ROCK BLASTING IN TUNNELS

Abstract

Constructiofl Of tunnels is one of the most out-standing and courage Ous feats of engLnearing. PDovtOnl.y only method of ti*melling 'was, by use of bier and cb. seq. t&ch psrsLsted. t pto 180. Heating of rock th3n qusnching hot surface idth wader causing .t to c'ack and split apart vas also used. These n thods re ecromely slov and no big tunnel c+ . d be constructed tV employing t ,' Zbdern drjJ.3.tng and blasting using ex osLve provides the means for achieving mum advance rates thereby s .ng the thne to a great extent and Bend.bing a limite d time of tUM01 excava. tio,. Tochuique of blasting is based on the unique property of the explosive and rock which are that the explosives are one of the most conntrated source of rapidly genare.ting energy available to mom, and rock is spak in tensicm. heo r of rock breakage has been described. Construction of tunnel s posa s n"' ' problems because of great Y.ongitud al extent covering varying conditions. Two zuu n problems rivclived are 3 U) econzty and (ii) variable para.meters of media, through ±ch it is to be driven* Deteimins.- cn or most a conc~mi c w5y of tunnel excavation is a complex problem. m sea rtat ion discusses the veq s by whLch 000now can be obtained in the cOnSUiiptiOn of explosive by improving degree• of pac ding and maintaining optima bench hed. ght s for a part ..-ctap.ar diame ter and hole. deviation. Methods of obtaining desired fregmentation and reduction 4 over break why. ch largely affect the cost have been described. Effect of blast hole diameter on the cost of blasting has been analysed.. basting is used for two purposes : (i) to displace the rock and (.i) to fragment it.' Principal of breakage, displacement and 'rag tation have been, described. adteble drilling pattern i, s most important for successful blasting. It should ensure minims over break, required frog mentatLon a td least amount. of drilling and e plo.s-ve per unit volume of blasted material. xplOve has to break as Pll as mo fe the rock against frictional and gravitational resistance. Therefore for better results drilling pattern along itLtb charge and rl g pattern should. be able to reduce the reels- tance to min~mumm. Various principles involved for achieving this have been stated and concerned methods have been described. Crater test not od *Loh may be used for revising drilling pattern has been stated*; A free face infront and parallel to a drill hole is gssential for efficient utilisation of explosive breaking power. Various types of its w t th their merits and demerits, v i.ch can be used for crewing free face in tunnel have been described. Drilling pattern depends on tjype of job and equuipment$ extent, type and structural geology of rock, degree of fragmentation re quired4 explosive used, degree of packing,, avelling, permitted throw and vibration etc. Explosives equipme: .,K. and tools used in tuxrnol s and effects of each .tom to arrive at correct di tUing pattern have been 6escxibo . Sequence of blasting and it various affects have been illustrated Too little exiiLosive results N in only heaving and excessive charge is not only expnffi.ve but also dangerous. t thods of xomputng correct eharg`e have described. Various works required In excavation of tunnel and method of tunnel excavation in vock have been described:,,