This standard details the procedure and equipment requirements for determining the in-situ undrained shear strength of soft, sensitive cohesive soils using a vane shear test. It includes specifications for standard vane dimensions, field methodology, and calculations for both undisturbed and remoulded shear strength.
Code of practice for in-situ vane shear test for soils
Quick Reference Values
Rate of rotation0.1 degree/second
Standard Height to Diameter (H/D) ratio2
Standard vane diameters37.5 mm, 50 mm, 65 mm, 75 mm
Number of revolutions for remoulded test25 revolutions
Maximum thickness of vane blades1.6 mm to 3.2 mm depending on diameter
Key Formulas
S = T / [pi * D^2 * (H/2 + D/6)] — Undrained shear strength (where T is Torque, D is Diameter, H is Height)
Practical Notes
The test is highly reliable for soft clays but completely unsuitable for stiff clays, sands, or gravels due to disturbance and drainage effects.
Always account for the friction of the extension rods; this is typically done using a dummy rod test if slip couplings are not utilized.
The vane must be pushed into the ground steadily without any twisting motion to minimize initial soil disturbance.