It is prone to occur dynamic disasters such as roof falling,sidewall slabbing and rock burst under dynamic disturbance of mechanical percussion drilling and explosive blasting in the roadway with hard rock.It is extremely meaningful to investigate the dynamic load effect on roadway deformation and failure mechanism.To understand the mechanical behavior of roadway surrounding rock under dynamic disturbance,a hard rock roadway was simplified as a hole in rock.And then,a series of impact tests were conducted on prismatic sandstone rock specimens with a hole by a modified split Hopkinson pressure bar testing system to explore the influence of hole size and shape on the dynamic mechanical properties,failure mode and energy dissipation characteristics.The results show that the existence of the hole has significant weakening effects on the dynamic strength,dynamic elastic modulus and peak strain.The dynamic mechanical properties of the rock decrease significantly with the increase of hole size.Among the specimens with different hole shapes,the dynamic strength and peak strain of the square-holed specimens are the largest,followed by the horseshoe-holed and the circle-holed specimens,but their elastic moduli show opposite results.In terms of rock failure modes,splitting tensile and tensile-shear failure occur respectively in intact specimens and pre-holed specimens under impact load.Additionally,the energy consumption density and fractal dimension of the horseshoe-holed specimens are the largest,which are 1.94 J/cm3 and 2.11 J/cm3,respectively.It indicates that the failure process is the most intense for the horseshoe-holed specimens,while the fragmentation degree of the circle and square holed specimens is not much different.

In order to explore the dynamic crack propagation law of beam members,bar defects with the heights of 22 mm,28.5 mm and 35 mm were designed in a three-point bending beam,and then tested by the digital laser dynamic caustic line experiment system and the drop weight impact test system.The results show that the crack propagation rate and stress intensity factor are affected by the defect height in two stages in the drop weight impact experiment.In the first stage,the maximum growth rates of crack propagation have a trend of first rising and then stabilizing as 247.49 m/s,292.49 m/s and 284.99 m/s with the increase of defect height,and the cracking stress intensity factor was respectively 1.480 MPa/m3/2,1.665 MPa/m3/2 and 1.812 MPa/m3/2,which increased with the increase of defect height.Meanwhile,the crack initiation and propagation rates respectively decreased by 634.42 m/s,524.97 m/s and 377.67 m/s,the cracking stress intensity factors of KⅠ type respectively decreased by 3.281 MPa/m3/2,3.192 MPa/m3/2 and 2.876 MPa/m3/2,and the cracking stress intensity factors of KⅡ type respectively increased by 1.254 MPa/m3/2,1.319 MPa/m3/2,and 1.398 MPa/m3/2.Furthermore,the KⅠ-KⅡ composite stress intensity factor was transformed into a KⅠ type stress intensity factor by deflection.

Blasting is widely used in tunnel engineering as a large scale and high efficiency method of rock breakage,but it inevitably brings some bad effects to the adjacent structures and surrounding rocks,among which blasting vibration is the first.Electronic detonator initiation can realize the active control of blasting vibration intensity and spectrum due to its accurate delay,high reliability and safety,which is an effective means to reduce the seismic effect of blasting.In order to explore the influence of the location and number of electronic detonators on the frequency spectrum of blasting vibration,field tests and numerical calculations were combined.The main frequency characteristics of blasting vibration are summarized for five different initiation locations,including the bottom of the charge,the top of the charge,the middle of the charge,simultaneous initiation at the top and bottom of the charge,and simultaneous initiation at two points evenly distributed in the charge section.Based on the spectrum expression of blasting vibration in viscoelastic medium,the characteristics of blasting loads under different working conditions were analyzed from the perspective of superposition of blasting sources,which was used to reveal the influence of detonator arrangement on blasting vibration frequency spectrum.The results show that the initiation conditions are ranked as simultaneous initiation of two uniformly distributed points,middle initiation,simultaneous initiation at the top and bottom,top initiation and bottom initiation,in the order of vibration frequency from largest to smallest.Multiple detonators actually divide the whole charge into several segments,which is equivalent to superposition of multiple sub-explosive sources.Changing the location or number of detonators is essentially to detonate the entire charge in segments at the same time.The more segments,the length of sub-explosive source charge and the detonation process are shorter,which means the energy release rate of explosives and the blasting vibration frequency are higher,and the rise of explosion load is faster.In addition,with the increase of distance to blast source,the influence of detonator position on blasting vibration frequency converges.

Ground blasting vibration control is one of the key contents in the blasting construction of subway tunnels in complex urban environment,and cut blasting is the key to determine the blasting vibration intensity.Combined with the actual project of the north extension line of WuHan Metro Line 7(Qianchuan Line),an optimization design was carried out on the basis of the original blasting cut method.The numerical simulation and field vibration test verification methods were used to calculate and compare the blasting vibration effects of single wedge cutting,burn cut with four holes and double wedge cutting.Then,the optimization method of cut blasting was proposed.The results show that single wedge cutting,burn cut and double wedge cutting have similar propagation rules of blast vibrations along the axis of tunnel excavation.The peak vibration velocity along the x direction(horizontal radial) decreases with the increase of the distance from the working face in the range of 0~-5 m.When distance exceeds 5 m,the peak vibration velocity increases first and then decreases.The excavated area of the upper bench of the left pilot tunnel has an amplification effect on the surface vibration velocity,which is referred as a “cavity effect”.The distribution of the x-direction(horizontal radial) peak vibration velocity on the left and right sides of the tunnel is roughly similar,and gradually decreases with the increase of the horizontal absolute distance from the origin along the direction perpendicular to the axis of tunnel excavation.The upper bench of the left pilot tunnel has a free face,which makes the peak vibration velocity along the x direction(horizontal radial) on the left side of the tunnel bigger than that on the right side.Due to the delayed initiation,the peak vibration velocity along the x direction(horizontal radial) by double wedge cut blasting is the minimum.The surface vibration velocity of the excavated area is 1.35~2.02 times than that of the unexcavated area ahead during the tunnel blasting construction,due to the “cavity effect”.Compared with other cutting methods,the “cavity effect” of the double wedge cutting is weaker.The comparative analysis of blasting vibration intensity of the three kinds of cutting modes shows that the order of advantages and disadvantages of the three kinds of cutting modes is: double wedge cutting>single wedge cutting>four straight hole cutting.

To study the complex mechanical movement and accumulation process of broken blocks in the process of underwater rock bench blasting,a fluid-solid coupling numerical calculation method based on FLUENT-EDEM was adopted.Firstly,the parallel bond and Hertz-Mindlin contact model were introduced between the particles,and the parameters of the parallel bond were calibrated by comparing the results of Brazilian splitting experiment and numerical calculation.Furthermore,the underwater bench blasting model was established,and the mechanical action mechanism of water on rock mass breaking and movement was analyzed.Finally,the whole ejection process of particles from a submerged step block was studied,and characteristics of the block velocity,block stacking and flow field were discussed.The results show that the accumulation and stratification of block particles are related to their initial velocity and height,and the horizontal movement distance of the block particles in the middle step is the biggest under the explosion load action.Meanwhile,the block particles in the upper blocking part mainly roll and cover the middle block particle layer under the action of gravity and buoyancy,which are less affected by the explosion load.Additionally,the explosion energy is mainly used to break the rock at the initial detonation stage,and the water has no obvious flow velocity.With the bulging and throwing movement of block particles,the fluid streamline velocity near the front surface of the bench is largest.When the block particles start to roll and slide,the streamline is mainly affected by the movement form of the particles.Therefore,the fluid-solid coupling model by Fluent-EDEM can accurately simulate the block motion in the underwater bench blasting,which can provide a new research method for underwater rock blasting engineering.

The authenticity of fracture distribution model is one of the key factors during numerical simulation of blasting in jointed rock mass,which would obviously affect the numerical simulation results.It is hard to represent the complex three-dimensional joint distribution in the existing joint construction method.To explore a simple and feasible operation method for constructing the complex 3D joint model in LS-DYNA software,a K file of blasting numerical model was analyzed and reorganized by MATLAB software.Furthermore,a 3D refined numerical model for jointed rock mass was constructed by the 3D joint distribution law and the constitutive joint model parameters.Finally,a statistical analysis of the three-dimensional joint distribution law was carried out in an open-pit limestone mine,and the joints were reconstructed in the numerical model of a bench blasting.Consequently,a comparative study of the numerical simulation and the field blasting test for open-pit bench blasting was carried out.The results show that the error between the joints built in the numerical model and the actual joints is less than 13%.The joint surface changes the damage distribution of the rock mass.Compared with the intact rock mass,the damage rock mass range increases by 12.04%,and the proportion of fragments with the size of 0~100 mm decreases by 8.11%.The damage results obtained by blasting simulation are close to the field rock breaking effect,and the percentage error of fragments with the size of 0~100 mm is 4.16%.The analytical reconstruction method is feasible and easy to represent the complex three-dimensional joint distribution,and the numerical results are close to experimental results.

In order to better study rock blasting mechanism better in layered rock strata,the dynamic tensile mechanical characteristics of the carboniferous shale surrounding rock mass around the Sujiayan tunnel were explored,which belongs to the north section of the Zhengwan high-speed railway project in western Hubei Province.To reveal the effects of impact angle and velocity on the dynamic tensile strength and corresponding failure mode of carbonaceous shale,dynamic Brazilian splitting tests were carried out under five impact angles(0°,30°,45°,60° and 90°) by the split Hopkinson pressure bar(SHPB) device with a high-speed camera and the digital image correlation technology(DIC).At the same time,different impact velocities for every impact angle were also tested by three impact pressures(0.1 MPa,0.2 MPa and 0.3 MPa).The results show that the dynamic tensile strength of the shale decreases first and then increases with the increase of impact angle under different impact velocities.The minimum value is reached when the impact angle is 30° and the maximum value is reached when the impact angle is 90°.The dynamic tensile strength of shale presents a significant anisotropy,and the degree of anisotropy decreases with the increase of impact velocity.With the increase of impact velocity,the dynamic tensile strength of shale increases correspondingly,and there is a significant linear relationship between the dynamic tensile strength and impact velocity.In addition,both impact angle and impact velocity have a great influence on the dynamic tensile failure mode of shale.

To explore the mechanical mechanism of burn cut blasting with a large-diameter empty hole,the stress concentration effect of the large-diameter empty hole was studied by theoretical analysis and numerical simulation.Firstly,a mechanical model for the stress concentration effect of the empty hole was established.Furthermore,the empty hole′s stress concentration effect was clarified based on the elasticity theory and wave dynamics.A numerical simulation under a typical working condition was then carried out,and finally the stress concentration effect of the empty hole was investigated based on the numerical results of stress wave propagation,rock damage,and the first principal stress.The results show that the stress concentration effect of the empty hole is mainly derived from the stress concentration around the cavity and the stress wave superposition effect.During the blasting process,the stress wave is reflected at the empty hole wall and superposed with the incident wave,which is mostly located in the vicinity of the empty hole and the region between the cut holes.The regions with high damage degree are mainly around the cut hole,near the empty hole,and within the triangle regions formed by adjacent cut holes and the empty hole,and the latter two regions correspond to the stress wave superposition regions.There is a significant stress concentration effect near the empty hole,and the closer the rock is to the empty hole,the more obvious the effect is.

In order to improve the quality of tunnel blasting and reduce the disturbance to surrounding rock during blasting construction,it is necessary to carry out optimization research on the original blasting scheme.Taking the parallel guide tunnel of a railway project as the engineering background,more reasonable blasting parameters are determined by using the empirical formula to calculate the powder factor,the number of holes and the parameters of each hole,aiming at the problems such as serious over-under excavation,poor working environment and slow construction progress.The number of medium and large diameter empty holes in the original blasting scheme is changed from 8 to 2,and the layout of cut holes is adjusted to provide better free surface for subsequent holes.At the same time,the orifice of the charging structure is blocked by water bags,which reduces the concentration of dust and harmful gases in the tunnel after explosion.The results show that the average linear over excavation can be reduced from 0.2~0.4 m to 0.15 m with smooth working face and bottom by using the optimized blasting scheme.At the same time,compared with the original scheme,the number of holes and the amount of explosives used in each cycle can be reduced by 37 and 49.2 kg,respectively.In addition,the construction time can be saved by 1.1 h and the cost is about 800 yuan,which has a relatively significant technical effect and economic value,and also verifies the feasibility of the optimized blasting scheme.

Aiming at the construction problems of a subway tunnel adjacent existing buildings in the section between Jialingjiang Road station and Xiangjiang Road station of Qingdao Metro Line 13,a new construction scheme of mechanical excavation combined with blasting is proposed.In the scheme,bench method is used with the upper bench in the weak stratum excavated by mechanical method,and the lower bench in the hard stratum excavated by blasting method.Furthermore,the vibration velocities of the adjacent buildings caused by the proposed scheme and the traditional full-section blasting scheme are analyzed and compared by using FLAC3D and blasting equivalent load method.The results show that,the peak vibration velocity of each monitoring point under the mechanical-blasting scheme decreases significantly compared with the full-section blasting with the maximum reduction rate of 61.1% which is within the allowable range and validates the new scheme.The construction parameters of the mechanical-blasting scheme are compared and selected based on the building settlement,plastic zone of surrounding rock mass,vibration velocity of the buildings,etc.Finally,the mechanical excavation advance of the upper bench is determined to as 0.5 m.Besides,the construction effect of the optimized parameters is monitored and evaluated.The mechanical-blasting construction scheme successfully solved the problems encountered in the project,and shortened the expected construction period by 3 months,which shows the rationality of the proposed construction scheme and parameters,as well as the validity of the calculation results.

At present,mining method is widely used in tunnel construction.The influence of blasting vibration on surrounding rock and supporting structure in tunnel and its disaster control are always hot issues.In order to study the propagation law of blasting vibration inside a tunnel,the vibration signals of simultaneous detonation and detonation at three benches were monitored on site based on the engineering background of a tunnel with soft surrounding rock.The nonlinear regression of Sadovski formula and Fourier transform method were used to analyze and study the test data.The results show that for the same section of the tunnel,the vault has the characteristics of large vibration velocity,high vibration frequency and slow attenuation rate.When 100 ms delay blasting is used between the three steps,the blasting energy can be discretely distributed in time and space,and the vibration superposition effect can be significantly weakened.A single hole blasting test was set in the middle of the cut area,and the single hole vibration waveform was obtained by setting the delay between the test hole and the entire blast as 100 ms.Based on the principle of linear superposition,the delay time was optimized by investigating vibration waveforms synthesized by cut blasting.The results show that when the delay time between holes is 4~7 ms,the peak vibration velocity caused by cut blasting decreases sharply,and the effect of interference is obvious.After the delay time exceeds 7 ms,the peak vibration velocity has no significant difference.

In order to ensure the construction quality of large section shaft horsehead gate and reduce the damage caused by blasting,an advance crack zone blasting technology is put forward.According to the section design and engineering geological conditions,the section of Matoumen excavation,the gates at -199.5 m and -258.2 m of a certain underground mine are divided into upper layer,middle layer,and lower layer excavation zones.The construction sequence is: upper layer→middle layer→lower layer.Firstly,the advanced fracturing holes should be constructed along the excavation contour lines of each layer.The hole depth is equal to the driving depth of the horsehead gate.They are charged with decks and detonated before the main blasting area,which can achieve mutual penetration between holes.The "shock absorption ditch" shall be formed along the excavation contour lines of the horsehead gate,which can reduce the effect of blasting seismic wave propagation.Besides,each construction area of the horsehead gate is equipped with hole by hole millisecond delay detonations with an interval of 5~20 ms,which can achieve the interference and offset of the vibrations from the subsequent blasting and reduce the blasting impact on the large cross-section horsehead gate.It has been validated that the half-wall hole rate of the excavation contour line is higher than 95 %.It can not only meet the requirements of controlling the quality of roof forming for the excavation of large cross-section gate in broken rock mass,but also reduce the cost of support and shotcrete.

Perimeter blasting is very important to control engineering quality in the process of roadway construction,and it is a common way to use slotted pipe blasting to improve the perimeter blasting effect.However,the unreasonable setting of slotted pipe blasting parameters still weakens the directional destruction effect,including the greatly damaged contour,low hole retention rate,common phenomena of over-excavation and under-excavation.In order to improve the directionality of blasting damage,the slotted pipe blasting parameters should be optimized.The reasonable blasting parameters were determined with the study of explosive slotted pipe uncoupling and different initiation positions by numerical simulation using ANSYS/LSDYNA.According to the numerical simulation results,the balance between the protection of surrounding rock mass and directional failure can be achieved when the uncoupling coefficient between the explosive and slotted pipe is 1.12.Meanwhile,the integrity of the contour line is greatly improved when the initiation positions of two adjacent explosives are changed to make the meeting position of the explosive shock waves on the same horizontal plane that shifted to 3/4 of the position between two blast holes.It can be concluded that the damage to the retained rock mass can be greatly reduced as adopting uncoupled structure between slotted pipe and charge,and changing the meeting position of stress wave between blast holes by adjusting the detonation position of charge.

In order to solve the problem that excessive blasting vibration affects the safety of village buildings(structures) on the earth′s surface during the mining process of an underground orebody,the inter-hole delays of 8 ms,10 ms,12 ms,14ms and 18ms and inter-row delay of 100 ms were selected for tests in the #63113 ore room of the orebody III in the mine.By combining the actual situation of the site and the empirical formula,the natural vibration frequency of the brick-concrete buildings with 1 to 2 floors in the village was 7.63~13.23 Hz.The blasting vibration data was collected on site and HHT transformation was applied on the measured blasting vibration signals by MATLAB.The characteristics of the signals were then analyzed from the perspectives of time domain,frequency domain and energy.The highly adaptive EMD decomposition was used to decompose the original vibration signal into the IMF components which were transformed by 10-layer db8 wavelet transform and the proportion of energy in the total energy of the frequency band 7.8~15.7 Hz of level 9 was summarized.The three-dimensional Hilbert spectrum and marginal spectrum were obtained by Hilbert transformation of the reconstructed signal with the IMF components.Through EMD decomposition and wavelet transform research on the blasting vibration signals,it is concluded that the three-direction energy ratio corresponding to the 12 ms delay time at No.3 measuring point is reduced by 14.07%,24.89% and 6.26%,respectively.The experiments show that the problem that the problem that the low frequency energy takes a large proportion in the total energy can be improved by optimizing the inter-hole delay,and the resonance effect can be effectively avoided.By comparing the Hilbert marginal spectrum and the three-dimensional Hilbert spectrum with different delay times,the main vibration frequency and the maximum instantaneous energy of the blasting with an inter-hole delay of 12 ms appear 200 ms after the detonation,concentrated in the range of 30~40 Hz which is higher than the natural vibration band of the buildings,and thus have the least influence on the structures.

Using traditional continuous charge blasting method in Zijin Mine is easy to produce powder near the crushing circle of the hole,resulting in substandard ore gradation and waste of resources.Therefore,in order to improve the ore gradation and increase the aggregate products,a blasting test was carried out under the conditions of 0 m,1 m,1.2 m,and 1.5 m in the middle of the air-decked charge blasting technology.Firstly,a limestone model using HJC constitutive relation was established to simulate the actual geological by ANSYS/LS-DYNA finite element software.And then,the damage distribution characteristics of rock mass under different spacing distance conditions were analyzed,and the relatively optimal air spacing charge length was obtained.Finally,the 1.2 m and 1.5 m middle air decking are selected to control the blasting powder rate.The field blasting tests and the comparison of rock gradations under different conditions show that it is effective to reduce the powder rate by adopting the intermediate air decked charge.When the air decking length is 1.5 m,the non-uniformity coefficient Cu and the blasting powder rate can be reduced.Before the technical transformation,the average powder ore rate is about 15.94%,and after the technical transformation,the powder ore rate below 4.75 mm can be reduced to about 9.37%,making the grading to a good level.

Reinforced concrete(RC) short beam is the key load-bearing component of buildings.In order to study its dynamic response and failure mechanism under impact load,drop hammer impact tests with different impact mass,impact velocity and impact energy were carried out by combining strain gauge sensor,high-speed photography and digital image technology(DIC).The results show that,the failure forms of the short RC beams under impact loads are arch collapse cracks and overall bending deformation,which are obviously different from those of shallow beams.The axial strain in the mid span of a short RC beam changes from tensile strain to compressive strain.With the increase of impact energy(18 061 J≤E≤49 831 J),the axial peak tensile strain and residual compressive strain in the mid span increase first and then decrease.The short RC beam is in the stage of elastic flexural deformation,elastic-plastic flexural deformation and punching shear failure mode in turn.The crack initiation and propagation process of the short RC beam under impact load is not unidirectional.And the fracture zone is formed by the multidirectional fracture propagation with multiple times,and then the plastic hinge is formed,resulting in the overall short beam failure.The deformation degree of the beam mainly depends on the impact speed rather than the impact energy.Specifically,the peak deflection and residual deflection in the middle span of the beam(26.81 mm≤wp≤29.85 mm;17.12 mm≤wr≤21.66 mm) increase with the increase of the impact speed(5.53 m/s≤v≤7.13 m/s) under the same impact energy(30 000 J).

The reasonable selection of the incision angle is an important factor for the success of blasting demolition of a typical reinforced concrete chimney.In order to determine the selection range of incision angle,the isolation method was adopted to establish a theoretical model according to the force and failure characteristics of the residual section.The solution formula of any angle position on the residual section was derived,and a revision coefficient k was defined to express the influence of the cylinder at the upper part of the unnotched section.Furthermore,the stress and bending moment conditions of the dumping cylinder were established,and the selection range of the incision angle was obtained by combining the solution formula and the damping conditions.The case study shows that with the increase of the incision angle,the maximum tensile stress,the maximum compressive stress and the bending moment generated by the upper cylinder of the incision tend to increase,while the resistance moment of the residual section tends to decrease.The upper limit of the selection of the incision angle can be obtained when the maximum tensile stress reaches to the material strength limit,and the lower limit can be determined when the two bending moments are equal.Changing the incision angle would have a greater effect on stress than changing the incision height.Under the condition that the actual incision height is 4.5 m in the engineering case,the selection range of incision angle based on the established theoretical model is 198°~237.6°,and the actual incision angle is 216° within the theoretical selection range,which further verifies the reliability of the theoretical model.More extensive application and guide engineering practice are expected.20A1160)

In order to further study the propagation characteristics of surge wave induced by underwater blasting loads,the multi-physical field coupling simulation method powered by the dynamic analysis software COMSOL was adopted to establish a transient solution model based on the second water source project-diversion project of Guilin City.The isosurface,peak stress and vibration velocity of surge wave under explosion load were studied and evaluated based on field monitoring results.The results show that the surge wave produced by underwater blasting essentially propagates around the center of the blast center,and the surge isosurface evolves from regular round to irregular ellipsoid with time.The surge waves decay rapidly during propagation,and with the increase of water medium velocity threshold,the influence range of surge wave action region is small.In addition,the stress of the surge wave has superposition effect under the condition of delayed blasting,and thus there are multiple peaks.When the distance to blast center increases from 28 m to 108 m,the attenuation rate of the peak vibration velocity of the surge wave reaches 96.3%,which has little effect on the structure.Meanwhile,the time of the peak velocity of the surge wave increases gradually with the increase of the distance to blast center.究开发计划重点课题(2017G007-D、2017G008-J); 中国中铁股份有限公司科技研究开发计划重点课题(20192001)

In order to explore the interaction mechanism between the structure of different sizes and the bubbles,an underwater explosion experiment of 2.5 g TNT was carried out at the bottom 15cm of the fixed square plates with side lengths of 20 cm,40 cm and 70 cm.Through the observation of the experimental high-speed video and the pressure data measured by the sensor,it is found that when the size of the plate is too small,the bubble will contact with the air during the expansion process,and the bubble pulsation process will be terminated.In order to further explore the matching relationship between the explosion bubble and the target size,CEL algorithm in Abaqus software was used to establish the fixed square plate with Lagrange grid and the remaining part with Euler grid.The dynamic behavior and pressure data of the near-field underwater explosion bubble were numerically simulated.The feasibility of the simulation method is verified by comparing the simulation results with the bubble phenomenon captured in the experiment and the measured pressure time history curve.Taking the explosion depth divided by the maximum bubble radius as the specific depth and the side length of the board divided by the maximum bubble radius as the side length,a series of simulations were carried out with the side length of the board being 0.455 to 3.182 times the maximum theoretical bubble radius and the explosion distance being 0.455 to 1.136 times the maximum theoretical bubble radius.The simulation results show that with the decrease of plate size,the bubbles are more likely to collapse in advance.With dimensionless plate size and dimensionless explosion depth as variables,a boundary function is given to complete the bubble pulsation.The closer the distance between explosion distance and plate size,the earlier the end time of bubble pulsation.

In channel dredging engineering,the underwater drilling and blasting technology is often used for underwater reefs higher than the designed bottom elevation.However,after drilling and blasting,there are still some rocks that cannot be completely removed and irregular and unstable underwater shallow points remaining.In actual construction,emulsified explosive is often used to remove such isolated stones.Compared with drilling and blasting,adobe blasting has small contact surface between explosive and rock face,large amount of explosive,low energy utilization rate,high explosive consumption,large noise and water shock wave,affecting ecological environment and so on.In order to analyze the influencing factors of shallow blasting,field monitoring research was carried out to compare the adobe blasting underwater and the drilling & blasting method.Under the same effect,the water hammer wave and seismic wave data of CO2 adobe blasting,drilling CO2 gas blasting and drilling emulsion explosive blasting were obtained.In this paper,taking the foundation groove,berthing excavation,reef blasting and reef clearing project of 18#~22# berth wharf in Fangchenggang as examples,the arrangement and amount of charge are formulated according to the property of rock strata,rock formation,water depth and shallow point thickness of the blasted rock top.The results show that the overpressure of CO2 adobe explosion is 1.87~41.9 times that of CO2 drilling gas explosion under the same cylinder condition.The overpressure of underwater drilling emulsion explosive blasting is 7.9~18.7 times of the water shock wave of CO2 drilling gas explosion,and the vibration value is 3~10 times of the latter.Based on the research on the propagation law of underwater blast wave,this paper comprehensively analyzes the harmful effect of underwater shock wave.市重点研发计划(防科AB21014001、防科AB20014013); 广西交通运输行业重点科技项目(桂交便函〔2022〕174号)

In order to solve the existing problems in the explosive welding technology of clad metal plate,such as low utilization rate of explosive energy,environment harm and potential safety hazard,a simple closed explosive charging process,namely a production method of energy-saving explosive welding of clad metal plate,was designed.More precisely,an isolation plate with a thickness about 2 mm was placed on the surface of ordinary explosive,and a 10~12 mm height emery sands layer was laid on the isolation plate.Then,experimental research was conducted to verify the difference of the mechanical properties between the energy-saving explosive welding and the ordinary explosive welding.Non-destructive testing and mechanical properties tests showed that the interface binding strength,binding rate and mechanical properties of clad metal plates produced by the energy-saving explosive welding technology could meet or exceed the technical requirements of the national standard GB/T 8165 and industry standard NB/T 47002.The new method of covering something on the explosive surface can achieve the purpose of saving 1/3 energy compared with the ordinary explosive welding process.And even under the condition of reducing the explosive consumption by 30%,the mechanical performance index of the clad metal is still higher than the national and industrial standards.The experimental results show that the mechanical properties of the clad metal produced by the energy-saving explosive welding process and ordinary explosive welding process are almost the same,which can meet the needs of large-scale chemical equipment manufacturing field.Therefore,the production process of clad metal plate by the method of energy-saving explosive welding is simple,efficient,safe and reliable, and the purpose of saving energy as well as reducing consumption is realized.

Due to the influence of complex environment of tunnel blasting and the electromagnetic interference of instruments,the measured blasting vibration signals mostly contain high-frequency noise,which makes it ineffective to analyze related laws by the raw blasting vibration data.In order to obtain the real blasting vibration characteristics,a signal smoothing and noise reduction model based on the optimal variational mode decomposition(OVMD) and the multi-scale permutation entropy(MPE) is adopted,which is verified by the simulated superposition signals and measured signals.Firstly,the signal is decomposed by OVMD to obtain the band-limited intrinsic mode functions(BIMF).Then,the high-frequency BIMFs larger than the threshold set by MPE are removed as noise.Finally,the remaining BIMFs components are reconstructed to obtain the noise-reduced signal.The results show that the OVMD-MPE model can accurately identify the signal frequency information,and the first two order components can effectively reflect the effective contents of the superimposed signal,which is suitable for high-precision data analysis and feature extraction.Compared with EEMD-MPE and CEEMDAN-MPE models,the OVMD-MPE model has better noise reduction performance.The noise reduction error ratio,root mean square error and smoothness are increased by 22.05%,48% and 33.34%,respectively.The denoised curve is closer to the original signal and is more suitable for blasting signal analysis with different source distances.The blasting vibration signals measured during the construction of the right line of Shuangzishan Tunnel are concentrated in the middle and the low frequency bands below 200 Hz.The natural frequency of the lining structure is similar to the main frequency of the blasting signal,which means shock absorption measures need to be taken to ensure the construction safety of the tunnel project.

In order to improve the analysis accuracy of loosening blasting vibration signals,a hybrid denoising method based on local mean decomposition(LMD),multiscale fuzzy entropy(MFE),and singular value filtering(SVD) was established.Firstly,the vibration signal was decomposed by LMD method to obtain a series of product components(PF).Then,the blasting vibration signal was preliminarily denoised by calculating MFE and correlation coefficients.Finally,the real signal components were denoised and extracted by SVD filtering on the residual noise of the main PF components.The results show that the proposed LMD-MFE-SVD denoising method can effectively deal with the noisy PF components.For the simulated signal with multiple components with noise,the LMD algorithm is more efficient than the EMD algorithm.Furthermore,the signal-to-noise ratio(SNR),root mean square error(RMSE) and percentage of distortion(PRD) of the proposed LMD-MFE-SVD method are significantly improved by 11.73%,22.07% and 9.25%,respectively,compared with the LMD algorithm,which indicates that the noise reduction efficiency is considerable.According to the waveform and spectrum comparison of the measured loosening blasting vibration signal after denoising by the proposed LMD-MFE-SVD method,the denoised signal waveform is more concentrated with most of the signal information retained.The frequency spectrum is clearer,and the signal frequency peaks are effectively displayed.

Distortion phenomenon would occur in time-frequency analysis when Hilbert-Huang Transform(HHT) is used to process the blasting seismic signal mixed with noise.In order to improve the analysis performance for noisy blasting seismic signals,the factors affecting the accuracy of time-frequency analysis of HHT were improved through an improved algorithm.Firstly,the empirical mode decomposition(EMD) was improved by the complete ensemble empirical mode decomposition with adaptive noise(CEEMDAN) to suppress the low-frequency trend terms.Furthermore,the multiscale permutation entropy(MPE) code was added to control the high-frequency noise.Finally,the normalized Hilbert transform(NHT) was performed on the IMFs obtained by CEEMDAN·MPE.Through the above three steps,the problem of insufficient precision in the time-frequency analysis of noisy blasting seismic signals by the traditional HHT can be improved.In order to verify the accuracy of the CEEMDAN·MPE-NHT algorithm,a comparative study on the HHT and CEEMDAN·MPE-NHT algorithm was carried out,and the CEEMDAN·MPE-NHT algorithm was used for underwater drilling blasting seismic signals.The results show that the time-frequency spectrum of the IMF decomposed by CEEMDAN·MPE and processed by NHT has a greatly improved high resolution compared with HHT in both time and frequency domain.The research results can be used for identifying and controlling the hazards of blasting seismic waves.

The slope stability is bound to be affected in the blasting process of open-pit mine,especially when the slope is in the karst area.In order to study the influence of karst on slope stability under blasting and based on Tangya limestone mine slope project,this paper takes the exposed karst at the 1014 m platform of the mine as the research object,and uses ANSYS/LS-DYNA finite element analysis software to conduct numerical simulation.Considering the effect of blasting vibration,the stress distribution of the surrounding rock is obtained,and the effects of blasting on slope stress,vibration velocity,rock damage and effective stress of slope with or without karst cave are compared.The results show that the force of the bench changes and stress concentration occurs for several times due to the existence of karst caves,but the stress value generated by the bench loads is only 7.6 MPa,which still cannot reach the degree of rock mass destruction.For monitoring points at different spatial locations,the difference of vibration velocity becomes larger due to the existence of karst caves,and the vibration velocity in the vertical direction changes more than that in the horizontal direction.In particular,the spatial locations of the monitoring points near the slope edge are more sensitive to this situation.The vibration velocity difference of the monitoring points on the slope edge is about 1 cm/s at most,which does not exceed the allowable vibration velocity.In the process of increasing blasting times,the damage inside the rock mass is also gradually increasing,and the damage is more obvious under the influence of karst caves.The larger the radius of karst area,the more blasting times,the more serious the damage.Compared with previous uniaxial compressive strength experiments,it is found that although the existence of karst caves will cause the change of stress value and stress concentration phenomenon,the peak effective stress generated is far lower than the uniaxial compressive strength of rock mass.In view of the influence of blasting process on slope stability,the support treatment measures of slope in karst area are put forward.

To explore the destructive forms of bridge damage caused by explosions of hazardous materials in vehicles and the distribution of explosion load pressures on the bridge deck,a refined numerical model was established using AUTODYN software.The study analyzed the regional distribution characteristics of the bridge load pressure field under various explosion conditions with different shapes and sizes of steel plates,and determined the critical dimensions at which the steel plates play a blocking role against shock waves.In response to the challenges of conducting bridge explosion experiments,which involve high risks and large expenses,the research referred to a detailed inspection report of a real bridge after an explosion accident and inferred its explosion damage process.Based on the least squares method,a polynomial curve fitting was applied to numerous of numerical calculation results,and the traditional calculation formula for explosion shock wave pressure in the free air domain was modified.A prediction formula for the peak overpressure on the bridge deck under the explosive effects from the vehicle-borne cargo,taking into account the blocking of carriage steel plates,was proposed.The load pressure distribution calculated by this formula corresponded well to the damaged areas on the bridge deck as reported in the real bridge inspection report.

Experiments of vented explosion were conducted in a 1 m3 vessel under the conditions of top ignition for premixed methane-air gas with a concentration from 7% to 13% to investigate the influence law of methane concentration on flame evolution and internal overpressure during the vented explosion process.The explosion venting mechanism was analyzed by analyzing the pressure-time curve and the flame evolution image.The results prove that concentration has a significant impact on the explosion venting characteristics of the methane-air premixed gas.The overpressure inside the container presents a double-peak phenomenon with a specific methane concentration.The first pressure peak P1 can appear at each concentration,while the second pressure peak P2 only occurs when the concentration is 9 %.P1 increases first and then decreases with the increase of concentration,while the trend of the timing of the peak is the opposite.However,both reach the extreme value at the methane concentration of 10%.This is mainly formed by the combined effects of initial flame propagation,external explosion,Helmholtz oscillation and Taylor instability,etc.The phenomenon that P2 is much higher than P1 is mainly formed by the mutual promotion of flame and sound pressure and the thermoacoustic coupling effect triggered by disturbance.The flame downward propagation velocity increases first and then decreases with the concentration,and reaches the maximum value when the methane concentration is 10%,and the combustion velocity is generally faster in the slightly rich combustion state.

In order to study the protective performance of minesweeper protective equipment on the chest and abdomen under the action of explosion shock wave,it is necessary to explore efficient test methods to improve the experimental research index system and overall performance of individual soldier protective equipment.In this paper,two sets of minesweeper protective equipment were taken as experimental research objects,and the real explosion test of minesweeper EOD operators for typical kneeling posture was designed based on Hybird III dummy model under different sealing conditions.The shock wave was generated by the explosion of 50 g TNT charge column.Two wall overpressure sensors were installed in the chest and abdomen of the dummy model to measure the shock wave overpressure generated by four real explosion tests,and a free field pressure sensor was set at the same distance relative to the explosion source to compare the test data.Using the dummy data acquisition system,the whole process data of overpressure on the chest and abdomen after the shock wave penetration of the minesweeper protective equipment were obtained.Through data processing,the pressure-time curve of chest and abdomen subjected to explosion impact and the peak attenuation rate of overpressure were obtained and compared.The test results preliminarily verify that the better the sealing performance of the joint,the higher the protection performance,which indicates that the protective equipment with high sealing performance has a certain blocking attenuation effect on the diffraction of explosion shock wave,and can reduce the damage caused by superimposed overpressure to the chest and abdomen to a certain extent.The experimental design and data analysis in this paper can be used for further equipment performance improvement.