An underground mine with large rooms or bays and pillars, with little additional bolting or stabilization...

An underground mine with large rooms or bays and pillars, with little additional bolting or stabilization required. Boat tours are provided and, normally, available to the public. Given the description, what would you expect the Rock Mass Rating to likely be and why?

Expert Solution

The rock mass rating (RMR) is a geomechanical classification system for rocks, developed by Z. T. Bieniawski between 1972 and 1973. It combines the most significant geologic parameters of influence and represents them with one overall comprehensive index of rock mass quality, which is used for the design and construction of excavations in rock, such as tunnels, mines, slopes and foundations.

The following six parameters are used to classify a rock mass using the RMR system

Uniaxial compressive strength of rock material
Rock quality designation (RQD)
Spacing of discontinuities
Condition of discontinuities.
Groundwater conditions
Orientation of discontinuities

Each of the six parameters is assigned a value corresponding to the characteristics of the rock. These values are derived from field surveys and laboratory tests. The sum of the six parameters is the "RMR value", which lies between 0 and 100

.

Below is the classification table for the RMR system.

RMR	Rock quality
0 - 20	Very Poor
21 - 40	Poor
41 - 60	Fair
61 - 80	Good
81 - 100	Very good

Application-

Rock Mass Rating RMR has found wide applications in various types of engineeringprojects such as tunnels, slopes, foundations, and mines. It is also adaptable for knowledge-based expert systems. Engineers informally classify rock structure into two general classifications: continuous homogenous isotropic linear elastic (what most geotechnical engineers would like to see) and discontinuous inhomogenous anisotropic non-elastic (what most in-situ rock masses actually are). A rock mass rating system provides a method of incorporating some of the complex mechanics of actual rocks into engineering design.

Moreover, the system was the first to enable estimation of rock mass properties, such as the modulus of deformation, in addition to providing tunnel support guidelines and the stand-up time of underground excavations.

Ally Wells answered 11 months ago

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