River Plate outfall excavation nears completion 07 Nov 2019

After starting in 2017, excavation of a nearly 12km long outfall under the River Plate is nearing completion. Under construction by Italian contractor Salini Impregilo, it is part of a megaproject conceived by the Government of Argentina to clean up the Matanza-Riachuelo Basin in Buenos Aires.

The site of the Riachuelo project on the River Plate

The project foresees the interception of wastewater from the Riachuelo treatment plant by means of a drop shaft made from four interconnected circular shafts to a depth of about 45m. The treated effluent will be then conveyed through a 12km x 4.3m i.d. outfall tunnel which will run for its entire route under the bed of the River Plate, one of the largest estuaries worldwide. The last 1.5km, known as the diffusion section, will be fitted with 34 vertical raisers for final discharge of the effluent into the river.

The geology includes alluvial soils, clayey sands, and soft clay.  All works are executed under the water table. The project includes also a number of major earthworks to form a protection embankment plus internal port road upgrades and a new port access road.

Riser jacking equipment being shipped to Buenos Aires

The next phase will require the use of a prototype made in Italy that is being shipped to Argentina from the port of Genoa in two separate shipments of disassembled parts. The riser jacking equipment, built by Italian civil engineering company Palmieri according to a conceptual design by the group, is an example of the kind of partnership to create innovative solutions for challenging projects that can be expected from Progetto Italia, the industrial plan launched by Salini Impregilo to consolidate the Italian construction industry to compete better in international markets together with the supply chain. The two ships, which were loaded in late October 2019, will arrive in Buenos Aires at the end of November 2019.

Once assembled, the equipment will be 70m long x 3.6m high x 3.5m wide. It will be used along the last 1.5km of the tunnel to install the series of steel tubes that will rise up, crossing a series of soft ground formations to reach the bottom of the River Plate.

50m deep shaft to the hydraulic tunnel under the river

The project has a considerable environmental and social value as it enables the decontamination of the Riachuelo river basin affected by a sharp increase in the city’s urban development, and industrial activities such as paper mills and tanneries that discharge process by-products into the river. It is part of a broader plan, of US$1.2 billion and financed by the World Bank, for the sustainable development of the Matanza–Riachuelo Basin and clean up of waters that are considered among the most polluted in the world. The project is due to be fully completed in 2022.

Fisia Italimpianti of the Salini Impregilo group recently won a contract worth US$215 million to build Lot 2 of the Riachuelo system, which includes construction of a pre-treatment wastewater plant and accompanying pumping stations with a capacity of 27m³/sec.