A possible slope failure is shown in the figure. Three soil samples are taken from different locations (I, II and III) of the potential failure plane. Which is the most appropriate shear strength test for each of the sample to identify the failure mechanism? Identify the correct combination from the following options:
P : Triaxial compression test
Q : Triaxial extension test
R : Direct shear or shear box test
S : Vane shear test
