BLAST DAMAGE ASSESSMENT IN AN UNDERGROUND QUARRY PROJECT - A CASE STUDY

Blasting is still the most cost effective methodology to break rock for mining; however, this can lead to damage to the host rock mass. Damage control is crucial; it allows to minimise failures, overbreak, and unstable ground. Therefore, knowing the extent of the fractures generated by a blast is important for designers to correctly plan the underground space; in fact, generally, pillars are left in place to ensure stability. Their dimensions are designed in order to have a sufficiently high bearing capacity based on the in-situ conditions; however, these conditions can worsen with blasting, reducing their bearing capacity and putting at risk the stability of the underground environment. The main objective of this thesis is to evaluate the exact damage extent. The efficiency of an already available method in literature is checked. This method is relatively easy to use, and can provide different levels of damage extent; however, it is still not entirely clear at which predicted level the actual damage extent can be identified. Geophysical tests are used to compare the damage calculated and the actual damage in the rock mass: the highly fractured zones are identified where the rock mass properties are reduced, namely the compressional wave velocity. This method depends not only on certain rock mass properties, but also on the Peak Particle Velocity. Therefore, a sensitivity analysis using different site laws will also be performed, considering two different equation structures, two different interpolation methods, and five different sets of data; totaling 20 site laws.