Estimations with RMi

On estimation of rockmass properties

The RMi system covers mainly jointed, brittle rockmasses as shown in the file on limitations, which also indicates limitations of RMi rock support estimates.

Jointed rockmasses comprise interlocking, angular pieces (particles or blocks) of hard, brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials. The strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement, which – in turn – depends on the number, orientation, spacing and shear strength of the discontinuities. A complete understanding of this material presents formidable theoretical and experimental problems and hence, simplifying assumptions are required in order to provide a reasonable basis for estimating the behaviour and strength of jointed rock masses for engineering design purposes.

Papers on rockmass estimations 

1. Rockmass uniaxial compressive strength. As shown in PhD. thesis on RMi, the RMi-value expresses approximately the uniaxial compressive strength of a rockmass, see also Papers on RMi.
2. Rockmass deformation modulus, see paper The deformation modulus – comparisons between in situ tests and indirect estimates.
3. Rockmass shear strength parameters, (based on Hoek-Brown shear strength criterion for rockmasses as described in the PhD. thesis on RMi, Chapter 8.1.
4. Rock support in tunnels is described in the paper Recent developments in rock support estimates by the RMi.

Rock support is also described in the Introduction paper to RMi.  The RMi support charts are presented here .

For measurements of jointing features, see the tag ‘Joints and jointing‘ and the paper on seismic velocities.

Estimations using the RMi spreadsheets (Excel)

Excel spreadsheets have earlier been presented for calculations of rockmass qualities and rock support. Further developments of spreadsheets for calculations of RMi as well as the Q and RMR systems have now been worked out. These are presented in the following versions:

1. Version-1: Simple RMi rock support estimate for tunnels. An early launched Simple rock support estimate using the RMi system is shown here.

2. Version-2: RMi rockmass observations, ground quality and shear strength estimate. Here, RMi is applied to estimate the Hoek-Brown shear strength parameters of rockmasses.

Take a look at the Introduction file and the Field observation scheme worked out for Version-3, but also valid for Version-2. 

3. Version-3: Rockmass observations & tunnel support estimate. The RMi-Q-RMR systems are combined; from the same set of input parameters of the rockmass the ground quality and rock support in drill & blast tunnel are calculated i all three systems. Also the rockmass deformation modulus is estimated.
   Help on how to use the spreadsheet is presented here. A Field observation scheme to note down the site mapping results in tunnel or on terrain surface, you find here.

4. Version-4: Rockmass observations & tunnel support estimate. Version-4 is similar to version-3. In addition, it can show the interpretations you make from observed site conditions outside the tunnel to the assumed ground conditions in the tunnel.

Help on how to use this spreadsheet is presented here. You can use the same Field observation scheme as for Version-3.

Graphical methods

The RMi value and rock support can be estimated by use of RMi charts.