EFFECTS OF JOINT ORIENTATION AND ROCK MASS QUALITY ON TUNNEL BLASTING

Citation
Ak. Chakraborty et al., EFFECTS OF JOINT ORIENTATION AND ROCK MASS QUALITY ON TUNNEL BLASTING, Engineering geology, 37(3-4), 1994, pp. 247-262
Citations number
NO
Categorie Soggetti
Geology,"Engineering, Civil
Journal title
ISSN journal
00137952
Volume
37
Issue
3-4
Year of publication
1994
Pages
247 - 262
Database
ISI
SICI code
0013-7952(1994)37:3-4<247:EOJOAR>2.0.ZU;2-K
Abstract
It is a well known fact that rock mass properties influence the proces s of fragmentation considerably. Model blasts and field investigations were carried out to find the effects of rock mass quality and joint o rientation on tunnel blasting. Propagation of shock waves are partiall y restricted by joint planes. It was observed that the blast results ( i.e., average fragment size and depth and cross-sectional area of the broken zone) were considerably influenced by joint orientation. Accord ingly, it has been concluded that loading equipment with a larger capa city and deeper blast holes are required in formations with joint plan es perpendicular to the tunnel axis. The number of blast holes, howeve r, should be greater when joints are parallel to the tunnel axis. Furt hermore, the powder factor (kg/m3) has been found to be directly relat ed to rock mass quality (Q). Optimisation of pull, powder factor and o verbreak is required in the case of weak formations with joints perpen dicular to the tunnel axis. The use of contour blasting technique seem s to be essential in poor and fair rock masses to minimise the overbre ak, reduce the support cost and improve the stability of the opening.