Soil Densification by Driven Piles to Reduce Liquefaction Potential

For construction sites with zones of loose soil and the potential for liquefaction during a seismic event, deep foundation elements such as driven piles are often recommended as an economical solution. Typically, the designed deep foundation elements would resist liquefaction by advancing piles to a depth below the liquefiable layer so they obtain the required allowable compressive capacity. However, foundation contractors may have difficulty installing piles successfully to the minimum penetration depth once adjacent piles have been installed. Because of such installation difficulty, specific analyses of the piles during installation may be beneficial to provide a combination of revised pile capacities and review of the susceptibility to liquefaction caused by soil densification from installing the piles. This paper discusses challenges posed by advancing piles with a hydraulic impact hammer, spaced 1.8 m (6 ft) on center, to the minimum-required penetration depth of 19.2 m (63 ft) to obtain the required compressive capacities of 533.8 kN (120 kips) and lateral capacities of 31.1 kN (7 kips). Seventeen of 586 piles were driven to depths between 1.5 and 4.9 m (5 and 16 ft) short of the minimum required penetration depths. This paper will describe an investigation consisting of 10 seismic cone penetration tests (SCPT) to evaluate the increase in relative density within the pile field resulting from pile driving. This paper also will summarize two analyses using the SCPT tests to determine the site’s susceptibility to liquefaction and revisions to the pile capacities as a result of the soil being densified.