Liquefaction Assessment in Gravels using Vs and DPT Blow count from Case Histories

Gravelly soils have liquefied at multiple sites in at least 27 earthquakes over the past 130 years. These gravels typically contain more than 25% sand which lowers the permeability and makes them susceptible to liquefaction. Typical Standard Penetration Tests (SPT)- or Cone Penetration Test (CPT_-based 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), less affected by gravel particles. These correlations are based on case histories where gravelly soils did and did not liquefy in past earthquakes. The new probabilistic triggering curves reduce the range between 15 and 85% probability of liquefaction in comparison to previously developed curves. 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 factor of safety computed by the DPT and Becker penetration tests (BPT) at sites in Idaho subjected to the 1985 Mw 6.9 Borah Peak earthquake.