# Due to the heterogeneity of samples if

If Sample #2 is stronger than Sample #1 ( Fig. 4b) α could be overestimated. Hence, prior to plotting the peak differential stresses for the Sample #2 (PDS2), the stresses were corrected to reduce the variation in strength between specimens according to Eq. (7).equation(7)PDS′2=PDS10PDS20×PDS2,where PDSi0 is the peak differential stress of Specimen #i under zero pore pressure (#i, Pp=0 in Fig.