Assessment of state-of-practice use of field liquefaction charts at low and high overburden using centrifuge experiments

Practical application of the state of practice field liquefaction charts at low and high overburden is assessed with centrifuge testing. Available results of four centrifuge experiments of a 5 m-thick clean sand layer having free drainage at the top are used as case histories. The centrifuge tests include relative densities of 45% and 80% and overburden pressures of about 1 atm and 6 atm. The shear wave velocity (Vs) was measured in the centrifuge models using bender elements. The cone penetration testing (CPT) tip resistance was estimated with correlations from the literature. Vs-based and CPT-based liquefaction charts proposed by Andrus and Stokoe (2000) and Idriss and Boulanger (2008) were used. Both liquefaction charts worked well for the centrifuge tests having an effective overburden, sigma'v0, of about 1 atm. This was expected as the charts were originally calibrated with field earthquake case histories having sigma'v0 < 2 atm. Both liquefaction charts are too conservative for the centrifuge tests having an effective overburden, sigma'v0 of about 6 atm. The agreement at 6 atm deteriorates even further when state-of-practice overburden correction factors, K sigma < 1 are applied, including a prediction of liquefaction when the measured maximum pore pressure ratio in the test was only 0.6. Values of K sigma > 1 were found to provide good agreement with the charts for the 6 atm tests.