The Shotcrete Shotcrete is suitable for shotcrete construction of railways, highways and municipal tunnels. The initial support of shotcrete in the tunnel adopts the wet spray process. The shotcrete is concentrated at the mixing station outside the cave, transported by a concrete mixer truck into the cave, and sprayed with a wet sprayer. After the completion of the tunnel excavation, the concrete shall be injected with not less than 4cm of concrete to seal the rock face, and then anchor rods shall be erected, erected steel racks, and steel mesh shall be suspended. The initial spray rock face shall be cleaned and then sprayed to the design thickness.
The construction process of Shotcrete Shotcrete Shotcrete is as follows: 1. The shotcrete operation procedure should be: open the accelerator auxiliary wind → slowly open the main air valve → start the quick-setting coagulant metering pump, the main motor, and the vibrator → add concrete to the hopper.
2. The shotcrete operation should be carried out in segments, slices, and layers in sequence. The injection sequence should be from bottom to top. The length of the segment should not exceed 6m. At the time of spraying, the low enthalpy is roughly leveled, and then it is stratified and reciprocally injected from bottom to top.
1 In the construction of shotcrete section, the slope of the last sprayed concrete shall be reserved. The width of the bevel shall be 200-300mm. The inclined surface shall be flushed and wetted with pressure water before spraying the concrete.
The two-slice jets are to be carried out from the bottom up, and first spray the concrete between the steel frame and the wall, and then spray the concrete between the two steel frames. Sidewall shotcrete should be sprayed upward from the foot of the wall so that the springback does not become trapped in the final spray.
3 When stratified injection, the next layer of spray should be performed after the final layer of concrete is finalized. If spraying is completed after 1h of final coagulation, the surface of spray layer should be cleaned with feng shui. The thickness of a shotcrete is such that the shotcrete does not slip and fall without falling. It cannot affect the bond strength and cohesive force of the shotcrete due to too large thickness, nor can it be too thin to increase the rebound amount. The shotcrete thickness of a side wall is controlled at 7 to 10 cm and the arch is controlled at 5 to 6 cm, and the thickness of the sprayed layer is kept uniform. When the concrete is sprayed on the top, in order to avoid the occurrence of slumping, the interval between the two should be 2~4h.
3, the jet speed should be appropriate to facilitate the compaction of concrete. The wind pressure is too high, the injection speed increases, and the rebound increases; the wind pressure is too small, the injection speed is too small, and the pressure strength is small, which affects the strength of shotcrete. Therefore, after starting the machine, observe the wind pressure and start the operation after the initial wind pressure reaches 0.5 MPa. Adjust the air pressure according to the discharge conditions of the nozzle. The general working wind pressure: 0.3-0.5 MPa on the side wall and 0.4-0.65 MPa on the arch. In the loess tunnel shotcrete, the jet pressure is generally not greater than 0.2 MPa.
4. Keep a proper distance between the spray nozzle and the sprayed surface when spraying, and the spray angle should be as close to 90° as possible so as to obtain maximum compaction and minimum rebound. The distance between the nozzle and the sprayed surface should be 1.5~2.0m; the nozzle should be continuous and slow to move in a horizontal direction, and the circle should be pressed half a turn. The ring circled by the sprayer should be 40~60cm in the horizontal direction and 15~20cm in height; When the surface is covered by a steel frame or steel mesh, the nozzle may be slightly deflected, but it should not be less than 70°. If the angle between the nozzle and the sprayed surface is large, it will cause the concrete material to roll on the sprayed surface, creating a bumpy wave spray surface, increasing the rebound amount and affecting the quality of the sprayed concrete.
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