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Vane shear test

Vane shear test

Vane shear test


I am currently doing a vane test on Kaolin clay at different moisture content. I have a spring calibration sheet from where I obtain the spring constant. However, from the data, the torque was found to increase with increase in moisture and the undrained shear strength also increases. which does not make sense, as I was expecting the stiffer the sample the greater the torque and shear strength. I am not sure where I am going wrong. I have repeated the test 4 times all shows the same pattern.
the formula I used are:

Cu = T/K T= torque and K is constant depending on vane dimensions (K= pi(D^2H/2 + D^3)
T = Spring constant/180*difference (I believe the difference is the difference between the initial and final reading in degrees)
This is what I obtained.

W% initial reading final reading difference Torque (kgcm) K Cu = T/K (kg/cm2)
35 5 310 305 5.05009E-05 78123.14831 6.46427E-10
61 5 97 92 5.73671E-05 78123.14831 7.34317E-10

Vane dimension

Diameter 25.5mm
Height 25.5mm

Can someone please assist me? I have attached the spring calibration. I am using Spring No1.

Many thanks

RE: Vane shear test

In my opinion the calibration reading and the torque formula is not related.
I think the procedure are the degree gives the load. The load multiplied by 50mm and divided by K, you will get the Cu

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