Study On Damage Scope Of Rock Mass Under Blasting Action In An Open Pit Copper Mine

At present,there are many theoretical studies on impact load-induced damage of a single piece of rock but few are the studies on rock mass cumulative damage under the action of multiple blasting.The rock mass blasting damage brings about destruction and hidden trouble to production and construction and raises production costs so solving the blasting cumulative damage is always the research focus in the blasting field both at home and abroad.This paper makes the following efforts on the basis of previous studies.(1)Fifty-four times of vibration measurements have been made on the platform which is two meters under the ground and statistics on blasting vibration in the three measured points have been chosen eight times each at random and analyzed.The conclusions drawn from that are:(1)The blasting vibration velocity changes like this: when there are any rock mass damage,then generally,the blasting vibration velocity will be higher with the increasing of blasting times but basically,it shows no evident regularity when there is no rock mass damage.The velocity changes on each direction and the sensitivity of blasting are also different.(2)The main vibration frequency changes like this: whether the rock mass has any damage or cumulative damage shows no obvious relation to the change of main vibration frequency.The vertical vibration frequency maintains basically twenty to forty Hz and its tangential velocity and radial velocity show random changes.The resonance phenomenon between tangential frequency and radial frequency at moderate or far distance and buildings and structures or roadways is particularly needed in blasting.(3)Blast vibration signals on the site have been analyzed based on HHT and the changing rules between energy and frequency have been therefore drawn.Most of the frequency centers on zero to twenty Hz and this frequency is close to the natural frequency of underground engineering so attention should be paid to the harm brought about by the resonance phenomenon.Meanwhile,the changing rules of time-varying instantaneous energy have also been obtained and it is found that the energy mainly focuses on zero point four to zero point five second.The effect of millisecond blasting is not obvious.Therefore,millisecond delay interval needs to be shortened and the effect of vibration reduction needs to be optimized.(2)Conclusion can be drawn from rock mass elastic modulus variation which represents rock mass damage:(1)The depth has a great influence on blasting damage.When the depth remains in a fixed value,there exists a positive correlation between the rock mass damage degree and blasting times.But once the depth changes,the rock mass damage degree decreases as the depth gets larger.As the blasting times increases,the rock mass damages of different depths all show the increasing of cumulative damages.When the depth remains the same,the damage amount varies in different direction in one single blasting.The rock mass cumulative damages differ a lot under multiple blasting,which indicates that rock mass has the anisotropic characteristic.(2)Under multiple blasting,it is a little difficult to describe the relation between rock mass damage and depth so the average value of rock mass damage under multiple blasting has been adopted and analyzed and the depth and average value of blasting damage have been fitted,which can be concluded that there is a good non-linear relation between the rock mass damage degree and depth.Accordingly,the relation between rock mass cumulative damage and depth can be drawn.(3)Based on LS-DYNA numerical simulation,the rock mass damage range under the action of blasting has been explored and the relation between the damage within two holes and distance of two holes has been obtained,from which the relation between the percentage of damage within two holes and distance of two holes has been acquired.