What are the requirements for shotcrete in tunnel construction?

(1) Before spraying concrete, the dust and sundries on the rock wall shall be washed clean with water or high-pressure air duct.

(2) loose stones or objects blocking sprayed concrete found during spraying shall be removed in time.

(3) The spraying operation shall be carried out in sections and pieces from bottom to top, and the length of each section shall not exceed 6mm.

(4) The primary injection thickness shall be determined according to the design thickness and injection position, and the initial injection thickness shall not be less than 4-6cm.

⑤ The spraying operation should be carried out in layers with appropriate thickness, and the latter layer should be sprayed after the final setting of the previous layer of concrete. If the interval after final setting exceeds 1h and the initial sprayed surface is covered with dust, the sprayed surface should be cleaned with high-pressure gas and water. When there is a depression on the rock surface, it should be leveled in combination with the initial spray.