To optimize the length-diameter ratio of the impact test specimen under three-dimensional static combination conditions,five mixed granite specimens with different length-diameter ratios(diameter 50 mm,length 30 mm,40 mm,50 mm,60 mm and 70 mm,respectively) under constant axial compression(4 MPa) and confining pressure(4 MPa) were test by a modified split Hopkinson pressure bar(SHPB).The influence of aspect ratio on stress equilibrium time and peak strength was analyzed from the aspects of stress equilibrium state,the relative value of the stress difference,and the dynamic stress characteristics.At the same time,a secant modulus is introduced to better illustrate the plastic deformation of the specimen under combined loading.The results indicate that the stress balance of the specimen changes in real-time during the test process,and it is in relative balanced in the period from the starting point of stress quasi-elasticity increase to the peak point of stress.The equilibrium time varies with the aspect ratio,and the equilibrium duration is 1.0>0.6>0.8>1.2>1.4.With the increase in the length-diameter ratio,the number of stress wave reflection required by the relative value of stress difference between the two ends of the specimen satisfying the uniform state increases,and the peak strength fluctuates.The secant modulus of the peak point increases gradually,and an obvious step occurswhen the length-diameter ratio increases from 1.2 to 1.4.It can be seen that the best length-diameter ratio of SHPB test specimens under the condition of low level(≤10 MPa) constant axial compression and confining pressure combined with static load is 1.0.The impact test results are different from those without combined static load servo.It can provide a reference for the optimization of length-diameter ratio of other rock species under similar conditions.

In practical engineering,rock tensile failures usually occur under impact loads,which is obviously different from its mechanical properties under static loads.Therefore,it is necessary to study the dynamic tensile properties of rock.First,to study the dynamic tensile strength,failure modes and stress waves under high strain rates,the Brazilian disk experiments of granite were performed under different impact velocities by using SHPB system.Meanwhile,LS-DYNA software was used to simulate the dynamic splitting test based on the HJC model,and the results were compared with the laboratory test results at similar impact velocities,which verified the applicability of the HJC model to the dynamic splitting test.The results show that with the increase of impact velocities,the dynamic tensile strength of granite increases gradually and is approximately linearly related to strain rates,and the failure cracks change from I type to Y type.The amplitude of the waveforms increases with the growth of the strain rates,among which the incoming and reflected waveforms tend to be rectangular gradually,and the transmitted waveforms change from "W" type to "V" type.The waveforms and amplitude of numerical simulation are similar to the test results.At lower and higher impact velocities,the difference of dynamic tensile strength is less than 10%,indicating that the HJC model is more suitable for the simulation of the dynamic splitting tensile test of granite in this case.The results can provide a reference for model selections in future finite element analysis of dynamic tensile tests.

In order to study the influence of weak interlayer parallel to the blast hole on rock blasting crack propagation,blasting simulation experiments was carried out by pouring cement mortar test blocks with 40 cm×40 cm×36 cm in length,width and height and different weak interlayers(soil and stone,soil,water) into steel mold.Six radial strain bricks with a depth of 10 cm were symmetrically embedded along the vertical direction of the weak interlayer and 8 cm,12 cm and 18 cm away from the blast hole in the pouring process of the test block,which were used to monitor the internal strain changes in the blasting process of the test blocks by using ultrahigh dynamic strainometer; At the same time,the blasting crack propagation process of the test blocks was observed by high speed camera.The crack propagation results and strain differences between the two sides of the same test block(the weak interlayer side and the intact side) and the weak interlayer side between different test blocks were compared and analyzed.The results show that:In the same test block,the blast hole crack growth rate near the weak interlayer side is faster than the complete side.Between different test blocks,as the strength of the weak interlayer decreases,the crack propagation speed of the blast hole near the side of the weak interlayer is faster,and the crack propagation is more adequate.The weak interlayer has the effect of preventing crack propagation,and the lower the strength of the weak interlayer is,the more obvious the crack arrest effect becomes.Wing cracks are generated at both ends of the weak interlayer,and the lower the strength of the weak interlayer,the faster the propagation speed of the wing cracks.The peak strain value of each measuring point of the test block is between 0.0178~0.0640,and the corresponding peak stress is 49.9~179.2 MPa.As the distance increases,the attenuation speed of the stress wave in a certain range shows a large to small,and then small to large trend.The lower the strength of the weak interlayer is,the faster the explosive stress wave attenuates.

The interface between the inclusion and the medium is not always perfect.That is,the displacement and stress are not continuous and equal on the boundary.The dynamic response of an incident P wave at an imperfect interface is different from the that of a perfect interface.A spring model is introduced as the imperfect interface model to calculate the dynamic response of the inclusion with an imperfect interface under the plane P wave incident.This interface model is assumed to be an elastic adhesive layer with an infinitesimal thickness and no inertia.Moreover,the wave function expansion method is used to calculate the dynamic stress concentration factor around the imperfect interface under the plane P wave incident and analyze the influence of spring stiffness,an important parameter of spring model,on the dynamic stress concentration factor.The results show that the spring stiffness has an obvious effect on the dynamic response with a low wave number,and this effect will gradually weaken with the increase of the wave number.At the same time,the resonance scattering phenomenon can be observed at a high wave number.The Ricker wavelet,a common seismic wavelet,is used as the transient disturbance waveform.Based on the steady-state results,the transient responses under different values of spring stiffness are obtained by Fourier transform.The distribution of the transient DSCF is similar to that under the steady-state conditions,but the amplitude has increased.In addition,the dominant frequency of the Ricker wavelet is negatively correlated with the transient DSCF.

At present,the analytical solutions of tunnel dynamic response under blasting disturbance are mostly steadystate.However,the actual blasting disturbance propagates in engineering construction are in the form of transient wave,and most of the tunnels are lined Meanwhile,the study of transient solution mainly concentrates on unlined tunnel,but most tunnels have lining in practical engineering.Therefore,taking the deep buried circular lined tunnel as the research object,the analytical solution of tunnel transient dynamic response under plane blasting P-wave disturbance is studied by combining wave function expansion method with trapezoidal quadrature.In addition,by analyzing the wave field in the lining and surrounding rock when plane P-wave incident and considering the boundary conditions of interaction between the lining and surrounding rock,the relevant parameters of steady-state response are determined.Furthermore,on the basis of the steady-state solution,a transient analytical solution of the dynamic response of a deep buried circular liner tunnel under plane blast P-wave perturbation is obtained by applying the trapezoidal quadrature method.The dynamic response of the dynamic stress concentration coefficient,radial and circumferential vibration velocity in the tunnel liner and surrounding rock contact surface and tunnel are then analyzed.The results show that:the theoretical solution in this paper are consistent with those obtained by FLAC and CASRock simulations,which verifies the feasibility and correctness of proposed method.Besides,the tensile stress concentration occurs in both sides of the tunnel during the dynamic disturbance,and the compressive stress concentration mainly occurs on the top and bottom slabs.The radial velocity vibration at both sides of the tunnel is significantly larger than that on the tunnel top,and the circumferential velocity vibration increases first and then decreases to zero with the addition and removal of the blast load.In a word,the analytical results can provide a theoretical basis for the support of deep-buried tunnels.

To treat the tendency term and high-frequency noise of blast vibration signals,a signal processing method based on the CEEMDAN decomposition and the wavelet threshold has been introduced.First of all,a group of IMF components is obtained through CEEMDAN decomposition of radial blast vibration signals,and then FFT transformation is carried out for each component.The trend component is screened out and removed by spectral analysis.Meanwhile,noise-containing IMF components and pure IMF components are distinguished by cross-correlation function analysis of the remaining IMF components,which is further checked by autocorrelation function.Then,the IMF components containing noise are filtered by wavelet threshold.Finally,the IMF components and the pure IMF components after the wavelet threshold filtering are reconstructed as the processed signal.The results show that this method has obvious advantages in eliminating noise and trend term interference.Compared with the widely used processing methods(CEEMDAN method,wavelet threshold method,EMD-wavelet threshold method,EEMD-wavelet threshold method,CEEMD-wavelet threshold method),the signal-to-noise ratio(SNR) of CEEMDAN wavelet threshold method is 20.460,and the root mean square error(RMSE) is 0.086.The objective evaluation indexes of the method all show better treatment effect.The 3D time-frequency-energy diagram before and after processing reflects that the processed signal fully retains the real energy information in the 2~200 Hz frequency band,which further improves the accuracy of blasting vibration signal analysis and can be applied to the joint processing of trend term and noise similar to blasting vibration signal.

When underwater explosions with different explosive equivalent are conducted near water surface,bubble movement has certain effect on water surface morphology.Thus,the formation of water spike of free surface,which is critical to this effect,was studied by establishing a bubble motion model of underwater explosion.And the model was realized based on ALE algorism and ANSYS software.More specifically,the morphological changes of the free surface spike,bubble motion characteristics and surface fluctuation characteristics induced by underwater explosion were analyzed by normalizing of time parameters under the conditions of same water depth and distance parameter and different TNT equivalents.The results show that the formation types of the spikes of free surface are in order of fragmented water spike,splash water spike,cup-shaped water spike and crown-shaped water spike with the increase of water depth and distance parameter.At the same time,the cavity radius of the spike of free surface also increases gradually with the maximum value for the cup-shaped water spike.At the same water depth and distance parameter,charge quantity has little influence on the basic morphology of water spike.However,with the increase of charge amount,both the first cycle time of bubble pulsation and bubble radius increase.The vertical displacement of bubble center point gradually moves upward after the first period of bubble contraction.In addition,greater charge amount also increases the characteristic width of crown-shaped water spike and the height of the center water column.The height of the surface fluctuation is increases gradually,and the normalized moment of the maximum surface fluctuation also advances continuously.

Abstract: The influence of blasting construction of new tunnel on the side wall a large-section underground cavern on the stability of adjacent underground caverns is the purpose of this research.Based on the water diversion project from Ningbo to Hangzhou bay,blasting vibration data monitored in a section of Tingxia tunnel from the blasting excavation of the Xixia tunnel are used to obtain vibration velocity distribution law.Finite element model established by LS-DYNA is used to simulate burn cut blasting process and obtain the distributions of vibration velocities and stresses in adjacent caverns under blasting effect.The stability of underground caverns are then assessed by considering the effect of dynamic loads.The calculation results show that the blasting vibrations predicted by numerical simulation agree well with the data of field tests.The vibration velocity and tensile stress reach the maximum values at the near-field area on the side wall closer to the blast source,which leads to a higher possibility of tensile failure.The distribution law of vibration velocity is similar to that of maximum principal stress.Combining with the criterion of rock tensile strength,the data of maximum principal stress and vibration velocity were fitted,and the safety criterion of peak vibration velocity was proposed.When the vibration velocity exceeds the critical value of 45.82cm/s,measures should be taken in time and protection should be strengthened.This research work can provide reference for similar tunnel blasting construction and vibration control.

As a new type of tunnel,a double-arch tunnel is connected by two arches without a middle wall.And too small a distance between them leads to a situation that the blasts in the subsequently excavated tunnel inevitably affect the support structure and surrounding rock of the antecedently excavated tunnel.So,it is necessary to monitor and control the blasting construction.Based on the Manla highway tunnel in Yunnan province,the blasting excavation of the subsequently excavated tunnel is studied by combining field test data with numerical simulation results.Blast vibrations of the antecedently excavated tunnel wall were first monitored during the blasting construction of the subsequently excavated tunnel to analyze the corresponding propagation and attenuation laws.Then,a numerical model was established to simulate the construction process of blasting excavation in the subsequently excavated tunnel,and the attenuation law of vibration propagation calculated by the model is compared with the field measured data to ensure the reliability and accuracy of the discrete element model.By analyzing the lining deformation and surrounding rock damage caused by blasting excavation in the model,the stability of lining supporting structure and surrounding rock is obtained.Based on the vibration propagation law and numerical simulation results,the maximum charge per delay for the tunnel is proposed on the premise of ensuring the safety of supporting structure and surrounding rock.Under the engineering conditions,it is suggested that the maximum charge per delay for the subsequently excavated tunnel should not exceed 15 kg.The maximum allowable vibration velocity is determined by combining the maximum charge per delay and vibration attenuation law,and the vibration velocity at the middle wall of the blasting side of the antecedently excavated tunnel on the same plane of the blasting working face is no more than 22 cm/s.The safety control method is reliable and effective in subsequent construction,which can provide reference for similar double-arch tunnel blasting excavation projects.

In tunnel construction by drilling and blasting method,the energy generated by explosive inevitably disturbs the surrounding rock.Therefore,the control of surrounding rock damage is very important to the safety and stability of the tunnel.At present,the damage evolution law of surrounding rock with different grades in the same tunnel and lithology is very rare.Based on the Xiaoxiku tunnel project of Xitong Road,the author studied the cumulative damage evolution law of grade Ⅲ,Ⅳ and Ⅴ dolomite surrounding rock under blasting loads with the help of acoustic testing technology.The results show that the P-wave velocity of grade Ⅲ dolomite is higher than 4200 m/s.When the charge per blast is 180 kg,the maximum damage range of surrounding rock is 1.8 m,and the damage of surrounding rock tends to be stable after the face is advanced by 24 m.The P-wave velocity of grade Ⅳ dolomite is about 3300 m/s.When the charge per blast is 168 kg,the acoustic wave velocity of rock mass decreases from 3300 m/s to less than 1000 m/s within the hole depth of 2.0 m.And the damage of surrounding rock tends to be stable after the face is advanced by 21 m.The P-wave velocity of class Ⅴ dolomite is lower than 3000 m/s.When the charge per blast is 144 kg,the rock mass within the entire hole is affected by blasting vibration with the deeper rock more disturbed.The tunnel surrounding rock can be divided into three areas:failure zone(within 0.8 m),disturbed zone and undisturbed zone(beyond 1.8 m).

Burn cut blasting with uncharged holes was adopted in a large-section tunnel project of Etihad Railway in the United Arab Emirates to ensure timely completion of the construction with a high standard.Engineering mathematical models are established to determine blasting parameters and guide the construction process.Considering the bit diameter on site,two burn cut plans with four 102 mm-diameter uncharged holes and six 64 mm-diameter uncharged holes are presented by using mathematical models.The theoretical excavation footage for each of the two plans is 4.5 m and 4 m,respectively.As a contrast,a wedge cut scheme is designed with a theoretical footage of 4m.According to the field test statistics of T7 tunnel,the average footage per cycle of the 4-uncharged-hole plan is 4.3 m with a hole efficiency of 95.6%,which is 0.6 m more than the footage of wedge cut plan.According to the field test statistics of T10 tunnel,the average footage per cycle of the 6-uncharged-hole plan is 3.8 m with a hole efficiency of 95.0%.Compared to the wedge cut plan,the maximum charge per delay has decreased by 85%,which has controlled the PPV below the allowed value indicated by the monitoring data.Numerous applications of burn cut with uncharged holes in this project have validated the effectiveness of the engineering mathematical model in medium-hard and hard rocks.At the same time,the burn cut plan can speed the construction process,reduce blast costs,and effectively control blast vibrations.

In tunnel driving blasting,the construction technique of replacing the stemming material or charge decks with water is also called water pressure blasting.The development of charge structure in tunnel blasting can be divided into three stages,from basically bottom initiation without stemming to stemming with solids or water at the hole collar,then to the present technique of water cushion,isolation and plugging in multiple parts of the hole.The first stage is from 2002 to 2015,when the main charging structure was based on the conventional charging structure.The hole was stemmed and both bottom and the collar of the hole were padded with a water bag,and the charge of the hole was reduced.The second stage is from 2016 to 2020.The main technological progress was that the charge section in a smooth blasting hole was replaced by a shaped tube device,which improved the half cast factor and reduced the number of smooth blasting holes.The new stage is from 2021 to now,with the new Meizhou to Longchuan railway Hegongtang tunnel as a representative project.In this project,water bags were used for decks and stemming instead of solid stemming materials.And the length of the water bag was increased from 20 cm to 60 cm.Practice proves that compared with conventional blasting technology,this new blast technique not only saves 25% of the explosive and reduces the workload of the smooth blasting holes,but also improves the efficiency of charging operations and the dust removal effect.

The excavation quality and progress control of slope protection layer of dam shoulder groove is of great significance to realize the safe and efficient construction of hydraulic engineering.In view of blasting excavation of the slope protective layer,a three-dimensional adaptive layout algorithm of the blasting holes is proposed and a three-dimensional geometric calculation model based on the algorithm is established,which consider the characteristics of the protective layer,such as multi-profile,multi-inclination and high excavation quality requirements.Using C#WinForm to achieve human-computer interaction interface design,a three-dimensional automatic layout system of the blasting hole is developed.By coordinating the two-dimensional layout of the blast holes in the top,bottom and side excavation contour surface of the protective layer,and using the offset contour method to determine the row relationship of the blasting holes in each contour surface,the three-dimensional automatic layout of the blast holes is realized,which effectively solves the adaptive layout problem of the contour holes in the blasting excavation of the protective layer of the dam abutment groove slope under the complex contour,and the main blast hole layout problem when the bottom end of the blasting hole does not fall on the bottom excavation face under the condition of the excavation slope.The design results of engineering examples show that the application of the system can automatically,quickly and efficiently complete the layout of blasting holes of the protective layer of the abutment groove slope.

Research on blasting process plays an important role in reducing mine costs and improving mine benefit.However,field industrial tests have the drawbacks of long period,large workload and high cost.Moreover,blasting simulation software such as LS-DYNA requires users to have strong professional knowledge and mechanical skills.This paper introduces the functional composition of blasting analysis software JKSimBlast,and analyzes the application process of 2DBench open-pit blasting simulation module.The study includes the two key techniques and solutions of the selection of the fragmentation analysis model,the source of rock mass damage analysis parameters.Based on the 3730 m bench in an open pit mine,blasting industrial application is carried out.According to the actual situation of blasting area,the burden is determined as 5.5 m and the hole spacing is determined as 8 m.There are two charge structures:One is decked charge with stemming of 7 m,decking of 3 m,charge lengths of 3 m and 4.8 m.The other is continuous charge with stemming of 7 m,charge length of 10.8 m.The initiation network includes in-hole delay of 425 ms and surface delays of 17/25/42 ms.The simulation results show that the current blasting boulder rate of the mine is high,and the fragmentation uniformity of the slope top surface is poor,and the boulder tend to be at the front of the blast pile.The reason may be the long stemming length on the upper part of the blast hole.The software analysis results are consistent with the field fragment analysis results,indicating that the simulation results of JKSimBlast software are reliable and feasible for daily blasting design and analysis in open-pit mines.

During bench blasting in open-pit mines,the surface profile of the muckpile and the movement trajectory of the internal particles are important influencing factors for precision mining in open-pit mines,especially for ore bodies with uneven mineralization.Aiming at the problem that the three-dimensional distribution of the muckpile spatial profile is a difficult problem in the evaluation of the blasting effect of open-pit mines,this paper proposed a calculation method based on discrete element and carried out the calculation and analysis of the bench blasting muckpile profile by relying on the Yuanjiacun Iron Mine of Taiyuan Iron and Steel Co.,Ltd.This method first used three-dimensional laser scanning to scan the joints in the area to be studied to obtain joint occurrences,and tested the mechanical parameters of the rock mass; then,the joint distribution model is established according to the statistical results,and the single-hole blasting charge and initiation mode are combined to carry out blasting calculation simulations.During the calculation process,monitor the cells near each blasting point,determine the motion trajectory of each particle,and determine the three-dimensional profile of the muckpile; finally,the accuracy of the numerical results is verified by comparing the actual shape of the muckpile with the slope angle.The results show that the height,impact distance and rupture angle of muckpile calculated by numerical analysis are in good agreement with the actual data measured by UAV.The simulated forward thrust distances of No.1 and No.2 in the muckpile are 26.1 m and 14.71 m,respectively,while the forward thrust distances of No.5 and No.6 are 9.18 m and 9.83 m,respectively,and the movement is relatively gentle.Through the numerical analysis of the space form of muckpile,it can provide a theoretical basis for the precision mining of open-pit mine.

In the practice of gas control engineering in coal mine,pre-split blasting is one of the effective measures to improve the permeability of low-permeability coal seams,and its effect depends on the generation and expansion of blast cracks.In order to research the generation and expansion characteristics of pre-split blasting cracks in low permeability coal seams,the blasting process is regarded as a plane strain problem.Then the numerical model for pre-split blasting is constructed based on the HJC model,the HIGH_EXPLOSIVE_BURN material model,the JWL equation of state,and meshing with hexahedral elements.Furthermore,the LS-DYNA software is used to solve the numerical model so that to analyze the generation and development process of the crushed and fractured zone areas around the blasting hole.In addition,the characteristics of cracks and stress changes in the coal body around the blasting hole are also worth discussion.Finally,reasonable suggestions are given for the selection of pre-split blasting parameters in coal seams.The research shows that when No.2 rock emulsion explosive with a diameter of 94 mm is charged into a blast hole with a diameter of 120 mm,the crushed area around the blast hole is 1.43m 1.25 m,and the radius of the fractured zone is about 3.4 m with the length of the main crack within 2.0~2.62 m.The connection direction between the blasting hole and the control hole is mainly affected by the compressive stress,while the tangential direction is mainly affected by tensile and compressive stresses.And the left and right sides of the control hole are also significantly affected by tension and compression.The stress waves generated by successively initiated blasting holes are superimposed on the stress field in the fractured area,which has a certain influence on the generation and development of the cracks.The reasonable layout of the pre-split blasting holes in the coal seam should be comprehensively considered with the attenuation effect of the coal seam on blasting stress waves,the reflection effect of the uncharged hole wall on the blasting stress waves and the superposition of blasting stress waves.

Taking the controlled blasting engineering of subgrade of a construction project as the research background,the blasting parameters and safety protection measures are designed to eliminate the potential safety hazards caused by blasting flying stones and vibration caused by subgrade blasting to the adjacent glass curtain wall.The design includes:More holes and less charge are used to drill dense holes with a spacing of 2.5 m×2.2 m,and a rectangular hole layout method is selected to facilitate covering and protection,By controlling the charge and filling quality of single hole,the uniformity of blasting energy release is ensured;In the way of cutting blasting,a method of simultaneous initiation of two holes in the millisecond delay initiation network is selected,and the delay time of each hole is set reasonably to avoid the phenomenon of section stacking and reduce the adverse impact of blasting vibration;In terms of safety protection,the advantages and disadvantages of the two safety protection measures of the quilt made of old tires cover and the quilt made of dense-mesh-pressurization old tires cover are compared.After comprehensive consideration,the safety protection measure of dense-mesh-pressurization old tires cover is selected.The engineering practice shows that the glass curtain wall is safe and nondestructive,and the blasting effect is good.Compared with the conventional full coverage protection method of blast holes,it not only effectively controls the harmful effects such as blasting vibration and blasting flying stones,but also reduces the protection workload,saves the protection cost and reduces the probability of damaging the network during protection.The successful application of the blasting parameters and safety technical measures can provide reference for similar projects to a certain extent.

The problem during the overall scheme of bidirectional fold implosion technology is the lack of calculation basis for selecting key parameters.Thus the quantitative design method of folding blasting plan is studied.Firstly,a multi-rigid body dynamic model of the building's motion posture is established.Based on the dynamic model and engineering case analysis,the design criteria for main parameters such as the position of the blasting incision,the sequence of initiation,and the delay time are put forward.It is proposed that there should be 2 to 3 blasting cuts,and the mass of each section should be close with a height-width ratio greater than 2.The opening directions of adjacent incisions should be opposite,and the bottom incision should face a spacious area.The initiation sequence of each incision should be from top to bottom with the minimum delay interval between adjacent incisions approximately equal to the time for the upper incision to rotate 1°~2° after initiation.While the maximum delay interval is equal to the time for the upper incision to close.Reasonable initiation delay time should ensure that the building is zigzag in the air before any blasting incision is closed. Through the blasting example of a 19-story building,the rationality of the design criteria and the kinematic model is verified.

A highway viaduct is a double-line reinforced concrete structure,and the bridge deck width of a single-line is 12 m.The northern section and the southern section of the bridge approach and the main bridge have 6 piers(pier number 4-9),5 piers(pier number 12-16) and 2 piers(pier number 10,11),respectively.When blasting demolition of this bridge is conducted,it is necessary to focus on the complex surrounding environment,flying rocks and touchdown ground vibrations.The finite element software ANSYS/LS-DYNA is used to analyze the combined effect of the blasting load and the intrusion load of the fragmentation group on the reinforced concrete pier columns of the main bridge,and simulate the whole collapse process of the bridge.As a key point of the study,three blasting schemes,symmetrical initiation,unidirectional initiation,and center initiation,are compared,and the muck pile parameters are evaluated by using the post-processing software LS-Prepost.It is revealed that if only consider the muck pile,center initiation performs the best.Between the other two blasting schemes,unidirectional initiation is better than symmetrical initiation.The peak particle velocities of touchdown ground vibrations for the three blasting schemes can be ranked in an descending order by numerical simulation,which is symmetrical initiation>center initiation>unidirectional initiation.At the same time,all the PPVs of the three blasting schemes are within the safety allowable ranges.After comprehensively evaluating the muck pile parameters and touchdown ground vibrations,it is determined that a long delay interval has a better blasting effect than a short delay interval.Finally,the blasting scheme of unidirectional initiation,long delay time within and between the bridge lines has been chosen.In general,the actual blasting effect coincides with the numerical simulation results,with all indicators in line with the corresponding regulations.In addition,a good vibration reduction effect is also achieved by using various vibration damping techniques.

The stress wave induced by CO2 phase transition can be used to generate rock fractures.It is important to investigate the propagation and influence law of this stress wave.Based on the self-developed triaxial strain testing device,a testing scheme was designed by utilizing a dynamic strain measurement system to collect strain signals during CO2 phase transition and rock fracturing.The research results indicate that the peak stress in the jet direction and perpendicular to the jet direction decays exponentially with the increase of propagation distance,and the peak stress in the jet direction is significantly greater than that perpendicular to the jet direction.CO2 filling amount and shear sheet thickness are important factors affecting the peak stress for CO2 phase transition fracturing.When the shear sheet thickness is constant,the peak stress increases with the increase of CO2 filling amount,but the increasing rate decreases gradually.Similarly,while the CO2 filling amount is constant,the peak stress increases with the increase of shear sheet thickness,showing a continuous growth trend.

Coal seams in China have many features，such as low permeability，high gas pressure and large gas content，so it is extremely difficult to extract gas from the original coal seam.The permeability has to be increased in order to improve the efficiency of extracting gas and shorten the time of extracting gas in advance.Among many technologies of increasing the permeability by cracking coal rocks，liquid CO2 can not only contribute to the increase of permeability，but also substitute for gas，which can improve the efficiency of extracting gas significantly.In order to explore the application and effect of the L-CO2 fracturing technology in high gassy and low permeability coal seams，a self-developed high voltage pulse discharge excitation supercritical CO2 test device is used.The complex process of electric,thermal and force coupling in liquid CO2 phase transformation induced by high voltage pulse discharge is quantitatively studied,and the dynamic response law in the supercritical state during the process is determined.According to the Span&Wagner equation state of CO2,the energy needed for liquid CO2 to supercritical CO2 gasification is analyzed and calculated,and the results show that the pressure of the supercritical CO2 will reach 11 MPa,18 MPa and 26 MPa respectively under the condition that the discharge energy in the reactor reaches 20 kJ,40 kJ and 60 kJ.The pressure of supercritical CO2 in the reactor is monitored by adjusting the initiation voltage level to 1500 V,2000 V and 2500 V respectively,and discharge energy of 20 kJ,40 kJ and 50 kJ respectively.The relation curve between pressure and time is then obtained,and the changing rule of the pressure curve is analyzed.The results show that the degree of liquid CO2 gasification is different under varying amounts of discharge energy,and the supercritical CO2 pressure in the reactor increases with the increase of discharge energy.The research results provide a reference for the application of anti-reflection technology of continuous and repeated cracking of coal seam under high pressure discharge excitation of supercritical CO2.

In order to study the blasting vibration characteristics of single-base gun propellant,blast experiments of single-base gun propellant and emulsion explosive were conducted.The attenuation law and energy spectrum distribution of the two materials were compared and analyzed.Sadowski formula and HHT method were used to analyze the experimental vibration signals to obtain the blasting vibration attenuation formula,the equivalence coefficient,and the marginal energy spectrum.The results show that the decay trend of peak velocity of single-base gun propellant and emulsion explosive are similar.But the vibration velocity of single direction and vector sum of the single-base gun propellant is lower than that of the emulsion explosive.The average equivalence coefficient of the single-base gun propellant was only 0.43 in present study,indicating that the blasting vibration effect of unit single-base gun propellant is much weaker than that of the emulsion explosive.In addition,the vibration energy of both the single-base gun propellant and the emulsion explosive was mainly distributed between 0 to 50 Hz.With the increase of charge weight,the blasting vibration energy distribution of emulsion explosive barely changed,whereas the main frequency of the vibration signal of the single-base gun propellant is concentrated within 15~25 Hz.Even though the blasting vibration energy of single-base gun propellant is lower than that of emulsion explosive,the difference of total energy between single-base gun propellant and emulsion explosive decreases with the increase of charge weight.In addition,the energy ratio of single-base gun propellant in 0~10 Hz fluctuates with the charge weight and test distance.

In this paper,the penetration behaviors of 4.6 mm thickness armor steel under different projectile velocities of type 537.62 mm common steel core bullet were studied by computer simulation analysis.The anti-ballistic performance parameters(including back projection height and crater depth) of the target plate under different projectile speeds was calculate by regression analysis with the least square method.Furthermore,a mathematical model between anti-ballistic performance parameters and projectile speed was constructed.And then,combined with the back projection height and crater depth when the target plate was shot through,the ultimate resistance velocity of the target was predicted.During simulation,the simplified J-C constitutive model was selected to set the material parameters of the target plate ignoring influence of temperature.The corresponding model parameters were calculated from the quasi-static and dynamic compressive stress-strain curves.In order to ensure the accuracy of the prediction model,the anti-ballistic performance of target plate was tested at different shooting distances.Thereby the prediction model was modified by using the actual measured results.The results show that,the simulation results are in good agreement with actual shooting results,and the simulation accuracy of crater depth and back projection height reach to 86.5% and 88.2%,respectively.This thin armor steel shows excellent anti-ballistic performance,and the ultimate velocity of its impact failure is estimated to be about 1000 m/s.Within the velocity range of the projectile,the back projection height(H) and crater depth(D) of target plate are approximately linear to the projectile velocity(v) and the square velocity(v2),which could be expressed as H=-9.575+0.01644v,H=-3.213+1.05988 10-5v2,D=-13.425+0.02372v and D=-4.247+1.52939 10-5v2 after modification,and the prediction accuracy of all the modified models are above 92%.

Jinwu Bridge is located in Jinhua,Zhejiang Province,which is an important transportation hub spanning three districts with large blasting workload and complex surrounding environment.In order to guarantee the safety of explosives during the 3-day and 2-night blasting operation and to complete the large-scale blasting security warning and evacuation work efficiently and reliably in the early morning with low visibility,for the first time,we combined the respective advantages of real-view monitoring by AR(Augmented Reality),drone and infrared thermal imager.Spherical cameras were set at a commanding height and the crossing of roads to cover the whole blasting security warning range.Gun cameras were fixed to monitor the charging operations.The drone maneuvered around and the infrared thermal imager searched hidden parts.All the signals together with the social probe video signals were transmitted to the AR back end.After intelligent signal processing,all important information could be displayed visually in the global monitoring screen to build a comprehensive three-dimensional real-time visual blasting security warning monitoring and search system with AR live-view monitoring as the main method.In the monitoring system,UAV mobile monitoring and infrared thermal imager search were used as the supplement measures to scan the overall situation and control the details.Blasting security warning could be conducted by this novel system together with conventional methods.The system was online for 60 hours with 373,140 m2 covered and 18 illegal intrusions reported.The task of blasting security warning was successfully completed within one hour by the assistance of the monitoring system.The construction of the system and its successful application in urban demolition solved the problem of safe storage of explosives around the clock and the problem of evacuation work of personnel in complex environment with low visibility.

The safety control standard of blasting vibration of high-voltage transmission tower is still not clear,which makes it difficult to guide the construction.Based on a highway tunnel under construction,this paper designs the blast hole network parameters for a tunnel with 200 kg explosive per round.The blast vibration signals are monitored near the tower foundation and statistically analyzed to study the bibration response characteristics of the high voltage tower and the attenuation law of the vibration signals.The results show that with the decrease of the distance to the blast source,the vector peak particle velocity of the tower foundation increases.The frequency band of vibration energy concentration tends to low frequency and the vibration frequency is obviously affected by the development degree of cracks in surrounding rock.The peak values of vibration velocity in the vertical direction are greater than those in the horizontal direction,so the vertical vibration damage of the foundation should be paid more attention to prevent any settlement of the medium.By adopting multi-delay initiation network and strictly controlling the maximum charge for lower delays,the damage effect of blasting vibration on the high voltage tower can be effectively weakened.Through data fitting,the attenuation formula of blast vibration in for this project is obtained.In this tunnel project,the blasting vibration velocity at the tower is controlled within 1.0 cm/s to ensure the safe operation of the high voltage transmission tower.Therefore,it is suggested that the competent authority of electric power and the law-making authority appropriately relax the control scope of blasting operations around the power facilities.

In order to study the influence of a complex filling body on the propagation characteristics of blasting seismic waves,blasting vibration data have been recorded on the monitoring points placed in the stopes on both sides of a filling body at -370 m level in Jiguanzui mining area of Hubei Sanxin Gold and Copper Mine.The signal analysis method,Hilbert-Huang transform(HHT) is used to analyze the changes of blasting seismic waves before and after propagating through the filling body from the perspective of marginal spectrum and transient energy spectrum.Furthermore,ANSYS/LS-DYNA numerical simulation is used to study the changes of maximum principal stress in the rock mass before and after the blasting seismic waves propagate through the filling body.The results show that the dominant frequency range of the blast vibrations before and after passing through the filling body are 60~80 Hz and 50~60 Hz,respectively.This indicates that the filling body has an effect of filtering high frequency contents.The energy accumulated in the frequency band 60~80 Hz after propagating through the filling body has attenuated to about 1/7 of that before propagating through the filling body.In addition,the energy distribution becomes more diffuse.Moreover,the maximum instantaneous energy of the seismic waves before propagating through the filling body is about 27 times that after propagating through the filling body.Although the blasting seismic waves reduce the maximum effective stress in the rock mass by about 14%,the stopes on both sides of the filling body still can generally keep stable.

In order to study the anti-explosion stability of a long-span underground chamber under the influence of multiple factors,simulation using FLAC3D,based on model tests,was conducted by changing the parameters of explosion strength,explosion source location and chamber span,so that to obtain the variation laws of stress,displacement and plastic zone of the surrounding rock and lining structure of the chamber under different conditions.The research results show that the stress wave propagates in a spherical form from the explosion center.In the process of propagation,the strength of the stress wave rapidly attenuates,and the reflection occurs when the wave spreads to the earth's surface and the free surface of the chamber.The reflected tensile wave makes the surrounding rock damaged,producing the phenomenon of "spalling",and splayed cracks appear on both sides of the chamber.After the explosion intensity increases,the stress values of the measuring points and the deformation of the vault increase.The tensile area and plastic zone above the chamber also become larger,and even join together,which might make the chamber collapse.With the increase of the chamber span,the stress value of each measuring point changes little,while the deformation of the vault increases significantly,which results in a worse anti-explosion performance.Under the same explosion intensity,the damage effect of top explosion is the most serious.The more the explosion source deviates from the chamber,the smaller the stress values of measuring points,deformation and plastic zone of chamber are.As a practice,increasing the buried depth of the chamber and making some surface camouflage can reduce the explosion damage effect,while increasing the strength of lining structure and anchoring the arch foot and the vault can enhance the stability of the chamber.

The influence of impact loading generated during the excavation blasting process on a buried gas pipeline near the blasting source has been widely concerned as a major safety issue in the engineering construction of an urban underground space.Based on a specific construction case,this issue is studied with a fluid-solid coupling model considering soil,pipeline and rock by using the dynamic finite element software LS-DYNA.The distribution laws of the effective stresses and the resultant velocities of vibration on the two sides of the pipeline towards and away from the blasting source are analyzed with four different wall thicknesses(δ) of 0.02 m,0.04 m,0.06 m and 0.08 m.At the same time,the attenuation characteristics of the peak blasting vibration velocities on the ground and the two sides of the pipeline towards and away from the blasting source are further investigated based on the established coupling model.The results present a nonlinear attenuation law of the effective stresses and the resultant velocities of vibration with the increase of the pipe wall thickness.Specifically,Moreover,the local peak stress on the side of the pipeline away from the blasting source is significantly higher than that on the side towards the blasting source,whereas the resultant vibration velocities on the side of the pipeline towards the blasting source is significantly higher than that on the side away from the blasting source.Now that the pipe wall thickness increases by an increment of Δδ=0.02 m,the attenuation rates of the peak effective stresses on both sides(towards and away) of the pipeline are κ1=25.2%,19.2%,10.7% and κ2=50%,25%,13.3%,respectively.For the four different wall thicknesses,the average attenuation rates of peak particle vibration velocities from the side of the pipeline towards the blasting source to the side of the pipeline away from the blasting source and from the side of the pipeline away from the blasting source to ground are η1=24.6%,18.96%,15.04%,14.78% and η2=73.46%,69.4%,66.52%,63.6% respectively.However,the change of attenuation coefficient is significantly smaller than the attenuation rate.Therefore,it is no longer accurate to use the Sadovsky formula,which needs to be corrected,to predict the vibration velocities of pipelines in such inhomogeneous geological conditions.

Flyrock is one of the most hazardous events in open-pit mine blasting operations.At present,the flying distance of flyrock is mainly predicted by several empirical formulas.However,due to the great difference between different engineering,blasting types and parameters,the accuracy of this kind of empirical model is not high.Besides,the unknown weight relationship of various parameters is the main reason for the inaccuracy of the empirical model.To solve this problem,artificial intelligence and other new methods can be used to predict the flying distance of flyrock.During the blasting operation of Yingtaojing limestone mine in Qingzhen city,Guiyang,flying stones were scattered far beyond expectations,resulting in the damage of surrounding protected buildings.In this paper,an attempt is made to predict and control flyrock in blasting operation of this mine using artificial neural network method.Based on 122 blasting test data,7 different neural networks are trained to model.Among them,a three-layer feedforward back-propagation neural network has the lowest root mean square error,which was composed of 16 hidden neurons,including 9 input parameters and 1 output parameter.By comparison,the average relative error between the predicted results and the measured data is within 3.31%,which has guiding significance.The sensitivity analysis of the model shows that the parameters that have the greatest influence on the distance of blasting flyrock are explosiveness index,delay time,charge per delay,hole diameter,hole depth and karst cave.

It is known that the safety management level of blasting operation units during the whole life cycle of purchasing,transporting,using and storing civil explosives still needs to be effectively improved,and the intrinsic safety management awareness of the explosive-related personnel needs to be further strengthened.To achieve this goal,the deficiencies and irregularities of current safety supervision in blasting operation units are discussed based on practical experience over many years and the systematical analysis of current laws and regulations and industry status.The discussion results show that the professional ability of blasting workers needs to be improved.There are still blind spots in the supervision of blasting equipment during and after blasting operations.Problems still exist in the safety management of civil explosive storage,such as unscientific distribution of economic resources and unreasonable long-distance transportation of explosives.In view of the above-mentioned problems,several corresponding suggestions and improvement measures are put forward.Firstly,the practical operation skills,theoretical level and essential safety management consciousness of civil explosive industry employees can be improved through the flexible combination of online and offline education.Secondly,the end monitoring of civil explosive items can be realized by means of information management in blasting operation sites.Thirdly,the control level of civil explosives magazine can be improved by standardizing the construction of the magazines of production and sales enterprises and perfecting the daily control standards of the magazines.The research results can play a positive role in promoting the standardization of blasting operation and improving the safety supervision of blasting operation units.

New internet technologies such as the internet of things and big data are playing a significant role in achieving the comprehensive and deep interconnection of all factors of production safety.Risk management has also received sustained attention in all fields and at all levels.However,in the risk management of high-risk profession,risk transfer still has some limitations such as the absence of risk costs and a risk probability model.Starting from the dilemma of risk management,this paper proposes a possible big data solution to the paradox of risk management and explores the applications and case studies of big data in the field of risk management.Industry regulators can serve as the framework builder of big data and the supervisor of data collection and utilization to discover potential risk factors through data modeling and monitoring,and thus avoid related problems from the root.The operational management side presents subjective and objective dimensions of risk management.Subjectively,as a rational economic person,the managers will make rational rather than reasonable judgments based on contradictory risk management methods and profit-seeking decision-making analysis.Objectively,the application of big data will delimit a reasonable threshold range for high-risk operation units so as to balance a reasonable risk premium.The attitude of risk transferers to risks depends on the risk management and pricing.The application of big data will make the field of risk management become indexable and digital to a certain extent,and.make mine value data to meet their comprehensive and personalized needs for reasonable risk transfer.Finally,this paper concludes that establishing the big data system requires clarifying the dominance of regulators,strengthening the participation of managers,and optimizing the supplementary and connective role of transferees.In addition,this paper provides application advices regarding the strategy of establishing the big data system.

In order to solve the game problem between the insurance demand of civil explosive production enterprises for transferring high risks and the declinature from insurance companies,the revised risk analysis method of operating conditions was adopted,and a risk management framework for civil explosive production was established.Risk identification,risk level measurement,risk control and other processes are analyzed according to indexes including the possibility of actual accidents occurring in the production process of civil explosive enterprises,the frequency of exposure to hazardous environment,loss etc.Then the final systemic risk value D is calculated and the risk is divided into expected loss risk,unexpected loss risk and catastrophic loss risk according to different ranges of D value.Control and financial risk management technologies can promote risk reduction to a certain extent,while financial insurance transfer is one of the most effective risk management technologies for civil explosive enterprises facing the most common unexpected loss risks.However,the high loss rate of high-risk civil explosive industry will inevitably make the commercial insurance company refuse insurance,leading to the dilemma of civil explosive production enterprises unable to transfer the risk.This paper argues that industrial explosive production enterprises can purchase group insurance and liability insurance.Enhanced integration of Internet and explosive production can provide many insurance subjects with homogeneous risk,and thus solve the problem of asymmetric information.These measures can help to solve the “prisoner′s dilemma” between the traditional industrial explosive risk management and declinature from insurance company.