The work and the technique: Riachuelo Environmental Restoration System, Argentina

In 2015, the Argentine government put out a tender for the Riachuelo System. The project, an integral part of the sewage network managed by AySA, is divided into three major lots.

• Lot 1: Main collectors and works for intercepting wastewater and stormwater.
• Lot 2: Water pretreatment plant, built by Fisia Italimpianti (a subsidiary of the Webuild Group).
• Lot 3: Subfluvial tunnel with an innovative diffusion system that enables the controlled dispersion of pretreated water into the river, built by Webuild.

The heart of the entire system is Lot 2, where wastewater is collected, lifted, pretreated, and prepared for controlled discharge into the river.
Located in the port area of Avellaneda, along the Río de la Plata, Lot 2 includes the construction of:

1. An inlet pumping station with a pumping capacity of 36 cubic meters per second
2. A water pretreatment plant with a flow rate of 27 cubic meters per second
3. An outlet pumping station that transfers the treated effluent to the final diffusion system

Lot 2 also included site preparation, construction of civil works, access roads, internal drainage networks, and technical and service buildings. It also covered the design, supply, installation, and commissioning of all electromechanical equipment required for the operation of the pretreatment plant.

Lot 3 includes the construction of the subfluvial tunnel, the core element of the entire system. Pretreated water is conveyed into the tunnel — which has an internal diameter of 4.3 meters — and directed toward the riverbed. There, it is uniformly released through an innovative diffusion system made up of 34 vertical steel pipes. This tunnel serves as the discharge conduit for the treatment plant and enables the dilution of treated wastewater by releasing it into the Río de la Plata through a system of 34 vertical steel pipes, known as risers, which connect the tunnel to the riverbed.

To build the tunnel, excavation began with the construction of the launching shaft — a quadrilobate underground structure 50 meters deep — followed by tunneling using an EPB-type TBM.
The tunnel features an internal lining specifically designed to withstand the difference between internal and external pressure. Special pre-drilled rings were installed between the tunnel segments to accommodate the risers — the project’s key innovation: a piece of equipment never before built anywhere in the world. Its prototype was designed and manufactured in Italy, then shipped by sea from the Port of Genoa to Buenos Aires.

Thanks to this new technology, known as the Risers Concept, it was possible to deploy the diffusers from inside the tunnel, minimizing underwater operations, enhancing worker safety and overall construction quality, and reducing the environmental impact of the intervention.

On November 22, 2019, after 24 months of excavation, the tunnel was completed.
Today, it ranks as the fourth longest subfluvial tunnel in the world and the third longest excavated using a TBM.