【導(dǎo)讀】料的塊度化小，變成碎塊，便于裝載、處理和運輸。便于裝運，也不要大到需要手工破碎或二次爆破。為了破巖，必須采用直接或間接的方式向巖石施加能量。能量的大小取決于巖石本身的性質(zhì)和技術(shù)裝藥系統(tǒng)的類型。表面，摩擦(塑性)，傳播彈性波能。決定破碎某種已知巖石時上述三方面的相對比例和所消耗的能量。較高的壓應(yīng)力場的約束時，破巖能量需要有所增加。量使巖石或礦石破碎的方法，對于決定破巖效率至為重要。巖石的強度受到周圍環(huán)境的影響。巖石的視強度就降低因為它減弱了約束力的作用。理和層理對破巖有很大影響。了半自動裝藥器，主要用于井下作業(yè)。藥作業(yè)中有可能捅壞和損壞導(dǎo)火索或電雷管腳線。壓風(fēng)裝藥器在瑞典已使用了大約二十年。半自動裝藥器可連續(xù)裝填藥卷，其裝藥速度與。藥的裝藥軟管必須能導(dǎo)電，其電阻最小為1千歐米。預(yù)裂爆破的深度受炮眼排列的限制，最大。側(cè)，以減少爆破對巖壁的損壞。緩沖爆破法結(jié)合使用。

　　

【正文】 e used. Although the cost is similar, the square shaft does not have the strength of either the circular of elliptical. The elliptical shaft has a good strength factor and is used where split ventilation is required. It is, however, more expensive to sink than a circular shaft. (4)Gunite or Shotcrete Lining——There have been some shafts sunk using gunite or shotcrete for wall support. The guides in this type of shaft usually are not required in the pleted shafe, the rope guides could be used in sinking. SUPPORT FOR TUNNELS In former years, the square or segmented timber set was the only known method for supporting underground excavations. As timber 25 bee more scarce and wide flange steel shapes made their appearance, steel rapidly displaced timber as a structuresupport material. More recently, rock bolting and pneumatically applied concrete have been added to the list of practical groundsupport media. Either rock bolting or pneumatically applied concrete concrete usually cost less per linear foot of tunnel than steel ribs . Sometime the two are used together and still show a saving over steel ribs. (1)Steel Rib Support—Steel rib sets monly are fabricated in two pieces with the side leg and half of the arch in each piece. The two identical pieces are stood up and bolted together at a butt joint in the crown . Size of steel required will depend upon the nature of the rock and the pressure being exerted by the ground . Generally speaking, a small tunnel section will require a 4or 5in .rib with spacing of 1(1/2)to 4ft。 mediumsized , 5to 6in. rib with spacing of 1(1/2) to 4 ft。 large, a 6to with spacing of 2 to 5 ft. On a project where full utilization is being made of rock bolting and pneumatically applied concrete, steel rib supports need be used only in fault zones and through stretches of badly broken rock or soft ground. Supplementing the steel rib, timber blocking and lagging must be installed as required. A standard tunnel crew usually erects a set of steel in 20 to 40 min. (2)Rock Bolting—A number of types of tensionable rockbolts presently are available , differing mostly in the arrangement of the 26 expandable device which anchors the end of the bolt to the rock prior to applying the tension by tightening the nut. Experimentation frepuently is necessary to determine the type of anchor most suitable to a particular formation of rock. Mildsteel bolts should be at least 1 in. in dia and 10 ft long, provided the tunnel is large enough to permit insertion of rods of this length. Rockbolts must be installed with careful consideration for the jointing pattern of the rock.. They must also be installed in a more or less uniform and regular pattern so that when tensioned they will, with the surrounding rock,produce a homogeneous arch structure against the external stresses acting upon the excavation opening. Average spacing of the rockbolts, throughout the roof of the tunnel above the spring line, will vary from a minimum of about 12sq ft of rock per bolt to a maximum of 25 or more. When rockbolts are installed by the regular tunnel crew, a standard tunnel crew usually will install the bolts required for one full round of advance of 8ft in 30 to 40 min. If a twoman crew alone is installing bolts, they probably will average two bolts per hour. (3)Pneumatically Applied Concrete—Shotcret or gunite, applied directly to the rock surface of the arched tunnel roof, is rapidly being accepted as an effective and economical means of ground support. It can be used in all types of fair to poor rock or firm earth provided the material will stand up without caving for a sufficient time to permit the sprayed 27 concrete to gain its initial strength. Accelerating additives are which, when added to the concrete at the spray nozzle, will cause initial set to occur within 3to 10 min. after the mortar has been applied. The concrete is applied in thickness of 2to 6 in. Dryprocess application usually produces better results than the wet process because it permits the placing of thicker layers, uses larger aggregates (maximum, 3/4 in.) and usually achieves a higher production rate per hour per nozzle (to cu yd. per hr). One of the economies which frequently can be achieved with pneumatically applied concrete reflects the fact that it can be applied readily to the tunnel roof during the mucking cycle, thereby shortening the total time required to plete the ―round‖. (4)Timber support—Supports for the tunnel roof and sides may be required while driving. Conventionally, temporary timbering is often used during driving and replaced later by permanent supports or lining. Permanent supports may be of timber too. For permanent support, timber should be well seasoned and treated with preservative. It is easily framed on the job and quickly erected without use of special tools or equipment. For temporary support, in local stretches of bad ground while advancing the heading timbers are readily cut and framed to suit requirements. Timber sets prises several timbers forming a framework across the tunnel section. The monest form for narrow tunnels is the 3piece set, consisting of a cap (crossbar or header) supported on two posts. The 28 batter of the posts is 1 to per ft, which is usually sufficient to prevent the bottoms of the posts. From pushing inward unless side pressure is excessive and the bottom soft. Posts are usually of hardwood, round, with small end 5in minimum diameter. The minimum thickness of the cap is usually 5in with width from 6 to 8 in. Lagging, usually 2 in thick, may or may not be set on the sides and top. In swelling ground the timber set usually has :batter blocks‖ to prevent the displacement of the posts。 where the bottom tends to heave, an inverted arch set may be used. The back (or r