Compressive Strength of Rock Cores at Natural Moisture Content

[geotech_ben]

FHWA Drilled Shaft Manual (section 13.3.5.3) requires uniaxial compressive strength testing of the rock at its natural moisture content. How can you get cores at natural moisture content when you are coring with water? This is also a requirement of ASTM 4543. Thanks!

 

[GoMizzou99]

ASTM D7012 section 8.3 tries to address core moisture but does not really provide guidance for your situation.

What I have done in the past is just tried to approach it with a little practicality...

For relatively non-absorptive rock we often follow ASTM C42 which is for compressive strength of concrete cores. Section 7.3 deals with moisture conditioning. Since the concrete cores are obtained in much the same manner as NQ & NX (wet) rock coring techniques - we often follow this method for testing the unconfined compressive strength of rock cores.

For absorptive rock - like some water sensitive shales - we do down-hole pressure-meter testing - assuming we can dry-drill (solid stem augers) to the test level.

 

[fattdad]

How does anybody know the natural moisture content of rock? I'll check this out further. However, we use d7012 and in many instances require Methods B and D to obtain Poisson's ratio.

f-d

ípapß gordo ainÆt no madre flaca!

 

[geotech_ben]

Thanks for the help! Our upcoming coring operation has about 650 feet of core. I am trying not to miss something....

 

[Okiryu]

I just got a report that shows moisture contents for limestone rock. The report indicates that the tests were done using BS 1377 PART 2 : 1990 Cl. 3.2. Moisture contents vary from 2 to 14.5%. It is interesting to see that the highest UCT result is for the W=2% sample (78.9 MPa), and the lowest UCT results is for the W=14.5% sample (6.2 MPa). The sample for with the highest result was above the groundwater level... the other was below the GWL...