Technology And Mechanism Of Deep Hole Multilayer Efficient Cut Blasting In Vertical Shaft

The shaft is the "throat" channel of mine construction and mining.In recent years,the long construction period and poor working environment of the shaft in deep resource development have restricted the rapid operation of the mine.The research means of similarity model test,theoretical calculation,numerical simulation,and field test were adopted comprehensively in the current paper to reveal the radial blasting energy enhancement effect of annular holes single charge layer.The double layers axial combined circular truncated cones cutting blasting model without clamp was constructed.Hence,the high-efficiency cutting method of blasting energy persistence and large-scale post-explosion space in radial and axial directions was finally formed.The main research results of our work are as follows:(1)Blasting energy enhancement effect in the radial direction of annular holes single charge layer was revealed.A super dynamic strain testing system was adopted to test explosion stress waves of single charge layer blasting crater tests in concrete similarity models.The analysis validated that compared with an equivalent single hole,the media in the middle and far area is loaded by higher stress,stronger energy,and a longer duration of annular holes blasting.Moreover,unlike the traditional conical blasting funnel formed by equivalent single hole blasting,it can be observed that the space after blasting of annular holes is a circular truncated cone.It is also noteworthy that circular truncated cones’ upper and lower surface sizes have increased,and the volume has multiplied at the same charge and burial depth.Like the concrete test model,the calculation formulas for the charge and shape parameters of the maximum volume circular truncated cone after the explosion of annular holes single charge layer in different blasting medium conditions were deduced based on the test data of the annular holes similarity model and blasting similarity law.(2)No clamp cut blasting model was constructed with circular truncated cones combination in the axial direction of annular holes double layers charge.The cut holes consisted of first-order cut and second-order expansion annular holes.Double layers charges were loaded along the axial direction of both annular holes.The upper charge layer was further cut and expanded to provide a free surface of unclamping blasting for the lower charge layer.After the upper-and lower-layers charge blasting,axial combined double layers of circular truncated cones and cylinders were formed.Furthermore,we observed that each charge layer of the firstorder cut annular holes was continuous charging.The explosive charge and buried depth have been optimized according to the maximum volume circular truncated cone of annular holes single charge layer after blasting.Each charge layer of the second-order expansion annular holes was a gradient charging structure,which was optimized to match the variable resistance line on the side of the circular truncated cone.In other words,each charge layer was further subdivided into two or three continuous cartridges separated by air,and the length of the cartridge decreased proportionally from hole top to bottom.Lastly,the formulas for calculating the drilling,charging and blasting parameters of the first-order cut and second-order expanding annular holes were derived.(3)The technical parameters and schemes of annular holes multilayer efficient cut blasting were determined.Using the charging and blasting parameter formula of annular holes mentioned above,the technical parameters and three technical schemes of annular holes cut blasting were calculated and determined based on the air intake shaft project at Shaling gold mine.(4)The characteristics and laws of annular holes multilayer efficient cut blasting were technically simulated.We used the CDEM software to perform numerical simulations for the three cutting technical schemes above.The results demonstrated that the radial stress distribution gradually attenuated with the increase of the distance from the blasting center.The increase of the top displacement was mainly caused by the initiation of the upper charge layer and decreased nonlinearly with the increase of the distance from the blasting center.Four initiation times gradually formed the fracture space of the axial double-layered composite circular truncated cones and composite cylinders,the fracture degree showing a stepwise growth with time.The fracture size of the block was mainly small and medium while its kinetic energy surged and slumped four times,and the fracture energy increased in a stepwise manner with time.The second scheme showed the best cut blasting effect.We noticed that the different initiation intervals and high-stress loading conditions had a minor effect on block displacement,fracture characteristics and fractured block size.However,adding one layer of charge would significantly raise the overall fracture degree of the model,and the fracture energy increment value of each layer’s blasting decreased with the increase of distance from the top initial free surface.(5)The multilayer efficient cut blasting field tests of circular holes were performed.Field industrial tests of the above-mentioned three cutting technical schemes were carried out in the air intake shaft at Shaling gold mine,and threedimensional scanning of the post-explosion space and evaluation of blasting effect were conducted.The results demonstrated that the blasting cycle footages of the three schemes were all longer than 5 m,and the utilization rate of holes was more than 98%,among which scheme two had the best effect.The field test results were consistent with the theoretical calculation and numerical simulation results.