Mar. 31, 2025
Just like for ponds, there are many different types of materials that get used to make tunnels watertight. Everything from inexpensive dampproofing materials that are meant to keep MOST of the water out, all the way up to full waterproof membranes that are designed to keep ALL water out of the tunnel. Depending on what's inside the tunnel will determine how much waterproofing protection will be desired. For example, for a pedestrian walkway under a road, it would likely be best to prevent water from entering the tunnel and dripping on pedestrians. However, if a little water did get through, it's not a mission critical failure. In contrast, if the tunnel contained some expensive electronics or other equipment that MUST remain dry at all costs, then it becomes much more important to choose a tunnel liner that is 100% waterproof.
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One of the biggest misconceptions we hear from people looking for a tunnel liner is they might not need a liner because they’re using high quality concrete that is supposed to be waterproof. While it’s true that PERFECT concrete should be fairly waterproof, in our experience, we’ve never seen concrete that doesn’t crack over time, even if it’s just a tiny bit. Water loves imperfections in concrete and will find and seep through even the smallest cracks. Another place for water transmission is concrete pour joints, which are the seams between an already hardened concrete section, and a new pour of concrete. An example of a pour joint would be the floor to wall transition. If you ever walk through an underground parking structure, you will often see moisture coming out of the floor to wall concrete pour joint for this very reason.
One of the main factors that will determine what kind of tunnel liner will be best is the location of the tunnel. Is the tunnel above ground or below ground? What kinds of water sources need to be protected against? For example, for an above ground tunnel that may go under a road, or another application where the tunnel is going ‘through’ something rather than ‘below’ something, you may only have to deal with rainwater that seeps through from above. However, if there is a ‘green roof’ or other types of irrigated vegetation above the tunnel, then perhaps a more robust waterproofing system might be required to prevent irrigation water from entering the tunnel. Similarly, if a tunnel is below ground, then groundwater may become an issue. Depending on the location, If the tunnel is deep enough, the structure may actually end up below the water table. This means that the tunnel will be subjected to very wet conditions most, if not all, of the time. If the structure is far enough down, hydrostatic conditions might become apparent, which means that water is being forced at the structure under pressure. In these situations, a very robust waterproofing system is required to prevent leaks. A tunnel under hydrostatic pressure could be likened to it being built through a lake or pond, where the pressure of the water is pushing down on the tunnel, trying to force it’s way through every crack or weakness in the structure.
Although there are a few options out there for liners, our favorite tunnel liner option is Premium RPE, which stands for reinforced polyethylene. It is strong, lightweight and can be MADE IN A SINGLE PIECE in any dimensions you like up to about 60,000 square feet. That means that if you have a tunnel that is 50 feet long and a 10 foot diameter, we could make a single piece of RPE liner to wrap the tunnel from end to end. All the seaming will done by us at our facility and as such , there is no welding or assembly on site required. This is in contrast to something like PVC, which is often sold in rolls, and then heat welded together on site. This requires full crews of skilled workers, which can increase the cost of the liner tremendously. Although RPE is commonly used as a lake or pond liner, it is also used in many different industrial applications to either contain water, or keep water out of a structure like a tunnel. We have millions of square feet of RPE in use in North America..
If you have a tunnel liner application you’d like to hear our recommendations on, please contact us. We provide free design assistance with no obligation to buy.
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Broadly speaking, the artificial support structure can be collectively referred to as lining, which can be divided into primary support and secondary support (secondary lining). Tunnel lining materials should first have sufficient strength, durability, impermeability, corrosion resistance and frost resistance. In addition, from an economic point of view, it should also meet the requirements of obtaining local materials, reducing the cost, convenient construction and easy mechanized construction.
Advantages: Good integrity, can be poured on site, can also be prefabricated in the processing field, and can be mechanized construction. Additives can be added to the cement to improve the performance of the concrete.
Disadvantages: Can not bear the load immediately after pouring, it needs to be kept in good health, and the mold can be demolished after reaching the predetermined strength, and it takes up more templates and arches. Ordinary concrete has poor corrosion resistance.
(1) For railway tunnels, in order to save cement, schist concrete is allowed to be used for the lining of side walls in good rock sections (the content of schist should not exceed 20% of the total volume). In addition, when there is over-excavation at a site other than 1m above the arch line, the over-excavated part can also be backfilled with rubble concrete.
(2) The selected stone should be hard, its strength grade should not be lower than MU40, and the stone with cracks and easy to weather should not be used to ensure the quality.
(3) The lining of highway tunnels is generally not used, and rubble concrete can be used for the inverted or over-excavated part. The dosage of rubble shall not exceed 30% of the total volume.
It is mainly used in open excavation sections such as tunnel doors and open tunnel linings, or when the tunnel passes through seismic areas, biased pressure, through fault fracture zones or silt, quicksand and other bad geological sections.
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Advantages: it can obtain materials on site, reduce the cost, ensure the thickness of the lining and bear the load earlier, save cement and formwork, and have better durability and corrosion resistance.
Disadvantages: poor integrity, many joints are prone to water leakage, poor waterproof performance, construction is mainly manual operation, difficult to mechanize construction, labor and time, slow construction progress, and high masonry technical requirements. Retaining walls of cave doors, retaining walls, and curbs of exposed lines can still be used. The strength grade of block stones should not be lower than MU60, and the strength grade of blocks should not be lower than MU20. Stones with cracks and easy weathering should not be used.
Shotcrete is made by spraying concrete dry mix, accelerator and water onto the clean rock surface at high speed with concrete sprayer.
It has high compactness and can quickly close the fissures of surrounding rock. It is closely attached to the rock surface and has high early strength. It can quickly seal the rock surface and support it. In addition, fiber materials can be added to the shotcrete to improve its performance. It is an ideal lining material.
In ordinary railway tunnels, shotcrete can be used as the middle inner lining, but its strength grade is not lower than C20, the cement grade used is not lower than 32.5, and ordinary Portland cement is preferred. The fine aggregate is made of hard and durable medium sand or coarse sand, the fineness modulus should be greater than 15, and the moisture content of the sand should be controlled within 5%-7%; the coarse aggregate should be made of hard and durable pebbles or gravel, and the particle size should not be larger than 15mm.
Anchor rod is a rod-shaped member inserted into the surrounding rock mass to reinforce the surrounding rock. It can be divided into mechanical anchors, bonded anchors and prestressed anchors. The diameter of the anchor rod should be 20～32mm, the material of the rod should be HRB335, HRB400 steel; the material of the backing plate should be HPB235 steel. The strength of various cement mortars used for bolts should not be lower than M20. The reinforcement mesh material can be HPB235 steel with a diameter of 6-12mm.
The steel frame is a section steel support or grid steel support placed in the primary support or secondary lining in order to strengthen the support rigidity.
The steel frame used for the initial support should be made of H-shaped, I-shaped, U-shaped steel, or steel pipe or rail.
In shield construction, fabricated materials are often used as lining materials, such as large prefabricated blocks of reinforced concrete and cast iron prefabricated blocks with reinforced ribs.
In the construction of shed-type open caves (referred to as shed-holes), prefabricated slabs or beams can be used to assemble plate-type sheds or beam-type sheds.
When using the new Austrian method of construction, in order to waterproof, anti-falling and beautiful requirements, you can also add an off-wall structure. Commonly used materials are corrugated steel arched large assembly preforms, and sometimes glass fiber reinforced plastic can be used instead of steel.
Various decoration materials can be pasted on the inner surface of the lining in order to improve the lighting, waterproof, ventilation, aesthetics, sight induction or reduce noise in the cave.
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