CEE 554 field Shear Strength Tests- full report

Field Tests • Field tests avoid problems with disturbance. However, these methods only determine the shear strength indirectly through correlations with lab results • Vane shear • Soft clays, silts and peats • Dutch ...

Field Tests • Field tests avoid problems with disturbance. However, these methods only determine the shear strength indirectly through correlations with lab results • Vane shear • Soft clays, silts and peats • Dutch Cone Penetrometer (CPT) • Soft clays and sandy soils • Standard Penetration Test (SPT) • Granular materials • Pressuremeter • Clay, weak rock, sand • Geophysical Soundings • All geological materials 5 3 Vane Shear Test 6 • The Vane Shear test is an useful method of measuring the in-situ undrained shear strength of clay • Reasonably cheap and quick method • Appropriate for very soft and sensitive clay soils Vane Shear Test Procedure • A rod with a four blade vane is pushed into the ground and rotated generally at a slow rate of 6° to 12° per minute (practically 1o every 10 sec) • Every 15-30 seconds the torque force is measured • Once the maximum torque has been reached, the vane is rotated rapidly for ten revolutions to induce shear failure • After shearing, the slow rotation rate is resumed to determine the remolded shear strength • The shear strength is proportional to the torque / blade diameter3 • The shear strength of the material is calculated from the Torque divided by a constant K, which depends on the dimensions and the shape of the Vane 7 4 Vane Shear Test • In the figure, the green arrow shows the amount of rotation • Red arrow shows a device that measures the required Torque • The procedure and the equipment should follow the procedures suggested by the ASTM D2573-72. • Considerable uncertainty exists in the interpretation and applicability of the results