Analysis About Road Tunnel Design

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Abstract: The road tunnel is playing a very significant role in improving the standard of highways, protecting ecology environment and increasing the efficiency of operating. And the design of road tunnels is the key to success. This essay will do the technical analysis from the tunnel entrance, tunnel structure and the design points of waterproof system.

Keywords: road tunnel waterproof system Technical analysis

With the constructions of highways, especially the rapid development of the road tunnel, the number and length of the road tunnel is increasing, and the problems of design and construction that need to be studied and explored is gradually apparent. This article wills shallowly analysis from a design perspective in a few questions.

1 The overall design principles

Based on the conservatories, geological, landscape, social cultural and environmental’ comprehensive survey, combining the position of the tunnel's axis plan, the plane and vertical line and the position of holes, then propose the best program,.

The position of specialty long tunnels should control the direction of the routes while the geological environment conditions are very poor to avoid from the bad geological sections of route. The positions of longer tunnels not only should avoid the bad sections as possible as they can ,too, but also should consider the direction of the route, The less longer and short tunnels can submit to the direction of the route.

The boundaries of traffic lanes and buildings are defined by the road grade and designing speed. Guarantee to satisfy the tunnel’s function and the structure’s good force, determine the economical and legitimate internal outline of cross sections.

The flat, vertical alignment to both the inside and outside of the tunnel should be coordinated to meet the traffic safety and comfort requirements.

According to the tunnel length, traffic volume and composition, direction of traffic and environmental requirements, choose a reasonable ventilation, to determine the set scale of the ventilation, lighting, traffic control and electrical facilities.

Long tunnel, when necessary, should be designed for defending disaster.

The highway grade, tunnel length, construction methods, schedule and operational requirements, both inside and outside the tunnel waterproofing and drainage systems, fire water supply system, supporting the same generation, debris handling, management, traffic engineering facilities and the environmental protection should be combined into account.

2 Design of tunnel entrance

China's highway tunnel design specification does not specify the range of the tunnel entrance, so we often regard the Tunnel portal as a single unit with the hole. Japanese highway tunnel design specification once indicated the cave design includes the tunnel entrance section, tunnel portal and its front and rear part of the road range of the overall design, and also regulated the entrance, portal and connect sections. In fact, in some of China's road tunnel design, in accordance with topographic and geologic conditions to separate the hole and the portal design, connect the with a window or a closed Myeong-dong, gallery-style studio holes in the middle to form the hole design.

Tunnel portal location should be selected to maximize the protection of the mountain state of nature. conducive to harmony with the environment, traffic safety and repair and maintenance ,and strive to avoid the high slope or deep drawing slot in front of the tunnel entrance. The location of Tunnel portal is mainly affected by terrain and determined by taking the use of topographic maps, the horizontal and vertical alignment maps of cross-sections. Vertical section diagram control with the elevation slope, and the cross-sections control with the slope in front of hole or cutting depth, topographic map for the overall layout to meet the functional requirements and aesthetic requirements. The location of the hole should be selected to ensure safety during the construction and contribute to driving safety and protection of natural ecological. It should also attach importance to the tunnel axis and the contour lines of the angle between generally 45 ° is appropriate is not small. Determine the location of hole is mainly considers the surrounding conditions, according to the geological vertical section diagrams, topographic maps and related information, and the thickness of top soil covering to the entrance should not less than 115 m.The geological Longitudinal map can control the height of the elevation slope, help to choose the construction methods and reinforcement measures to rock, Control the angle from the topographic map size, then layout the construction sites.

3 Tunnel figure structural design

In spite of the entrance taking the Myeong hole structure,he remaining sections of the supporting cavern are designed according to principles of NATM. Ⅳ, Ⅴ grade rock use the composite lining, Advanced pipe roof and

Small pipe grouting to reinforce the layer, and which are constituted by I-beam gantry(or Grille arch),system anchor, steel mesh and the shotcrete. And the

Ⅲ Grade surrounding rock are taking the system anchor, steel mesh and shotcrete as the initial support. Between the steel arch set a few ¢ 22cm vertical connection steels. And the arching dense paste with rock.. Bolt set to play at rock levels should be perpendicular. Under normal circumstances the secondary lining take use of plain concrete for constructions. But when the design load is higher, especially shallow, soft rock sides, and post-load deformation is large, it must use concrete to ensure the safety of tunnel support structure. A reasonable time to the secondary lining should be based on monitoring data. Maximize the carrying capacity initial support .Make sure not exceed its carrying capacity, giving full play to the use of self-stability of rock.

4 Discussion of the tunnel longitudinal

The design specifications of highway tunnel longitudinal is as greater than 013% and less than 3%. only 50m long tunnel is not limited by slope, and this is very difficult for the tunnel of mountain road. The topography of mountain changes frequently, the most of high grade roads tunnel are whose length below 50m and the standard writing is difficult if the longitudinal is limited to less than 3%, sometimes can only meet the situation by extendingthe line. It is also hard even in third or fourth grade roads. The main factors to managed the tunnel Longitudinal is ventilation.

Because the longitudinal is large and reduce the cars’ speed, so the amount of the harmful gases and smoke that cars discharged is large. Considered sanitation conditions inside the tunnel, it is better if the longitudinal is small. But for the length is 500m below, tunnels in mountain road, there is no need to require mechanical ventilation because natural wind and piston wind generated by vehicle traffic can dilute the harmful gases and smoke. not necessarily ideal for small longitudinal. With the rising level of automobile manufacturing technology, accelerate the rapid improvement of vehicle performance, and the amount of CO emissions is sharply decreased. Meanwhile, China's auto scrapping time has been reduced from 10 to 14 years to 8 to 10 years, indicating that the speeded-up update rate of car.

5Waterproofing system design requirements and priorities

The current waterproofing design for road tunnel is more rough and it is reflected in the contents of the file: the material is too simple, not specific to the construction requirements, and so on. We know that waterproof design including three aspects: drainage inside and outside the caveand water protection and water shut-off inside the cave, and these three constitute a complete waterproofing system of tunnel. However, the location of the various parts, the base surface state and water is not the same, so the choice of materials, construction and technical requirements should also be different. The water protection inside the cave and water shut-off, for example. the former with a waterproofing membrane and the latter with a rubber band, but the aging of their requirements are the same, cause the requirements on their mechanical properties is not the same , with the base surface for the waterproofing membrane is uneven, and the rubber band (of) the base surface is flat. Therefore, only label the material design file type is not enough. Moreover, because the targets to the eligibility criteria set too low, there is a great performance difference between a qualified product and a great product. Such as the tensile strength to the PVC waterproof board, the qualified product is

7Mpa, superior product reached 15Mpa, and chooses what kind of design documents should be clearly defined. So, the waterproof design should be detailed in the content, the requirements should be clear and specific, attention should be paid to the waterproof design and construction technology to match the construction process and construction quality, so can ensure the design consistent to the implementation results.

The waterproofing system design of highway tunnel is necessary to meet the functional requirements of waterproofing and drainage, but also should consider the maintenance and easy replacement. Water system located in the injection mold after injecting the concrete is worthy of adoption and promotion, and here is its structure: bedrockSprayed anchor concrete module Injection the concrete Waterproof layer Protective layer. This structure has the following advantages:

( 1) The base surface flat enough to adapt to a wide range of waterproofing membrane.

(2) can reduce the time of the Injection andcasting progress of the concrete. and also is conducive to stability and security of construction of the tunnel rock

(3) The construction period about waterproof layer is not controlled by the tunneling process, neither affect the progress of other processes.

(4) Waterproof layer’s repair or replacement is more convenient.

(5) To meet the Man-made landscape expectations and achieve the maximum aesthetic requirements.

three kinds of the form of protective layer:

Form 1: poured 10cm thick steel mesh concrete protective layer to a outer layer of waterproof. The advantage is it’s strong and consistent with the injection mold concrete arc. The disadvantage is when there have a once more hanging, vertical mold process, maintenance, replacement waterproof layer , must chisel out the steel mesh concrete, really labor-and time-consuming.

Form 2 : Use the exemplar of the ChongQing JIULONG tunnel. Easy maintenance and enhance effect ion of the piston, enabling ventilation, reducing noise is the advantages, the disadvantage is lacking of a sense of linear appearance.

Form 3: laying decorative plate along the steel door frame and located circular steel door frame a certain distance intervals along the tunnel. The advantage is more convenient to construct and pack the waterproof layer during the construction and operation process of installing. The drawback is decorative plates resistance to external damages become weaker when close to the ground within 2m.

The form of sheath is variety,use which form should be determined based on the actual situation . The waterproofing system design and structure of highway tunnel still have the room for improvement and breakthrough with the advancement of technology and new materials development.