Some soil properties like stiffness depend on the strain level in the test.

Yes, mechanical properties of materials like strength are not fixed properties but depend on external testing conditions ( parameters ) like specimen size and geometry, loading conditions, moisture content etc. These properties must be distinguished from physical properties like density which depend on the constitution of the materials themselves. Physical properties of the same material are expected to remain the same but not the mechanical properties unless the testing conditions are the same.

Some soil properties like stiffness depend on the strain level in the test.

I have almost the same experience with DC(T) fracture test. Although the thickness of the samples is taken into account when we calculate the fractured surface, we applied a correction factor to account for the effect of thickness on fracture energy. It appears that when the combination of the stresses and/or strains is complicated, such as in DC(T), IDT and ... we should come up with a correction factor accounting for 3D geometry. On the other hand, a simple test, (e.g. unaxial compression test) does not need any correction factor, because the stress/strain distribution is straight forward.

Sir,

Thanks for mentioning about DC(T) test. I didn't understand the point about correction factor, like how do you realise when to use it. in case of coated specimens either the tensile or compressive test is a complex phenomenon.

Thanking you

Kalyan

Sure. The correction factor in DC(T) fracture test is applied whenever the thickness of tested sample is not 50 mm.