Liquefaction Mitigation Using Vertical Composite Drains: Full Scale Testing: Fid-Bau Portal

Liquefaction Mitigation Using Vertical Composite Drains: Full Scale Testing

K. M. Rollins / J. K. Anderson

This project involved performing full-scale field tests to investigate the use of vertical composite drains (EQ-Drains) in dissipating pore pressure to prevent liquefaction during an earthquake. The EQ-Drains were evaluated at a test site in Vancouver, British Columbia, using controlled blasting technique to liquefy loose sand. Installing EQ-Drains using high vibration typically increased relative density by about 10% and produced volumetric strains of 2.5%. This effectively reduced the amount of settlement and increased the rate of pore pressure dissipation relative to untreated sites. Controlled basting also showed the potential to produce significant densification of liquefiable soils. Settlements of 2 to 4% of volume were produced for small charge masses and relative density was typically increased by 7-10%. The presence of EQ-Drains significantly increased the rate of excess pore water pressure dissipation relative to untreated areas. Even though drains did not prevent liquefaction for the high stress levels imposed by the blast tests, settlements in areas where drains were installed using conventional procedures was reduced to only about 60% of the settlement measured in untreated areas. Computer model analyses also successfully matched measured pore pressure and settlement response during blasting. Results of the computer model analysis indicate that the drains can prevent liquefaction and excessive settlement when drain diameter and spacing are properly designed for the expected earthquake.