When we think about geosynthetics, the recurring image is usually that of a large mining or agricultural pond. However, one of the most demanding applications of geomembranes lies beneath our feet, in the infrastructure that connects our cities and crosses mountain ranges. Tunnel and deep foundation waterproofing is a high-engineering field where water management determines the service life of concrete structures.

At SAI, we apply our environmental containment expertise to the heavy civil construction sector, solving groundwater infiltration problems that can compromise structural integrity and end-user safety.

Water: The Main Enemy of Tunnels

A leaking tunnel is not just an aesthetic issue; it is a sign of deterioration. Water infiltration can cause:

• Reinforcement corrosion: Water carries chlorides and sulfates that attack concrete reinforcing steel.
• Excessive hydrostatic pressure: If not properly managed, accumulated pressure can crack the tunnel lining.
• Roadway instability: Seepage can wash out fine materials from the subbase, causing potholes or subsidence.

Tunnel Waterproofing Systems (Double-Lined Tunnels)

Unlike ponds, tunnel waterproofing is typically installed “from the inside outward.” The most common approach is the drained tunnel system:

• Primary support layer: Shotcrete applied over the rock surface.
• Drainage geotextile: A high-weight nonwoven fabric that channels infiltrating water toward side drains.
• PVC or TPO geomembrane: A flexible geomembrane acting as the watertight barrier. PVC is preferred due to its flexibility and weldability in confined spaces.
• Final lining: Structural concrete cast in place.
  
  

Welding and Quality Control in Confined Spaces

Geomembrane welding inside a tunnel presents unique logistical challenges. Space is limited, lighting is artificial, and humidity is often high—factors that directly affect thermal weld quality.

At SAI, we use dual-channel welding equipment that allows air-pressure testing of seams. This step is critical because once the structural concrete is poured over the membrane, repairs are virtually impossible. We also employ sectorized leak detection systems, which allow resin injection if future leakage occurs, pinpointing damage to a specific section.

Foundations and Basements in High Water Table Areas

In major Latin American cities, where limited space forces construction downward, waterproofing basements and foundation slabs is critical. A leak at a third basement level can shut down an entire building. SAI installs pre-applied membrane systems that mechanically bond to fresh concrete, preventing water migration between the membrane and the structure.

Durability Underground

A tunnel designed to last 100 years requires a water barrier that will not fail. Investing in high-quality geomembranes and precision technical installation is the only way to avoid costly future repairs. SAI provides peace of mind by ensuring water stays outside the structure—protecting both the investment and public safety. Contact us to learn more about our solutions.

Frequently Asked Questions

Can HDPE be used in tunnels?
It is possible, but its rigidity makes it difficult to adapt to irregular excavated rock surfaces. PVC is the international standard due to its flexibility.

How are leaks detected if the membrane is covered by concrete?
Compartmentalization systems using waterstops and injection tubes are installed, allowing specific sections to be tested and sealed after concrete placement.

What is the service life of a PVC membrane in a tunnel?
In a protected environment without UV exposure and with stable temperatures, these membranes are designed to last as long as the structure itself, often exceeding 75–100 years.