Approach of Boulanger and Idriss (2014) for liquefaction analysis requires performing iterations to determine I_c and q_{c1N,cs}. In case you need to develop an excel spreadsheet that evaluates liquefaction based on Boulanger and Idriss (2014) approach, you may need to use the Macro below. Please note that based on my personal experience Excel’s built-in iteration module does not work appropriately for this purpose. You can examine it yourself by comparing against the results (I_c and q_{c1N,cs}) of the computer program CLiq. I highly recommend to use the macro below to perform the iterations which is in an entire accordance with CLiq software.

It is to be noted that the macro uses the approach of Robertson and Wride (1998) and Boulanger and Idriss (2014) for calculation of I_c and q_{c1N,cs}, respectively. I have already performed verification on the macro by comparing the values against the values of Cliq. See Figure 1 below for comparing the results. It is highly recommended that you perform your own in-house verification.

You can download the macro here:  Ic-and-qc1Ncs-Calculations_Macro.zip

Please read the “Notes” in the code carefully before using it. I look forward to hearing your feedback.