Drilling and blasting is common economical technique for excavating of tunnels in hard rock masses where the Uniaxial Compressive Strength (UCS) of intact rock is relatively high. Most important issue in this method is the undesirable induced damage by blasting around the excavation. Using contour blasting methods such as smooth blasting are the way to avoid a thick damaged zone. Since the damaged zone consists of a large number of micro/macro fractures which have a great influence on support system, advance rate, water inflow into tunnel and in general tunnel life time; predicting the thickness of this part is very important. The object of this research work is to study the effect of blasting parameters on Blast Induced Damage (BID) zone around the tunnel. In this case two different blasting patterns (eg. conventional and contour blasting) were designed and the induced fractures due to these two patterns were investigated. The Universal Distinct Element Code (UDEC) was used as a numerical dynamic modeling tool. The numerical results show that using strong explosives with a high density and velocity of detonation in blastholes cause an intense damaged zone around the tunnel. In short time, the induced stress contours around the tunnels violate more when an ordinary blasting pattern is used compared with the contour blasting pattern.
