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Calculation of Hoek-Brown Parameters

If rock mass is descripted using GSI (Geological Structure Index) is known then it is possible to let the program to determine the H-B parameters as follows:

where:

GSI

-

Geological Structure Index

D

-

damage coefficient of rock mass

mi

-

strength material constant of the intact rock for peak conditions

Values of damage coefficient D for rock slope

Description of rock mass

Suggested value of coefficient D

Small scale blasting in engineering slopes results in modest rock mass damage, particularly if controlled blasting is used. However, stress relief results in some disturbance.

(Good blasting).

0.7

Small scale blasting in engineering slopes results in modest rock mass damage, particularly if controlled blasting is used. However, stress relief results in some disturbance.

(Poor blasting).

1

Very large open pit mine slopes significant disturbance due to heavy production blasting and due to stress relief from overburden removal.

(Production blasting).

1

In some softer rocks excavation can be carried out by ripping and dozing and the degree of damage to the slope is less.

(Mechanical excavation).

0.7

Approximate vlaues of strength material constant of the intact rock mi (after Hoek)

Type of rock

Representative rocks

mi [-]

Limestone rocks with well developed crystalline cleavage

Dolomite, calcite, marble

≈ 7

Consolidated clayey rocks

Mudstone, siltstone, silty shale, slate

≈ 10

Sandy rocks with solid crystals and poorly developed crystalline cleavage

Sandstone, quarzite

≈ 15

Fine grained igneous crystalline rocks

Andesite, dolerite, diabase, rhyolite

≈ 17

Coarse grained and metamorphic rocks

Amphibolite, gabbro, gneiss, granite, diorite

≈ 25