Geotechnical and Materials Engineering Standards for Bridge ...

INTACT ROCK STRENGTH - Although rack masses are non-isotropic and the
main feature of their weakness 1s the strength along
discontinuities, it is oftcn useful to have some information
about tha uniaxial cc~pressive strength of the intact rock.
The tabla below gives seven grades of rock strength and simple
methods of identification. These grades have been based on
results of unconfined compressive stkength tests for which
standard methods have been ruggcsted3,
Strength Fleld Rgnge of unconfined
Grsds Classification Identification Compressive strength
Hethad INf a3
RO Extremely vesk Idtnted by thumbnail < 1
R1 Very weak Crumbles under firm 1 - 5
blows of gtologfcal .
hzmtr; can b6 petlcd
with a pocket knifa
R2 Weak rock Can ba peeled by a pocket
knife vith difficuity;
shallov indentations mads
by a fim blow with point
of gcalogical hammer
R3 Hedim strong Cannot be scraped or
peeled vlth a pocket hife;
spechen can be fractured
vith a single firm blow
. of geological hamer.
R4 Strong Specimen requires more SO - 100
than one blow of geolog-
ical h-er to fracture
R5 Very strong Spechen requires many 100 - 250
blows of geological h-er
to fracture:
R6 Extremely strong Specben can only be
chipped by a geological
hammer