- Inverse filtering algorithm from Boulanger and DeJong (2018) is adopted for thin layer correction. The baseline parameters, z’50,ref = 4.0, mz = 3.0, m50 = 0.5, and mq = 2.0 are adopted.
- Cone resistance (qc) and cone tip resistance (qt) are used interchangeably in the analysis. All analysis were conducted using qc.
- Negative cone resistance (qc) and sleeve friction (fs) values are replaced with 1 kPa and 0.1 kPa respectively. If the user would like to use alternative replacement values, please use the ‘customised CPT trace’ option in the ‘Inverse Filtering’ tab in the CPT Transform module.
- The normalised cone resistance (Q) calculated in Eqn. 2.27 in Boulanger and Idriss (2014) has a minimum value of 1.0.
- The normalised sleeve friction (F) calculated in Eqn. 2.27 has a minimum value of 0.1.
- The soil behaviour type index (Ic) is calculated using Eqn. 2.26 in Boulanger and Idriss (2014), which is referencing Robertson and Wride (1997). The same relationship is reference in Robertson (1990) and Robertson and Wride (1998).
- When calculating Ic using Eqn. 2.26 in Boulanger and Idriss (2014), the stress exponents (n) from Robertson and Wride (1998) are adopted as suggested in Boulanger and Idriss (2014). Robertson and Wride (1998) uses three iterations with different values of n based on the Ic value:
- In this first iteration, n = 1.0 is used in the initial Ic calculation. Q is calculated using Eqn. 2.27 in Boulanger and Idriss (2014) or Eqn. 5 in Robertson and Wride (1998). If the Ic > 2.6 when n = 1.0, no further adjustments are required and the calculation ends in first iteration. However, if Ic ≤ 2.6 when n = 1.0, n needs to be modified and Ic is recalculated in the second iteration.
- In the second iteration, for Ic ≤ 2.6 when n = 1.0, recalculate Ic using n = 0.5 as per Robertson and Wride (1998). As per suggested in Robertson and Wride (1998), qc1N is substituted for Q in Eqn. 2.26 in Boulanger and Idriss (2014) or Eqn. 5 in Robertson and Wride (1998) in the second iteration. qc1N is calculated using Eqn. 3 from Robertson and Wride (1998). The overburden correction factor (CQ) in Robertson and Wride (1998) is adopted. The maximum value for CQ is suggested to be 2.0 in Robertson and Wride (1997) and Robertson and Wride (1998). However, the overburden correction factor (CN) in Boulanger and Idriss (2014) is essentially the same as CQ from Robertson and Wride (1998), but with a different maximum value of 1.7. CQ value of 1.7 is applied in the CPT Liquefaction Calculator. If the recalculated Ic remains ≤ 2.6 when n = 0.5, no further adjustments are required and the calculation ends in the second iteration. However, if Ic ≤ 2.6 when = 1.0, but the recalculated Ic > 2.6 when n = 0.5, n needs to be modified further and Ic is recalculated in the third iteration.
- In the third iteration, for Ic that fluctuates below and above 2.6 when n = 1.0 and 0.5 respectively, recalculate Ic using n = 0.75 as per Robertson and Wride (1998). Similar to the second iteration, qc1N is substituted for Q in Eqn. 2.26 in Boulanger and Idriss (2014) or Eqn. 5 in Robertson and Wride (1998) in the third iteration. A maximum CQ value of 1.7 is also adopted in the third iteration.
- In this first iteration, n = 1.0 is used in the initial Ic calculation. Q is calculated using Eqn. 2.27 in Boulanger and Idriss (2014) or Eqn. 5 in Robertson and Wride (1998). If the Ic > 2.6 when n = 1.0, no further adjustments are required and the calculation ends in first iteration. However, if Ic ≤ 2.6 when n = 1.0, n needs to be modified and Ic is recalculated in the second iteration.
- For each parameter, when the correlation option is selected, the user can choose to calculate that parameter using a single method or a weighted average of multiple methods. These weightings must all sum to 1. For example, with shear wave velocity estimates, there are 5 methods available. The user can solely use one method by assigning a weighting value of 1 to that method and a weighting value of 0 to all the other methods. A user could also estimate the shear wave velocity using a weighted average of various methods. For example, the user can select 0, 0.2, 0.2, 0.3 and 0.3 for methods 1 to 5 respectively, which means that method 1 will not be used, less weighting will be given to methods 2 and 3 and more weighting to methods 4 and 5 in accordance with the proportions entered.
- At each depth increment, when one or more methods do not calculate a value because they are out of range (i.e. exceed minimum or maximum threshold limits), then the weightings are automatically recalculated for the methods that do produce calculated values in accordance with the proportions entered. I.e. the wasted vote is re-proportioned to the remaining methods for which values are able to be calculated. Using the example above, if method 4 does not calculate a value, then the new weightings will be 0.286 for method 2, 0.286 for method 3 and 0.429 for method 5. This keeps the final calculated value weightings proportionally the same as intended by the user.
References:
- Robertson, P. K. (2009). Interpretation of cone penetration tests—a unified approach. Canadian geotechnical journal, 46(11), 1337-1355.
- Boulanger, R. W., & Idriss, I. M. (2014). CPT and SPT based liquefaction triggering procedures. Report No. UCD/CGM.-14, 1.
- Robertson, P. K., & Cabal, K. L. (2014). Guide to Cone Penetration Testing for Geotechnical Engineering, 6th Edition.
- Boulanger, R. W., & DeJong, J. T. (2018). Inverse filtering procedure to correct cone penetration data for thin-layer and transition effects. Proc., Cone Penetration Testing, 25-44.