Explosion Energy Release And Transmission Mechanism In Rock Blasting

Rock blasting excavation is not only a critical link of hydropower engineering,railway construction,municipal engineering and other infrastructure construction,but also the most important means of mineral resources exploitation.Drilling and blasting is the most widely used and cost-effective method of rock fragmentation.In the new period,higher requirements on engineering blasting are put forward.The effective use of explosion energy and reasonable control of blasting hazard are inevitable requirements in response to the energy-saving and environment-friendly society and sustainable development.Therefore,investigating the mechanism of explosion energy release and transmission in rock blasting will be great help to a better understanding of fragmentation mechanism and distribution of consumed explosive energy.Furthermore,it also finds its engineering applications in optimizing design of rock mass blasting excavation,controlling engineering disasters and improving the utilization rate of blasting energy.This dissertation focuses on the mechanism of explosion energy release and transmission in rock blasting and a series of related studies are conducted with methods of theoretical analysis,numerical simulations and field experiments.The main research content and results are as follows:An improved non-ideal detonation model was performed by adopting the Murnahan equations of state(EoS)for the unreacted explosive,Jones-Wilkins-Lee(JWL)EoS for its reaction products,and the three-term ignition and growth reaction rate model for the chemical reaction rate for the conversion of unreacted explosive to reaction products.And the improved non-ideal detonation model was verified by the detonation simulation of explosive under different charge diameters and confinement conditions.Furthermore,based on the non-ideal detonation model,the explosive-rock interactions under different coupling mediums and different charge structures were studied as well as the influence factors on explosion energy release characteristics.According to the mechanism of quasi-static rock blasting fragmentation,a modified model was presented to calculate the size of crushed zone around a blasthole in drill-and-blast,with the hoop compressive stress and cavity expansion effect taken into account.The material in the crushed zone is assumed to be granular medium without cohesion,but with internal friction.Based on those assumptions above,the improved model in this paper can better reflect the actual destruction of rocks around blasthole.On this basis,the formula,considering the effect of cavity expansion,for crushing zone radius of drilling blasting is deduced.Compared with other models,this model is in better agreement with the existing experimental data.Finally,the effect of rock properties,the characteristics of the explosives,the charge structure and in-situ stress on the size of crushed zone were investigated and suggestions are made on how to decrease the size of crushed zones.Based on the theory of rock impact dynamics and explosion mechanics,the energy transfer equation between explosives and rocks is deduced considering the yield strength of rock near the borehole.The optimization method of explosive selection and charge structure based on explosive impedance and energy comprehensive matching control is proposed in this dissertation.The results indicates that,the explosive-rock energy transfer efficiency is related to the rock elastic wave impedance,but as well as the incident wave intensity,rock strength and rock plastic wave impedance.The acoustic impedance of explosives does not have to be equal to or close to that of the rocks.The rock-explosive match relationship should vary with the rock type and blasting control objectives.To improve the energy utilization and fragmentation effect on rock blasting,the explosion energy transmission under side initiation and its effect on rock fragmentation were studied by theoretical analysis,which reveal the significant differences in the partition of shock and gas energy between two initiation methods.In addition,field blasting tests and numerical simulations were conducted to investigate the fragment sizes distribution and blasting vibration of two initiation methods.The results show that the energy release rate of explosives under continuous side-initiation with detonating cord is obviously lower than that of end initiation,with more energy released in the sparse wave after the detonation shock front.Compared with end initiation,shock energy can be converted to gas energy,which results in a reduction in shock energy and an increase in gas energy.The results of this study demonstrate that the partition of shock and gas energy for rock fragmentation can be adjusted by changing the initiation methods to improve the energy utilization in rock fragmentation.It is unwise to use side initiation in the blasting of hard and compact rocks because it will reduce the proportion of shock energy.The energy aggregation effect of in-hole wave collision created by simultaneous initiation is analyzed theoretically.Combined with the dynamic damage model,the damage zone of different types under double-point imultaneous initiation and traditional initiation methods are analyzed.And the position of the initiation points in the double-point imultaneous initiation is further optimized from the point of energy utilization.By changing the detonation wave waveform with the in-hole wave collision,the peak stress and the blasting shock impulse can be significantly increased locally,which can improve the fragmentation degree of the local rock.A quantitative assessment of the effect of free surface number and blast-generated free surfaces on blasting seismic energy transfer and conversion was carried out through experimental and numerical studies.Blasting vibration from the first and followed delays in the same row in bench blasting with millisecond-delays was compared and analyzed in two field experiments.A coupled numerical approach with smooth particle hydrodynamics(SPH)and dynamic finite-element methods(DFEM)was also conducted to simulate the fragmentation process and the blasting vibration.The results show that with the increasing number of free surfaces,the peak particle velocity decreases nonlinearly,and if the blasting geometry parameters and charge weight are the same in each blast delay in the same row,the explosive detonated in those followed delays will always produce 14%-22%lower vibration compared to the first delay.The study indicated that the effect of the blast-created free face should be considered in the blasting design.The charge weight of the first delay in every row should be reduced by certain percentage if the same peak particle velocities are expected from followed delays in the same row.