Effect of Blasting Stress Wave on Dynamic Crack Propagation

Stress waves affect the stress field at the crack tip and dominate the dynamic crack propagation.Therefore,evaluating the influence of blasting stress waves on the crack propagation behavior and the mechanical characteristics of crack propagation is of great significance for engineering blasting.In this study,ANSYS/LS-DYNA was used for blasting numerical simulation,in which the propagation characteristics of blasting stress waves and stress field distribution at the crack tip were closely observed.Moreover,ABAQUS was applied for simulating the crack propagation path and calculating dynamic stress intensity factors(DSIFs).The universal function was calculated by the fractalmethod.The results show that:the compressive wave causes the crack to close and the reflected tensile wave drives the crack to initiate and propagate,and failure mode is mainly tensile failure.The crack propagation velocity varies with time,which increases at first and then decreases,and the crack arrest occurs due to the attenuation of stress waves and dissipation of the blasting energy.In addition,crack arrest toughness is smaller than the crack initiation toughness,applied pressure waveforms(such as the peak pressure,duration,waveforms,wavelengths and loading rates)have a great influence on DSIFs.It is conducive to our deep understanding or the study of blasting stress waves dominated fracture,suggesting a broad reference for the further development of rock blasting in engineering practice.

Assessing the range of blasting-induced cracks in the surrounding rock of deeply buried tunnels based on the unified strength theory

Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse,posing significant safety risks.However,previous theoretical studies on the range of blasting-induced cracks often ignore the impact of the in-situ stress,especially that of the intermediate principal stress.The particle displacement−crack radius relationship was established in this paper by utilizing the blasthole cavity expansion equation,and theoretical analytical formulas of the stress−displacement relationship and the crack radius were derived with unified strength theory to accurately assess the range of cracks in deep surrounding rock under a blasting load.Parameter analysis showed that the crushing zone size was positively correlated with in-situ stress,intermediate principal stress,and detonation pressure,whereas negatively correlated with Poisson ratio and decoupling coefficient.The dilatancy angle-crushing zone size relationship exhibited nonmonotonic behavior.The relationships in the crushing zone and the fracture zone exhibited opposite trends under the influence of only in-situ stress or intermediate principal stress.As the in-situ stress increased from 0 to 70 MPa,the rate of change in the crack range and the attenuation rate of the peak vibration velocity gradually slowed.

EXPERIMENTAL STUDY OF MECHANISM AND TECHNOLOGY OF DIRECTED CRACK BLASTING

The dynamic stress-fields and their distribution characteristics around boreholes in the directed crack blasting were measured with the dynamic photo-elastic laser holography apparatus and the ultradymamic measurement system. The directed crack mechanism and its mechanical model have been analysed and expounded. Through the 43 production experiments using slotted cartridges and the double triangle center cut-holes for directed crack blasting in underground rock drift, the results of which the rates of half-hole marks and efficiency of borehole,and the nonsmooth grades of the cut contours are 96%, 98% and 10cm respectively have been achieved.

Propagation and Coalescence of Blast-Induced Cracks in PMMA Material Containing an Empty Circular Hole Under Delayed Ignition Blasting Load by Using the Dynamic Caustic Method

In this paper,dynamic caustic method is applied to analyze the blast-induced crack propagation and distribution of the dynamic stress field around an empty circular hole in polymethyl methacrylate(PMMA)material under delayed ignition blasting loads.The following experimental results are obtained.(1)In directional-fracture-controlled blasting,the dynamic stress intensity factors(DSIFs)and the propagation paths of the blast-induced cracks are obviously influenced by the delayed ignition.(2) The circular hole situated between the two boreholes poses a strong guiding effect on the coelesence of the cracks,causing them to propagate towards each other when cracks are reaching the circular hole area.(3)Blast-induced cracks are not initiated preferentially because of the superimposed effect from the explosive stress waves on the cracking area.(4) By using the scanning electron microscopy(SEM)method,it is verified that the roughness of crack surfaces changes along the crack propagation paths.

Rock-breaking mechanism and experimental analysis of confined blasting of borehole surrounding rock

The rock-breaking mechanism and effect of confined blasting were analysed by blasting and impact dynamic mechanics, fluid dynamic mechanics, fracture mechanics as well as blasting experiment. The results showed that the fracturing of surrounding rock in confined blasting condition is the result of coaction of rock pre-cracking by shock wave and stress wave and the continuing expanding crackenhancement of confined medium, and the model of crack development of borehole surrounding rock in confined blasting condition was established. This study acquired the damage range of surrounding rock under the action of shock wave and stress wave, as well as the crack development characteristics of surrounding rock after the wedge-in confined medium into the crack space. Deep-hole confined blasting experiment on large rock showed that the high-efficient utilisation of in-hole explosive was achieved and the safety of rock blasting operation was ensured. Safe static rock-breaking under the action of high-efficient explosive blasting was achieved as well as the unification of super dynamic load of explosive blasting and static rock-breaking of water medium.

Research progress of the fundamental theory and technology of rock blasting

Investigating rock fragmentation mechanisms under blasting and developing new blasting technologies are important and challenging directions for blast engineering.Recently,with the development of experimental techniques,the fundamental theory of rock blasting has been extensively studied in the past few decades and has made important achievements in the full understanding of the rock fracturing process under blast loading.It is thus imperative to systematically review the progress in this direction.This paper mainly focuses on the experimental study of rock blasting,including the distribution characteristic of blast energy,evolution of the blast stress field,propagation mechanism of cracks,interaction mechanism between blast waves and cracks,and influence of geostatic stress on rock fragmentation.In addition,some newly developed blasting technologies and their applications are briefly presented.This review could provide comprehensive insights to guide the study on the rock fracturing mechanism under blasting and further provide meaningful guidance for optimizing blast parameters in engineering.

Influence of blasting load directions on tunnel stability in fractured rock mass

Tunnels in fractured rock masses are typically damaged by dynamic disturbances from various directions.To investigate the influence of blasting load directions on the stability of a tunnel with a precrack nearby,blasting tests were conducted on the physical models of an external crack around a tunnel(ECT)in this study.Failure modes of the tunnels were analysed based on stress wave theory.The Riedel-Hiermaier-Thoma(RHT)material model was employed to perform the numerical simulations on ECT models.Stress distribution around the tunnels and final failure patterns of the tunnels were characterised.The results show that,under blasting loads,the pre-crack propagates and then new cracks initiates on the incident side of the tunnel.These cracks extend towards each other and eventually coalesce.Blasting load directions significantly influence the ultimate failure mode of the tunnel in the fractured rock masses.The new cracks on the shadow side of the tunnel appear at different positions when the blasting stress waves come from various directions.The results are meaningful to the analysis of tunnel stability and optimisation of the tunnel support scheme.

Effects of Rock Mass Conditions and Blasting Standard on Fragmentation Size at Limestone Quarries

The size distribution of fragmented rocks depends on not only the blasting standard but also the mechanical properties, joint system and crack density of rock mass. As, especially, the cracks in the rock mass are heavily developed at the limestone quarries in Japan, the joints and/or cracks in the rock mass have big impacts on the blasting effects such as the size of fragmented rocks. Therefore, if the joint system and/or crack density in the rock mass can be known and evaluated in quantity, the blasting operation can be done more effectively, efficiency and safety. However, the guideline for designing the appropriate blasting standard based on the rock mass condition such as mechanical properties, joint system and/or distribution of cracks, discontinuities, from the scientific point of view, has not been developed yet. Therefore, a series of blasting tests had been conducted in different mines and faces, geological conditions and blasting standards in order to know the impacts of each factor on the blasting effects. This paper summarizes the results of blasting tests and describes the impacts of rock mass conditions and blasting standard on the size of fragmented rocks.

THE DISTANCE BETWEEN BOREHOLES OF SMOOTH BLASTING BY WATER COUPLING

The stress strength factor, length and opening degree of cracks around boreholes as well as movement regularity Of blockage with the smooth blasting by water coupling are calculated out according to the theories of fracture mechanics and explosion dynamics, and the relation between the pressure in holes and the change of hoIe volume is pointed out, thereby the distance between boreholes is worked out in this paper. For limestone, when uncoupling coefficient is 3,diameter of holes is 100 mm, the hole distance of water coupling smooth blasting is 2. 3 m. The result is consistent with practice.

二氧化碳相变爆破致裂机理与应用研究进展

煤岩体结构改造是解决煤矿许多技术难题的共性核心科学问题,二氧化碳相变爆破因其安全可控、能量易调节等优点成为煤岩体致裂的有效手段之一。为确定二氧化碳相变爆破致裂机理,扩展相变爆破致裂工程应用,分析了二氧化碳相变爆破原理和致裂器材与装备,统计比较不同方式相变爆破能量计算方式,相较于传统炸药爆破,相变爆破属于一种低能量致裂方式;通过分析二氧化碳相变射流传播特征,探究相变爆破中等应力起裂和高压气体协同作用方式,煤岩体在中等冲击作用下,受到拉应力破坏产生径向初始断裂,并在冲击波和卸载波综合作用下形成多重起裂特征,高压气体在多重裂隙中进一步扩展,驱动裂隙向外扩展,明确了相变爆破应力气体协同致裂过程;进一步研究了泄能方向、煤岩体性质、爆破参数、初始地应力、钻孔布置参数和钻孔切槽特性等因素对相变爆破致裂效果的影响,泄能方向对煤岩体破坏起到直接作用,引发非对称损伤破坏,煤岩体抗压强度和致裂孔间距是影响致裂效果的关键因素,初始地应力、钻孔布置参数和钻孔切槽特性等影响裂纹发育扩展特征;在相变爆破致裂工程应用方面,揭示了相变爆破多重裂隙渗流特征,确定了高瓦斯煤层致裂增透效果,对比了预裂前后煤体截割特征,验证了预裂提升块煤率可行性,并探究了相变爆破预裂顶板垮落特性。针对相变爆破致裂应从多速率冲击破碎、损伤破坏多尺度分析、致裂过程多物理场耦合及延时相变爆破技术等方向进一步扩展研究,拓宽二氧化碳相变爆破应用场景。

炮孔间距对偏心不耦合装药贯通裂纹扩展的影响

为研究光面爆破中偏心不耦合装药炮孔间距对贯通裂纹扩展的影响,利用同心不耦合装药的孔壁压力计算公式并结合应力波叠加原理,推导偏心不耦合装药的炮孔间距计算方法。基于求得的炮孔间距范围,计算3种岩石介质在不同炮孔间距条件下贯通裂纹的扩展位置,并选择砂岩材料进行数值模拟。结果表明:偏心不耦合装药爆破中,贯通裂纹主要集中于偏心侧;抗拉强度大的岩石,贯通裂纹偏离炮孔连心线的程度也较大。砂岩的炮孔间距为60 cm时,贯通裂纹扩展方向与炮孔连心线重合,连心线下方出现裂纹比较集中的贯通区域;炮孔间距的增大导致贯通裂纹远离炮孔连心线,从而造成欠挖。偏心不耦合装药爆破后,偏心侧岩石的损伤明显大于非偏心侧。

高应力扇形中深孔采场边帮控制爆破参数优化

针对扇形孔采场爆破边帮控制问题,提出了一种将靠近边帮的扇形炮孔施工成垂直平行孔用以控制边帮的构想。首先,通过理论计算得到4组平行炮孔不耦合系数与炮孔间距匹配下的模型参数,使用LS-DYNA对4组参数进行数值模拟;然后,通过对比分析4组模型在无地应力作用和不同方向地应力作用时的爆破裂纹扩展情况,获得最优参数;最后基于优化参数开展工业试验。结果表明:高地应力会促进最大应力方向爆破裂纹扩展;4种模型中,不耦合系数为1.65,炮孔间距为1.1 m时开挖区域破岩效果最为合理;在试验采场开展工业试验,使用优化后的爆破参数进行爆破,采场回采后边帮平整,稳定性较好,验证了研究结论的正确性。

宽孔距爆破模型试验及近场动力学计算研究

针对宽孔距爆破破岩技术中炮孔密集系数合理取值的问题,在总结国内外宽孔距爆破破岩机理的基础上,开展了炮孔密集系数为1.7、2.5、3.5、4.5的有机玻璃板室内爆破试验,并基于常规态型近场动力学原理,开发了爆破计算模块,对宽孔距爆破破岩中裂纹扩展过程、介质位移响应规律进行了研究。结果表明:临空面一侧的径向裂纹受到临空面反射拉伸应力波的作用,表现出向临空面拐角分叉的特征,并逐渐向临空面扩展,最后形成主裂纹组成漏斗形状。在最小抵抗线固定不变条件下,随着炮孔密集系数的增加,应力降低区逐渐增大,同排炮孔间的径向贯通裂隙消失,过大的炮孔密集系数也进一步造成前后排孔间贯通裂纹消失,最后导致单孔爆破的情况发生。位移计算结果进一步证实了上述规律,并且当炮孔密集系数较小时,前排炮孔留下的岩埂刚好被后排炮孔爆破破碎,随着炮孔密集系数的增大,后排孔爆破对前排炮孔所留下的岩埂破碎作用效果逐渐降低。建议实际工程中根据岩体力学性质、地质条件以及爆破目的适当调整密集系数来降低炸药单耗与大块率。

水耦合爆破破岩的数值模拟研究

水耦合爆破因其节能、高效等优势在工程爆破中具有广阔的应用前景。利用数值模拟水耦合爆破破岩过程及最终破坏特征,与空气耦合爆破对比表明,水介质加快了岩体裂纹扩展速度,提高了岩体的破碎程度与范围;岩体中的初始裂纹与爆源交叉时,水增强了初始裂纹对破坏的导向作用;岩体中的初始裂纹与爆源无交叉时,闭合裂纹使爆炸破坏作用向弱面集中,水增强了闭合裂纹周围的岩体破碎效果。

露天矿山大孔径预裂爆破参数研究与应用

预裂爆破是控制边坡成形、降低爆破动载影响的重要手段。为研究炮孔直径203 mm预裂爆破最佳不耦合系数和炮孔间距,运用LS-DYNA数值软件建立以不耦合系数、炮孔间距为变量的数值模型,分析不同工况下炮孔周围的裂纹扩展和峰值应力强度。结果表明:在空气不耦合系数分别为2.53、2.90、3.38、4.06、5.07、6.77的6种工况中,不耦合系数为4.06时,爆炸能量的利用率最高、裂纹扩展良好,与理论公式推导相符;进一步建立空气不耦合系数为4.06,炮孔间距为1.5、2.0、2.5、3.0、3.5 m的5组模型,得到炮孔间距为2.5 m时满足孔间裂纹贯穿条件,符合现场工况要求;现场应用效果较好,为类似工程提供借鉴。

爆炸冲击波下地应力对岩石裂纹扩展的影响

随着地下工程深度的增加,地应力对爆炸引起的断裂影响不容忽视。为了探讨地应力大小和方向对岩体爆破的影响,文章以花岗岩为研究对象,通过有限元程序LS-DYNA和颗粒流程序(Particle Flow Code,PFC)相结合的爆破模拟方法研究了爆炸冲击波下地应力对岩石裂纹扩展的影响。结果表明:双轴等压应力对岩石近场裂纹的影响较小,而对远场裂纹发育有较大的抑制作用;单轴应力条件下,与应力垂直方向的压缩效应得到增强,而拉伸效应受到抑制,应力垂直方向的裂纹数量远小于平行方向的。

柱状聚能药管聚能罩角度对煤层爆破增透效果试验研究

为解决传统预裂爆破煤体裂隙无序扩展导致增透效果不佳的问题,开展了聚能爆破药管不同聚能罩张开角度对煤层增透效果影响研究。通过建立聚能罩微元闭合理论模型,分析了随着聚能罩角度减少时形成聚能射流的速度和质量变化;以此为基础对聚能爆破增透机制进行了分析。在实验室搭建了可从煤体宏观裂纹和应变数据多角度对试验模型进行分析的双向加载气固耦合爆破相似模拟试验系统,对含瓦斯煤体试块进行普通爆破和不同聚能张开角爆破模拟对比试验。结果表明,使用聚能药包相较于普通爆破能够有效引导裂纹在聚能罩开口方向上定向发育;随着聚能罩角度减少,聚能爆破后形成的裂纹在聚能方向上更加平滑,裂纹宽度也随之增加,试块剖面更加平整;根据超动态应变仪反演结果,1号测点60°、80°和100°聚能爆破的压应力峰值分别为普通爆破的1.52倍,1.26倍和1.08倍,且60°聚能爆破到达应力峰值的时间最短,表明随着聚能罩开口的减小,聚能方向上能量集中现象越明显。通过ANSYS/LS-DYNA软件对4种不同角度的聚能爆破进行对比分析。模拟结果中60°聚能爆破初始形成的聚能射流有效应力最大,聚能方向产生的裂纹最长。试验和模拟结果表明通过使用60°聚能药包可得到更好的爆破效果,研究成果对松软高瓦斯煤层聚能爆破增透有一定的参考意义。

爆破振动对边坡稳定性及建筑物开裂影响分析

八渡村移民安置点采用爆破方式进行场地平整,弄中屯房屋出现大量裂缝,分析爆破振动对弄中屯边坡稳定性和建筑物开裂影响非常必要。笔者基于实际工程,采取理论公式推导在爆破工况下边坡稳定性计算方法;运用大型有限元软件ANSYS模拟爆破振动,推导出建筑物安全允许振动速度的炸药量。结果表明:当移民安置点齐爆炸药量为350kg,边坡受到爆破振动力相当于地震烈度为7度时产生的地震水平力;移民安置点齐爆炸药量大于建筑物安全允许振动速度的炸药量时,房屋结构性裂缝由爆破引起。

大红山铜矿点柱预裂爆破损伤控制

地下矿山在采用房柱法或者房柱法嗣后充填采矿法开采的过程中,为保证采场的稳定性,往往会预留大部分的矿柱来支撑着上部岩体。目前采用的一些采矿方法在一定程度上会对矿柱的稳定性造成损伤,因此研究和预防矿柱损伤变得至关重要。通过对比大红山铜矿西矿段180中段360-B144采场常规点柱法回采与点柱边界预裂爆破法两个方案,对矿柱造成的损伤来研究矿柱的稳定性。结果表明,常规点柱法回采爆破对矿柱的损伤深度在1.47 m左右,而点柱边界预裂爆破对矿柱的损伤深度在1.21 m左右,点柱边界预裂爆破与常规点柱法回采爆破相比,对周边矿柱的损伤影响较小。点柱边界预裂爆破区矿柱岩体声速变化幅度为9.02%,小于常规点柱法回采爆破区矿柱岩体声速变化幅度14.65%。

球团配加钒钛磁铁精矿试验研究

为充分利用哈密地区钒钛磁铁精矿,进行了配加钒钛磁铁精矿球团试验及球团矿冶金性能试验。试验结果表明:钒钛精矿球团生球爆裂温度均大于600℃,可满足竖炉生产要求;与普通精矿相比,钒钛磁铁精矿需要更高的焙烧温度,本次试验将焙烧温度提高了50℃左右,但球团矿抗压强度仍略偏低;成品球团矿还原膨胀率在8.19%~12.09%;成品球团矿900℃还原度在54.50%~63.20%。