Drilling and blasting is the controlled use of explosives and other methods, such as gas pressure blasting pyrotechnics, to break rock for excavation. It is practiced most often in mining, quarrying and civil engineering such as dam, tunnel or road construction. The result of rock blasting is often known as a rock cut.
Engineering Rock Blasting Operations
Drilling and blasting currently utilizes many different varieties of explosives with different compositions and performance properties. Higher velocity explosives are used for relatively hard rock in order to shatter and break the rock, while low velocity explosives are used in soft rocks to generate more gas pressure and a greater heaving effect. For instance, an early 20th-century blasting manual compared the effects of black powder to that of a wedge, and dynamite to that of a hammer.[1] The most commonly used explosives in mining today are ANFO based blends due to lower cost than dynamite.
Before the advent of tunnel boring machines (TBMs), drilling and blasting was the only economical way of excavating long tunnels through hard rock, where digging is not possible. Even today, the method is still used in the construction of tunnels, such as in the construction of the LÃtschberg Base Tunnel. The decision whether to construct a tunnel using a TBM or using a drill and blast method includes a number of factors. Tunnel length is a key issue that needs to be addressed because large TBMs for a rock tunnel have a high capital cost, but because they are usually quicker than a drill and blast tunnel the price per metre of tunnel is lower.[2] This means that shorter tunnels tend to be less economical to construct with a TBM and are therefore usually constructed by drill and blast. Managing ground conditions can also have a significant effect on the choice with different methods suited to different hazards in the ground.
The standard method for blasting rocks was to drill a hole to a considerable depth and deposit a charge of gunpowder at the further end of the hole and then fill the remainder of the hole with clay or some other soft mineral substance, well rammed, to make it as tight as possible. A wire laid in the hole during this process was then removed and replaced with a train of gunpowder. This train was ignited by a slow match, often consisting simply of brown paper smeared with grease, intended to burn long enough to allow the person who fires it enough time to reach a place of safety.[4]
An early major use of blasting to remove rock occurred in 1843 when the British civil engineer William Cubitt used 18,000 lbs of gunpowder to remove a 400-foot-high chalk cliff near Dover as part of the construction of the South Eastern Railway. About 400,000 cubic yards of chalk was displaced in an exercise that it was estimated saved the company six months time and Â7,000 in expense.[4]
Rock blasting is the process of drilling holes in a rock mass at depths, and spacing to allow an explosive to fracture the rock. In this process, the rock must fracture enough to be broken down to the size intended.
The explosives used for blasting are usually commercial grade and formulated to provide a controlled amount of energy release as it is detonated. The explosive itself has little effect on the way in which the rock fractures, but instead, the geometry of the drilled hole and the manner in which it is loaded with explosives affects this.
Rock blasting's design is not an exact process, but an iterative process of designing the blast hole layout and estimating the number of explosives needed to blast the rocks. This process requires professional assistance and experience.
One of the greatest challenges of rock blasting is to accurately determine the bounds of the blast area. This is particularly true in geologically disturbed rock that is to be blasted. The determination of the bounds of the blast area is the first step in ensuring safety.
With today's technological advances in the civil engineering industry, operators can now explore blasting areas remotely using drones. This can help them locate potential hazards and ensure that blasting is done safely and accurately.
A professional engineer/blaster can help you save money by minimizing explosives usage and ensuring that a safe, efficient rock blasting job is done correctly. Rock blasting can be a cost-effective way to achieve your project goals, but it must be done carefully and correctly. Using a professional engineer/blaster is essential for this.
For seismic effects, vibration amplitude (measured as the size of velocity or acceleration) and frequency content, or dominant signal frequency, are commonly monitored. The wide spectrum of frequencies is then dependent on the properties of the material to be disintegrated, the properties of the explosive used and the technology of the blasting operation to be performed. The frequency spectrum of the blasting operation seismic recording is also significantly influenced by the environment in which the waves propagate. With increasing distance, the components of higher frequencies are damped faster in the rock mass. The dependence of the frequency range of the seismic signal on the distance from the blasting operation implies that it is necessary for the seismic channel to have the widest possible frequency range at short distances from the blasting site. The frequency spectrum of seismic signals induced by the near blasting operation in rocks may contain frequencies from 1 to 300 Hz [6,7]. Also, the monitoring of acoustic noise from blasting operations, both in the excavation of underground works and in the extraction of mineral resources, is necessary according to hygiene regulations and legislation (for example, based on the regulation entitled Coll. on health protection against adverse effects of noise and vibration [8]).
The paper is a pilot study that is to show alternative possibilities of measuring vibration caused by blasting operations using other physical principles than have been commonly used so far. In the paper, the original results obtained from the pilot measurements using an experimentally developed fiber-optic interferometric sensor and an experimentally developed acoustic sensor when detonating a small amount of explosive during the excavation of a sewer gallery are compared with the results obtained from standard instrumentation for seismic monitoring, both in the amplitude and frequency range. It was an experiment in the so-called near zone, i.e., within the first tens of meters from the dynamic load [10], and the dynamic response of the rock mass was monitored.
In the frequency domain, there is a significant agreement in the width of the band measured, which corresponds to the blasting operation effects [7], and also in the maxima where the interferometric sensor has a greater match compared to the amplitude domain. With an acoustic sensor, the maxima are shifted to higher frequencies, which may be caused both by the design and the alignment of the sensor, wherein the device is primarily designed for installation in a rock mass.
The advantage of experimentally developed sensors from the perspective of a broader frequency range is the possibility of measuring both vibrations and acoustic noise by a single device. Pilot research is currently underway, where building constructions are monitored by measuring vibration, and acoustic noise from large-scale blasting operations carried out in quarries using standard instrumentation intended for this purpose (a seismic station with the range 4.5 Hz to 100 Hz and acoustic meter with linear range 0.5 Hz to 20 kHz) and also fiber-optical interferometer.
Rock is blasted either to break it into smaller pieces such as in most mining and quarrying operations or large blocks for dimensional stone mining and some civil engineering applications, or to create space. The conditions under which blasting is carried out also affect the operations and the results. Precise engineering of operations are needed to achieve the desired objectives. The engineering of blasting operations needs clearly defined objectives, materials, skilled techniques, the necessary theoretical background of the process of rock fragmentation and effect of rock conditions and experience in combining them.
In mining and quarrying, the main objective is to extract the largest possible quantity at minimum cost. The material may include ore, coal, aggregates for construction and also the waste rock required to remove the above useful material. The blasting operations must be carried out to provide quantity and quality requirements of production in such a way that overall profits of mining or quarrying operation are maximised. In-situ rock is reduced in size by blasting and crushing into the required size or with additional grinding, into a finer powder suitable for mineral processing. Large blocks needing secondary breakage or an excess of fines, can result from poorly designed blasts or due to adverse geological conditions. A well designed should produce shapes and sizes that can be accommodated by the available loading and hauling equipment crushing plant with little or no need for secondary breakage. While optimising the fragmentation, it is also important, for safety and ease of loading, to control the throw and scatter of fragments. However, other times controlled displacement is provided, as in the case of casting of overburden or explosive mining, where part of the overburden is thrown to such a distance that it need not be handled again.
In civil engineering, rock is removed to create tunnels or caverns, or deep excavations at the ground surface for road cuts, foundations, or basements. The emphasis is not on high rates of production, although the job must be done as quickly and as cheaply as possible, but on creating space and leaving behind stable rock walls that are either self-supporting or require little reinforcement and lining. Requirements smooth walls and long-term stability exist also in mine shafts, crusher stations and to a lesser extent, in mine development drifts that must remain open for moderate periods. Problems in the blasting of civil engineering works are most often associated with overbreak and underbreak. Special blasting techniques are applied in carrying out controlled blasting to produce smooth walled excavations. Often adjustments to conventional procedures needed.
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