(1) When concrete is mixed in the order of sand → crushed stone → cement → water, full-automatic metering force mixer is used for mixing, and the construction ingredients are strictly operated according to the mixing ratio; after adding the compound pumping agent, the mixing is performed for more than 2 minutes. Over 4 minutes, so as not to affect the quality of the concrete.
(2) When spraying concrete, spray from the bottom of the tunnel to the top and move in an S curve to prevent the rebound material from contaminating the washed rock surface and affecting the quality of sprayed concrete; the next spray should be the previous concrete After final coagulation,
If it is sprayed again more than 1 hour after the final setting, the surface of the concrete shall be cleaned with feng shui; the tunnel shall be sprayed from the bottom of the side walls on both sides and closed to the centerline of the vault to complete a test spray of a ring of sprayed concrete.
(3) Wind pressure should be strictly controlled when spraying concrete. If the wind pressure is too small, the spraying force will be weakened, which will not meet the requirements for the compactness of the sprayed concrete, or even meet the design and specification requirements. The subsequent strong impact blows away, and both will increase the rebound of the aggregate, thereby directly increasing the rebound. Generally, the initial wind pressure ≥0.5 MPa is required to start the operation, and the wind pressure is adjusted according to the discharge of the nozzle. The side wall wind pressure should be controlled between 0.3 and 0.5 MPa, and the arch part should be controlled between 0.4 and 0.65 MPa.
(4) When spraying concrete, the appropriate initial shot thickness should be determined according to the type of surrounding rock and hydrogeological conditions: Type II surrounding rock is divided into 3 times, type III surrounding rock is divided into 2 times, and type IV surrounding rock is divided into 1-2 times; Using wet spraying, the thickness of the initial sprayed layer was determined to be 4 to 5 cm, and the thickness of the second sprayed layer was more than 10 cm.
(5) When spraying without steel mesh, the nozzle should be as close as possible to the rock surface at an angle of 90 °, and should be biased towards the newly sprayed part (the inclination angle should be controlled within 10 °), maintaining a distance of 0.8 to 2 m to ensure the compactness of the concrete. The sprayed surface on which the steel mesh is hung, the fuel injection is slightly inclined, and the distance should be controlled within the range of 0.6 to 1.0 m.
(6) The spray head should run uniformly along the spiral trajectory, divided into sections, generally not more than 6 m, from top to bottom, press a circle for half a circle, and move slowly, each circle diameter 15 ~ 20 cm; if the spray surface is uneven, it should First spray the pits to level.
(7) Water spray curing should be carried out 1 hour after the final setting of sprayed concrete to keep the sprayed surface moist and the curing time should be no less than 7 days.