Bian Xiao inquired and sorted out relevant information through the architectural knowledge column of Construction Network, the encyclopedia website of the construction industry. The basic contents are as follows:
Basic situation of gas tunnel construction:
Gas is a general term for harmful gases in underground tunnels, and its composition is mainly methane (methane CH4), commonly known as methane.
When the tunnel passes through or near the coal seam, oil shale or asphalt-bearing stratum, the surrounding rock is broken and joints are developed, and gas may be encountered. If the gas concentration in the air in the tunnel reaches the explosion limit and comes into contact with the fire source, it will cause an explosion and bring great harm and loss to the tunnel construction. Therefore, in the construction of tunnels in gas-bearing strata, corresponding measures must be taken to ensure the safe and smooth construction.
Matters needing attention in gas tunnel construction:
(1) When the tunnel crosses the gas overflow area, the gas detection method should be determined in advance, and gas dilution measures, explosion-proof measures and emergency rescue measures should be formulated.
(2) Full-face excavation should be adopted as the construction method of tunnel crossing gas area. Because of its simple process, large area and good ventilation, it can quickly shorten the time of coal seam gas emission and narrow the exposed surface of surrounding rock, which is beneficial to gas drainage. Due to many processes, the total exposed area of rock stratum is large, the hole-forming time is long, and the processes in the hole are staggered and dispersed, resulting in uneven gas concentration. Using this construction method, it is required to shorten the distance between working procedures as much as possible, and seal the gas section with lining as soon as possible to ensure the compactness of concrete and prevent gas from overflowing.
(3) Strengthening ventilation is the most effective way to prevent gas explosion. Blow the gas concentration in the air below the explosion concentration1/5 ~110, and discharge the roadway. Natural ventilation is absolutely not allowed, and mechanical ventilation must be adopted. Ventilation equipment must prevent air leakage and be equipped with a backup ventilator. Once the original ventilator fails, the spare mechanical energy will supply air immediately. Ensure that the gas concentration in the air of the working face is within the allowable range. When the ventilator fails or stops running, the workers in the roadway should be evacuated to the fresh air area, and they are not allowed to enter the working face to continue their work before the ventilation returns to normal.
(4) The allowable gas concentration in the air in the cave shall be controlled within the following provisions:
(1) The total return air volume of the chamber is less than 0.75%.
② The air volume of other working faces is less than 0. 5%.
(3) The heading face is less than 2%.
(4) The working face before charge blasting is lower than 65438 0%.
If the gas concentration exceeds the above regulations, the staff must immediately evacuate to the area that meets the requirements and cut off the power supply.
(5) When the gas concentration reaches 65438+/-0.5% in the airflow around the tunneling face and the motor within 20m, it is necessary to stop the operation, stop the work, evacuate the personnel, cut off the power supply and deal with it. When the gas concentration accumulated locally in the heading face reaches 2%, it is necessary to stop working, cut off the power supply and deal with it within 20 meters nearby. Electrical equipment cut off because the gas concentration exceeds the specified value can only be started when the gas concentration drops below 1%.
(6) The ventilation of gas tunnel must be strengthened to prevent gas accumulation. Because of power failure or maintenance, the main ventilator stops running, and there must be safety measures to restore ventilation, eliminate gas and send electricity. After the normal ventilation is restored, all areas affected by the wind stoppage must be inspected by monitoring personnel to confirm that there is no danger before returning to work. The gas must be checked within 20m of all locations where the motor and switch are installed, and the machine can only be started if it meets the requirements. When the local ventilator stops running, before the ventilation is resumed, the gas must also be checked, and the local ventilator can be started only after it meets the requirements, and the normal ventilation can be resumed.
(7) If the tunneling enters the coal seam, the gas emission is large, and it is difficult to dilute it to the safety standard by general ventilation means, the fully enclosed pre-grouting around the advance can be adopted. At the front of excavation, holes are radially distributed in the arch, side wall and bottom contour of tunnel face, forming a fully enclosed gas barrier curtain. Especially for the vertical direction of coal seam and fault zone, the effect will be better. After excavation, shotcrete and anchor support should be carried out in time, and its thickness should be guaranteed to avoid air leakage and instability of surrounding rock.
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