| The traditional blind shaft excavation at the Datun Tin Mine relies on the use of ordinary air-legged rock drills to cut and blast the rock in sections from the bottom up,with an average single cycle feed of only around 1.4 m.There are disadvantages such as high production costs,poor working conditions,low construction efficiency,high dust concentration,high labour intensity and poor safety.The use of blind shaft blasting technology greatly reduces mine production costs,improves the working environment for workers,increases construction efficiency,and eliminates the huge safety hazards associated with shaft boring and blasting operations.The thesis is based on the National Natural Science Foundation of China’s "Research on the Blasting Mechanism of Deep Hole Blasting in Blind Sky Wells" and the University’s "Research on the Technology of Forming Wells in One Session by Deep Hole Blasting".With reference to a large number of domestic and international papers on blasting in one pull,the blasting theory,numerical simulation and field tests were combined to study the design of blasting solutions for one pull blasting in blind sky shafts.(1)Based on the existing theory of rock fragmentation by explosive stress waves,this paper analyzes the shortcomings of the existing calculation models for the crushing and fracture zones of rock mass caused by explosive gas,The shortcomings are lack of the consideration of the comprehensive effect of explosive gas on the blasting mud,rock mass crushing and fracture zones and violate actual laws of explosive gas body action.Therefore,through theoretical analysis,this article analyzes the comprehensive effect of explosive gas on the rock mass crushing zone,fracture zone,and blasting mud,and establishes a calculation model for the rock mass crushing zone and fracture zone under the action of explosive gas.Furthermore,a model for the damage range of rock mass under blasting loads is established.In order to verify the accuracy of the newly constructed rock mass damage model,four different pore size rock mass crushing zones and crack zones were calculated under the same working conditions,and they are verified through numerical simulation and empirical formulas.The results indicate that the calculation results not only conform to the range of traditional blasting theory empirical formulas,but also have an error of less than 10% compared to the numerical simulation results,verifying the credibility of the rock damage range model.(2)The distance L between the cut charging hole and the empty hole is an important factor affecting the effectiveness of cut blasting.A reasonable distance between the holes is conducive to the full utilization of explosive energy,the fragmentation and throwing of rocks.Therefore,in order to obtain the distance L between the charging hole and the empty hole,a newly constructed rock mass damage model is used to substitute the physical and mechanical parameters,explosive parameters,charging hole diameter,empty hole diameter,and other data of the mining rock into the model for calculation.The radius of the crushing zone of the rock mass was determined to be0.09 m,and the radius of the fracture zone of the rock mass was determined to be 1.186 m.As the empty hole needs to be located within the range of rock mass fracture zone,it is known that the distance L between the charging hole and the empty hole should be greater than the radius of the rock mass crushing zone and less than the radius of the rock mass fracture zone.Besides,L should also be within the compensation space of the rock mass.Therefore,it is concluded that L should be 0.09 m<L<0.258 m.When it is combined with on-site practice,L can be equal to 0.2m.(3)Based on the distance L=0.2 m between the charging hole and the empty hole in the cutting groove,four different cutting schemes were designed: six hole barrel shaped cutting,seven hole barrel shaped cutting,nine hole barrel shaped cutting,and spiral cutting.Numerical simulation analysis was conducted on these four different cutting schemes,and the analysis results showed that the spiral cutting had the largest damage area,followed by the nine hole barrel cutting.The damage areas of the six hole barrel cutting and the seven hole barrel cutting were not significantly different.Therefore,the nine hole barrel cutting and the six hole barrel cutting were selected for on-site experimental research.The experimental research results indicate that the clamping effect of rocks is crucial for the blasting effect.Therefore,in order to reduce the impact of rock clamping on the blasting effect,the charging structure adopts layered and segmented charging.Divide the depth of the 8 m borehole into two layers: the first layer is filled with 0.3 m and the charge is 3.7 m,and the second layer is filled with 0.8 m and the charge is 3.2 m.For the blast hole with normal initiation and avalanche,the slot depth measured by the laser rangefinder reached 7.8 m,and some even reached 8 m,which fully met the expected target of the test. |
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