Blast-induced Damage Research Articles

Blast-Induced Damage Identification of Rock Mass using Wavelet Transform Analysis

The rock mass is usually damaged/fractured during the blasting. Quantitative investigation of the damaged depth is needed for stability of underground structures such as tunnels. This study deals with the blast-induced damage identification of rock mass using the surface wave method based on wavelet transformation. A series of site test were conducted on the granite rock walls for fresh and damaged zones. The damaged depth is determined by comparing the attenuation coefficients, which are obtained from the wavelet coefficients. The results indicate that wavelet transform analysis provides an easy method to evaluate the blast-induced damage in the rock mass.

Rock damage control in bedrock blasting excavation for a nuclear power plant

Drill and blast is a major method for bedrock excavation in nuclear power plant engineering. Under blasting excavation, blast-induced vibration propagates in rock mass and induces damage to surrounding rock. Studying the characteristics of wave propagation and blast-induced damage to rock mass is most important to restrict the damage extension. In the present paper, in support of the bedrock blasting excavation for the Linao Nuclear Power Plant project (LNPP), the site seismic survey and sonic wave test are presented to study the characteristics of wave propagation and the blast-induced damage for rock mass. The explosive load, rock damage characteristics and peak particle velocity (PPV) attenuation law are also investigated by numerical simulation using commercial software. It can be seen that the numerical simulation results agree well with that obtained by site monitoring. Based on the site monitoring and the numerical simulation, the relationship between PPV at 30 m away from the charge hole and the damage depth of rock mass is established. A simple method based on safety threshold of vibration velocity for rock mass to restrict the damage depth of rock mass under blasting excavation is presented. According to the damage controlled method and the presented safety threshold of vibration velocity for rock mass, the remained bedrock can be simply and effectively protected during blasting excavation.

Field Testing of Blast – Induced Ground Excitation due to Explosion in Rock Mass

Abstract This paper presents results of an experimental investigation to study the effect of blast wave propagation in rock mass due to explosions. The aim of this study is to observe the dynamic response of rock mass under blasting vibrations and the effect of different geological conditions of rock mass on the wave propagation of the explosion. A series of field experiments were conducted including different variables such as, charge weight, horizontal charge–target distance and target location below the ground surface. The main results show that the geological conditions of rock mass such as, joints, fractures, cracks and cavities have a direct effect on blast wave propagation and the value of pressure on rock mass due to explosion. The effect of rock joints on blast wave propagation can be used to assess the quality of rock mass and hence can be utilized to protect underground structures from blast-induced damage.

Blast Induced Damage Due to Repeated Vibrations in Jointed Gneiss Rock Formation

Blasting is the most common method of rock excavation technique in mining and civil construction and infrastructure projects. Rock blasting produces seismic waves similar to those produced by earthquakes, but with relatively high frequency and low amplitude. General blast induced damage was extensively studied by researchers globally, but the studies on damage due to repeated blast vibrations is not yet reported, quantitatively, on underground openings. This paper deals with the research work carried on the effect of repeated dynamic loading imparted on the jointed rock mass from subsequent blasts in the vicinity, on the jointed rock mass at Lohari Nag Pala Hydroelectric Power Construction Project. The blast induced damage was monitored by borehole extensometers, borehole camera inspection surveys and triaxial geophones installed at three test sites of different joint orientations at the Main Access Tunnel of power house. The study reveals that there was extra damage of 60%, exclusively due to repeated blast vibrations. The results of the study indicate that repeated dynamic loading, resulted in damage even at 33% of the conventional damage threshold vibrations (Vc) in case of favorable joint orientations and 23% of Vc in case of unfavorable joints. The paper concludes in quantification of effect of repeated blast loading and the orientation of joints on the extension of damage zone in jointed rock mass of underground excavations.

Stability analysis of the blast-induced damage zone by continuum and coupled continuum–discontinuum methods

The presence of a blast-induced damage zone (BIDZ) around a tunnel boundary is of significant concern mainly with regard to safety, stability, costs and the overall performance of the tunnel. The BIDZ is essentially characterized by reduction in strength and stiffness, and increase in permeability. Guidelines have been developed based on perimeter blasting experiences and overbreak characterization to regulate damage due to blasting. Although the over-break approach of assessing the degree of blast-induced damage is practical, the method does not provide a measure of the competency of the damaged rock. Very often it is important to know how the damaged rock mass will behave under any given conditions. In this paper a series of numerical analyses was performed using continuum and coupled continuum–discontinuum methods to study the behaviour of the blast-induced damage zone. In the coupled continuum–discontinuum method FLAC and PFC 2D were coupled together. The inner segment of the model was simulated using PFC 2D, while the outer segment was simulated using FLAC. This enabled the tracking of failure and fallout from the PFC 2D model. The tunnel was excavated within the PFC 2D segment. Blast-induced radial cracks were traced and individually implemented in the models. Models were also run independently in FLAC and Phase 2 and the results were compared to those of the coupled models. The results show that the failure around the tunnel was confined in most parts to the damaged zone at shallow depths, but not in deep excavations. The failures and fallouts mapped with the coupled models were consistent with practical observations. Since the continuum models cannot simulate failure, results from the coupled model were used to identify indicators for failure in the continuum models. It was seen that yielding due to volumetric straining (in FLAC) and 100% yielded elements (in Phase 2) were consistent with the failures mapped in the coupled models for shallow excavations, but was less consistent for deep excavations.

Learning from disaster to prevent progressive collapse

When the Alfred P. Murrah federal building in Oklahoma City was destroyed by a terrorist bomb in 1995, its progressive collapse compounded the blast damage and increased loss of life. Subsequent studies suggested ways that structural design changes might have improved the building's performance as well as that of other buildings subject to similar attacks. This paper reports on how the original structural design could be virtually ‘retrofitted’ to meet current codes for areas of high seismicity. Three different strengthening schemes are analysed for their responses to the 1995 blast, two of which substantially reduce the degree of blast-induced damage and subsequent progressive collapse.

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.

Impact of electronic blasting detonators on downstream operations of a quarry

In 2005, CANMET-MMSL used its pool of expertise in ground control, open pit and underground mine engineering, mineral processing, information technology and applied mineralogy to launch a mine-to-mill research project. The objective of the project was to optimize the distribution of rock breakage energy among blasting, crushing and grinding activities, thereby maximizing the efficiency of energy utilization within comminution processes. Tests were designed to demonstrate that this approach could reduce energy consumption, thus contributing to the reduction of green house gas (GHG) production in the Canadian mining industry. The project was accomplished in collaboration with DynoConsult and Dyno Nobel Canada Inc., a world leader in commercial explosives. Data analysis from 12 blasts (six with electronic and six with pyrotechnic detonators) in three different geological formations of a quarry (soft, medium and hard rock) shows that electronic blasting technology increases rock fragmentation by 15% (in hard rock) to 20% (in soft rock). A more uniform rock fragment size distribution is also obtained. The impact of the improved quality blast product on downstream processes of the quarry is a productivity increase of 5% in rock excavation and transportation, an energy reduction of 10% at the primary crusher and an increase of 15% of the primary crusher throughput. Extended to the Canadian mining industry, such results would represent a GHG emission reduction of about 0.05 Mt/y. A soft-sensor prototype, based on primary crusher data (i.e., energy consumption, throughput, feed and product size distribution) and a simplified computerized process model, was developed for on-line measurement of the rock operating work index. Additionally, 385 rock samples and specimens were collected and prepared to determine the tensile and compressive strength of the rock material, to evaluate the aggregate crushing work index and to examine the development of micro- and macro-fractures by means of binocular and SEM microscopy. Blast-induced rock damage was evaluated at the end of the laboratory-testing program. Even though a reduction of rock hardness of around 30% was observed after blasting, the impact of the blasting method (i.e., use of electronic or pyrotechnic detonators) on the induced rock damage could not be observed. It is either absent or not perceptible with the accuracy of the measuring techniques and the number of samples analyzed.

Numerical analysis of blast-induced wave propagation and spalling damage in a rock plate

The paper focuses on the numerical analysis of blast-induced stress wave propagation and related spalling damage in a rock plate or wall. Firstly, a large-scale contact explosion is simplified as a one-dimensional (1-D) strain problem, and a cross-format centered finite-difference scheme is presented. Secondly, the finite-difference code is used to explore the wave propagation in a rock plate, and compared with the commercial software LS-DYNA. Thirdly, a continuum damage constitutive model for rock is introduced and successfully incorporated into the LS-DYNA through its user-defined subroutine. Coupling with the erosion technique, the improved LS-DYNA is used to simulate the blast-induced spalling damage at the back-side of rock plate. Numerical results show that the 1-D finite difference code is convenient and accurate. Also, the user-defined subroutine can well describe the process of spalling damage.

A study on the dynamic behavior of the Meuse/Haute-Marne argillite

Excavation of underground tunnels can be conducted by tunnel boring machines (TBM) or drill-and-blast. TBMs cause minimum damage to excavation walls. Blasting effects on excavation walls depend on the care with which the blasting is executed. For blast-induced damage in excavation walls, two issues have to be addressed: rate of loss of confinement (rate of excavation) and dynamic loading from wave propagation that causes both intended and unintended damage. To address these two aspects, laboratory dynamic tests were conducted for the determination of the dynamic properties of the Meuse/Haute-Marne argillite. In the present study, 17 tensile (Brazilian) and 15 compression split Hopkinson pressure bar (SHPB) tests were conducted. The test revealed that the dynamic strengths of the argillite are strain rate dependent. The average dynamic increase factors (ratio of dynamic strength to static strength) for tensile and compressive strength are about 3.3 and 2.4, respectively. A high-speed video camera was used to visualize the initiation of failure and subsequent deformation of the specimens. The direct compression specimens were found to deform and fail uniformly around the circumference of the specimen, by a spalling process. The SHPB Brazilian tests indicated that failure occurred in tension along the line of load application. Radial fractures were also observed. The test results can be used for the development of a dynamic constitutive model for the argillite for the prediction of damage in underground excavation utilizing the drill-and blast method.

Blast-induced damage analysis in anisotropic rock condition

A numerical analysis is performed to investigate blast-induced anisotropic rock damage around a blast hole. For comparison, user-subroutines for isotropic as well as anisotropic rock damage models is coded based on continuum mechanics. Since natural rock usually includes initial rock damages, the influence of initial rock damage is also considered in the analysis. The results of this study show that the blasting pressure and the elastic modulus are major influential parameters on isotropic rock damage. However, anisotropic rock damage analysis reveals that the blasting pressure is the most influential parameter, and the influence of elastic modulus is relatively low. The comparison results also show that rock damage zone from anisotropic damage analysis is approximately 34% larger in horizontal direction and 12% smaller in vertical direction than that from isotropic damage analysis. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

A theoretical concept of structural dynamics to evaluate blast-induced damage on structures

The significant audible and inaudible parameters, in any excavation area, that give rise to complaints and damage to structures are air-overpressure and blast-induced ground vibration. A building can sustain high, safe levels of vibration, but the human response to the magnitude of vibration varies and depends on an acceptability limit. Moreover, from the structural point of view, the safe level of vibrational magnitude depends upon a building's shape and the quality of its construction. As the response spectrum can be correlated with structural strains, structural dynamics are preferred to Fourier frequency analysis to formulate a theoretical model for the determination of safe levels of blast-induced ground vibration for structures. A mathematical model is developed for determination of the natural frequency of structures together with a mathematical concept to explain possible causes of cracks in the interior and exterior plaster of walls.

Can Strengthening for Earthquake Improve Blast and Progressive Collapse Resistance?

Some engineers suggest that current seismic design provisions, both for new buildings and for strengthened existing buildings, can improve resistance to blast loads and progressive collapse. However, there have been few attempts to quantify such improvement. To begin analyzing this possible relationship between seismic detailing and blast and progressive collapse resistance, the Federal Emergency Management Agency of the Department of Homeland Security sponsored a study at the U.S. Army Engineer Research and Development Center. The study was an analysis of the Alfred P. Murrah Federal Building, which was severely damaged in a 1995 terrorist attack. The building was first evaluated for seismic vulnerabilities as if it were located in a seismically active region. Three strengthening schemes were then designed for the vulnerabilities found during the evaluation: a pier-spandrel system and a new special concrete moment frame, both for the street face of the building, and a set of internal shear walls. In addition to these strengthening schemes, the original ordinary concrete moment frame on the street face of the building was redetailed to bring it into compliance with current building code provisions, without including a lateral load analysis. The three strengthening schemes and redetailed frame were then analyzed for their responses to the same explosion that occurred in 1995. Blast and corresponding progressive collapse analyses showed that the pier-spandrel and special moment frame schemes, as well as the redetailed original system, reduced the degree of direct blast-induced damage and subsequent progressive collapse, compared with the behavior of the original building. Internal shear walls, however, were not as effective in reducing the blast and progressive collapse damage. A key finding of the study was that strengthening the perimeter elements using current seismic detailing techniques improved the survivability of the building, while strengthening elements internal to the building envelope was not nearly as effective in reducing damage.

Field Investigation of Blast-Induced Damage of the Sedimentary Strata Rock Mass at PT Kaltim Prima Coal, Indonesia

Field Investigation of Blast-Induced Damage of the Sedimentary Strata Rock Mass at PT Kaltim Prima Coal, Indonesia

Blasting technologies for tunnelling and underground construction

The methods of forming excavations, tunnels or underground chambers in rock rely on either blasting or mechanical boring machines. In both cases, the aim is to create the excavation rapidly while ensuring the remaining rock incurs minimum damage in terms of its ability to maintain the desired excavation shape, but also to restrict the extent of support requirements. Advances in the technology of mechanical excavation methods have developed in tandem with various aspects of material science and mechanical design of machine components. Advances have also occurred in blasting technologies which sometimes go unnoticed. The present paper elaborates on blasting technologies that deliver significant benefits in hard rock excavations. In particular, the advent of new, purpose-designed explosives and loading systems have demonstrated benefits in logistics, fume control, safety, fragmentation and blast-induced damage control. Explosives are now loaded in blastholes using sophisticated remote control techniques which keep operators away from regions of potential concern. Once the explosives are loaded, revolutionary electronic delay detonator systems provide unique opportunities to release the explosive energy in a controlled and engineered manner. Such approaches have the potential to yield lower blast-induced damage, lower ground vibrations - either through extended timing approaches or in spectral content control, and improved excavation shape control. A number of case studies will be presented to demonstrate the types of improvements and success offered by the blasting technologies. The benefits are identified and delivered as cost savings in excavation, support and lining as well as improvements in safety and project risk management, reduction in nuisance and increased community utility. In some cases, these areas of specific interest have been benchmarked using packaged explosives and then reviewed after conversion to bulk emulsion technology and the changes are quantified in the case studies. In this paper the authors seek to indicate where further significant improvements can be realised in construction over traditional drill and blast methods. Whilst there is a limit to the amount of experimentation and measurement that can take place in a construction project without starting to adversely impact on progress, it appears there is still more scope to improve performance and reduce costs. This paper demonstrates how suppliers are working with contractors to improve overall performance as well as focus specific requirements. The application of new technologies coupled with greater knowledge of explosives/ground interaction have reduced or eliminated many of the undesirable side effects experienced in the past, and will continue to deliver improvements. (A) Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Blast Induced Damage and Dynamic Behaviour of Hangingwalls in Bench Stoping

This paper presents the results of a comprehensive monitoring program designed to investigate the extent of blast induced damage experienced by rock masses extracted by bench stoping methods. An array of triaxial geophones and extensometers were used to monitor blast vibration attenuation and measure hangingwall deformations during stope extraction. In addition, pre and post surveys of the hangingwall rock mass were conducted using a TV borehole camera and cavity survey instrumentation. These surveys were later used to calibrate damage profiles into the stope hangingwalls. Peak particle velocity, hangingwall deformation measurements and stope surveys were used to develop a site specific damage model that allowed engineers to asses drilling and blasting configurations to minimise the extent of pre-conditioning and damage. In addition the study included the analysis of the frequency response, displacements and accelerations experienced by the excavation as extraction and mine filling progressed. This work aimed at improving our understanding of the influence of blasting on the dynamic behaviour of stope hangingwalls. The study demonstrated that estimates of the maximum extent of rock mass pre-conditioning and/or damage made through the application of the Holmberg-Persson approach compared well with measured results. In addition, the study found that dynamic loading imparted on an exposed hangingwall from subsequent stope blasting was also expected to contribute to rock mass weakening and that mine filling was crucial to arrest further deterioration. Hangingwall accelerations were used to demonstrate that larger openings may be more susceptible to dynamic loading.

Quantitative Assessment of Extrinsic Damage in Rock Materials

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.

Problem of predicting the blast-induced damage sustained by crystals in dense media

Problem of predicting the blast-induced damage sustained by crystals in dense media

Prediction and measurements of blast vibrations

ABSTRACT Imminent ground vibrations are often an undesirable by-product of blasting. The “peak particle velocity” (PPV) of vibrations is often used as a means of predicting and/or assessing blast-induced damage The common prediction models for vibration incorporate the quantity of explosive per delay, without giving any consideration to its degree of coupling and/or its distribution in one or more blast holes. Two phases of small scale blasting experiments were conducted on a rock like material called hydro-stone. The tests examined the effects of decoupling and the simultaneous firing of multiple holes on the resulting PPV. It was observed that the PPV decreased with a reduction In coupling ratio, which can be accounted for by incorporating a decay factor into a standard prcdictory equation. The PPV produced by the simultaneous firing of multiple holes was less than the predicted values. The measured PPV at any single point was found to be less than double the PPV for a single blast hole. When lhe number...

Geostatistical approach to the study of induced damage around underground rock excavations

The problem of nuclear waste disposal has emphasized the need for research on blast-induced damage around underground excavations. This paper shows how geostatistical methods might be used to delineate zones of damage when the systematic rock testing approach is used. Some basic concepts of the theory of regionalized variables are presented and then illustrated by a typical application. The conclusions drawn from the latter using the theory of regionalized variables are quite different from those drawn from a previously published study based on the same data but using conventional statistical methods. Key words: rock mechanics, regionalized variable, induced damage, geostatistics, dilatometer.