Developing Liquefaction Prediction Equations for Gravels Based on DPT Blow Count and Shear Wave Velocity at Field Case History Sites

Abstract

Gravelly soils have liquefied at multiple sites in at least 20 earthquakes over the past 130 years. These gravels typically contain more than 25% sand which lowers the permeability and makes them susceptible to liquefaction. In other cases, a low permeability layer at the surface impedes drainage and causes liquefaction. Typical SPT- or CPT-based liquefaction correlations can be affected by large gravel particles and lead to erroneous results. To deal with these problems, we have developed liquefaction triggering curves for gravelly soils based on (1) shear wave velocity (Vs) and (2) a 74-mm diameter dynamic cone penetrometer (DPT), that are less affected by gravel particles. These correlations are based on case histories where gravel did and did not liquefy in past earthquakes. The VS-based liquefaction triggering curves for gravels shift to the right relative to similar curves based on sands. Good agreement has been obtained with liquefaction resistance from the DPT and the CPT when these methods could all penetrate the gravel in Wellington New Zealand. Correlations are developed between Vs and blow count from the DPT.