With the wide application of highway tunnels, the complex tunnel construction technology also puts forward higher requirements for the technical level of construction personnel, so it is very necessary to further strengthen its research and take effective measures to solve the problems, so as to continuously improve the quality of highway tunnels and promote the development of highway construction. On this basis, the related technologies in highway tunnel construction are analyzed.

1 construction technology of highway tunnel engineering

Project overview

In the construction of a highway route, the axis of a tunnel project points to the north-south direction, and the starting point of the tunnel project is located in the north of the mountain. The terrain of tunnel excavation is not very good, and it is inclined. There is a river near the project construction area. When the tunnel was excavated to about 30m, it was found that the coating on the construction site gradually declined, with a slope of 1.5%, which seriously hindered the smooth progress of the project. After many studies by constructors and designers, the construction scheme of simultaneous construction of both ends of the tunnel was finally decided.

Reasonable arrangement of construction operation line

According to the actual situation of the tunnel, it is necessary to arrange the operation line in strict accordance with the design requirements. First, the internal excavation is controlled at 40-50 m, and then the middle wall is poured. When the concrete strength reaches the relevant requirements, the left hole can enter. At this time, the distance between the tunnel faces of the left and right tunnels is controlled at about 10m, and the distance between the secondary lining and the tunnel faces of the left and right tunnels is between 25m and 35m. Its main purpose is to make the excavation of the middle pilot tunnel, the middle wall, the left and right tunnels and the secondary lining well formed at the entrance and exit of the tunnel, and its main purpose is to facilitate the construction and shorten the construction period.

Initial support

The initial support includes three processes: pipe making, drilling, pipe installation and grouting.

In pipe making, hot-rolled seamless steel pipes are mainly used in the initial support of this project, with the length, outer diameter and wall thickness of 5m, 5cm and 0.5cm respectively. At the same time, the two ends of the pipe are made into cone heads and welded with steel hoops to drill holes. It should be noted that the spacing should be controlled at 150mm, and the others are grouting holes.

Drilling, the first is to fix the hole, mainly to excavate the support point of the working face in the nearest place, and then arrange the spacing of each small conduit, which is 3.2m and 2.5m respectively.

Pipeline installation and grouting, its main job is to do a good job of hole cleaning. Under normal circumstances, high-pressure air will be used, and grouting work will be carried out after the small conduit is installed.

Tunnel excavation

The tunnel excavation of this project is mainly divided into two parts, the middle pilot tunnel and the left and right tunnel excavation.

Pilot hole, the excavation of pilot hole can start after the completion of hole-forming surface. The specific process is circular excavation with a distance of 0.5m-1.2m. After excavation and molding, concrete pouring can be started after inspection. Then locate the anchor hole, and finally start drilling construction. After completion, hole cleaning and cement mortar grouting will be carried out. When finished, start to butt the arch. The main method is splicing with U-shaped steel bars. Because the main excavation method of the pilot tunnel in this project is two steps, the excavation sequence should be upper steps, support and lower steps.

The excavation of the left and right holes can only be carried out after the strength reaches more than 70%. In this process, two-step parallel excavation is mainly adopted. It should be noted that in actual engineering construction, it is necessary to dig an annular pilot pit when excavating the steps, and then start the excavation of the core, and the distance between the core and the vault should be controlled within a certain range.

Secondary lining

The secondary lining should not only support the surrounding rock, but also beautify the appearance of the tunnel, so the lining quality must achieve the effect of solid inside and light outside to ensure the beauty of the tunnel. If the deformation around the initial support shows no signs of slowing down. When the specification requirements are seriously exceeded and the initial support cracks, temporary emergency support measures must be taken in time. If the quality of the secondary lining system is affected, the support type and parameters must be adjusted in time to effectively control deformation, avoid collapse and ensure the engineering quality. In addition, when choosing a trolley for secondary lining, we should try to choose a large formwork or integral formwork trolley with flat surface and tight joints, which must meet the design requirements. Appropriate rigidity should be selected to reduce formwork deformation and other problems to ensure smooth and flat lining surface, and waterproof and drainage measures should be taken to avoid water leakage.

Management of construction difficulties in No.2 tunnel project

Combined with the project, we can summarize the difficulties in the construction technology of highway tunnel engineering, and analyze the technical difficulties and countermeasures in the construction of highway tunnel engineering below.

Material selection

In the construction of highway engineering, a very important part is material, which directly affects the quality of the project, so we need to pay attention to it. For highway tunnel engineering, its pavement needs to have corresponding conditions, including vehicle use requirements, rainwater leakage and so on. Therefore, in general, the mixture with smaller particle size and smaller gap will be selected, which can play an anti-seepage effect and prolong the service life of the highway.

Construction treatment of karst cave

One of the major difficulties in highway tunnel construction is the construction of karst caves, which are ever-changing. As far as the current situation is concerned, we have also taken some corresponding measures to solve the problems of various caves. It mainly includes: under normal circumstances, we will choose the method of reinforced concrete beam crossing to solve the problem of soft filling in large karst caves, but it will greatly increase the cost. So the actual operation needs to be carried out according to the time in the hole. However, if it is a dry hole, more factors need to be considered.

Treatment of waterproof and drainage engineering

Water accumulation will directly affect the service life of highway tunnels, so it is very important to solve the drainage problem. Before construction, reasonable design should be made in combination with the actual situation, and at the same time, the drainage problem of waterproof platform and back should be fully considered to ensure the normal operation after drainage.

Safety management issues

Safety management in highway tunnel construction is a very important part. It directly affects people's life safety and the reputation of the construction unit, so it needs our attention.

The construction unit shall implement the design requirements of the project, combine the specific construction site conditions, often analyze the construction situation in the process of organizational design, construction and implementation, do a good job in the safety organization and management of construction, ensure the safety and quality of construction, and strive to complete the task of highway tunnel construction on time. The construction unit should improve the safety system and organization, establish the concept of "safety first, prevention first", and set up a special safety management organization to check and supervise the safety of the construction site in time. In addition, construction enterprises should implement the target system, strengthen safety management, conduct dynamic analysis of construction safety, and improve the overall safety management level of highway tunnel construction units.

3 Conclusion

In a word, highway tunnel construction is a very complicated underground linear project, and there will be many uncertain factors in the construction process, which will bring many security risks to highway tunnel construction, so it is necessary to further strengthen its research. This paper analyzes the related technical aspects of highway tunnel engineering in order to provide some reference.

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