RMR value
The RMR value or RMR index (Rock Mass Rating) is a classification system for rock. It was developed by ZT Bieniawski in 1972/1973 . The system is used in geotechnical engineering when building tunnels, caverns , mines , embankments , foundations , etc. in order to evaluate the quality of the rock with regard to its stability. However, the RMR value cannot answer all questions; it is only an estimate and an approximation.
definition
The following six parameters are required to classify a mountain range using the RMR method:
- Rock strength given by uniaxial compressive strength (UCS - Uniaxial Compressive Strength) or as a point load index (Point Load Strength Index)
- RQD value (Rock quality designation)
- Distance between the gaps
- Condition of the clefts
- Mountain water conditions
- Orientation of the clefts
Each of the six parameters is assigned a value that corresponds to the rock characteristics. The rock properties are assessed with field measurements using forms. The six parameters are then added up to a sum; the sum is the RMR value, which is between 0 and 100.
Classification table
The mountain quality is divided into one of five levels (very good to very bad) according to the RMR value.
RMR | Mountain quality |
---|---|
<20 | very bad |
21-40 | bad |
41-60 | moderate |
61-80 | Well |
81-100 | very good |
The RMR value always applies to a mountain area with more or less uniform properties. Therefore the mountains have to be divided into such areas. The limits of such areas can be e.g. B. be disturbances.
application
The RMR value can be used, for example, to determine the necessary dimensions, construction methods or driving methods for tunnels . It is also suitable as an input variable for expert systems or when using fuzzy methods.
Other classification systems besides the RMR value are:
- Barton Q value
- MRMR value according to Laubscher
- Deere RQD
- RSR according to Wickham
literature
- Bieniawski, ZT: Engineering Rock Mass Classifications. John Wiley and Sons, New York 1989.
- Bieniawski, ZT: The Rock Mass Rating (RMR) System (Geomechanics Classification) in Engineering Practices. In: Rock Classification Systems for Engineering Purposes. 17-34. Philadelphia, Pennsylvania: American Society for Testing and Materials, 1988.
Web links
- [Matteo Berti]: On-line classification of rock masses: background and basic reference. University of Bologna ( Memento from November 6, 2002 in the Internet Archive )
- Evert Hoek : Practical Rock Engineering. Chapter: Rock Mass Classification. Edition 2007 (PDF, 1.2 MB)