‘tools’ in the rock engineer’s
toolbox are a combination of methods to predict
the outcome of a certain set of circumstances
and procedures to follow in order to mitigate
unfavourable conditions. Commonly, the procedures
involve reinforcing the rock mass and providing
support to an area of exposed rock mass. Area
support usually comprises shotcrete, mesh and
newer surface membranes. Shotcrete is both a product
and a process. As a product it is a fine aggregate
concrete mix with or without additives and admixtures.
The aggregate is usually smaller than 10 mm in
The placement of the material is the shotcrete
process. This can range from dry-mix where materials
remain in the dry state as they are conveyed to
the placing nozzle where water and accelerator
are added immediately prior to being shot onto
the receiving surface. Wet-mix placement uses
equipment similar to that used for concrete pumping.
The plastic mix is conveyed to the delivery nozzle
where air is added to accelerate the materials
for compaction on the receiving surface.
Engineering design of shotcrete is commonly carried
out using empirical methods, backed up by numerical
models, if required. Shotcrete application suitability,
mix design, placement specifications, pre-construction
testing requirements, acceptance criteria are
part of the range of services offered.