1、 第12页翻译部分英文原文APPLICATION OF BLASTING IN DRIVING TUNNEL1 FRAGMENTATIONFragmentation is the breaking of coal, ore, or rock by blasting so that the bulk of the material is small enough to load, handle and transport. Fragmentation would be at its best when the debris is not smaller than necessary for ha
2、ndling and not so large as to require hand breaking or secondary blasting.Energy must be supplied to rock by direct or indirect means to fragment that rock and the type of loading system. Fragmentation energy is consumed by the main mechanisms: (1) creation of new surface area (fracture energy), (2)
3、 friction (plasticity) and (3) elastic wave energy dispersion.The loading method determines the relative proportions and the amount of energy consumed in fragmenting a given rock type. Unconfined tensile failure consumes the least energy .With an increasing amount of energy required as the rock is m
4、ore highly confined within a compressive stress field during fragmentation. The way energy is applied by tools to cause rock or mineral fragmentation is important in determining fragmentation efficiency. To best design fragmentation tools and optimize fragmentation systems it would be desirable to k
5、now how rock properties influence breakage.The strength of rock is influenced by the environmental conditions imposed on the rock. Those of most importance in rock are (1) confining pressure, (2) pore fluid pressure, (3) temperature and (4) rate of load application .Increase in confining pressure, a
6、s with increasing depth beneath the earths surface or under the action of a fragmentation tool, causes an increase in rock strength .Apparent rock strength decreases as pore fluid pressure increases, since it decreases the effect of confining pressure. Although chemical effects of pore fluids influe
7、nce rock strength, they generally are small compared to the confining pressure effect, except for a small minority of rock types .Increase in rock temperature causes a decrease in rock strength. This effect is very small because of the small ambient temperature changes found during mining. An increa
8、se in rate of load application causes an apparent increase in rock strength.Rock exhibits directional properties that influence the way it breaks. These are embodied in the concept of rock fabric, which connotes the structure or configuration of the aggregate components as well as the physical or me
9、chanical property manifestations. Rock fabric not only relates to the preferred orientation of mineral constituents and their planes of weakness, but also to the configuration of discontinuities, micro cracks and pores. Joints and bedding planes have great influence on fragmentation at field scale.P
10、hysical properties of rock (density, indentation, hardness, abrasive hardness and porosity,) are frequently used in conjunction with mechanical properties to develop better empirical estimations of rock fragmentation.2 BLASTHOLE CHARGING METHODSDrill hole charging can be carried out in different way
11、s depending on whether the explosive used is in cartridges or in the form of loose material. The oldest charging method implies the use of a tamping rod and this system is still used to a very great extent .During the last 20years, compressed air chargers have been used and these machines provide bo
12、th good capacity and also an improved level of charge concentration so that the drill holes are utilized to a higher degree. During the last few years semi-automatic chargers have been taken into use, primarily in underground work. Compressed air chargers for blasting powder in the form of loose mat
13、erial have also come into use on a large scale. As far as slurry blasting is concerned, special pumping methods have been developed through which charging capacity in the case of large diameter drill holes is practically good.A tamping rod must be made of wood or plastic. It must not be too thick in
14、 relation to the drill hole diameter since this can crush and damage fuse or electric detonator cables during charging work. If a good degree of packing is to be obtained during charging with a tamping rod then only one cartridge at a time should be charged and tamped. The detonator must be correctl
15、y fed into the drill hole during charging work.Compressed air chargers have been in use is Sweden for about 20 years. The first type consisted of aluminum pipes connected together and the cartridges were blown into the hole with an air pressure of 42 pounds per square inch .since that time the charg
16、ing tube has been replaced by anti-static treated plastic hose of a special design. A charger includes a foot-operated valve, reduction valve with air hose, breech, connecting tube and charging hose.The semi-automatic charger permits the continuous insertion of explosive cartridge at the same rate as they are charged in the hole by the hose .Instead of a valve being used, the cartridges pass through an air lock between two flaps. The air
