Numerical analysis of vibration-isolating effect of vibration-isolating slot under buried pipe subjected to millisecond blasting

Research on vibration-isolating effects of vibration-isolating slot on buried pipe can be done by numerical method, without being disturbed by external environmental factors. It has measured data without relatively high experiment cost and analyzed the influence of some key parameters according to the results of numerical simulation. The results show that the vibration speed of the pipeline with vibration-isolating slot tends to have a larger decrease than those without vibration-isolating slot. What’s more, the homogeneous explosive charge is discrepant in different working conditions, but the vibration-isolating ratio is similar in the vibration-isolating slot with same structure parameter. The millisecond blasting is hardly affected by total explosive charge. But the blasting seismic intensity is influenced by explosive charge in each stage directly

A Study of Blast Pressure from Underwater Borehole Blasting

The paper presents an experimental study conducted under laboratory conditions on the measurement of the pressure waves transmitted into water that are radiated from following the detonation of an explosive charge buried in a block. In order to simulate full scale blasting operations at sea, small explosive charge of 1.8g PETN was buried in a concrete block and detonated under water. Information concerning the test set-up, instrumentation, type of explosives used, scaling factor and measurement of pressure is briefly described. The paper also presents analysis of the test results in the form of FFT’s and Transfer functions and details of its importance to practical blasting operations at sea using buried explosive charges

Evaluation of explosives using ground vibration criterion

Recent times have experienced an increase in infrastructure and mineral resource developments. As a result, mining activities have also increased to supply the needed mineral. Blasting has been the main technique for loosening insitu rock before use. Consequently there is a growing concern of the effects of blasting activities on the environment. These effects are normally nuisances to the neighboring residence as they come in the form of: dust, toxic gases, noise, fly rocks and ground vibration. Of the set of nuisances the one that is of most concern is ground vibrations which can cause damage to structures. In most cases worldwide, after blasting activities there are the usual complaints about damage to residence, and less mining activities which is also a focus of the thesis. A study was conducted to evaluate the effect of heavy blasting in open-pit coal mines on the stability of adjoining under ground coal mine workings. There have been researches on the subject of ground vibrations to help refute some of these complaints. The works of Lewis Oriard and Charles Dowding are the foundation on which standards and regulations are built as guides to assist blasters in the prevention of creating unnecessary nuisances. Most countries have developed their own regulations with respect to blasting and parameters are set according to the geological conditions. This is of importance as the rock structures determine the transmission of the peak particle velocity. However, most countries in the west adopt standards similar to ones put forward by the United States Bureau of Mines. It my opinion that a whole scale adoption should not take place as the criteria used may not be suitable for other countries’ geological conditions. For this thesis the aim was to identify a vibration level that will not cause damage to structures close to a mining area and increase production by effective blasting. Based on the literature review it was revealed that there are a number of parameters that needed to be considered. These ranges: construction material, age of structures, distance from structures, geology of the location, type and quantities of explosives and the blast design. There was also the review of standards to building threshold with respect to the level of ground vibration. The case study with its main focus on evaluation of explosive using ground vibration criterion which will not result in any form of damage to the structures. However, having established a PPV limit using the USBM that appears reasonable there is the need for criteria similar to those of the USBM using blasting and geological conditions

Blast optimisation with In Situ rock mass characterization by seismic profiling at an opencast coal mine in India

Blast optimisation studies were conducted at an opencast coal mine in India for selection of a site specific explosive for different rock types. This seismic refraction survey technique was applied at sandstone benches of a coal mine for rock mass characterisation and blast optimisation by impedance matching of explosives. Field experiments were conducted on seismic profiling to characterise sandstone rock mass on the basis of P-wave velocity (Vp) measurements. The running benches were selected for the experimentation so as to cross check the results of the Vp with the exposed faces of the benches. The instrument used for seismic profiling contains 24 geophones of 14 Hz frequency. The mode of survey was the „refraction method‟ which could give the Vp profile up to 50-60 m depth and about 100 m stretch. The source of vibration generation was by hammering of specific Sledge hammer. The raw seismic data collected in the field was analysed by a software called ‟Seismic imager‟ for generating a Vp profile of the rock strata. The Vp profiles were determined for three benches of the mine, which include weak, medium and hard type of rock mass. The rock impedance was calculated based on the Vp determined by seismic profiling. This data was used for the selection of explosive with desired velocity of detonation and density, so as to match the impedance of the rock mass. The blast performance with the suitable explosives with impedance matching was obviously better than that of impedance mismatching. Trials were also conducted with heave energy-rich ANFO explosive with mismatched impedance properties and observed better results. The optimisation studies resulted in reduction of back break by 50-75% and reduction of mean fragment size by 15-47%. The paper stresses the need for conducting impedance matching exercise for all the blast sites for blast optimisation and productivity improvement

Explosively-induced ground vibration in civil engineering construction

Research has been undertaken to improve techniques used in the prediction of ground vibration caused by civil engineering construction works. In particular, the effects of explosive excavation of rock for subsurface structures is considered. Factors affecting the input and propagation of explosive energy in the rock mass are investigated, and recommendations made on procedures for trial blasting and the most effective data processing and presentation for the derived predictive equations. These developments are supported by blasting trials at two major road construction sites, where vibration measurements were taken during conventional and innovative blasting operations. A critical review of contemporary dynamic structural damage and intrusion criteria is provided. It is concluded that vibration prediction and control techniques, together with workable damage/intrusion criteria, can be applied which substantially mitigate vibration hazard. The distribution of vibration associated risk between employer and contractor is discussed and contractual options presented. Techniques to determine the engineering properties of rock masses by analysis of stress waves from explosive and hammer impact sources have been developed and successfully tested. The advantages and limitations of the most promising seismic methods are discussed and field seismic classifications are compared with known rock mass properties and established geotechnical classification systems. The research shows that both rock mass properties and 'site specific' laws of vibration decay may be obtained during the trial blasting sequence of a site investigation programme

Experimental Study on the Measurement of Water Bottom Vibration Induced by Underwater Drilling Blasting

Due to the lack of proper instrumentations and the difficulties in underwater measurements, the studies about water bottom vibration induced by underwater drilling blasting are seldom reported. In order to investigate the propagation and attenuation laws of blasting induced water bottom vibration, a water bottom vibration monitor was developed with consideration of the difficulties in underwater measurements. By means of this equipment, the actual water bottom vibration induced by underwater drilling blasting was measured in a field experiment. It shows that the water bottom vibration monitor could collect vibration signals quite effectively in underwater environments. The followed signal analysis shows that the characteristics of water bottom vibration and land ground vibration induced by the same underwater drilling blasting are quite different due to the different geological environments. The amplitude and frequency band of water bottom vibration both exceed those of land ground vibration. Water bottom vibration is mainly in low-frequency band that induced by blasting impact directly acts on rock. Besides the low-frequency component, land vibration contains another higher frequency band component that induced by followed water hammer wave acts on bank slope

The measurement and analysis of accelerations in rock slopes

Imperial Users onl

Near-field blast vibration monitoring and analysis for prediction of blast damage in sublevel open stoping

The work presented in this thesis investigates near-field blast vibration monitoring, analysis, interpretation and blast damage prediction in sublevel open stoping geometries. As part of the investigation, seven stopes at two Australian sublevel open stoping mines were used as case studies. The seven stopes represented significant ranges in stope shapes, sizes, geotechnical concerns, extraction sequences, stress conditions, blasting geometries and rock mass properties.The blast damage investigations at the two mine sites had three main components. The first component was rock mass characterisation, which was performed using static intact rock testing results, discontinuity mapping, mining-induced static stress modelling and geophysical wave propagation approaches. The rock mass characterisation techniques identified localised and large-scale variations in rock mass properties and wave propagation behaviours in relation to specified monitoring orientations and mining areas. The other components of the blast damage investigations were blast vibration monitoring and analysis of production blasting in the seven stopes and stope performance assessments.The mine-based data collection period for the case studies lasted from January, 2006 to February, 2008. A key element of the data collection program was near-field blast vibration monitoring of production blasts within the seven study stopes. The instrumentation program consisted of 41 tri-axial accelerometers and geophone sondes, installed at distances from 4m to 16m from the stope perimeters. A total of 59 production firings were monitored over the course of the blast vibration monitoring program. The monitoring program resulted in a data set of over 5000 single-hole blast vibration waveforms, representing two different blasthole diameters (89mm and 102mm), six different explosive formulations and a wide range in charge weights, source to sensor distances, blasthole orientations and blasting geometries.The data collected in the blast vibration monitoring program were used to compare various near-field charge weight scaling relationships such as Scaled Distance and Holmberg-Persson prediction models. The results of these analyses identified that no single charge weight scaling model could dependably predict the measured near-field peak amplitudes for complex blasting geometries. Therefore, the general form of the charge weight scaling relationship was adopted in conjunction with nonlinear multivariable estimation techniques to analyse the data collected in the study stopes and to perform forward vibration predictions for the case studies.Observed variations in the recorded near-field waveforms identified that instantaneous peak amplitude such as peak particle velocity (PPV) did not accurately describe the characteristics of a large portion of the data. This was due to significant variations in frequency spectra, variable distributions of energy throughout the wave durations and coupling of wave types (e.g. P- and S-wave coupling). The wave properties that have been proposed to more accurately characterise complex nearfield vibrations are the total wave energy density (ED[subscript]W-tot), stored strain energy density (ED[subscript]W-SS) and the wave-induced mean normal dynamic strain (ε[subscript]W-MN). These wave properties consider the activity of the blast-induce wave at a point in the rock mass over the entire duration instead of the instantaneous amplitude.A new analytical approach has been proposed to predict blast-induced rock mass damage using rock mass characterisation data, blast vibration monitoring results and rock fracture criteria. The two-component approach separately predicts the extent of blast-induced damage through fresh fracturing of intact rock and the extent from discontinuity extension. Two separate damage criteria are proposed for the intact rock portion of the rock mass based on tensile and compressive fracture strain energy densities and compressive and tensile fracture strains. The single criterion for extension of existing discontinuities is based on the required fracture energy density to activate all macro-fractures in a unit volume of the rock mass.The proposed energy-based criteria for intact rock fracture and extension of discontinuities integrate strain rate effects in relation to material strength. The strainbased criterion for intact rock fracture integrates the existing mining-induced static strain magnitudes. These factors have not been explicitly considered in existing empirical or analytical blast damage prediction models. The proposed blast damage prediction approach has been applied to two stopes during the two mine site case studies

Fragmentation Analysis in the Dynamic Stress Wave Collision Regions in Bench Blasting

The first step in many mining operations is blasting, and the purpose of blasting is to fragment the rock mass in the most efficient way for that mine site and the material end use. Over time, new developments to any industry occur, and design and implementation of traditional techniques have to change as a consequence. Possibly the greatest improvement in blasting in recent years is that of electronic detonators. The improvements related to safety and increased fragmentation have been invaluable. There has been ongoing debate within the explosives industry regarding two possible theories for this. Shorter timing delays that allow interaction between adjacent shock waves or detonation waves, or the increase in accuracy associated with electronic detonators. Results exist on the improved accuracy of electronic detonators over that of electric or non-electric, but data on the relationship between the collision of dynamic stress waves and fragmentation is less understood. Publications stating that the area of greatest fragmentation will occur between points of detonation where shock waves collide exist, but experimental data to prove this fact is lacking. This dissertation looks extensively at the head on collision of shock (in the rock mass) and detonation (in the detonation column) waves with relation to fragmentation through a number of small scale tests in concrete. Timing is a vital tool for this collision to occur and is the variable utilized for the studies. Small scale tests in solid masonry blocks, 15 x 7⅞ x 7⅞ inches in size, investigated shock and detonation wave collisions with instantaneous detonation. Blocks were wrapped in geotextile fabric and a wire mesh to contain the fragments so that in situ tensile crack formations could be analyzed. Detonating cord was used as the explosive with no stemming to maintain the shock pressure but reduce the gas pressure phase of the fragmentation cycle. Model simulations of these blocks in ANSYS Autodyn looked at the stress and pressure wave patterns and corresponding damage contours for a direct comparison with the experimental investigation. Detonation wave collision in a single blast hole was found to positively influence the fragmentation and throw of the material. Mean fragment size decreased compared to tests with no detonation wave collision. Area of greatest throw occurred at the point of detonation collision where a buildup of gas pressure exited the block from one location. Head on collision of shock waves did not positively influence the muck pile. Largest fragments were located at the point of shock collision. The lack of particle velocity with relation to shock collision in previous literature could be attributed to the increased particle size here. Directional particle velocities could actually increase the strength and density of the rock at this location, decreasing the degree of fragmentation rather than increasing it