Diseño Pilares Mineros



Hoek and Brown introduced their failure criterion in an
attempt to provide input data for the analyses required for
the design of underground excavations in hard rock.



The criterionwas derived from the results of research into
the brittle failure of intact rock by Hoek and on model
studies of jointed rock mass behaviour by Brown .



The criterion started from theproperties of intact rock and
then introduced factors to reduce these properties on the
basis of the characteristics of joints in a rock mass. The
authors sought to link the empirical criterion togeological
observations by means of one of the available rock mass
classification schemes and, for this purpose, they chose the
Rock Mass Rating proposed by Bieniawski.

Está expresada como:

where mbis a reduced value of the material constant mi and
is given by:

s and a are constants for the rock mass given by the
following relationships:

D is a factor which depends upon the degree ofdisturbance to which the rock mass has been subjected
by blast damage and stress relaxation. It varies from 0
for undisturbed in situ rock masses to 1 for very
disturbed rock masses.

s and aare constants for the rock mass given by the
following relationships:

D is a factor which depends upon the degree of
disturbance to which the rock mass has been subjected
by blast damage andstress relaxation. It varies from 0
for undisturbed in situ rock masses to 1 for very
disturbed rock masses.

Failure initiates at the boundary of an excavation when
σc is exceeded by the stressinduced on that boundary.
The failure propagates from this initiation point into a
biaxial stress field and it eventually stabilizes when the
local strength, is higher than the induced stresses δ1and δ3.
Most numerical models can follow this process of
fracture propagation and this level of detailed analysis
is very important when considering the stability of
excavations in rock and when...