According to the size of the proposed hanging area outside the tunnel, cut 2-3 sheets of relatively narrow rolled waterproof boards, and then lay them on the ground and weld them into large-scale waterproof boards which are convenient for transportation and hanging, so as to reduce the number of welding seams in the tunnel operation and improve the welding quality. Joints shall be reduced for waterproofing sheets. The splicing of waterproof board is welded by double welding seam of heat sealing machine, and the lap width is required to be no less than 100 mm. The temperature and speed of heat sealing machine shall be well controlled to ensure the welding quality. The weld shall be tight, and the effective welding width of a single weld shall not be less than 12.5mm

Before welding, the surface of the head plate to be welded shall be wiped clean, and the welding temperature and speed shall be determined by testing according to the material. During welding, missed welding, false welding, scorching or welding penetration shall be avoided. The length of the first laying along the longitudinal direction of the tunnel should be about 1.0m more than that of the secondary lining construction, so as to connect with the waterproof layer of the next cycle; at the same time, the joint of the waterproof layer and the joint of the lining concrete can be staggered by about 1.0m, which is beneficial to prevent the leakage of the concrete construction joint.

Key points of Construction:

In order to ensure the quality of the waterproof board, the trial laying and positioning should be carried out first. The control of fixed point spacing: the distance between fixed points is 0.5-0.7m at the arch and 1.0-1.2m at the side wall. The fixed points should be appropriately added at the concave and convex places and evenly arranged. Relaxation rate: the spacing between rings of waterproof board shall be determined according to the requirements of laying relaxation rate. The empirical value of circumferential relaxation rate is generally taken as 10%, and the longitudinal relaxation rate is generally taken as 6%. Proper adjustment shall be made according to the smoothness of initial support surface to ensure that the slab surface and shotcrete surface can be closely adhered during concrete pouring.

The waterproof board hole should be laid from bottom to top and ring-shaped. The lifting ring welded on the waterproof board should be fixed on the expansion pipe with wood screws. The waterproof board should be laid 1-2 lining sections ahead of the second lining construction section to form the second lining construction section of the paving and hanging section inspection section