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Wet shotcrete machine in tunnel construction steps

2018-05-05 13:36:49

Wet shotcrete machine is widely used in the tunnel construction process. The wet spray method to spray the commercial concrete construction process is to produce the finished commercial concrete at the cement concrete mixing station according to the mix ratio, and after the commercial concrete is transported to the working surface, the wet spray machine is used. The pressure is sent to the nozzle part, the accelerator is sprayed at a high speed after the nozzle is added, the commercial concrete and the quick-setting agent are fully combined in the high-speed spraying process, and the construction method of the commercial concrete spray layer is impacted on the surrounding rock. The wet spray method adopts a relatively small water-cement ratio, the commercial concrete is fully mixed in the mixing machine, and the amount of the sand stone material and the water-reducing agent can be accurately controlled, and the accelerator is added during the spraying process. Therefore, the wet spraying product is used. The concrete has good strength, high early strength, and less rebound (rebounds of 15% to 20%), which saves materials and reduces dust pollution, and improves the working environment.

Wet shotcrete machine in tunnel construction

1. Preparation for wet spray construction.

Before construction, it is necessary to first check whether the excavation profile of the tunnel preparation injection operation meets the design requirements. The surveyor should measure the basic size of the surrounding rock to be sprayed, make up for the under-excavated site, knock on the roof, remove the pumice, and use high-pressure water or high-pressure air to flush the surrounding rock. Second, check whether the wet shotcrete machine is working properly. After the wet shotcrete machine is transported to the working surface, it is energized for no-load operation, checking whether the power supply is normal, whether the air pressure system is stable, whether the pipeline is unblocked, and whether the inlet shaker is properly installed, and whether the wet shotcrete machine chute is in place. We need check whether construction workers are in place.

2. Supply air.

The supply air is the high-pressure air that is used to supply the wind and passes through the air duct and enters wet shotcrete machine. The commercial concrete in the wet jet engine is transported to the nozzle by the compressed air and then injected at a higher speed to the sprayed surface. Above, the commercial concrete is impacted and compacted during the injection process to form dense commercial concrete. The wind pressure is generally controlled within the range of 0.4-0.6Mpa, to avoid falling out of the mortar layer because the air pressure is too large after the rough aggregate hits the surrounding rock or the air pressure is too small. The best wind pressure is Commercial concrete rebound is small, easy to adhere, the surface of wet luster.

3. Commercial Concrete Preparation and Transportation.

Commercial concrete preparation is prepared in a mixing station. The cement should be preferably Portland cement or ordinary Portland cement, and the strength grade should not be less than 32.5. The coarse aggregate should be selected to meet the requirements of the gravel, the particle size should not be greater than 15mm, the aggregate grading should be continuous grading The fine aggregate should be hard and durable medium coarse sand, its fineness modulus should be greater than 2.5, and the commercial concrete sand rate is generally 45-55%. Water uses potable water or water that meets the requirements. The superplasticizer uses a superplasticizer to reduce the water content of the commercial concrete, and to ensure that the commercial concrete has sufficient slump, generally 80~130mm. Commodity concrete mixing time should not be less than 2min to avoid uneven mixing. Transportation is carried to commercial tunnels using commodity concrete tankers. The tanker should be reversed before loading commodity concrete, and the remaining water in the tank should be unloaded to avoid increasing the slump and reducing the strength of the commodity concrete.

4. Wet Spray Operation.

Spray the commodity concrete from the bottom of the tunnel from the bottom up to prevent the rebound material from contaminating the washed rock surface. When spraying, the nozzle is about 1.0m away from the rock surface, strictly in accordance with the wind pressure requirements, and the commercial concrete conveying pipe speed. The condensate pipe is used so as to avoid sharp bends or other phenomena in the transfer pipe when the sprayer changes his/her direction, resulting in a phenomenon such as blockage of the pipe or discharge, and failure of the quick-setting agent.

In the process of spraying, the wind pressure must be reasonably controlled, and at the same time, the material must be evenly and continuously fed. The hopper must have a certain amount of mixture; in order to ensure the stable and uniform injection of commercial concrete, the problems of pulse, blockage and the like are avoided, and the vibrating screen is The debris and large aggregates must be promptly cleaned.

The thickness of the initial spray layer of the commercial concrete is designed with reference to the surrounding rock and actual construction conditions. If the initial spray layer is too thin, the aggregate is not firmly bonded to increase the rebound. If the initial spray layer is too thick, the commercial concrete will weigh more than the adhesive strength between the commercial concrete and the rock surface or exceed the internal cohesion, causing the primary spray layer to fall. Its thickness is generally controlled at about 5cm.

When spraying, the operator must pay attention to the spray beam perpendicular to the spray surface, the angle between the vertical line of the material beam and the spray surface should not exceed 0-15 degrees, to avoid the spray angle is too large, so that the mixed material in the rebound by the spray surface caused by falling, Increase the amount of rebound or produce bumpy wave jets. Some parts are equipped with a blind pipe, in order to form a water-permeable space behind it, the blind pipe must be sprayed; some rock faces are equipped with reinforced mesh, and the distance between the spray surface and the spraying surface should be minimized during the spraying process. At the same time, there is a certain angle with the vertical direction to ensure that the compactness of the commercial concrete sprayed behind it meets the design requirements.

When spraying, it is necessary to determine the spray thickness according to the construction design. If the spray thickness is not enough, the aggregate may rebound. If the spray thickness exceeds the design requirements, the spray layer will fall, flow, and even produce hollow drums and other defects. Under normal circumstances, a shot thickness of at least 2 times the size of the aggregate, the thickness of the spray layer is about 5cm thick for one spray and at least 10cm for the secondary spray layer. A reasonable arrangement of stratified spray Time interval; At the same time, in order to make the bonding of the upper and lower commercial concrete meet the construction specification, the surface shall be sprayed with wet water first during the secondary injection.

5. Leveling and Maintenance.

The natural leveling after completion of commercial concrete injection can increase the durability of the structure and ensure that its strength reaches the design requirements. If vibration leveling is performed after spraying, it may cause the connection of commercial concrete and reinforcement, and there may be cracks in commercial concrete. These phenomena all cause some damage to the structural strength. In fact, it is not appropriate to adopt a natural leveling treatment method. After the establishment of the commercial concrete surface is too rough, it will have an impact on the second liner construction in the later period, so in the leveling construction process, after the initial setting of the commercial concrete, operation Personnel can use scraper to remove excess commodity concrete, and then use cement slurry, spray leveling.

The surface of the commercial concrete after wet spraying is rough, and the water disperses quickly, which causes the cement to not fully hydrate or cause shrinkage cracking of the commercial concrete, and reduces the strength of the commercial concrete. Therefore, the maintenance of the concrete is very important. According to the normal construction sequence, at least 7 days of sprinkler maintenance should be started when the concrete is finally settling. For the palm surface humidity is relatively high (humidity reaches 90%) can’t take special sprinkler measures. 

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