Blasting
Blasting is a special method of tunneling . The tunneling is carried out by means of blasting (mining shooting ). Jacking is the designation for the construction method, but also the distance gained, which is specified in meters per day.
Procedure
This process takes place in the following work phases: first the holes to be loaded with explosives are drilled. This is followed by loading and blasting. Then the suction of dust and combustion gases or the supply of fresh air (ventilation) is necessary. The next phase consists of knocking (ringing) and the first securing work. This is followed by the uptake and removal of the blasted debris (rubble) . Finally, the shoring is brought in.
The individual blasts take place in the boreholes individually or in groups one after the other within fractions of a second (millisecond blasts) . A favorable arrangement and firing sequence of the individual boreholes (drilling pattern) is necessary for a successful blast . Each individual blast must be arranged in such a way that it reduces the rock tension for the subsequent blast and causes material to be ejected (break-in) .
Areas of application and history
Blasting was the first major new development in the 19th century that was able to replace manual driving with excavation. It was made possible by the development of safe, transportable explosives, especially dynamite .
Compared to drilling ( tunnel boring machines , shield driving machines ), blasting is in principle more effective, faster and cheaper. However, the method can only be used in solid rock . In addition, in long tunnels and tunnels there are problems with ventilation (in particular the formation of nitrous gases ), dust and pressure pollution, and risks such as backbursts in unstable mountain conditions. Furthermore, blasting can have negative influences (eruptions, deformations) both on the already developed route and on neighboring tubes. For this reason, this method is now mostly only used for short drives (up to about 2–3 km), drives with non-circular and / or very large cross-sections (e.g. in cavern construction ), and for hard, abrasive rock where drilling is too wear-intensive , also in sections.
Web links
- Practice blasting (PDF)
- Blow up (PDF)