Flagship Project 2 Comparison between deterministic and probabilistic liquefaction triggering assessment approaches over the Christchurch area V Lacrosse, B Bradley, s van ballegooy

Project Outline Deterministic liquefaction assessments commonly undertaken in NZ (as recommended by NZGS, MBIE) Conservatism is compounded, therefore overly conservative predictions Unable to determine likelihood of level of liquefaction consequence being exceeded (because liquefaction consequences considered at discreet levels) Full probabilistic assessment can account for these variables (e.g. uncertainty in triggering, seasonal variations, hazard curves) Understand deterministic v. probabilistic at site-specific and regional scale Address gap in industry knowledge and practice

Methodology Site-specific analysis at 4 sites in Chch with high quality data - using Boulanger & Idriss 2014 - 25yr, 100yr, 500yr return periods - using LSN - focus on sites where triggering is well understood - incorporate triggering uncertainty, GW variations, FC and Ic correlation distributions - understand site-specific variables - output distribution/likelihood instead of absolute LSN value Regional analysis - same parameters as above - identify areas were probabilistic approach is more appropriate 10 12 14 16 18 20 22 LSN

Timeframe FEB MAR APR/MAY JUNE - Meet with Brendon & Sjoerd to discuss methodology - Start computing CPT analyses for site-specific study MAR - Gain better understanding of site-specific results and variables that impact LSN - Calculate probability that LSN > x for a given return period APR/MAY - Complete site-specific study of deterministic v probabilistic analysis - Meet with Brendon to discuss results & improvements JUNE - Start looking into regional analysis

Expected Impact Understand uncertainties that drive liquefaction assessments Understand advantages of the use of probabilistic assessments Use of probabilistic assessment in areas were more appropriate Therefore, make more informed decisions about liquefaction hazard LONGTERM… Possible liaison with MBIE/NZGS about future updates to guidance docs Improve the standard of liquefaction assessments in NZ