On Investigation Methods

Published on February 13 2015

The main aim to perform investigations for a rock excavation is to provide sufficient information and a basis to carry out the planning of and to evaluate the consequences for the rock excavation in question. This means to characterize the ground qualities with respect to the actual construction works and find the distribution of the qualities along the actual excavation. 

There should be good reasons for selecting the type(s), amount and locations of the investigations to be performed, for providing data and relevant, useful information on the ground conditions to be applied in the further evaluations and calculations.

The geological conditions of the sites may vary within wide limits. Each site has its own characteristics, and there are no “standard investigation procedures or methods”, which in all cases will be the only right one. Therefore, the investigations have to be tailored for each site.

Most investigations are performed

  1. during planning (before construction),
  2. during excavation, or
  3. during operation for maintenance purposes

There are numerous methods to perform investigations for an underground excavation project. A list of various types performed in the field and/or in the laboratory is given here 

See also the ISRM suggested methods, which also can be found on the ISRM website http://www.isrm.net/gca/?id=177  

Additional information on collection of geological and rockmass information is presented in 'Geo-observations'.  More can be found in the Rock Engineering book, especially in Chapter 3   from which a couple of tables are presented.

The investigation should be planned in a way that all investigation results can be utilized in the evaluations and assessments made during rock engineering, calculations and design.

 Thus, it is of little use to map the orientation of joints and work out a joint rosette when joint orientation (with regard to the tunnel) is not used in the evaluations/assessments made, such as in the Q system, which has no input parameter on joint orientation.

 The results from different investigation methods can be combined for the derived result to be further used in the rock quality assessments, see the Rock Engineering book where examples are shown on:

  • how core drillings and seismic measurements can be combined
  • core drilling and engineering geological observations can be combined
  • geological setting with information on rock properties

 

Important quotations are presented below from time to time:

"If the art of soil classification is far from satisfactory, the confusion is often made worse in that users are unaware of its limitations and apply it for purposes other than that originally intended".

Arthur M. Casagrande (1948)