Research On Smooth Blasting Cracking Mechanism And Parameters Optimization Of Fractured Rock

With the rapid development of China's economic constructions,infrastructure constructions are in full swing throughout the country.In underground space excavation process such as tunnel?hydropower and mining,smooth blasting,as an effective means of excavation,has been proved that it can effectively overcome the disadvantages caused by the ordinary blasting.But its theoretical research is not enough,especially when smooth blasting technology is used in the cracked rock mass,less consideration in the initial fracture of fractured rock influences on smooth blasting holes,so smooth blasting parameters sometimes are not reasonable.Therefore,this paper will combine experimental and numerical simulation to explore the fracture mechanism and parameters optimization of applying smooth blasting to fractured rock mass.Based on the rock blasting mechanism,the stress wave's propagation characteristics when passing the crack surface and the cracking mechanism of smooth blasting,in this paper we design multiple sets of concrete slabs with cracks for smooth blasting experiments.In these experiments,the strain and acceleration of the specific point on the model were collected by using the dynamic strain gauge.The fissures' expansion of different groups under different blast hole spacing,different uncoupled coefficients and different fractures were analyzed,and smooth blasting parameters under different crack occurrence have been adjusted to optimize.Finally,the ABAQUS / Explicit modules were used to simulate the experiment process,also supplement and verify the results of the experiment.It is found that the stress wave is consumed by the relative sliding between the fissure surfaces after passing the fracture.The measured strain value and acceleration value decrease with the increase of the blast hole spacing,with reduce of the uncoupling coefficient,and the strain and acceleration values ??are more sensitive to the uncoupled coefficient.Through the strain and acceleration time-history curve,we can find that in the actual engineering,it is difficult to simultaneously ignite between blasting holes,and the superpositionbetween the stress waves is not obvious.It indirectly illustrates limitations of stress wave superposition theory in practical engineering.In the premise of ensuring the same amount of drugs,we found that the distance between the smooth blasting holes should not be too large,otherwise the gap between adjacent holes will deviate,which dose bad to the formation of smooth.The effect of fissure occurrence on the smooth blasting is very serious.When the original fissure passes through the two blasting holes,the burst fissure preferentially extends to the vertical fissure plane.When the original fissure is parallel to the blasting line,if the vertical distance is less than or equal to half of the holes' distance,secondary cracks will yield between the hole and fissure surface,which affects the formation of smooth effect,also reduces the stability of the surrounding rock.