Calculation of Hoek-Brown Parameters
If rock mass is descripted using GSI (Geological Strength Index) is known then it is possible to let the program to determine the H-B parameters as follows:
where: | GSI | - | Geological Strength 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 values 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, quartzite | ≈ 15 |
Fine-grained igneous crystalline rocks | Andesite, dolerite, diabase, rhyolite | ≈ 17 |
Coarse-grained and metamorphic rocks | Amphibolite, gabbro, gneiss, granite, diorite | ≈ 25 |