The second lining construction of the tunnel is also the secondary lining support method of the tunnel. The white point is that the concrete layer that we can see on the expressway is not subject to any force.
“Second lining” is a term used in tunnel construction. When the tunnel is excavated, it is moved forward along the face of the hand, and the four sides of the tunnel that has been dug afterwards need to be reinforced. “Second lining” refers to the work that needs to be continued for secondary reinforcement around the reinforced tunnel.
Key points for construction of secondary lining concrete in tunnel
1. A tunnel is a building built underground or under water or in a mountain, with railways or roads for motor vehicles. According to its location, it can be divided into three categories: mountain tunnel, underwater tunnel and urban tunnel.
2. A mountain tunnel that passes under a mountain or hill to shorten the distance and avoid large slopes; an underwater tunnel that passes through the river or the sea to cross the river or the strait; to adapt to the needs of the railway through the big city A city tunnel is crossed underground in the city. Among the three types of tunnels, there are many mountain tunnels.
(1) Before concrete mixing, the moisture content of sand and gravel should be determined and the amount of materials should be adjusted according to the test results, and the construction mix ratio should be proposed.
When mixing concrete mix, the cement quality deviation shall not exceed ±1%, the aggregate quality deviation shall not exceed ±2%, and the water and admixture quality deviation shall not exceed ±1%.
(2) Before the concrete is poured, the base gravel, dirt, and accumulated water in the foundation pit should be removed. It is strictly forbidden to pour the concrete dry mix into the foundation pit with accumulated water.
(3) Before pumping concrete, the cement slurry mixed according to the design mix ratio or the concrete lubrication pipe prepared by halving the aggregate should be used.
(4) Concrete should be transported by concrete mixer truck to ensure that there is no segregation, withdrawal, and mixing of debris during transportation.
(5) Stratified from bottom to top, alternating left and right, and symmetrically perfused from both sides to the vault. The height, order and direction of each layer should be determined according to factors such as mixing capacity, transportation distance, filling speed, temperature inside the cave and vibration. In order to prevent the displacement of the trolley caused by excessive pressure deviation on both sides during pouring, the height difference of the perfusion surface on both sides should be controlled within 50cm, and the casting speed should be controlled reasonably.
(6) Pouring concrete should be directly placed into the warehouse as far as possible. The conveying pipe section should be connected with the hose control nozzle and the casting surface. It should not directly flow to the surface of the waterproof board to the pouring position. The offset should be controlled at 1.2. Within m, to prevent segregation.
(7) During the construction process, the pump should be continuously operated and pumped continuously for construction. It is advisable to avoid “cold seam” caused by stoppage. If it is interrupted for any reason, the interruption time should be less than the initial setting time or remodeling time of the concrete before the concrete. When the allowable time is exceeded, it should be treated according to the construction joint: the concrete at the joint should be tapped before the initial setting, and Make the seam surface have a reasonable, even and stable slope. Concrete that has not been tempered and exceeds the initial setting time of the cement should be removed.
(8) When pouring the concrete to the working window 50cm, before the working window is closed, the residue and other debris in the vicinity of the window should be cleaned, the release agent should be applied, and the sealing agent should be closed to prevent the surface of the window from being uneven. The patch even leaks.
(9) The anti-arc part below the arch line of the tunnel lining is the difficult part of the pouring operation. The rafting performance, slump and tamping method should be controlled to reduce the bubble in the reverse arc and improve the surface quality of the lining.
(10) The mold temperature of concrete should not be lower than 5 °C in winter construction and should not be higher than 32 °C in summer construction.
(11) Concrete should be vibrated and vibrated with vibrators, and reliable measures should be taken to ensure that the concrete is compact. When vibrating, do not shift the formwork, steel bars, drainage facilities, embedded parts, etc.
(12) The top cover is connected to the conveying pipe by the top mold center top sealer, and the top cover is gradually pressed. When the observation hole on the stop plate has a slurry overflow, the mark is completed.
(13) When pouring the concrete lining of the arch, the grouting hole should be reserved in the vault, the spacing of the grouting holes should be no more than 3m, and the reserved holes in the range of each template trolley should be no less than 4.
The grouting filling of the vault should be carried out after the strength of the lining concrete reaches 100%. The strength of the injected mortar should meet the design requirements, and the grouting pressure should be controlled within 0.1 MPa.
(14) After the concrete pouring is completed, the abandoned concrete and garbage at the site shall be cleaned in time to keep the construction site clean and tidy.