The DST results presented in Fig. 2

The DST results presented in Fig. 2 show the shear stress–
horizontal displacement behavior for OTW-A and VBS-A over
a range of normal loads. For all of the stress-displacement
curves, a peak shear stress followed by a reduction to a steady
state shear stress, characteristic of drained tests on dilatant
specimens, is observed. The VBS exhibits a higher strength
compared to the OTW, which is reasonable because the angular
particles are more interlocked and thus more resistant to
shear than are the rounded particles.
The typical relationship between peak friction angle and relative
density at a fixed normal stress is illustrated in Fig. 3