to induce liquefaction for full-scale testing of deep foundations. The results of this investigation confirmed that controlled blasting techniques could successfully be used to induce liquefaction in a well-defined, limited area for field-testing purposes. The tests also confirmed that liquefaction could be induced at least two times at the same site with nearly identical results. Excess pore pressure ratios greater than 0.8 were typically maintained for at least 4 min after blasting. The test results indicate that excess pore pressure ratios produced by blasting could be predicted with reasonable accuracy when single blast charges were used. However, for multiple blast charges, measured excess pressures were significantly higher than would have been predicted for a single blast with the same charge weight. The measured particle velocity attenuated more rapidly with scaled distance than would be expected based on the upper bound relationship developed from previous case histories. Settlement was typically about 2.5% of the liquefied thickness, and about 85% of the settlement occurred within 30 min after the blast. Cone penetrometer test results show that blasting initially reduced the soil strength, but after several weeks the strength had substantially increased.