Hello everyone
I have been performing direct shear test on cemented sandy soil samples ( pre stressed by normal stress or in other words compacted ) after curing them for certain period of time, I applied normal stress ( same as before) and by steady strain rate of .75 mm per min , performed the test
When I am reading the horizontal dial displacement Gage and ring shear Gage , after a steady increment in horizontal displacement Gage suddenly I am facing a huge jump for example from .02 mm to .08 in horizontal displacement , I have some clues such as dilatancy of sand (( but vertical displacement Gage dial which is placed on top of the sample is not jumping like horizontal and It keeps its pace but another dilemma is that It increases and again decreases but overall is increasing and again no sudden movement in vertical dial Gage compare to horizontal Gage))
So what are the reasons and keep in mind that test apparatus is calibrated and works fine
Thanks for your contributions
I dont know the terminilogy, but with sandy soils there is a vertical limit to compaction, then the vertIcal pressure has no choice but to go horizontal. Im not a soil scientist, so I think it may be like a huge stack of bbs or ball bearings. If the particles are touching each other, there is no verticle give without going horizontal
I am uncertain if you are headed down this path - but the 1st thing that caught my eye is whether you are looking at shear stress and shear strength variables. There is considerable research in these variables regarding soils; soil fluid relationships; slope relationships; parent material; slip planes; bedding structure; buoyancy; intergranular pressure; and then into related factors such as root deterioration. One last item to look at is Coulomb's formula where....shear strength = (coefficient of friction x net force normal to slide plane which exprtesses the relationship for cohessionless soils.
Simply some thoughts - but uncertain if this addresses your questions directly.
Thanks John for your reply
I am familiar with the concept of shear strength and its belongings , of course that I am working on shear strength variables and trying to record and represent collected data through diagrams , But the problem of sudden and huge jump in Gage remains
I attached a part of a datasheet which consist of two columns h-displc is tantamount to horizontal displacement and R-GAGE is reading data as you can see up to 1.8 I have a steady trend but after 1.8 sudden jump happens and I will be unable to record any data
My question is what should I do in this case? first is it normal for sandy soils due to dilatancy if so the readings are none or equal to zero , so if i put zero my diagram will be incorrect
Is your table potentially showing you the shear stress value for that particular material where the pressure is applied to - and once you hit the pressure where you have no values it exceeds the hydrostatic pressure of the material sampled?
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