Assumptions
The following assumptions have been adopted in the Liquefaction Calculator module for SPTs.
Liquefaction analysis:
- Pre-drill depth is not analysed. On the liquefaction triggering plots it is shown as a greyed-out zone.
- The static shear stresses are assumed to be negligible in the liquefaction analysis (i.e. the calculations assume flat ground).
- In Boulanger and Idriss (2014), no probabilistic sensitivity analysis was done for the SPT-based liquefaction triggering procedure. Therefore, the default C0 value of 2.8, suggested in Eqn 2.25, is adopted.
- CSR is not calculated when the vertical effective stress is 0.0 due to a cut. This occurs when a cut extends below an SPT investigation.
- When calculating the post-liquefaction volumetric strain (εv) for free-field liquefaction induced settlement based on Fig. 2 in Zhang, Robertson and Brachman (2002), the relative density (Dr) values less than 30% and above 90% are bounded to 30% and 90% respectively. For ranges of the curves not shown below a specific factor of safety, the lines are assumed to extend vertically. i.e. at Dr = 30%, εv is assumed to be the same when the factor of safety gets below ~0.8.
- When Dr is estimated using Eqn 1 in Zhang et. al (2004), N1(60) values greater than 42 are capped at 42 in this equation.
References
- Boulanger, R. W., & Idriss, I. M. (2007). Evaluation of cyclic softening in silts and clays. Journal of geotechnical and geoenvironmental engineering, 133(6), 641-652. Boulanger, R. W., & Idriss, I. M. (2014). CPT and SPT based liquefaction triggering procedures. Report No. UCD/CGM.-14, 1, 134.
- Zhang, G., Robertson, P. K., & Brachman, R. W. (2002). Estimating liquefaction-induced ground settlements from CPT for level ground. Canadian Geotechnical Journal, 39(5), 1168-1180.
- Zhang, G., Robertson, P. K., & Brachman, R. W. I. (2004). Estimating liquefaction-induced lateral displacements using the standard penetration test or cone penetration test. Journal of Geotechnical and Geoenvironmental Engineering, 130(8), 861-871.
- Tatsuoka, F., Zhou, S., Sato, T., & Shibuya, S. (1990). Evaluation method of liquefaction potential and its application. Report on seismic hazards on the ground in urban areas. Ministry of Education of Japan, Tokyo, 75-109.