In the management of critical infrastructure, the aging of waterproofing systems is a latent risk that many organizations postpone addressing due to fears of high demolition costs and prolonged operational shutdowns. However, modern engineering offers a technically superior alternative: overlining. This over-lining technique makes it possible to restore the full integrity of soil protection without removing the original liner, transforming obsolete infrastructure into a state-of-the-art containment system.

The Challenge of Degradation in Legacy Barriers

Many containment systems installed 20 or 30 years ago were designed under regulations far less stringent than those in force today. Over time, factors such as environmental stress cracking, thermo-oxidative degradation, and mechanical damage compromise the ability of an HDPE liner to act as an effective barrier.

When a barrier fails, the risk of subsurface leakage increases exponentially. In the past, the standard solution was total removal: draining the facility, removing the damaged material, repairing the subgrade, and performing a new geomembrane installation. This process is not only costly, but also generates massive amounts of contaminated plastic waste that must be properly managed. Overlining breaks this paradigm by using the existing system as a strategic support layer.

Overlining Engineering: Components and Methodology

The success of an overlining project does not lie merely in placing one layer over another; it requires an engineering design that considers the management of trapped fluids and gases.

1. Preparation and Assessment of the Base System

Before proceeding, it is essential to perform a thorough cleaning of the existing liner. Areas with accumulated liquids or gases (commonly known as “whales” or bubbles) must be identified. SAI uses diagnostic equipment to evaluate whether the supporting structure remains mechanically suitable to receive the additional weight and stresses of the new system.

2. Transition Layers and Geotextiles

Installing a new geomembrane directly over an old one can generate friction and puncturing if the original material has rough cracks. For this reason, a high-grammage protective geotextile is installed between layers. This component acts as a cushion and, in many cases, as a drainage layer that allows residual moisture between the layers to migrate toward collection points, preserving the geomembrane durability / lifespan of the new liner.

3. Selection of the New Barrier: HDPE or BGM?

Depending on the application, the new system may vary:

• HDPE Liner: Ideal for its chemical resistance and cost-effectiveness over large areas.
• Bituminous Geomembrane Liner (BGM): Its exceptional flexibility and low coefficient of thermal expansion make it perfect for rehabilitating reservoirs with steep slopes or irregular geometries where HDPE could experience excessive stress.

The Critical Role of Welding in Rehabilitation

Geomembrane liner welding in overlining projects is technically more complex than in new construction. Technicians must achieve hermetic joints not only between new panels, but also mechanical perimeter seals against existing concrete structures (walls, pump pedestals, or piping).

At SAI, we apply double-wedge welding for long seams and extrusion welding for critical details such as penetrations. Every centimeter of weld undergoes non-destructive testing to ensure the new soil protection system is completely impermeable. As IAGI-certified installers, we ensure that the human factor is never the weak point of the system.

Economic and Sustainability Advantages

From a geomembrane liner cost perspective, overlining drastically reduces logistical expenses. By avoiding the transport of tons of old material to hazardous waste landfills, budgets can be reinvested in higher-quality materials or in state-of-the-art geomembrane leak detection systems.

Furthermore, this approach aligns with circular economy principles and ESG (Environmental, Social, and Governance) policies. By extending the service life of a pond or secondary containment structure by another 30 years without generating debris, companies demonstrate a genuine commitment to global environmental sustainability.

Global Use Cases for Overlining

• Wastewater Treatment Plants: Rehabilitation of aeration lagoons where the original liner has lost flexibility.
• Oil Terminals: Reinforcement of secondary containment in dikes where concrete has developed structural cracks.
• Mining: Over-lining of solution channels where abrasion has reduced the thickness of the primary liner.

Rehabilitation through overlining is modern engineering’s answer to the need for environmental safety combined with financial efficiency. It is not simply a “patch,” but a complete technological upgrade of containment infrastructure. At SAI, we combine optimal material selection with precision geomembrane installation to ensure that your most critical assets continue to operate under the highest standards of soil protection.

Frequently Asked Questions (FAQ)

1. How are gases trapped beneath the new liner managed?

   Passive or active venting systems are installed. These conduits allow air or decomposition gases to escape without lifting the new geomembrane, preventing mechanical failures due to tension.

2. What service life can be expected from an overlining system?

   When a high-quality HDPE geomembrane and certified installation are used, the system can provide durability of more than 30 years, matching or even exceeding that of a new installation.

3. Is a special environmental permit required?

   Generally, since this is an improvement in environmental safety rather than new construction, permitting processes tend to be more streamlined than those for full civil works.