Bearing capacity from Rock properties

[nagatalluri]

Guys:

Is there anyway we can estimate Bearing capacity from Rock properties (RQD/ UCS of rock cores) ? Is there any correlation. We have rock with low RQD (<50) at footing depth. Is there any charts available.

Thanks
Naga

 

[oldestguy]

Some might relate your situation to a dense soil. However, weathered rock, possibly with karst features, is not something that lends itself to a chart. Aside from significant replacement of questionable material down there, the least one can do is relate the situation to local building codes. Even then there may not be a relationship.

Under similar circumstance I usually call for an extended additional investigation with numerous quarry drill holes looking for the better and worst zones, depending on the structure involved. Then I decide on the competency of the support.

 

[Mccoy]

I second oldest guy if an important building is involved. Cavities may be lurking underneath.
Shallow cavities may be revealed by Electrical tomography though.
What I usually do in your situation is to apply the known Hoek & Brown method

Hoek et al.: “Hoek-Brown failure criterion – edition 2002”

with a procedure for very poor rocks described in this article (involves observation of drilled cores):

Osgoui, Ulusay, Unal: “An assistant tool for the geological strenght index to better characterize poor and very poor rock masses”, International Journal of Rock Mechanics and Mining Sciences, 47 (2010) 690-697.

 

[fattdad]

determine your rock-mass friction angle and cohesion and solve the rational bearing pressure equation.

Now determining your rock-mass properties is the problem. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[ORUSA]

Here is the NAV Fac for Rock. See citation.

DEPARTMENT OF THE ARMY EM 1110-1-2908
U.S. Army Corps of Engineers
CECW-EG Washington, DC 20314-1000
Manual
No. 1110-1-2908 30 November 1994
Engineering and Design
ROCK FOUNDATIONS

 

[ORUSA]

Here is the link to the publication. It has a treatment for various types of rock fabric (Chapter 6).