Hoek - Brown

The modified Hoek-Brown failure criterion describes the failure of a rock mass (based on the performed analyses of hundreds of underground structures and rock slopes) as:

where:	σ1ef	-	major principal stress during rock failure
	σ3ef	-	minor principal stress during rock failure
	σc	-	strength of the intact rock in simple compression
	mb,s	-	nonlinear material constant depending on the rock quality
	a	-	coefficient depending on the rock breaking

Basic parameters of the modified Hoek-Brown model should be determined from in-situ and laboratory measurements. To become more acquainted with this model, a brief list of ranges of individual parameters is provided.

If rock mass classification using GSI is known then it is possible to let the program to determine the H-B parameters by itself.

For actual analysis the H-B parameters are transformed into the M-C parameters. The solution procedure then becomes identical to that of the Mohr-Coulomb criterion.

This transformation employs the solution derived by Hoek and Brown in 1990 for known value of the effective normal stress σ_n, which is typical for the solution of slope stability problem.

where:	σc	-	strength of the intact rock in simple compression
	m	-	nonlinear material constant depending on the rock quality
	a	-	coefficient depending on the rock breaking

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Literature:

Stability analysis of rock slopes with a modified Hoek-Brown failure criterion, ANG Xiao-Li ; LIANG LI ; YIN Jian-Hua International journal for numerical and analytical methods in geomechanics   ISSN 0363-9061, 2004, vol. 28, no2, pp. 181-190