Cone Penetration Resistance Variation with Time after Blast Liquefaction Testing

Blast liquefaction testing was used to evaluate the effectiveness of vertical drains in preventing liquefaction. As part of the study, settlements associated with drain installation and blasting were measured. In addition, CPT soundings were made before and after drain installation and at 1, 2, 4, and 8 weeks after blasting. Drains installed with high vibration produced 350 mm of settlement while drains installed with low vibration produced only 100 mm of settlement. Despite the settlement, CPT soundings 3 to 5 days after drain installation showed decreases of 66% to 50% in the cone resistance at the low and high vibration test areas, respectively. In contrast, 13 days after drain installation and 7 days after blasting, which produced another 300 to 400 mm of settlement, the cone tip resistance was 30% to 60% higher than prior to treatment. Although there was some evidence of increased penetration resistance at times greater than 7 days, the trends were inconsistent.