Safety technology for tunnel expansion in the main return air tunnel?

1. Project Overview The total return air tunnel is 160m long. Due to the small cross-section, it does not meet the regulations. The tunnel is expanded and repaired according to the requirements. This section was originally supported by anchor net spraying, with a net cross-section of 6㎡. It will be replaced. It is 25# U-shaped steel support or anchor shotcrete support, with a net section of 9㎡. In order to ensure construction safety, these safety technical measures are specially formulated and are expected to be implemented conscientiously. 2. Construction technical plan 1. The roadway support adopts 25# U-shaped steel support or anchor shotcrete support, with a lower clear width of 3.93m and a clear middle height of 2.8m. The U-shaped steel tunnel is made of rafters and double-resistant nets for the back roof. The rafter specifications are φ (50mm~60mm)-800mm, the double-resistant net specifications are 0.8m-8m, and the mesh is 3cm-3cm. It must be anti-static and flame-retardant. The anchor net spraying tunnel is supported by anchor net spraying. The spacing between anchor rods is 800-800mm. The overlap length of the diamond metal mesh is 100 mm. Each 200 mm interval is tied with 12# iron wire. The anchor rods are made of equal-strength threaded steel anchor rods. The diameter of the anchor rod is 18mm and the length is 1800mm. Each anchor rod is fixed with a piece of resin anchoring agent. The anchoring length is not less than 500mm. The length of the exposed wire of the anchor rod is ≤50mm. The pallet is square and the specifications are length-width=100mm- 100mm, pressed into an arc shape with 10mm steel plate. The diameter of the resin anchoring agent is 28mm, and the length of each piece is 500mm. The anchor rods are fastened with matching standard nuts. The anchoring agent model is Z2350. The anchoring force (rock) of each anchor rod is ≥75kN. 2. When using shotcrete, high-quality cement with a grade not lower than PC32.5 must be used. The sand is pure river sand. The particle size of the gravel is 3 to 5 mm. The mix ratio is cement:sand:gravel=1:2:2 (weight ratio); speed The amount of coagulant added is generally 2 to 3.5% of the weight of the cement. The upper limit of the spray arch is used. When spraying the water area, the amount of accelerating setting agent can be increased according to the situation. The accelerating setting agent must be added evenly at the feed port of the shotcrete machine. . 3. During the construction period, the support standards specified for U-shaped steel must be strictly followed. The distance between sheds is 0.7m (middle to middle), and construction is based on the middle and waist lines. Each shed has 31 rafters and an overlap of 0.35m. 4. For roadway expansion, use manual rock-falling brushing for large cross-sections. For rocks that are hard and cannot be peeled off, rock blasting and hand-assisted rockfalling are used. The old tunnel is reinforced by expanding rods, and the roof is broken by using rafters to control the roof in advance. The U-shaped steel tunnel uses two π-shaped steel beams with a length of 3.5m as a temporary support method after rockfall. The maximum roof control distance cannot exceed 0.7m, the maximum ceiling distance of the anchor-blasting tunnel cannot exceed the distance of one shot. 5. Rock transportation route: main return air lane → 13 mining area return air lane → auxiliary shaft east alley → auxiliary shaft 6. Material transportation route: auxiliary shaft → auxiliary shaft east main lane → 13 mining area return air lane → main return Wind Alley 3. Safety Technical Measures (1) Construction Measures (1) Before expansion, all roof-fall prevention materials must be prepared: 20 pit logs, 30 brazing rafters, 100 wattle fences, and 100 rafters. (2) Before construction, mine technicians will hang the middle and waist lines to mark the direction and slope of the tunnel. The construction team must carefully inspect the construction site and transportation routes and deal with all unsafe factors, and check the old lanes 5m before and after the construction site. For reinforcement, the method of reinforcement is to expand the rods, which must be done firmly to ensure the safety of construction workers. (3) Before construction, the construction team must prepare all types of support materials, maintain normal ventilation in the original tunnel, and strictly prevent harmful gases from exceeding the limit. (4) During construction, the construction site and nearby debris must be cleaned up, and wind, water pipes, cables and other facilities 10m before and after the construction site must be protected to avoid damage. (5) After the cyclic construction operation is completed, the construction team must clean up the debris in the tunnel to ensure smooth transportation lines. (6) The construction team should strengthen roof management and implement the system of asking for help and asking questions continuously during the construction period. (7) Keep the wind flow in the original tunnel smooth, and no windless and breeze operations are strictly prohibited. (8) When erecting permanent supports, temporary supports must be laid first, and risky operations are strictly prohibited. (9) Before drilling, first strictly check the cross-section specifications of the tunnel according to the middle and waist lines. If it does not meet the requirements, it must be dealt with first; before drilling, first knock on the roof and ask about the roof, carefully check the surrounding rock conditions on the roof, and remove live gangue and dangerous rocks. The rock can only be started after confirming that it is safe. The position of the anchor eye must be accurate, the eye position error shall not exceed 100mm, and the eye direction error shall not exceed 15°. The depth of the anchor eye should match the length of the anchor. When drilling, a mark should be made on the drill. The hole should be drilled strictly according to the length of the anchor. The depth of the anchor should be 1700mm for a length of 1800mm. After the anchor eye is drilled, the hole in the hole should be drilled. Clean up rock debris and stagnant water. When drilling, it must be done under the cover of the initial spray.

The order of drilling should be carried out from the outside to the inside, first the top and then the top. (10) Before installing the anchor (net), the accumulated water and rock powder in the eyelet should be blown away with high-pressure wind. When blowing, the operator should stand on one side of the hole, with no one in the direction of the eye hole. Send a tube of resin anchoring agent into the fundus of the eye, insert the anchor rod into the eye of the anchor rod, so that the anchor rod resists the resin anchoring agent, and cover the outer end of the head. Install the nut and install it with the MJ-80 anchor installation machine. Let the anchor installation machine drive the rod to rotate and screw the anchor into the resin anchoring agent. Stir the anchoring agent until the anchor reaches the design depth before removing the anchor. For the rod installation machine, after stirring and rotating for more than 35 seconds, remove the nut, put it on the tray, and tighten the nut. After 15 minutes, tighten the nut to apply a certain pre-tightening force to the anchor rod. The tightening torque is not less than 120N-m. The anchor rod is exposed. The length cannot be greater than 50mm (with the supporting plate exposed). (11) Shotcrete 1. Preparation work ① Check whether the installation of anchor rods and laying of steel strips meet the design requirements, and deal with any problems found in a timely manner. ② Clean up the gangue and debris at the spray site, and connect the air and water pipelines. The conveying pipeline must be straight and without sharp bends. The joints must be tight and there must be no air leakage. It is strictly prohibited to use non-antistatic plastic pipes as conveying pipes. ③ Check whether the shotcrete machine is in good condition, and perform a no-load test run with power, and tighten the friction plate to prevent air leakage. ④ Before spraying, the rock surface must be washed with high-pressure feng shui, and spray thickness signs should be installed on the top and sides of the tunnel. ⑤ Spraying personnel must wear complete and effective labor protection supplies. 2. Process requirements for sprayed concrete. The spraying sequence is: wall first and then arch, starting from the wall base and proceeding from bottom to top. The spray gun head and the sprayed surface should be kept vertical as much as possible. The appropriate vertical distance between the spray gun head and the sprayed surface is 0.6 to 1.0 m. When artificially mixing materials, use tide mixing materials. The cement, sand and gravel should be cleaned and stirred three times to make them evenly mixed. When spraying, the air supply pressure of the shotcrete machine is 0.4MPa, and the water pressure should be about 0.1MPa higher than the wind pressure. The amount of water added is controlled based on the shooter's experience. The most suitable water-cement ratio is between 0.4 and 0.5. During the spraying process, the water supply should be adjusted in time according to changes in the discharge volume to ensure an accurate water-cement ratio. The sprayed wet concrete should have no dry spots, no flow, strong adhesion, and less rebound material. The thickness of the concrete sprayed at one time should be 50mm. When spraying, use high-pressure water to re-flush the sprayed surface. 3. Spraying work The order of spraying work is that when starting up, water must be supplied first, then the air is turned on, then the machine is turned on, and finally the material is loaded; when the machine is shut down, the material must be stopped first, then the water, then the machine, and finally the air. After the spraying work starts, it is strictly prohibited to aim the spray gun head at personnel. If a blockage occurs suddenly during spraying, the spraying hand should hold the spray head tightly and point the nozzle downward. 4. Spraying quality: Before spraying, the rock wall must be cleaned and the floating gangue should be cleaned up. The spray should be even and there should be no cracks, skirts or bare feet. (12) Special types of work must be trained by a third-level institution, hold a certificate to work, and be familiar with the job responsibility system. (13) It is not allowed to conduct maintenance and transportation of various electrical equipment with power on. The power supply must be cut off before servicing the equipment. Maintenance with power on is strictly prohibited. (2) Roof management measures (1) The construction team should appropriately reduce the spacing between anchor bolts according to the lithology of the surrounding rock in the tunnel. When the hanging net shotcrete cannot meet the support conditions, a U-shaped steel frame shed should be used for support. (2) During the expansion, blasting wind was used to assist rockfall. During the construction, the old lane within 5m of the expansion point was built and reinforced with lifting sheds, and the construction process was strictly followed. (3) When the rock mass is soft or broken due to geological changes, use rafters to strike wedges forward from the shed beams as a temporary false roof, and then lower the shed on the temporary false roof. (4) Erect the shed in strict accordance with the quality standards of the shed, so that the shed is firm, the roof is reasonable, there is no empty roof, and the roof of the roadway is flat. It is strictly forbidden to work on the empty roof. (5) When dealing with roof collapse, the mine manager, security inspector, and excavation team leader must follow on site. (6) Follow up with security inspectors to strengthen tunnel inspections. Substandard or deformed sheds must be replaced or repaired by the construction team in a timely manner to prevent roof collapse and blockage accidents. (3) Safety technical measures to prevent roof collapse (1) The expansion site is a rock tunnel, and roof management needs to be strengthened. Changes in the surrounding rock must be frequently observed during construction. If signs of continuous slag falling or roof collapse are found, rapid evacuation must be carried out. personnel, and report to the dispatching room in time. Only after the roof is stable can measures be taken to deal with it. Risk-taking operations are strictly prohibited. (2) If the roof is relatively loose due to the influence of secondary faults during expansion, the method of short excavation and short support should be adopted to minimize the exposure time of the surrounding rock. If necessary, the shed distance can be reduced, and a certain number of tunnels should be prepared near the expansion site. When installing rafters, use the impact wedge method to control the roof in advance to prevent roof collapse.

(3) Treatment of large and small roof collapses. If roof collapse occurs at the construction site due to various reasons during expansion, targeted safety technical measures will be formulated based on the roof collapse situation on site. ① When dealing with roof collapse, departments and construction teams must be on-site to follow and direct and coordinate the work. ② When dealing with roof collapse, you must first control the roof and use the front beam to prevent the situation from expanding; use the wedge method to lift the rafters above the roof beam at the expansion site. The depth and number are determined according to the actual conditions on site. (4) Technical measures for blasting safety (1) During construction, more than three people must cooperate, and a dedicated person should be assigned to observe the roof and surrounding conditions. If any unsafe hazards are found, the work should be stopped immediately to deal with them. Construction can only continue after ensuring safety. (2) During construction, strictly implement the system of knocking on the roof and asking for the top and assigning people to observe the mountain, and strictly prevent the roof from falling on the roof. (3) For construction sites where the rock is relatively hard and pneumatic tools cannot meet production needs, blasting is required. ○1 Before firing, the old alley must be expanded and reinforced. The pipelines in the tunnel must be well protected to prevent damage to the pipelines by falling rocks. ○2 If you need to fire small cannons or vibrating cannons when firing, no more than 2 holes should be fired at a time, and the charge of each eye should not exceed 1 roll. The amount of charge should be strictly controlled. ○3 When firing, one shot, three inspections and a three-person chain firing system are strictly implemented. When firing, all personnel in the construction tunnel must notify each other to evacuate to 100m of straight lanes and 75m of crooked lanes outside the construction site. The entrance is cordoned off and no one is allowed to move in the cordoned area. ○4 The underground blasting work must be performed by full-time blasting personnel, who must hold a certificate and operate in strict accordance with the operating procedures. ○5 All blastholes must be charged forward, and reverse charging is not allowed. The direction of the energy-gathering holes of the detonator and the explosive must be consistent, facing the fundus. ○6 The gunfire crew must place the explosives and electric detonators in a place where the roof is intact, the bracket is intact, and away from mechanical and electrical equipment. Each time the gunfire is fired, the explosive tube box must be placed in a safe place outside the cordon and locked. . (4) During construction, safety supervisors and tile inspectors must follow to the site, frequently check the tunnel conditions and gas concentration, identify problems, and deal with them in a timely manner. (5) During construction, the gangue falling from the tunnel expansion must be cleared away in time. It is strictly forbidden to block the tunnel or affect ventilation and production. (6) During construction, various safety facilities must be in place, otherwise construction is strictly prohibited. (7) During the construction process, the district captain must be on site to identify problems and deal with them in a timely manner. (8) Others are still strictly implemented in accordance with the relevant provisions of the "Coal Mine Safety Regulations", "Operating Regulations for Various Types of Work" and "Quality Standardization". 4. Project quality requirements 1. The net width under the tunnel is 3.93m. The allowable error: qualified products do not exceed 0~100mm, and excellent products do not exceed 0~80mm. 2. The net height of the tunnel is 2.8m. The allowable error is: no more than -30~100mm for qualified products and no more than 0~100mm for excellent products. 3. The bracket faces the mountain reasonably and must not lean forward or backward. It must not exceed the specified value +1° and cannot exit. The legs of the shed must stand on a solid base and be padded with wooden shoes. The depth of the column socket must be 200mm and not less than the design value of 30mm. 4. The back roof is made of double anti-net rafters. The overlap of the double anti-nets is not less than 100mm, the spacing between the nets is not more than 150mm, and it is fastened with three rings and two buckles. 5. Position and quantity of tie rods: There are 3 tie rods in each shed, namely one at the center of the arch, one at the lower clamp connection, and one at 200mm below the U-shaped steel leg. The tie rod bolts must be tightened firmly and connected with the adjacent ones. The sheds are in a straight line. 6. There are 31 rafters between each shed. One rafter should be laid every 0.3m (center to center). The number of rafters between sheds should be set to two, and they should be laid evenly, straightly and securely. They should not be There is a phenomenon of empty side and missing top. 7. After the karabiners, column legs and beams are overlapped according to the designed length (the overlap length is 350mm), two large karabiners are fixed on both sides of each shed, and the spacing between the karabiners is 150mm. When fixing the clasp bolts, use a wrench with a booster rod to tighten firmly and make the front and back become a straight line. 8. Other allowable deviation items: (1) Shed beam level: the allowable deviation does not exceed 50mm. (2) Bracket beam torque: the error is not greater than 100mm. (3) The interface is tight, and the misalignment and clutch should not be greater than 5mm. (4) The error in shed spacing shall not exceed the designed 50mm. 9. The distance between anchor rods is 800mm-800mm, and the allowable error is ±100mm. 10. The thickness of shotcrete is 100mm, and the allowable error cannot be less than 90% of the design value. 11. It must be stable and not skewed, the top must be fully filled, and the back must be tightly mounted. 12. It is required to achieve height, width, flatness, straightness and cleanness after repair.

5. Organizational measures 1. Strictly implement the on-site follow-up system of the shift leader, provide on-site command, and be fully responsible for the safety and project quality on duty. 2. It is necessary to arrange for 1-2 veteran workers with rich experience to operate it in person, and one person to watch the mountain full-time and deal with danger immediately if any danger is discovered. 3. During the construction period, the security inspectors on duty should pay close attention to the situation in this tunnel, take timely measures if any abnormalities are found, and notify the dispatch room. 4. The security inspectors and technicians on duty must strictly control the safety situation and project quality on duty to ensure safe construction and project quality. 5. Other matters shall be strictly implemented in accordance with the relevant provisions of the "Coal Mine Safety Regulations". 6. Emergency disaster evacuation route to avoid fire, gas route: main return air alley → 13 mining area return air alley → auxiliary well east main alley → auxiliary well water avoidance route: main return air alley → 13 mining area return air lane → auxiliary well Dongda Alley → Fujing

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