A Statistical Approach to Predict the Effect of Confinement on the Detonation Velocity of Commercial Explosives

Summary Commercial explosives behave non-ideally in rock blasting. A direct and convenient measure of non-ideality is the detonation velocity. In this study, an alternative model fitted to experimental unconfined detonation velocity data is proposed and the effect of confinement on the detonation velocity is modelled. Unconfined data of several explosives showing various levels of non-ideality were successfully modelled. The effect of confinement on detonation velocity was modelled empirically based on field detonation velocity measurements. Confined detonation velocity is a function of the ideal detonation velocity, unconfined detonation velocity at a given blasthole diameter and rock stiffness. For a given explosive and charge diameter, as confinement increases detonation velocity increases. The confinement model is implemented in a simple engineering based non-ideal detonation model. A number of simulations are carried out and analysed to predict the explosive performance parameters for the adopted blasting conditions.     

空气间隔装药爆破机理研究

利用爆轰波理论分析了空气间隔装药炮孔内一维不定常激波的相互作用及其在炮孔堵头、孔底的反射过程,同时分析了孔内各点的压力随时间的变化过程,介绍了空气间隔装药爆破的机理及设计参数。基于此,认为应充分利用空气间隔爆破结构的优势,并在梯段爆破中满足以下两个条件：（1）在设计过程中要尽量使稀疏波及从孔底反射的稀疏波传播过程能在整个孔内每一断面都作用到,即稀疏波到达孔底的时间要比从堵头反射的压力波到达孔底要早;（2）反射压力波应该到达空气与爆生气体接触面的时间比从孔底反射的稀疏波到达空气与爆生气体接触面的时间要早。由此通过计算得到了在梯段爆破工程中合理的空气层长度比例值约为30 %～42 %。计算结论与已有实测成果基本一致。     

An innovative priming system - emulsion-based booster

The mineral industry is leading towards a technology driven optimization process. Drilling and blasting are such unit operations in a mine, which can alter the balance sheet of the mine if not planned properly. The development, improvement and utilization of innovative technologies in terms of blast monitoring instruments and explosives technology are important for cost effectiveness and safety of mineral industries.

The ever-growing demand for minerals has compelled the industry to adopt large opencast projects using heavy equipment. This has necessitated use of a few hundred tonnes of explosives in each blast. The bulk delivered fourth generation explosives have solved the problem of explosive loading to a large extent as it provides improved safety in manufacturing, transportation and handling. Bulk delivered emulsion is non-explosive until gasification is complete and a large quantity of explosive can be transported and loaded into blast holes efficiently and with safety. The priming of bulk delivered explosives in Indian mines uses the conventional PETN/TNT-based boosters. The conventional booster possesses safety problems in terms of handling and use, so Indian Explosives Ltd has developed an emulsion-based booster (Powergel Boost).

This paper explores the potential of an emulsion-based booster used as a primer to initiate bulk delivered emulsion explosives used in mines. An attempt has been made at a comparative study between the conventional booster and the emulsion-based booster in terms of the initiation process developed and their capability of developing and maintaining a stable detonation process in the column explosives. The study has been conducted using a continuous velocity of detonation (VOD) measuring instrument, the VODMate two channel system manufactured by Instantel Inc. of Canada. During this study three blasts were monitored. In each blast two holes were selected for study, the first hole was initiated using a conventional booster while the other one used an emulsion-based booster. The findings of the study advocates that the emulsion-based booster is capable of the efficient priming of bulk delivered column explosive with a stable detonation process in the column.     

Influence of Gassing Agent and Density on Detonation Velocity of Bulk Emulsion Explosives

The demand for coal from surface mining projects are on the higher side like never before for which blasting is the basic unit operation. The explosive plays an important role in blasting and also influence the explosive-rock interaction. The most common explosive type used in surface mines is emulsion explosives. This paper presents the study on the detonation velocity of bulk emulsion explosives due to variation in gassing agent and density. In this study Sodium Nitrite (NaNO₂) has been used as the gas generating additive and the performance of emulsion explosives with different concentrations of gassing agents at different temperatures has been observed. This study was undertaken to also understand the cyclic variation of temperature on gassing kinetics and performance of explosive. The effect of cooling on detonic-behaviour of bulk emulsion explosives has also been studied and presented in this paper.     

Analysis of the Effect of Borehole Size on Explosive Energy Loss in Rock Blasting

In this paper, studies were conducted on the effect of borehole size on explosive energy loss in rock blasting. Since most industrial explosives are nonideal ones, the charge size and the confinement condition have significant impact on the detonation performance of these explosives. Analyses indicated that smaller boreholes will cause more loss of explosive energy than larger ones. This is especially true for most industrial explosives. The paper presents the analyses of energy loss for a number of different explosives with various borehole sizes. Based on these analyses recommendations and guidelines were given for borehole size determination in rock blasting operations.     

Finite element analysis of vibrations induced by propagating waves generated by tunnel blasting

Summary The excavation of underground tunnels close to existing substructures or the ground surface presents problems especially when blasting is being carried out. The high intensity waves which are generated and propagated through the rock medium, due to the detonation of explosives, may still have large amplitudes when they reach the ground surface. In order to study the vibration effects due to these propagating waves associated with blasting, a finite element simulation of tunnel blasting has been carried out in this paper.An example of a new tunnel excavated below an existing tunnel has been studied. Even though this problem is three dimensional in nature, due to the large computational efforts involved in three dimensional dynamic analysis, a two dimensional finite element analysis has been adopted. A pseudo-plane strain concept has been used since it has been found that the results obtained using such an approach are more realistic than the conventional plane strain analysis.It is concluded that results from such a numerical analysis could compliment the field investigations to produce guidelines for safe and controlled blasting.     

不耦合装药爆破对硬岩应力场影响的数值分析

爆破地震勘探石油是一种重要的方法,但爆破地震效应与爆破参数、地质条件等密切相关。采用动力有限元软件ANSYS/LS-DYNA,对柱状炸药与药孔壁之间为空气或其他介质以及空隙间距变化时碳酸盐岩岩石中爆炸应力波的传播规律和爆炸地震波能量的衰减特性进行了数值模拟研究,得到了不耦合装药爆炸时岩石应力、振动速度的衰减规律以及与不耦合系数、间隙介质的关系,分析了不耦合效应对爆炸地震波能量的影响。研究表明,不耦合或耦合不好时会使岩体中爆炸应力波的强度大大降低;耦合状态对岩体应力及速度的衰减系数和衰减指数影响较大;在空隙中注水或灌满泥浆会改善它们的耦合关系,增大下传的爆破能量。所得成果可为我国西南地区优选适合碳酸盐地层地震勘探的激发因素提供技术途径和方法。     

A Further Study on the Mechanism of Airdecking

Airdecking is used in mining for two quite different applications. One is to enhance the fragmentation by amplifying the induced fracturing and the second is for pre-split blasting in which the borehole fracturing is reduced. This paper deals with the first of these effects. A forth coming paper will describe pre-splitting by airdecking. The use of air decks to enhance rock fragmentation and so to reduce explosive costs has been the practice for quite long time. Although a number of studies has been conducted to verify the advantages of blasting with air decks and to investigate the mechanisms involved, the proposed mechanisms still cannot explain clearly the phenomena observed in practice and the design approach adopted for this kind of blasting is still primary based on rules-of-thumb. In this paper, the theory of shock tubes is adopted to (a) investigate the processes of the expanding detonation products, (b) study the interactions between the explosion products and the stemming or bottom of blasthole, and (c) to decide the distribution of the changing pressure of explosion products along blasthole. Numerical simulation and theoretical analyses are then performed to study the physical process of blasting with air decks. Finally, a reasonable value for the airdecking ratio is decided theoretically. It is shown that the pressure-unloading process caused by the propagation of the rarefaction wave and the reflected rarefaction waves in the detonation products plays an important role in the enhanced fragmentation of rock when blasting with air decks. The unloading process can induce tensile stresses of rather high magnitude in the rock mass surrounding blasthole. This favors fracturing of the rock. The reflected shock wave with a magnitude of gas pressure higher than that of the average detonation pressure in a fully charged blasthole acts as the main energy source to break the rock in the air deck and stemming portions. The second and succeeding strain waves induced by the unloading or reloading of the pressurewithin the blasthole also contribute to form the initial fracture network in the rock around the blasthole. It is also revealed that there exists a reasonable range of values for the airdecking ratio. For ANFO, this value varies from 0.13-0.40.     

Numerical Analyses of the Influence of Blast-Induced Damaged Rock Around Shallow Tunnels in Brittle Rock

Most of the railway tunnels in Sweden are shallow-seated (<20 m of rock cover) and are located in hard brittle rock masses. The majority of these tunnels are excavated by drilling and blasting, which, consequently, result in the development of a blast-induced damaged zone around the tunnel boundary. Theoretically, the presence of this zone, with its reduced strength and stiffness, will affect the overall performance of the tunnel, as well as its construction and maintenance. The Swedish Railroad Administration, therefore, uses a set of guidelines based on peak particle velocity models and perimeter blasting to regulate the extent of damage due to blasting. However, the real effects of the damage caused by blasting around a shallow tunnel and their criticality to the overall performance of the tunnel are yet to be quantified and, therefore, remain the subject of research and investigation. This paper presents a numerical parametric study of blast-induced damage in rock. By varying the strength and stiffness of the blast-induced damaged zone and other relevant parameters, the near-field rock mass response was evaluated in terms of the effects on induced boundary stresses and ground deformation. The continuum method of numerical analysis was used. The input parameters, particularly those relating to strength and stiffness, were estimated using a systematic approach related to the fact that, at shallow depths, the stress and geologic conditions may be highly anisotropic. Due to the lack of data on the post-failure characteristics of the rock mass, the traditional Mohr–Coulomb yield criterion was assumed and used. The results clearly indicate that, as expected, the presence of the blast-induced damage zone does affect the behaviour of the boundary stresses and ground deformation. Potential failure types occurring around the tunnel boundary and their mechanisms have also been identified.     

Blasting: Another environmental woe

The much increased use of explosives to move and extract rock masses in construction and mining over the past two decades has resulted in a plethora of complaints from the general public in areas of close proximity to public facilities, communication, and transportation systems. Air blasts and ground vibrations caused by explosive detonation can have desultory and damaging effects to public and private property, impose adverse effects on underground mining operations, and change the course of flow or effect the availability of surface and groundwater.Attempts to prevent damage and alleviate problems from blasting have been initiated by the federal and state governments by the promulgation of rules and regulations to prevent against vagrant and negligent blasting procedures. The Office of Surface Mining, Reclamation and Enforcement (OSMRE) provided regulations in the Federal Register on March 8, 1983, with particular reference to surface mining practices. Most of the states have adopted the OSMRE guidelines to enforce these rules and regulations.This article refers to surface mine blasting within the State of Alabama and describes some of the research efforts conducted by The University of Alabama, Department of Mineral Engineering, Tuscaloosa, Alabama, over the past several years. The article does not provide answers to the environmental problems caused by blasting but describes research activities in the past and present time frames. Although restricted to Alabama, the problem is worldwide.     

大型基坑内支撑体系爆破拆除技术

阐述了采用控制爆破技术在复杂环境下拆除大型基坑内钢筋混凝土支撑的方法。在特殊的环境条件下进行支撑爆破时,采用预先切断振源、减少单段起爆药量的防震方法以及搭建防护棚的方法,可以有效控制爆破振动、飞石、扬尘对周围的影响。实践证明,采用控制爆破技术拆除大型基坑内钢筋混凝土支撑是安全、高效的。     

Quantitative Assessment of Extrinsic Damage in Rock Materials

Summary   Comminution (crushing and grinding) of rock materials is energy-intensive and expensive. Much effort has been directed to improve the efficiency of conventional milling practice, but relatively little attention has been given to the potential benefits of blast-induced (extrinsic) damage on comminution processes. The objective of this research is to investigate the effect of shock-induced “crack-like” damage on rock properties for three petrologically distinct rock materials under laboratory conditions. In order to evaluate the effect of shock-induced damage, a quantitative measure of rock damage is needed. Shock loading of rock material was accomplished with an explosively driven split Hopkinson pressure bar. Laboratory measurements show that the average uniaxial compressive strengths for damaged specimens are slightly lower than those for intact specimens. Based on damage mechanics, the scalar damage variable () was experimentally determined as the relative reduction in ultrasonic wave velocity of damaged versus intact rock. increases as the shock energy dissipated in rock material increases. A crack density was determined by confocal image analysis. Measurements following shock loading indicate that ultrasonic wave velocity in rock partially recovers with time. Ultrasonic wave velocity and confocal image analysis may be useful in quantitatively assessing the internal crack-like damage in rock materials.     

节理岩体爆破的DDA方法模拟

在非连续变形分析（DDA）方法中,通过跟踪炮孔扩张和炮孔周边裂隙的发展贯通求得爆腔的即时体积,进而根据爆生压力状态方程计算爆腔即时压力,并将爆生压力载荷作用到主炮孔内壁和贯通裂隙面上,实现了爆生产物作用下节理岩体爆破的DDA方法模拟。采用DDA方法模拟了节理岩体中的水平柱状炮孔抛掷爆破问题,得到了爆腔的体积扩张和压力衰减时间曲线,模拟很好的再现了岩石爆破过程中的炮孔扩张、岩体破坏、块体抛掷和爆堆形成过程。     

Two-dimensional dynamic finite element simulation of rock blasting

In the present study, the two-dimensional blast model has been simulated using finite element software Abaqus/CAE. The John–Wilkins–Lee equation of state has been used to calculate the pressure caused by the release of the chemical energy of the explosive. Detonation point from center of hole has been defined for the traveling path of explosive energy. Elastoplastic dynamic failure constitutive with kinematic hardening model was adopted for rock mass responses under high explosive pressure to understand the mechanism of blast phenomena. In this model, it is assumed that failure of rock occurs under tensile failure when yield plastic stress exceeded to its static tensile strength. The hydrostatic pressure was used as a failure measure to model dynamic spall or a pressure cut off. Variation of detonation velocity has been measured in terms of simulation blast output energies index results.     

深孔爆破装药结构优选数值分析方法及其应用

针对地下深孔爆破采矿过程中常出现的爆破后冲作用严重以及爆破块度不均匀等若干问题,以南方某铅锌矿实际采用的爆破、炸药和岩石参数为基础,采用ANSYS/LS-DYNA对矿山拟采用的不同装药量、不同耦合系数的6种装药结构建立了数值计算模型。通过分析爆炸仿真过程中的Von Mises有效应力信息,结合爆破破岩机制及Mises屈服理论,确定了深孔爆破的最佳炮孔装药结构。现场试验表明,优化的装药结构爆破块度均匀且爆破后冲作用得到有效控制,基本上解决了矿山深孔侧向爆破存在的问题,研究结果为深孔爆破的优化设计提供理论依据和技术支持。     

浅埋大跨隧道施工爆破监测与减震技术

以沪-蓉线庙垭分岔隧道工程为背景,研究了其浅埋大跨段掘进爆破的地表震动效应及大断面开挖减震控制技术,并结合爆破监测数据的回归分析,确立了地震波垂向衰减规律的数学模型。综合分析地表及洞内地震波的震动特性发现,地表质点振动主振频率主要集中在低频段;由于表土的滤波作用,主振频率随距离的增加而减小的趋势并不明显;洞内混凝土衬砌减弱了爆破对围岩的冲击,高频地震波衰减极快;开挖区上部的地表振速通常大于未开挖区的振速,浅埋大跨隧道爆破安全控制应以已开挖区顶部的地表振速为准。     

基于声速变化的岩体爆破累积损伤效应

声速变化是表征损伤变量的有效参数。为揭示岩体爆破累积损伤效应及损伤演化规律,在某地下工程中开展了反复爆破作用下围岩损伤的声波测试,并对测试数据进行了回归分析。在此基础上,分析了多次爆破作用下岩体损伤与声速变化的对应关系,建立了以岩体声速降低率为基准量的岩体爆破累积损伤扩展模型。研究表明：（1）回归分析的相关系数大于0.981 6,说明岩体爆破损伤非线性累积回归预测模型是正确的;（2）岩体爆破累积损伤模型将岩体损伤总量定义为初始损伤和爆破损伤之和,综合考虑了爆破损伤累积效应和岩体初始损伤的影响,能够真实反映岩体损伤程度,是合理可行的。     

P and S Mach Waves Generated by the Detonation of a Cylindrical Explosive Charge - Experiments and Simulations

During blasting operations in a competent rock mass without open joints or faults, the structure of the wave fields generated by the detonation of a cylindrical charge depends mainly on the relation between the velocity of detonation ( c d ) and the velocity of the P and S waves, c P and c S , respectively, in the medium. If c d is larger than c P , detonation is supersonic and Mach P and S waves appear. If c d is between c P and c S , detonation is transonic, and only an S Mach wave is generated. If c d is less than c S , subsonic detonation occurs. In this paper, we describe an experiment conducted at the Andina mine (Chile) in order to demonstrate the differences between the wave fields generated by supersonic and transonic detonation. We also present a simulation of the detonation of a cylindrical charge using the finite differences Itasca software FLAC3.4. In particular, we show how important it is to secure a good adjustment of the rheological behaviour of the medium, in our case, a strain softening elasto-plastic model.     

某水电站聚碴坑高边墙稳定分析和加固措施研究

受大药量岩塞爆破时爆破强烈震动和强震时水压力、高速水流作用下的岩塞聚碴坑高边墙围岩稳定问题显得十分突出。在研究边墙围岩的软弱结构面的物理力学特征及其组合形式与边墙的交割关系的基础上，充分考虑皮震动荷载影响因素，选择滑体单位宽度，按视倾向下滑，应用岩体力学和工程力学的有关理论进行稳定分析计算和锚索锚固计算的研究方法，经运行实践证明是可行的。     

Comparative study of analytical and numerical evaluation of the dynamic response of buried pipelines to road-cut excavation blasting

ABSTRACT

This study develops a mathematical model of buried pipelines subjected to surface blast loading based on the theory of beam on elastic foundation. The Fourier transform, a mathematical formula that converts the time domain of the problem to the frequency domain, was used in order to solve a fourth-order non-homogeneous partial differential equation. Transforming the solution back to the time domain, the blast-induced Peak Particle Velocity (PPV) of the pipeline can be calculated. In addition to the mathematical model, a three-dimensional finite element model has been established, thereby drawing a comparison between analytical and numerical results. It can be concluded that the analytically calculated PPV values are found to be higher than the corresponding numerical values. Lastly, the safe distance from the pipeline to blast source and the maximum allowable ANFO explosive weight for two types of rock have been presented in the form of graphs by imposing a limit of 50 mm/s for PPV. This comparative study has investigated the effect of road-cut excavation blasting on pipelines buried under only two types of rock mass. However, it can be used for different types of rock and explosives, mainly thanks to the comprehensiveness of the analytical solution.