i) The undrained shear strength of soft clays can be determined in a laboratory by a vane shear test
ii) Apparatus –
A) Consist of a vertical steel rod having four thin stainless steel blades fixed at bottom end
B) Height (H) of vane equals twice the overall diameter (D)
(D = 2.5 mm and H = 60 mm)(Length of rod = 24 mm ) recommended values
C) Container having d = 38 mm and ht = 75 mm is fixed securely to the base plate.
D) Vane is gradually lowered into container having soil mass at a depth of 10 to 20 mm below the top of specimen
E) Torque is applied at rate of 6o per minute till the specimen fails is shear, Torque applied is measured.
iii) Measurement of shear strength
The shear strength of soil is measured using
Both top & bottom end partakes in shearing and
Only bottom end partakes in shearing where τ is in N / mm2 and T is in N – mm