RQD and UCS?

[fattdad]

ASTM D6032 is the standard for calculating RQD. RQD is measured on, "Sound core." ASTM describes sound core as any core that is fresh to moderately weathered and that has sufficient strength to resist hand breakage.

Separate and unrelated to RQD, FHWA claims any rock that has an UCS (unconfined compressive strength) less than 250 psi should be treated as, "Soil like" in its resistance to scour.

FHWA also claims that RQD>50 is considered resistant to scour.

Anybody think USC less than 250 psi is resistant to hand breakage?

f-d

ípapß gordo ainÆt no madre flaca!

 

[miningman]

not in my world it aint!!!!!

 

[Ron]

Cement treated bases and soil cement are in that range. Even the weak ones, down to about 175 to 200 psi are still resistant to hand breakage....doesn't mean it can't be done, just still obviously resistant.

Another thought is that hand breakage and scour potential are not as closely related as they would like to believe. I would see a higher limit for scour potential and a lower limit for hand breakage threshold.

 

[Panars]

I would say 250 psi is resistance to hand breakage. That is qu=36 ksf (1720 kPa) which is still two to three times harder than a hard glacial till which I have a hard time breaking by hand.

 

[fattdad]

I'm working with Annandale's erodibility index, which has a parameter that can be derived from RQD. If RQD is applied incorrectly (i.e., obtained from dirty limestone, shale or such that can be broken by hand) then there'd be a bad conclusion. I'd be glad to share how I'm getting from RQD to scour potential - just not sure how many of you all are familiar with Annandale's erodibility index.

f-d

ípapß gordo ainÆt no madre flaca!