What Are the Best Methods for Tunnel Waterproofing?

By Emily Newton

Tunnel waterproofing is critical for maintaining structural integrity and reaching the expected life span. Using the appropriate tunnel waterproofing methods prevents moisture and soil from getting inside while protecting the structure from sudden collapse. Knowing how to waterproof a tunnel helps people proceed confidently and find the most suitable project options.

Tunnel Waterproofing Sheets

Applying a waterproofing sheet to the tunnel interior is a relatively fast, straightforward option, even if people must utilize it when the tunnel’s surface is already wet. Polyvinyl chloride, polypropylene and ethylene-propylene rubber blends or polyethylene (HDPE) are some of the most popular materials for tunnel waterproofing sheets.

People should strongly consider waterproofing sheets when they want a conventional, easily accessible option and work with large, flat surfaces. However, this method requires precision welding during installation and only works for tunnels with noncomplex shapes.

Tunnel Waterproofing Sprays

Spray waterproofing for tunnels is a significantly faster method than sheets. Application speeds can be up to 150 square meters per hour, whereas the rate is about 25 square meters per hour for sheets. Additionally, the sprayed material will attach to the tunnel’s primary and secondary linings, preventing the moisture from spreading if water ingress occurs.

Waterproofing sprays are good choices for tunnels with complex geometries. However, they may not last as long as other tunnel waterproofing methods if subjected to frequent severe weather. Thus, people should always consider the area’s typical conditions and how climate change could alter them over the coming years.

Injectable Slurries

Injectable slurries are tunnel waterproofing options that both protect and seal. People choose them for new construction and remediation projects. Most of these substances expand after application, forming a barrier to keep water out and cover former ingress points.

One real-life example of this application occurred on a London Underground tunnel with significant water seepage at its crown. The people overseeing the repair work wanted a stretchable, permanent repair solution that could tolerate the stresses of frequent train traffic and the complications of an aging structure.

After individuals assessed the project, they decided to use injection lances to deliver grouting resin through specially placed ports. The chosen injectable substance was a resin-based grout with a similar viscosity to water. The formula turns into a gel after application, and this slurry slowed and stopped all moisture from entering the tunnel within 15 minutes.

The Three-Component Approach

Tunnels are massive structures that must accommodate specific landscape features, traffic patterns and other specifics, so people must use in-depth processes when building or improving them. For example, construction crews use metal or timber structures to reinforce trenches. This helps retain the proper shape and prevent cave-ins.

All tunnel waterproofing methods require a similarly comprehensive approach to maintain safety and effectiveness. Sometimes, people must use multiple methods at different stages to achieve the desired results. Such is the case with the aptly named three-component approach to tunnel waterproofing.

The first step is to apply sprayed concrete as the first layer, creating a 3-millimeter tunnel-sealing membrane that can retain water despite high-pressure conditions. Next, a nonwoven geotextile clay liner — the second layer — was placed behind the membrane. A cement filling on the tunnel’s inner shell is the third component of this approach.

Another later part of the process involves adding waterstops to the outside of the structure, using them to divide the geotextile. The waterstops are welded directly to the geotextile, making it easier for people to identify and localize leaks after installation.

Environment-Appropriate Waterproofing Measures

Many civil engineers, city planners and others involved in infrastructure planning realize their projects must offer sustainable and resilient solutions that meet current and future needs. One way to address that is to ensure all infrastructure can handle the Earth’s changing climate.

In one instance, a multibillion-dollar flood control project in Chicago failed when heavy rain fell exceptionally quickly. Some Western suburbs received up to 8 inches of rain during the daytime alone. More trouble occurred with Chicago’s Deep Tunnel Project. Rather than being just a single structure, this name refers to an extensive network that can hold billions of gallons of sewage and prevent it from getting into local waterways.

However, the system eventually became so overwhelmed by the torrential rains that — after trying many other strategies first — utility workers had no choice but to relieve pressure by allowing more than a billion gallons of water to flow into the region’s primary drinking water source. When the Deep Tunnel Project began in 1975, those working on it felt confident it would keep the Chicago River and Lake Michigan free from pollution.

However, weather patterns have changed significantly since construction, and the infrastructure can no longer prevent sewage overflows or basement backups. Marcelo Garcia, a University of Illinois hydrological engineer who studies the Deep Tunnel, explained that rain now falls too intensely, too frequently and in high amounts. These combining factors make the former tunnel waterproofing methods inadequate.

Indeed, anyone overseeing tunnel waterproofing projects can only work with the data available at the time. No one can predict the future with certainty. However, advanced methods, such as artificial intelligence algorithms and digital twins, can help people see how things could change five or 10 years from now.

Choosing tunnel waterproofing measures to align with environmental trends proactively avoids problems later and ensures the tunnel functions as expected in demanding conditions.

Match Tunnel Waterproofing Methods to Specific Needs

Although these are some of the most common and effective ways to waterproof a tunnel, people should always analyze a project’s particulars before deciding on an option. Those include the tunnel’s size, shape, surface and function.

Consider factors such as the project’s budget, the number of people working on it and applicable deadlines. Assessing all those details will help people make the most competent decisions. Additionally, part of the work may involve preparing the structure to cope with a changing climate. In that case, several stages might concern consulting with people who can handle such needs. Collaboration is often a vital part of a project’s success.

Emily Newton is a construction and industrial journalist. She enjoys exploring the impact technology has in the construction and utilities sectors. When Emily isn’t writing, she enjoys building Lego sets with her husband.