RMR value

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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:

  1. Rock strength given by uniaxial compressive strength (UCS - Uniaxial Compressive Strength) or as a point load index (Point Load Strength Index)
  2. RQD value (Rock quality designation)
  3. Distance between the gaps
  4. Condition of the clefts
  5. Mountain water conditions
  6. 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:

  1. Barton Q value
  2. MRMR value according to Laubscher
  3. Deere RQD
  4. 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.

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