weak rock

[kzaman]

Hi.. I'm looking for any sugestion on how to core soft rock (eg. shale)in laboratory.

 

[GeoPaveTraffic]

You want to take a rock core of a block of shale that you have in the lab?

Well....a few questions come to mind

What size and length of core are you trying to get?
What is the size of the block of shale?
How hard/soft is the shale?
How quickly does the shale react to water, i.e. does it soften quickly?

Oh yea, lastly WHY?

If you give me answers to some of the above, I might have some ideas. I have done odder things in the past, though maybe not much odder.

 

[soiledup]

When I first started working I asked my principal engineer the definition of 'soft rock'?

He replied 'Bryan Adams and Meatloaf'

Semantics aside, do you call it Soft in the states?? British Standards calls it weak.

 

[GeoPaveTraffic]

Generally, rock is referred to as weak not soft. However, some of us have bad habits that have been hard to break.

 

[BigH]

GPT - is that because we've 'aged' - no more Metallica?
-

 

[GeoPaveTraffic]

Definitely no more Metallica...more like The Foggy Bottom Boys.

 

[soiledup]

GPT - Honestly no criticism was intended, I've five years experience (mostly site supervision) and have recently moved into the office for reporting. I always respect BigH and your posts and am finding this site an invaluable part of my learning curve!

Apologies

 

[Stoph]

I thought for sure you would have come up with the Nitty Gritty Dirt Band.



Stoph

 

[GeoPaveTraffic]

None taken soiledup.

We all should be more careful with the terms that we use. For geotechnical engineers, most of the product that we produce is written. If we are sloppy and/or inconsistent in what we write, then it not only reflects badly on the individual doing the writing but on the profession as whole.

 

[eric1037]

The 2000 International Building Code (IBC) uses the term "soft" rock.

 

[GeoPaveTraffic]

That's a shame.

 

[epongra2]

Here in So Cal, we would likely take a hand sampler and drive it into the "soft" (or weak, semantics aside) shale, whether it be in the field or in the laboratory. The thick-walled, split barrel sampler would be lined with 2.5" diameter rings, 1" high. Disturbed, well yeah, but a bit easier than trying to core or shape the bulk sample in the lab.

 

[kzaman]

Thanks ...

The diameter of the core is 55 mm. The sample is prepared for uniaxial compressive strength test. Instead of using water during a coring process, is there any method or liquid / foam which more preferable?.

The hardness of the sample could be considered as "soft" rock

 

[soiledup]

Kzaman - personally, if I was asked to carry this out I would use the smallest barrel available on a hand held concrete coring unit probably using just a water flush. Changing the flush shouldn't make much difference on such a small core, just be sure to use alot of water. If it is that important I would be most worried about disturbance / vibrations from the drill shearing this 'shale'.

Incidentally,,, the hardness of a mineral sample could be soft, but the strength of a rock should be very weak to very strong. ( I thought that we'd covered this already?)

 

[GeoPaveTraffic]

If the shale reacts quickly with water, i.e. starts to soften or swell, then you might want to use a polymer drilling fluid. There are several types available and which one works best depends on the specifics of the rock. As far as I know the only way to determine the one that works best is through trial and error. You might be able to speak with some drillers in the area where the rock came from and get an idea of the best one to use.

Otherwise I agree with soiledup.

 

[kzaman]

Thanks to everyone ... I would appreciate all of your suggestions and recomendations