Aiming at the common waterproof and drainage treatment methods of expressway tunnels, this paper introduces the construction technology and matters needing attention in each process of tunnel waterproof and drainage treatment.

Keywords tunnel; Waterproof and drainage; construction technique

With the gradual completion and opening of the national expressway network, water leakage sometimes occurs at the construction joints and secondary lining joints of completed expressway tunnels, which seriously affects the safety of operating vehicles. It is more and more important to do well in tunnel waterproof and drainage during construction.

1 Waterproof and drainage treatment before entering the tunnel

1) Before entering the tunnel, according to the hydrogeological data provided by the design drawings, survey the terrain of the tunnel site and check whether there is surface water. If there is surface water, it should flow through the line as far as possible without passing through or being smaller than the tunnel site, so as to reduce the influence of surface water on the tunnel after tunnel excavation.

2) According to the requirements of design drawings, the intercepting ditch at the top of the cave should be done well before entering the tunnel to prevent surface water from entering the excavated tunnel, which can also reduce the rain washing the excavated slope in rainy season.

3) Before entering the tunnel, slope treatment shall be carried out according to the requirements of design drawings.

2 waterproof and drainage in the process of excavation

1) After the tunnel excavation, the original flow direction of fissure water and groundwater in the surrounding rock of the tunnel changes, and a large amount of groundwater and fissure water: even a large amount of surface water flows into the tunnel under the condition of poor surface treatment of the tunnel, so whether the simulated drainage treatment after the tunnel excavation is timely and the scheme is correct directly affects the stability of the tunnel. The principle of waterproof and drainage treatment after tunnel excavation is: drainage is the main principle, and prevention, blocking, interception and guidance are combined. Immediately after tunnel excavation, the tunnel face after excavation shall be sprayed with concrete at the beginning, and the thickness of sprayed concrete is generally 3-5 cm. The purpose of initial shotcrete mainly includes the following points:

(1) Close the tunnel face to reduce the flow of fissure water and groundwater into the tunnel;

(2) Reduce the deformation rate of surrounding rock after excavation, and provide a safer construction environment for initial support;

(3) After tunnel excavation, especially in the case of poor surrounding rock conditions, the over-excavation and under-excavation of surrounding rock often exceed the allowable values in the specifications, resulting in uneven surface of surrounding rock after excavation. After the initial spraying, the surface of surrounding rock is required to be basically smooth to ensure the drainage effect after the drainage pipe is laid.

2) After the initial shotcrete is completed, drill holes to drain the water seepage place according to the water seepage situation of surrounding rock, so that the water seepage flows out from the drilling place, and the drainage half pipes are arranged in a tree shape according to the drilling situation, and are collected to the longitudinal drainage pipe every 3~5m according to the water seepage situation.

At present, in the process of expressway tunnel construction, some units pay insufficient attention to the process of timely initial spraying after excavation, and the construction is perfunctory, resulting in uneven drainage pipe laying. Drilling and drainage are not serious, the laying of drainage half pipes is not standardized, and the quality of drainage half pipes is uneven. When some drainage pipes are laid and sprayed with concrete, the coating of the drainage pipe is broken down, which leads to the blockage of the drainage pipe, which greatly affects the drainage effect of the drainage pipe.

3 geotextile waterproof board construction

If the construction of drainage pipe after excavation is the first line of defense for tunnel waterproof and drainage treatment, then the construction of geotextile waterproof board is the second line of defense. For large areas with water leakage or water accumulation, materials such as waterproof cloth, film and plastic cloth must be used to guide water away from the construction surface. When the waterproof board is laid in a suitable position and then removed, the water will flow down the geotextile with a drain pipe. Before waterproof board construction, the following work should be done:

1) Sharp protrusions on the sprayed concrete surface must be chiseled or smoothed to prevent the waterproof board from being punctured after laying, and the sprayed concrete surface should be smooth.

2) If it is found that there is still water seepage on the sprayed concrete surface, the drainage pipe should be drilled and laid according to the above method.

3) After the above work is completed, start laying geotextile. The hanging point of geotextile is in the arch 3N4 and the side wall 2-3, and the geotextile should have a certain degree of looseness. The general inspection method is to press the geotextile on the sprayed concrete surface by hand, so as to feel tight. Geotextiles are usually fixed by heating nails and melting washers. After the geotextile is laid, the waterproof board is laid and welded on the hot melt pad. It is required that the melting point of the hot-melt pad should be compatible with that of the waterproof board, so as to prevent the waterproof board from being welded through due to mismatched melting points during welding. The circumferential lap of waterproof board shall not be less than 10cm, and it shall be welded with a special welder to check the air tightness of welding effect. Inspection method: the inflation pressure is 0. 15Mpa, and the constant pressure time is not less than 2min. Waterproof board should also be laid with a certain degree of looseness to prevent the second lining concrete from crushing the waterproof board due to insufficient looseness.

4) After the waterproof board construction is completed, protective measures should be taken to prevent the waterproof board from burning through during the construction of the second lining steel bar. Measures taken include placing iron sheets or wooden boards between waterproof boards and steel bars.

4. Construction of longitudinal and transverse drainage pipes

The seepage in the surrounding rock of the tunnel leads from the drainage semi-pipe to the longitudinal drainage pipe, then to the transverse drainage pipe, then to the central drainage pipe or drainage ditch, and then to the outside of the tunnel, forming the drainage system in the tunnel. In the design of longitudinal drainage pipe, some design drawings require drilling the upper part, while others require drilling all holes. In order to ensure that all the accumulated water in the tunnel side wall outside the longitudinal drainage pipe can flow into the longitudinal drainage pipe, it is suggested to drill all the longitudinal drainage pipes. The following points should be paid attention to during the construction of longitudinal drainage pipeline:

1) The elevation of the concrete surface of the longitudinal drainage pipe base must be consistent with the longitudinal slope of the tunnel to avoid water accumulation in the pipe after the installation of the longitudinal drainage pipe. In the actual construction process, when pouring the foundation of longitudinal drainage pipeline, the construction personnel often ignore the control of the top elevation of the foundation, which is easy to cause the actual top elevation and design foundation of the foundation to exceed the allowable values in the code. When the longitudinal slope of the tunnel is small, it is easy to form water in the longitudinal drainage pipe.

2) When winding the longitudinal drainage pipe, the filtered gravel in the winding layer should be washed clean before use. Geotextile should completely wrap the drainage pipe of the head office to avoid debris blocking the drainage hole of the longitudinal drainage pipe. The winding method of longitudinal drain pipe is shown in Figure 1:

5 waterproof and drainage treatment of secondary lining

The secondary lining waterproof and drainage treatment is the last line of defense for tunnel waterproof and drainage treatment. During construction, a water stop or hose shall be added between the secondary lining of each board and the secondary lining of the next board along the circumferential direction of the tunnel, and the design requirements of the water stop or hose shall be located in the center of the thickness of the secondary lining.

6 conclusion

In fact, it doesn't need complicated technology to do well the waterproof and drainage treatment of tunnels. The key is to take every working procedure seriously during construction, starting from every working procedure of tunnel construction. The construction quality of primary support, waterproof board laying, secondary waterproof lining and drainage facilities has great influence on the waterproof and drainage effect of the tunnel, and a slight negligence in construction may cause hidden dangers of water leakage. Therefore, the construction quality of each process must reach the expected effect of design, so as to ensure the quality of tunnel waterproof and drainage engineering.

;