direct shear test - load values

[Structures33]

Hey there - I'm looking for some general information regarding direct shear tests. When these tests are performed, is there a specified/typical load that is applied to the specimens and what is the standard/typical area of specimen?
I have some values obtained from a direct shear test performed in another country and I am trying to determine if they used similar values.
Also, is there an ASTM standard for these tests?
Thanks in advance!
(this was posted under SE first so you may see it twice)

 

[theCorkster]

Structures 33:

Direct shear tests are one way of measuring the angle of internal friction of a soil or rock. The normal stress applied, the rate of displacement, the size of the shear box, and the orientation of the shearing plane all have impact on results.

In general, the normal stressed are selected to cover the range of inplace stresses that the analysis is addressing. The rate of displacement should be based on the specimen's drainage, based on the consolidation of the specimen under the normal stress prior to displacement. The size of the shear box is critically important for several reasons; the area of the shear box should meet particle size criteria to reduce the likelihood that the size adversely influences the result. Finally, the orientation of the test specimen relative to bedding planes, joints and/or fractures will influence results.

I believe that ASTM D3080 covers the soil standard; I don't recall what standard covers direct shear of rock specimens.

 

[oldestguy]

Besides size of shear box, there are other factors. One, what is the deflection-shear stress relationship? How far was the specimine sheared? Timing of shearing action, what speed? Did a peak shearing stress occur, followed by a drop off to "residual" shear stress?

Did the apparatus keep the load centered on the remaining shearing area?

 

[Structures33]

I appreciate all the insight and information reagarding the testing procedure and factors involved. It's clear that there are many things to analyze -- however, I only have access to the load, specimen area, normal stress, weight of specimen, horizontal and vertical displacements, shear force and shear stress. I need to know if the shear stresses calculated are accurate in terms of how we would perform this test in the states.
Is this something that I can determine based on the given information?
Thanks

 

[fattdad]

Typically what you need to know from a direct shear test is the friction angle. Is there some reason that you are focused on whether the analysis meets some standard of care as applied in the United States?

It sounds like you have the appropriate data set to look at shear stress v. shear strain relationships for varying normal loads, prepare a plot for each load increment and determine peak (or residual) shear strength values (normalized for the area of the shear plane). If you do this for each load increment, you will develop a strength envelope that can be used to determine your friction angle.

Hope this helps.

f-d

¡papá gordo ain’t no madre flaca!