Mining rock mass rating
Encyclopedia
Laubscher developed the Mining Rock Mass Rating (MRMR) system by modifying the Rock Mass Rating
(RMR
) system of Bieniawski. In the MRMR system the stability and support are determined with the following equations:
The parameters to calculate the RMR value are similar to those used in the RMR
system of Bieniawski. This may be confusing, as some of the parameters in the MRMR system are modified, such as the condition parameter that includes groundwater presence and pressure in the MRMR system whereas groundwater is a separate parameter in the RMR system of Bieniawski. The number of classes for the parameters and the detail of the description of the parameters are also more extensive than in the RMR system of Bieniawski.
The adjustment factors depend on future (susceptibility to) weathering
, stress environment, orientation, method of excavation, and the amount of free block faces that facilitate gravity fall.
The combination of values of RMR and MRMR determines the so-called reinforcement potential. A rock mass with a high RMR before the adjustment factors are applied has a high reinforcement potential, and can be reinforced by, for example, rock bolts, whatever the MRMR value might be after excavation. Contrariwise, rock bolts are not a suitable reinforcement for a rock mass with a low RMR (i.e. has a low reinforcement potential).
Laubscher uses a graph for the spacing parameter. The parameter is dependent on a maximum of three discontinuity sets that determine the size and the form of the rock blocks. The condition parameter is determined by the discontinuity set with the most adverse influence on the stability.
The concept of adjustment factors for the rock mass before and after excavation is very attractive. This allows for compensation of local variations, which may be present at the location of the rock mass observed, but might not be present at the location of the proposed excavation or vice versa. In addition, this allows for quantification of the influence of excavation and excavation induced stresses, excavation methods, and the influence of past and future weathering of the rock mass.
RMR
RMR, a three-letter acronym meaning:*Rear mid-engine, rear-wheel drive layout*Recurring Monthly Revenue*Registered Merit Reporter, a certification offered by the National Court Reporters Association*Resting Metabolic Rate, see basal metabolic rate...
(RMR
RMR
RMR, a three-letter acronym meaning:*Rear mid-engine, rear-wheel drive layout*Recurring Monthly Revenue*Registered Merit Reporter, a certification offered by the National Court Reporters Association*Resting Metabolic Rate, see basal metabolic rate...
) system of Bieniawski. In the MRMR system the stability and support are determined with the following equations:
- RMR = IRS + RQD + spacing + condition
-
- in which:
- RMR = Laubschers Rock Mass Rating
- IRS = Intact Rock Strength
- RQD = Rock Quality Designation
- spacing = expression for the spacing of discontinuitiesDiscontinuity (geotechnical engineering)A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
- condition = condition of discontinuitiesDiscontinuity (geotechnical engineering)A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
(parameter also dependent on groundwater presence, pressure, or quantity of groundwater inflow in the uderground excavation)
- RMR = Laubschers Rock Mass Rating
- in which:
- MRMR = RMR * adjustment factors
- in which:
- adjustment factors = factors to compensate for: the method of excavation, orientation of discontinuitiesDiscontinuity (geotechnical engineering)A discontinuity in geotechnical engineering is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane...
and excavation, induced stresses, and future weathering
- adjustment factors = factors to compensate for: the method of excavation, orientation of discontinuities
- in which:
The parameters to calculate the RMR value are similar to those used in the RMR
RMR
RMR, a three-letter acronym meaning:*Rear mid-engine, rear-wheel drive layout*Recurring Monthly Revenue*Registered Merit Reporter, a certification offered by the National Court Reporters Association*Resting Metabolic Rate, see basal metabolic rate...
system of Bieniawski. This may be confusing, as some of the parameters in the MRMR system are modified, such as the condition parameter that includes groundwater presence and pressure in the MRMR system whereas groundwater is a separate parameter in the RMR system of Bieniawski. The number of classes for the parameters and the detail of the description of the parameters are also more extensive than in the RMR system of Bieniawski.
The adjustment factors depend on future (susceptibility to) weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
, stress environment, orientation, method of excavation, and the amount of free block faces that facilitate gravity fall.
The combination of values of RMR and MRMR determines the so-called reinforcement potential. A rock mass with a high RMR before the adjustment factors are applied has a high reinforcement potential, and can be reinforced by, for example, rock bolts, whatever the MRMR value might be after excavation. Contrariwise, rock bolts are not a suitable reinforcement for a rock mass with a low RMR (i.e. has a low reinforcement potential).
Laubscher uses a graph for the spacing parameter. The parameter is dependent on a maximum of three discontinuity sets that determine the size and the form of the rock blocks. The condition parameter is determined by the discontinuity set with the most adverse influence on the stability.
The concept of adjustment factors for the rock mass before and after excavation is very attractive. This allows for compensation of local variations, which may be present at the location of the rock mass observed, but might not be present at the location of the proposed excavation or vice versa. In addition, this allows for quantification of the influence of excavation and excavation induced stresses, excavation methods, and the influence of past and future weathering of the rock mass.
See also
- Core recovery parameters
- Geotechnical engineeringGeotechnical engineeringGeotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but is also used by military, mining, petroleum, or any other engineering concerned with construction on or in the ground...
- Hoek-Brown failure criterion
- Rock mass classificationRock mass classificationRock mass classification systems are used for various engineering design and stability analysis. These are based on empirical relations between rock mass parameters and engineering applications, such as tunnels, slopes, foundations, and excavatability...