Effect of grain shape and angularity on the undrained response of fine sands

The objective of this paper is to discuss the effect of grain shape and angularity on the undrained behaviour of sands. Four fine to medium (D 50 = 0.15–0.29 mm) and uniform sands were examined. These sands have similar and (or) identical grading curves, but differ with respect to the angularity of their grains. Under the electron scanning microscope two sands have rounded grains and the other two have subangular to angular grains. For sands with rounded grains, evidence of undrained behaviour undergoing systematic weakening (shear stress reduction after a transient peak deviator stress) is provided by torsional hollow cylinder tests. However, sands with the same grading curve and void ratio, but angular grains, show stable response with a continuous increase in strength after a transient peak. A small variation in the sand gradation, i.e., D 50 = 0.22 ± 0.07 mm, does not appear to alter the pattern of undrained response described earlier, with the angular sand (D 50 = 0.15) exhibiting stable response to shear and the rounded sands (D 50 = 0.22 and 0.29) having unstable response to shear. The stiffness characteristics of the sands are also presented. Triaxial compression tests were performed to confirm the pattern of response observed under torsional testing.