Literature-Phi (Lashkaripour and Dusseault, 1993)

UCS = 145.2 ´ Φ^–1.143

where

142.2 is in psi.

This equation is based on laboratory measurements on 13 shale samples, with nine samples having core porosity less than 10%; it gives a slightly lower UCS than Horsrud’s (2001) model. The average measured UCS in the data set is 11,500 psi.