Defining the Rock Mass

As the structure of the rock can have such a significant effect on the success of a blasting program, care should be taken to fully define the structural characteristics of the rock. This will usually involve drilling, mapping, laboratory testing, and exploration while a project is in the design phase and before plans and specifications are completed. Rock structure exists in three dimensions and any exploratory program should keep that well in mind.

Design checks will need to be made for final wall stability and to assess the potential to undermine any surrounding structures by daylighting a structural feature that could cause a rock failure mode. Kinematic analysis and rock stability analysis should always be performed if critical structures are to be located near or beside a rock excavation, even where blasting is not used.

All rock types, stratification, voids, and water conditions should be assessed for the project and information provided to the contractor and to the blaster to allow for good blast design. Many of these features can have detrimental effects on blasting that cannot be mitigated in design if they are unexpected.

There will be a need for laboratory testing of samples. Intact rock samples should be tested in the laboratory to provide information for the blaster. ASTM laboratory testing methods listed should be used to provide the data. Published tables give a good place to begin a design, but intact rock values can be highly variable, even across a site. A published table is not adequate for final blast design.