(1) In the case of concrete mixing, the materials are fed in the order of sand→ gravel→cement→water. The mixing is carried out by automatic metering forced mixer. The construction ingredients are strictly operated according to the mixing ratio; after adding the composite pumping agent, the mixture is stirred for more than 2 minutes. More than 4 minutes, so as not to affect the quality of concrete mixing.
(2) When wet shotcrete equipment spraying concrete, start from the bottom of the tunnel from bottom to top and move with the S curve to avoid the rebound material contaminating the washed rock surface and affect the quality of the shotcrete; the latter injection should be in the previous concrete. After the final setting, if wet mix shotcrete machine is sprayed more than 1 h after the final setting, the concrete surface is wet mix shotcrete machine cleaned with feng shui; the tunnel is sprayed from the bottom of the side walls, and the spray is closed to the center line of the vault to complete a test spray of a ring of shotcrete.
(3) The wind pressure should be strictly controlled when wet shotcrete equipment spraying concrete. If the wind pressure is too small, the jetting force will be weakened, and the requirements for the compaction of the sprayed concrete will not be met, and even the design and specification requirements will not be met. If the wind pressure is too large, the shotcrete will touch the rock face (or the upper spray layer). The subsequent strong impact blows away, both of which will increase the rebound of the aggregate, which directly causes an increase in rebound. Generally, the initial wind pressure ≥0.5 MPa can be started, and the wind pressure should be adjusted according to the discharge condition of the nozzle. The wind pressure of the side wall should be controlled between 0.3 and 0.5 MPa, and the arch control should be between 0.4 and 0.65 MPa.
(4) When wet shotcrete equipment spraying concrete, the thickness of suitable initial spray layer should be determined according to the surrounding rock type and hydrogeological conditions: Class II surrounding rock is divided into 3 times, Class III surrounding rock is divided into 2 times, and Class IV surrounding rock is divided into 1~2 times; The wet spray is used to determine the thickness of the initial spray layer to be 4 to 5 cm and the second spray thickness to be more than 10 cm.
(5) When no steel mesh is sprayed, the nozzle should be perpendicular to the rock face at an angle of 90 ° and deflected to the just-injected part (the inclination angle is controlled within 10 °), maintaining a distance of 0.8 to 2 m to ensure the compacting effect of the concrete. The sprayed surface of the steel mesh is hung, the injection is slightly inclined, and the distance should be controlled within the range of 0.6 to 1.0 m.
(6) The nozzle should be evenly operated according to the spiral path, sub-section, generally not more than 6 m, from top to bottom, one-turn pressure half-turn, slowly moving, each circle diameter 15 ~ 20 cm; if the surface is not flat, should be First, the pit is leveled.
(7) Sprinkle water for 1 h after the final shot of the shotcrete, keep the spray surface moist, and the curing time is not less than 7 d.
