CPT-Based Liquefaction Triggering Procedure

Abstract

A probabilistic cone penetration test (CPT) based liquefaction triggering procedure for cohesionless soils is derived using a maximum likelihood method with an updated case history database. The liquefaction analysis framework includes revised relationships for the magnitude scaling factor (MSF) and for estimating fines contents from CPT data when laboratory test data are not available. The updated case history database and methodology for developing the liquefaction correlation are described. Measurement and estimation uncertainties, the potential effects of false positives and false negatives in the case history database, and the effects of the choice-based sampling bias in the case history database are accounted for. Sensitivity analyses showed that the position of the most likely triggering curve and the magnitude of the total error term are reasonably well constrained by the data. The sensitivity study provides reasonable bounds on the effects of different interpretations, from which probabilistic and deterministic relationships for practice are recommended.

Correction of Mechanical CPT Data for Liquefaction Resistance Evaluation

“…While the soil classification criteria adopted is generally the same originally proposed by Robertson ([11]) and the normalisation procedure applied to qc is quite similar, the greatest difference among most of the CPT-based methods rely on the fine content evaluation and the correction applied to define the equivalent clean sand cone resistance, qc1Ncs, as shown in Figure 2, where qc1Ncs are calculated from the 3915 pairs of CPTe measurements by applying both the considered procedures and compared. The correction proposed by Boulanger and Idriss ( [2]) furnishes much higher values of qc1Ncs as the fine content increases (and the cone tip resistance decreases).…”

“…These relationships generally provide the liquefaction resistance ratio in terms of equivalent clean sand cone tip resistance, qc1Ncs, and are continuously updated as the worldwide liquefaction case history database increases. Among the most recently adopted CPT-based procedures, those proposed by Boulanger and Idriss ( [2]) and Juang et al ( [3]), hereinafter mentioned as "B&I" and "J&al" respectively, were selected as the most representative and reliable for liquefaction hazard evaluation especially if the most recently observed liquefaction case histories of Christchurch (New Zealand) and Emilia-Romagna (Italy) are included ( [10]). While the soil classification criteria adopted is generally the same originally proposed by Robertson ([11]) and the normalisation procedure applied to qc is quite similar, the greatest difference among most of the CPT-based methods rely on the fine content evaluation and the correction applied to define the equivalent clean sand cone resistance, qc1Ncs, as shown in Figure 2, where qc1Ncs are calculated from the 3915 pairs of CPTe measurements by applying both the considered procedures and compared.…”

“…1st and 2nd grade polynomial and power laws were tested to fit mechanical to electrical data. Results of regression analyses are shown in Figures 3a and 4a with reference to the equivalent clean sand cone resistance, qc1Ncs, following the procedure proposed by [2] (B&I) and [3] (J&al), respectively. Further comparisons between corrected mechanical (estimated) values and electrical (target) values are shown in Figures 3b and 4b, for "B&I" and "J&al" approach respectively, where it is evident how the estimate errors are independent from the regressed variable, qc1Ncs.…”

“…Firstly, LPI was determined on both the mechanical (LPIm) and the electrical (LPIe) CPT profiles collected from all the selected sites using both the procedures suggested by Boulanger and Idriss ( [2]) and Juang et al ([3]). Three reference earthquakes of different severity (named SS1, SS2 and SS3) characterised by different moment magnitude, Mw, and peak ground acceleration on the ground surface, PGA (SS1: Mw=6; PGA=0.15g; SS2: Mw=6.5; PGA=0.30g; SS3: Mw=7; PGA=0.45g) were considered.…”

“…For more than 30 years, there has been considerable interest in using CPT to evaluate the liquefaction resistance of soils and several simplified methods have been based on CPT results following both deterministic and probabilistic approaches (e.g., among the most recent, [1], [2], [3] and [4]). It cannot be excluded that some early work on liquefaction is based on data collected using a mechanical cone ( [5]).…”