Numerical analysis in rock engineering : response of rock mass under dynamic loading condition

Abstract

Rock tunneling deals with material that is two or three times stronger, or more, than the normal concrete which makes it more challenging to cut through. Tunnel boring machine (TBM) can be used for soft rock, in the event of hard rock drill and blast method might be a better choice. Drill and blast method destructive ability often cause overbreak frequently, which result in extra cost of excavating. This paper presents a way of reducing overbreak and misfire while having the most necessary damage. Methods for evaluating damages, controls and coupling of explosive, rigorous procedure and field monitoring with trained operators have been done to minimize the unnecessary damages but misfire still occurs. In order to develop a new approach on dealing with blasting technique, this report provides the use of DDA program of blast-induced fracture in rock to evaluate the crack extent if it propagated adequately such as to remove the fragments without causing a need of another fire. A 2m by 2m model of rock block was used with three cases of different way of detonating explosives. In the first study, all the explosives were blast simultaneously. For the second and third cases, the blasts were sequenced with 2ms delay. From the analysis, it was deduced that simultaneous blast were not as effective as the delayed one in the case of free boundary since it didn’t create the needed fracture so as the cracks can be linkage together. Better results were performed by sequenced blast with an alternate blast might be the best form desired by the contractor.