Vertical composite drains for mitigating liquefaction hazard

Liquefaction has typically been mitigated by in-situ densification; however vertical composite drains offer the possibility of preventing liquefaction and associated settlement while reducing the cost and time required for treatment. To evaluate the behavior of these drains, controlled blasting techniques were employed to liquefy loose sand at two field test sites. Similar blast charges were then detonated at adjacent sites treated with drains. Measurements demonstrated that the drains could significantly increase the rate of pore pressure dissipation. In addition, the installation process typically densified the surrounding soil, thereby decreasing the liquefaction potential. Computer analyses successfully matched the measured response.