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1、精选优质文档-倾情为你奉上SHAFT AND DRIFT EXCAVATION BY BLASTING AND SHAFT SUPPORT1 APPLICATION OF BLASTING IN SHAFT AND DRIFT EXCAVATION1.1 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 wou
2、ld be at its best when the debris is not smaller than necessary for handling 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 ma
3、in mechanisms: (1) creation of new surface area (fracture energy), (2)friction (plasticity) and (3)elastic wave enegy dispersion.The loading method determines the relative proportions and the amount of energy consumed in fragmenting a given rock type. Unonfined tensile failure consumes the least ene
4、rgy with an increasing a,mount of energy required as the rock is more 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 to
5、ols and optimize fragmentation systems it would be desirable to know 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
6、)rate of load application .Increase in confining pressure, as with increasing depth beneath th earths surface or under the action of a fragmentation tool, causes an increase in rock strength .Apparent rock strength decreases as porc fluid pressure increases, since it decreases the effect of confinin
7、g pressure. Although chemical effects of pore fluids influence 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
8、ambient temperature changes found during mining. An increase in rate of load application causes an apparent increase in rock strength.Rock exhibits directional properties that in fluence the way it breaks. These are embodied in the concept of rock fabric ,which connotes the structure or configuratio
9、n of the aggregate components as well as the physical or mechanical property manifestations. Rock fabric ont only relates to the preferred orientation of mineral constituents and their planes of weakness, but also to the configuration of discontinuities, microcracks and pores.Joints and bedding plan
10、es have great influence on fragmentation at field scale.Physical properties of rock (density,indentation,hardness,abrasivehardness and porosity ,)are frequently used in conjunction with mechanical properties to develop better empirical esti mations of rock fragmentation.1.2 BLASTHOLE CHARGING METHOD
11、SDrill hole charging can be carried out in different ways 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 a
12、ir chargers have been used and these machines provide both 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 a
13、ir chargers for blasting powder in the form of loose material 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
14、 be made of wood or plastic. It must not be too thick in 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 shou
15、ld be charged and tamped. The detonator must be correctly 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
16、 of 42 pounds per square inch .since that time the charging tube has been replaced by anti-static treated plastic hose of a special design. A charger includes a foot-operated valve, reduction vavle with air hose, breech, connecting tube and charging hose.The semi-automatic charger permits the contin
17、uous 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 pressure in the charging hose is retained while cartridges are pressure in the charging hose is retain
18、ed while cartridges are beins inserted .The semi-automatic charger permits considerably higher charging capacity than the normal type of charger.Explosives in the form of the form of loose material, usually ammonium nitrate explosives(ANFO), require special chargers. Two types can be differentiated:
19、 pressrure vessel machines and ejector units. Pressure vessel machines are particularly suitable for crystalline An explosives with good charging capacity. Ejector units are operate by an ejector sucking up explosive from a container through a charging hose. The explosive is then blown through the c
20、harging hose into the drill hole .There are, also combined pressure ejector machines. The charging hose used for ANFO charging operations must conduct electricity and have a resistance of at least 1K/m and max.30K/M.Nitro Nobel has developed a special pumping procedure which consists of a tanker veh
21、icle which is used to pump explosive directly the drill holes. The charging capacity is very high in the case of large diameter drill holes.1.3 CONTROLLED BLASTING TECHNIQUTES Controlled blasting is used to reduce overbreak and minimize fracturing of the rock at the boundary of an excavation. The fo
22、ur basic controlled blasting techniques are: line drilling, presplitting, cushion blasting and smooth blasting.Line drilling, the earliest controlled blasting technique, involves drilling a row of closely spaced holes along the final excavation line, providing a plane of weakness to which to break.
23、Line drill holes, 2or 4 diameters apart and contain no explosive. The blastholes adjacent to the line drillholes normally are loaded lighter and are on closer spacing than the other blastholes. The maximum depth for line drilling is about 30 ft .Line drilling involves no blasting in the final row of
24、 holes, and thus minimizes damage to the final wall.Presplitting, sometimes called preshearing ,involves a single row of boreholes ,usually 2 to 4 in .in diameter ,drilled along the final excavation at a spacing of 6 to 12 borehole diameters .Dynamite cartridges 1to 1.5 in . in size on 1 to 2 ft .ce
25、nters usually are string-loadde on detonating cord ,although special small-diameter cartridges with special couplers are available for total column loading .In unconsolidated formations ,closer spacings with lighter powder loads are required .The bottom 2 to 3 ft .of borehole usually is loaded somew
26、hat heavier than the remainder .Stemming between and around the individual charges is optional .The top 2 to 3 ft . of borehole is not loaded ,but is stemmed. The depth that can bu presplit is limited by hole alignment ,with 50 ft .being about maximum .The presplit holes are fired before before the
27、adjacent primary holes to provide a fracture plane to which the primary blast can break .In presplitting it is difficult to determine the results until the adjacent primary blast is shot .For this reason ,presplitting too far in advance is not recommended .Presplitting seldom is done underground.Cus
28、hion blasting involves drilling a row of 2 to 6-in .diameter boreholes along the final excavation line ,loading with a light well-distributed charge ,completely stemmed and firing after the main excavation is removed rather than before ,as in presplitting. The burden on the holes is slightly larger
29、than the spacing .Wedges may be used to abut the charges to the excavation side of the borehole and minimize damage to the final wall .Eeplosive loading is similar to that in presplitting .Cushion blasting has been done to depths near 100 ft .in a single lift with the larger-diameter boreholes becau
30、se alignment is more easily retained .Cushion blasting seldom is done underground.Smooth blasting is the underground counterpart of cushion blasting .At the perimeter of the tunnel or drift ,closely spaced holes with a burden-to-spacing ratio near 1.5:1 are loaded with light well-distributed charges
31、 .Smooth blasting differs from cushion blasting in that (1) except at the collar ,the charges are not stemmed and (2) the perimeter holes are fired on the last delay in the same round as the primary blast .Total column loading is most common ,although spacers may be used .The holes are stemmed to pr
32、event the charges from being pulled out by the detonation of the previous delayed holes .Smooth blasting reduces overbreak in a drift and also provides a more competent back requiring less support .It involves more perimeter holes than does normal blasting.Combinations of controlled blasting techniq
33、ues are used .In unconsolidated rock,line drilling sometimes is desirable between presplit or cushion boreholes . Corners sometimes are presplit when cushion blasting is used.1.4 TUNNEL BLASTINGThe most common methed of driving a mining tunnel is a cyclic operation in three sequences:(1) Drilling sh
34、ot holes ;charging them with explosives and blasting.(2) Removing the resulting muck pile.(3) Inserting the tunnel linings into the newly excaved area; and advancing the ralls. ventilation arrangements, and power supplies ready for the next cycle of operations.The basic principle of tunnel blasting
35、,in its simplest term, is to loosen a volume of the virgin rock in such a way that when it is removed the line of the tunnel has advance in the correct direction with as nearly as possible the correct cross-section.The dilling pattern in which the holes to receive the explosives are drilled into the
36、 working face is designed so that :the holes are easy to drill; the minimurd total quantity of explosive is required ;and the periphery of the space left after the blast conforms as nearly as possible to the required tunnel section.A blast round consists of cut ,relief, breast and trim holes . The c
37、ut portion is the most important . The objective of the cut is to provide a free face to which the remainder of the round may break.The two general types of cuts are the angled cut and the burn .These can be used in combinations to form various other cuts .Angled cuts are more advantageous than burn
38、 in wide headings ,due to the fewer boles and less explosive required per foot .A disadvangtage is the possibility of large pieces of rock being thrown from the “V”.The wedge or V-cut consists of two holes angled to meet or nearly meet at the bottom . The cut can consist of one or several Vs, either
39、 verticao or horizontal .For deeper rounds or hard-breaking rock ,double Vs can be used .The smaller is called the baby cut . It is useful in small headings.Large-diameter burn holes provide excellent relief in big headings .Burn cuts permit deeper rounds than angled cuts and , due to the increased
40、advance per round ,may prove more economical .In burn cuts ,the holes must be drilled parallel , with proper spacing ,and 0.5 : 1 ft deeper than the remainder of the round .Usually ,one or more holes (large-diameter) are left unloaded to provide relief for the loaded holes . Various combinations of
41、spacing ,alignment and holes loaded are possible.Innumerable typesofblastingrounds are used in underground headings .Even in the same heading the round may have to be altered as different rock charateristics develop.An important factor in any round is the firing sequence .In general ,the holes are f
42、ired so that each hole or series of holes is blasted to the free face provided by the preceding holes .The depth of drift rounds depends on the complete drifting cycle and drift size.A general rule is that a round will not break much deeper than the least cross-sectional dimension of the drift . Rou
43、nds can be arranged that provide certain muck-pile shapes and positions for more efficient loading and cycles . In drifts requiring close support , rounds can be arranged to prevent damage.2 SHAFT SUPPORT 2.1 WELLBORE SUPPORTIn the USA, brick, stone and cast iron shaft linings are rare; formerly, ti
44、mbering was almost universal but concreting and steel framing are increasing in use. Choice of support depends on ground and water conditions, shape of shaft and cost of materials. (1)Timber SetsUntil relatively recently, most rectangular shafts have used square-set timbering for ground support and
45、compartment division .Size of the timber used and set spacing is dependent on ground conditions encountered .The disadvantages of timer sets are the cost, strength , short life and fire hazard involved. In swelling ground timbering fails slowly and with ample warning .in most cases , a concrete coll
46、ar is poured at the start of a shaft to tie the sets in and provide a good bearing for the shaft-timbering installation .Timber sets usually are hung from the preceding set with steel hanging rods .After the set is in place , the posts are inserted and the hanging rods are tightened up . The lagging
47、 is placed in around the sides of the shaft.(2)Steel Sets-Steel sets sometimes ate used instead of timber. Wood lagging generally is employed in conjunetion. The laggling can be placed in the web of the steel sket very quickly and effectivelt. Properly designed steel sets go in faster and more accur
48、atelt than wooden sets, as they can be bolted together and lined up perfectly when assembled.(3)Concrete Lining-Circular concrete-lined shafts are more and more used today. For example, in South Africa, almost 100% of the shafts installed are circular concretelined .Also almost without exception, th
49、e best sinking time is achieved. Besides the good sinking rate, there are numerous other advantages. The circular concrete section provides the greatest strength factor for ground support ,the best air-flow characteristics, and by far the lowest maintenance of any shaft type. It can be stripped easily and changed to another hoisting configuration, or to a ventilation shaft, without disturbing ground conditions. Water can be controlled or sealed off much easier in this type of shaft. There a