Liquefaction Hazard Mapping Using Various Types of Field Test Data: Fid-Bau Portal

Liquefaction Hazard Mapping Using Various Types of Field Test Data

Nilay, Nishant / Chakrabortty, Pradipta / Popescu, Radu

The so-called “Simplified Method” is the current state-of-practice (SoP) for liquefaction hazard assessment. It is based on correlations between observed soil behaviour during seismic events and common in-situ soil properties, such as: standard penetration resistance (SPT-N), cone penetration resistance (CPT-q), or shear wave velocity (Vs). The method has been certified by the 1996 and 1998 NCEER/NSF Workshops on evaluation of liquefaction resistance for all three types of in-situ test results. The major objective of this study is to determine the liquefaction susceptibility of the IIT Patna campus soil and prepare microzonation maps. Results of extended in-situ soil test programs, comprising all three soil index properties mentioned above (SPT-N, CPT-q and Vs), are available for the campus of IIT Patna (about 500 acres in size). The study presents and compares hazard maps in terms of factor of safety for liquefaction and liquefaction potential index for all three types of field test results. Susceptibility for lateral spreading is also discussed. As a significant part of the campus subgrade consists of fine-grained soils, the potential for cyclic softening of these soils, as addressed by various SoP methods, is also analysed. All three methods indicated various degrees of liquefaction susceptibility for the “safety criterion” (assuming structural damage without collapse). The study analyses the details of the three approaches and concludes that the CPT-based method along with a comprehensive procedure for assessing liquefaction potential of soil with high fines content may be the most appropriate for a site such as the IIT Patna Campus.