Abstract:

Field data from liquefaction case histories are essential for the development, calibration and validation of the liquefaction evaluation methods, and prime standard for the validation of current liquefaction theories. By collecting liquefaction data from Chi-Chi, Bachu and Songyuan earthquakes in China, the volume of data in the Chinese liquefaction database based on the standard penetration test (SPT) is significantly increased from 121 to 465. This database is then used to validate the reliability of four liquefaction evaluation methods based on SPT, i.e. evaluation method suggested in Code for Seismic Design of Buildings (code method for short), two hyperbolic models, and the simplified cyclic stress ratio (CSR) method. The results indicate that the two hyperbolic models can satisfactorily distinguish the liquefaction data from the non-liquefaction data, with success rates higher than 85% for both liquefaction data and non-liquefaction data. The code method and the simplified CSR method exhibit disadvantages for liquefaction evaluation. The predicted results are not satisfactory for all four evaluation methods for seismic intensity of 7, as the liquefaction data are mixed with the non-liquefaction data for this intensity. The overall success rates of the four evaluation methods are high for the data when the seismic intensities are 8 and 9. A new probabilistic liquefaction evaluation equation based on the CSR method is proposed by regression analysis of the new liquefaction data. The predicted liquefaction critical state lines are in reasonable agreement with reported probabilistic equation, even though the number of datasets adopted is different. The Chinese code method has obvious limitation with conservative results for soil layers at the depth greater than 10 m. The analytical results provide reference for improving the liquefaction evaluation method in Chinese code.

Key words: sand liquefaction, database, standard penetration test, liquefaction evaluation, probability level