Examination of Existing DMT-Based Liquefaction Evaluation Methods by Side-by-Side DMT and CPT Tests

This study employed the field measurements of flat dilatometer test (DMT) and cone penetration test (CPT) presented by a recent study (Tsai et al. 2009) and additional DMT and CPT data conducted in this present study to examine the existing DMT-based liquefaction evaluation methods. Specifically, the DMT and CPT were conducted side-by-side at each of six in-situ sites and thus it is feasible to incorporate those test results into validating the existing DMT-based methods such as Grasso and Maugeri (2006), Monaco et al. (2005), and Rena and Chameau (1991). The DMT parameter, horizontal stress index (KD), is used as an indicator for assessing liquefaction resistance of soils. The analysis results revealed that the existing KD-based liquefaction evaluation methods would overestimate CRR of soils, which leads to overestimate the factor of safety against liquefaction. Also, the estimation of DMT-KD values by using the CPT-qc as well as the correlation between DMT-KD and CPT-qc proposed by the previous studies would be significantly less than field measurements of DMT-KD. However, it should be noted that it is desirable to incorporate more field measurements to further verify this finding

EVALUATING MODEL UNCERTAINTY OF AN SPT-BASED SIMPLIFIED METHOD FOR RELIABILITY ANALYSIS FOR PROBABILITY OF LIQUEFACTION

In this paper, an innovative procedure is developed for estimating the uncertainty of an empirical geotechnical model. Here, the Youd et al. (2001) method, a deterministic model for liquefaction triggering evaluation, is examined for its model uncertainty. The procedure for evaluating this model uncertainty involves two steps: 1) deriving a Bayesian mapping function based on a database of case histories, and 2) using the calibrated Bayesian mapping function as a reference to back-figure the uncertainty of the model. Details of the developed procedure within the framework of the first-order reliability method (FORM) are presented. Using FORM with the calibrated model uncertainty, the probability of liquefaction can be readily determined, and thus, the results presented in this paper extend the use of the Youd et al. (2001) method