Research On Optimization Of Pre-splitting Blasting Hole Network Parameters In Open-pit Mines And Their Influence On Steep Slope Stabilit

In the pre-splitting blasting operation of open-pit mines,unreasonable hole network parameters will lead to unsatisfactory blasting effect,waste of explosives,and even delay the production progress of mines;in addition,the use of blasting technology for a long time and high frequency is easy to cause negative phenomena such as slope instability,which in turn threatens the personal and property safety of mine workers.In this paper,the steep slope of an open-pit mine in Inner Mongolia is taken as the engineering background.The response characteristics of rock mass under different hole network parameters and the stability of slope under blasting load are studied by means of field investigation,mechanical test,numerical simulation,field test and mathematical method.The optimization formula of hole diameter-hole spacing is put forward.The prediction formula of blasting vibration velocity and its application range are clarified.The dynamic response law of slope under blasting load is revealed.The change of slope safety factor and the sensitivity of each factor under multiple blasting loads are explored.The following research results are obtained:（1）The basic mechanical parameters of rock are obtained by rock mechanics experiments.The multi-dimensional analysis of rock specimens under single air pressure and different air pressure cyclic impact is carried out by using Hopkinson pressure bar experimental system and SEM scanning electron microscope system.The mechanical properties,failure process and failure degree of rock specimens under different impact conditions are obtained.In the micro dimension,the deformation failure mode and fracture morphology of the specimen are mainly step-like,fracture,dislocation,plastic deformation,block shedding,impact crater and pressure melting.（2）A slope model with a hole diameter of 90 mm～130 mm and a hole spacing of 7～12 times the hole diameter was established.Combined with LS-DYNA and Matlab software,the stress wave propagation,stress change and damage evolution characteristics after initiation were analyzed.The 90 mm～130 mm hole diameter（non-clogging part）is 7～9 times,7～9 times,7～10 times,7～11 times,and 7～11 times the hole spacing.The blasting effect is better,and the cracks between the two blast holes are interconnected;under the condition of 90 mm and 130 mm aperture,the cracks between the two boreholes are almost connected at the same time,and the time required for the cracks between the two boreholes in the other working conditions is inversely proportional to the aperture size.The effective tensile stress data are post-processed to obtain the optimization formula y=1.12+0.076 x.（3）Based on the proposed optimization formula,the applicability of the formula is verified by field tests.The pre-splitting blasting results show that the pre-splitting blasting effect is better,the half-hole rate is above 89%on average,and there is no over-excavation or under-excavation.According to the optimization formula,the blasting parameters are designed for multiple blasting operations,and multiple blasting vibration monitoring points are set up.The blasting vibration velocity prediction formula is obtained by combining the collected monitoring data with the Sadaovsk formula.Based on the vibration frequency,the maximum vibration velocity that the slope can withstand is determined.Combined with the relevant calculation formula,the maximum charge of pre-splitting blasting is 758 kg.（4）Based on the geological conditions and blasting parameters of the blasting area,the stability of the steep slope under single and multiple blasting loads was studied by using the finite element numerical software FLAC 3D.According to the numerical simulation results and related theories,it can be seen that under the condition of single blasting,the overall trend of stress increases gradually from top to bottom in the horizontal direction,and the stress concentration is easy to form at the foot of the slope.In the vertical direction,the displacement near the blasthole is the largest.With the propagation of the explosion stress wave,the phenomenon of rock settlement appears near the 1380 m step of the slope,but the overall displacement is small.After multiple blasting,the overall displacement of the slope has a cumulative phenomenon.The horizontal stress gradually increases with the increase of the number of blasting times.The vertical stress changes in a state of oscillation.The peak velocity has a more obvious correlation with the blasting impact.The acceleration is still not 0 for a period of time after the end of the blasting,indicating that it takes a long time for the energy to completely dissipate.（5）Combined with FLAC 3D software simulation,the safety factor of slope under multiple blasting is analyzed.It can be seen that the safety factor of slope will be reduced by 2.69%～13.94%by each blasting vibration until the end of blasting test.The safety factor of the slope decreased by 34.56%.According to the theory of blasting engineering and the grey correlation degree method,the sensitivity of each factor is:single charge（X₅）>total explosive（X₆）>hole spacing（X₃）>blasting distance（X₂）>blasting vibration time（X₄）>hole number（X₁）.