The following method is implemented in NovoLiq for estimating the probability of soil liquefaction which is recommended in NCEER Workshop Report:

 

Youd and Noble, 2001

They used a logistic analysis to analyze case history data from sites where effects of liquefaction were or were not reported following past earthquakes. This analysis yielded the following probabilistic equation:

 

Logit (PL) = ln(PL/(1-PL)) = -7.633 + 2.256 Mw - 0.258 N1(60)cs + 3.095 ln(CRR)


Where PL is the probability that liquefaction occurred, 1 - PL is the probability that liquefaction did not occur, and N1(60)cs is the corrected blow count, including the correction for fines content. Youd and Noble recommend direct application of this equation to calculate the CRR for a given probability of liquefaction occurrence. In lieu of direct application, Youd and Noble define MSF for use with the simplified procedure. These MSF were developed by rotating the simplified base curve to near tangency with the probabilistic curves for PL of 50%, 32%, and 20% and various earthquake magnitudes. These MSF are defined as the ratio of the ordinate of the rotated base curve at the point of near tangency to the ordinate of the unrotated simplified base curve at the same N1(60)cs. Because the rotated simplified base curves lie entirely below the given probability curve, CRR calculated with these MSF are characterized by smaller probability of liquefaction occurrence than the associated probabilistic curves.

 

Thus the MSF listed in this table, are denoted by PL<50%, PL<32%, and PL<20%, respectively. Because the derived MSF are less than 1.0, Youd and Noble do not recommend use of MSF for PL<32% and PL<20% for earthquakes with magnitudes greater than 7.0; Equations for defining the Youd and Noble MSF are listed below:

Probability, PL < 20% MSF = 103.81/M4.53 For M < 7

Probability, PL < 32% MSF = 103.74/M4.33 For M < 7

Probability, PL < 50% MSF = 104.21/M4.81 For M < 7.75

 

Cetin et al, 2004

A complete explanation of this method is resented in the following paper:

 

Standard Penetration Test-Based Probabilistic and Deterministic Assessment of Seismic Soil Liquefaction Potential
K. Onder Cetin, M.ASCE; Raymond B. Seed, M.ASCE; Armen Der Kiureghian, M.ASCE; Kohji Tokimatsu; Leslie F. Harder Jr., M.ASCE; Robert E. Kayen, M.ASCE ; and Robert E. S. Moss, M.ASCE

 

Note: Recently there has been technical discussions (by Dr Boulanger and Dr Idriss, 2010) about the accuracy and reliability of Cetin et al (2004) method. Therefore it is recommended that this method is used with cautious and full understanding of its risks. To obtain the full report please contact us.