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Uncertainties and tunnelling risks

The rockmasses surrounding an underground opening form a complex structure. Interpretations and extrapolations that are necessary to work out the geological setting in an underground excavation from the known conditions at the terrain surface, may introduce considerable uncertainties. 

The site presents methods, descriptions and recommendations to improved collection of geological information for application in rock engineering and design. See 'Field observations'. 

Lots of useful information is given under 'Miscellaneous'.

Rock engineering and classification systems
An important requirement in rock engineering is that the method or tool used adequately covers the behaviour of the ground surrounding the tunnel or cavern. Rockmass classification systems play an important role here. How can such systems be applied correctly?  What are the limitations?

Take a look at topics under 'Classification and design' to learn more about this.

Characterization and the RockMass index (RMi)
Contrary to civil engineering and mining, the quality if the construction materials (rockmasses) in underground excavations cannot be measured by strength tests, but have to be characterized by several geological parameters. As a consequence of this, the RockMass index (RMi) has been developed, with input of the parameters that have the greatest influence on rockmass strength. Being based on strength properties, the RMi values found can be used for various purposes. Take a look at topics under 'Classification and design' to learn more about this.

The RMi system includes more parameter inputs than most of other systems. The structure of RMi is, however, such that RMi can be found also when only a few parameters are found. This is shown in Excel spreadsheets presented in 'Estimation'.

The spreadsheet for documentation of geo-observations with calculations of Q, RMR, and RMi values has been updated. You find it here                                                                 front


The second edition of the Rock Engineering book was published in December 2015. It is a must for those working in geo-planning of under-ground rock constructions, as it presents the use of geolo-gical data from investigations through planning to construc-tion. Proper characterization of rockmass conditions and correct use of rock engineering tools plays an important part in the book. More information can be found in Information

Important quotations are presented below from time to time:

"…..there is still no acceptable substitute for the field mapping and core logging carried out by an experienced engineering geologist."
Evert Hoek, 1986.