What are the concepts and functions of cut eye, auxiliary eye and peripheral eye in tunnel drilling and blasting construction?
Auxiliary eye: used to improve and expand the free surface formed by the blasting of cut holes.
Peripheral eye: make the section, shape and direction of blasting roadway meet the design requirements.
Brief introduction of detailed explanation of drilling blasting method
Rock excavation by drilling, charging and blasting is called drilling and blasting for short. In the early days, this method developed from manual drilling and hammering, using fire detonators to detonate individual explosive charges one by one, to drilling with a drill rig or dobby, using millisecond blasting, presplitting blasting and smooth blasting. Before construction, according to geological conditions, section size, supporting methods, time limit for a project requirements, construction equipment, technology and other conditions, the excavation method is selected.
Driving mode
Full-face excavation method: the full-face excavation section is drilled and blasted once, excavated and shaped, and fully advanced. When the tunnel is high, it can also be divided into upper and lower parts to form steps, synchronous blasting and parallel excavation. When geological conditions and construction conditions permit, full-face tunneling method is preferred.
Pilot hole method: First, use a part of the excavation section as a pilot hole, and then gradually expand the whole section of the excavation section. This is a construction method with small and medium-sized machinery as the mainstay when the tunnel section is large and it is difficult to adopt full-face excavation due to geological or construction conditions. The cross section of the pilot tunnel should not be too large, and it should be suitable for ballasting of ballasting machinery, transportation of ballasted vehicles, installation and construction safety of feng shui pipes. The free surface can be increased when the pilot tunnel is excavated and blasted, which is beneficial to find out the geological and hydrogeological conditions of the tunnel and create conditions for tunnel ventilation and drainage.
Local excavation method: When the stability of surrounding rock is poor and support is generally needed, when excavating a tunnel with a large section, a part of the section can be excavated first, and the support can be done in time, and then the excavation can be expanded step by step. When excavating a tunnel by drilling and blasting, it is generally regarded as a tunnel excavation cycle from the first drilling sequence, through the processes of charging, blasting, ventilation, smoke dispersion, slag discharge and so on, to the end of the second drilling sequence. Try to compress the operation cycle time and speed up the excavation.
Matters needing attention in blasting site
Wet drilling must be used for drilling. It is forbidden to continue drilling holes in residual holes, and it is forbidden to drill holes while charging.
Detonators should be kept by special personnel, and keys should be carried with you. When initiating, the blasting equipment box should be placed in a safe place outside the warning line. Before the final connection of the electric detonator transported to the operation surface, the foot wire should be twisted into a short circuit to prevent the electric detonator from exploding prematurely due to stray current.
It is forbidden for blasting workers to wear chemical fiber clothing. Irrelevant personnel should be evacuated to a safe place. Lighting equipment with voltage not higher than 36V shall be used for the lighting of blasting charge operation site. When charging, you should use a wooden gun stick to charge, and kindling is prohibited. When charging, the cartridge should be gently pushed into the fundus to make the cartridge in close contact. Do not bump or knock the ink cartridge.
Before using electric detonator to connect blasting network, electric lights and wires should be evacuated from the working face, and the working face should be cut off. The working face should be illuminated by safety battery lamp or insulated flashlight, and there should be no other stray current. Stray current tester should be used to measure stray current value, and the stray current of working face should not be greater than 30mA.
All joints between detonator crural line and crural line, and between crural line and connecting line and bus bar must be tightened and hung, and shall not contact with any object.
Before the final blasting, the blasting bus should be twisted into a short circuit and wrapped with insulating tape to prevent premature explosion caused by stray current.
The connection of blasting network should be filled in all blasting holes in the working face, and after irrelevant personnel are evacuated to a safe place, they should be carried out from the working face to the blasting station in turn. The connection of blasting bus, the inspection of blasting line and electrified blasting work are only allowed to be operated by blasters and shift supervisors. After the operation is completed, the blaster should sound the horn to warn him. The blaster must finally leave the blasting site and detonate in a safe place. The distance from the safe place in the tunnel to the blasting face should not be less than 200 meters.
After blasting, first remove the detonator key, then remove the bus from the detonator and screw it into a short circuit.
Full-time blasters and shift supervisors should enter the working face after blasting ventilation and smoke exhaust 15 minutes, and check whether there are any blind guns, residual explosives and detonators. When misfires, residual explosions and detonators are found, they must be handled by the original blasting personnel in accordance with the regulations, and other personnel can enter the working face only after being relieved by the shift supervisor.