Increase in Cyclic Liquefaction Resistance of Sandy Soil Due to Installation of Drilled Displacement Piles

Drilled displacement piles are installed by the displacement of soil and subsequent placement of fluid cement grout within the evacuated volume. Depending on the soil grain-size characteristics, soil behavior, in situ soil density, pile spacing, and pile diameter, the installation process can result in measurable densification and an increase in lateral stress. Thus, it follows that the drilled displacement process may be used to mitigate cyclic liquefaction in sandy soils. In an effort to quantify the increase in cyclic liquefaction resistance resulting from drilled displacement piles, the authors performed pre- and post-installation cone penetration testing at a site in North Myrtle Beach, South Carolina. The results support that the installation of drilled displacement piles generally increases the liquefaction resistance of the surrounding soil. For a specific area replacement ratio, the trend is that improvement decreases with increasing pre-installation (q_tlN)_cs and approaches unity at very high values of pre-installation (q_tlN)_cs. The improvement can be significant for values of pre-installation (q_tlN)_cs generally as high as 250. Overall, the degree of improvement is greater for higher area replacement ratios.