I am working on shear behaviors of natural rock discontinuities. I have observed that back portion of upper half of shear box (where hydraulic jack exerts force to move upper half) tilts slightly during shearing. I would like to ask experts of this field. Please suggest me, what will be possible reasons behind said problem.
Hi
do you have any picture of that?? and are upper and lower part movable? do you use direct shear test with strain control or displacement one?
Dear Moghadam,
Yes! I am using direct shear test with strain control. Only upper part movable whereas lower half is fixed.
Dear Hemant,
I assume that this behavior is not related to the tipical dilation that occurs during shearing on rough surfaces.
If your direct shear equipment applies shear load ortogonally to normal load it is possible that the upper part tilts upward a little bit as you mentioned. We have solve this applying the shear load in angle to normal load (see file attached) in manner that shear vector intercepts normal vector at the center of the tested fracture.
You must keep in mind though that this angled shear load will gradually add some normal load to the sample during the test too.
I sense this may help you solve your problem.
Dear Wunder,
Thanks for sharing a nice pics of an instrument which may probably solve my query.
P.S. Would you provide me some references related to my query and shared image by you!
Dear Hemant,
This was the subject of my master degree work back in 1999. I have based on Barton-Bandis JRC-JCS method casting mortar samples with different and predefined strength e surface roughness.
It was developed at University of São Paulo - Brazil thereforeit is all in portuguese. The title is "Estudo das Propriedades de Resistência e Deformabilidade de Fraturas Rochosas Simuladas por Argamassa" meaning Study of the Shear Strength and Deformability Properties of Rock Fractures Simulated in Mortar.
The abstract goes attached.
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