The environmental redevelopment project of the Matanza – Riachuelo river basin also bears the signature of Mapei

Sadly known for being among the most polluted places in the world, the Matanza - Riachuelo basin is now the subject of a vast environmental redevelopment project which, among other companies, also involves Mapei for its technologies dedicated to soil conditioning and mechanized tunnelling.


Project

The “Desarrollo Sustentable de la Cuenca Matanza-Riachuelo” to treat wastewater and later to discharge it into the “Rio de la Plata” river consists of different lots.
Lot 3 consists of three main parts: 50 m deep upstream main shafts, 12 km long sub-fluvial outfall tunnel and 34 risers.
The 12 km tunnel, in which have been employed different solutions of Mapei, has been excavated using a 5.2 m diameter EPB Earth Pressure Balance)-TBM through very complex geotechnical and hydrogeological conditions and numerous environmental restrictions.

Geotechnical conditions

The geological region surrounding the tunnel alignment is characterized by two different sedimentary deposits: a “Puelche” formation made of almost mono-granular and very permeable sand and a “Postpampeano” formation of soft to very soft silt and clay.
The outfall tunnel has been excavated mainly through the “Puelche” formation whose characteristics represented a “tricky” scenario both for soil conditioning and back-filling grout injection.

Tunnel face support

The counter pressure at which the TBM had to operate during the construction of the whole outfall tunnel was higher than 4 bars, which is a value close to the limit of EPB technology. To properly satisfy this critical design request, the Mapei foaming agent for soil conditioning and its application parameters played a key role for the success of the TBM excavation.

Final lining requirements

The tunnel lining design had a lot of critical aspects: high net internal pressure, peak flow rate higher than 25 m³/s, service life longer than 100 years, etc. Consequently, the segments production and the concrete mix-design study were very important aspects of the final lining quality.

Environmental restrictions

One of the most valuable benefits of the project is to avoid the discharge of sewer drains into the “Riachuelo” river in order to reduce its pollution. In agreement with this objective, the use of chemical products able to minimize the environmental impact of the tunnel construction was preferable.


Mapei products and solution for the project

Since the preliminary stages of the project, Mapei Underground Technology Team (UTT) division sets up a strong cooperation both with Designer and Contractor for the selection of the most suitable chemical products for the project as well as to provide high level Technical Service needed to support the management of the tunnel construction.

Soil conditioning with POLYFOAMER ECO/100 PLUS

The foaming agent POLYFOAMER ECO/100 PLUS has been selected for the soil conditioning during the EPB-TBM excavation and it has been successfully used for the whole tunnel drive both through the very difficult sand of the “Puelche” formation and when some lenses of silt/clay soil have been encountered.
Furthermore, POLYFOAMER ECO/100 PLUS represents an innovation among the soil conditioning products thanks to its extremely low toxicity and high biodegradability.
Using the POLYFOAMER ECO/100 PLUS and varying its conditioning parameters, it was possible to keep high TBM advancing performance through all geological conditions encountered.
Thanks to the extremely low environmental impact of POLYFOAMER ECO/100 PLUS, the excavated soil has been reused as filling material within an industrial district promoting the develop of vegetation and “green” area.

Backfilling grout with MAPEQUICK CBS SYSTEM 1

The TBM used for the excavation of the outfall tunnel was equipped to inject a traditional one-component grout to fill the annular void between segments and ground. As it is well known by technical literature and practical experience, this backfilling technology is very sensitive to raw material availability and quality as well as to the mix-design study. The continuous monitoring of ingredients’ characteristics (cement, sand, fly ash, etc.) and the consequent adjustment of MAPEQUICK CBS SYSTEM 1 dosage was part of the jobsite weekly activity. The Contractor’s Quality Department Technicians and MAPEI UTT international team worked together to fully meet the project’ requests and to guarantee the proper injection of the grout in the TBM.

Segments production with MAPEI admixtures

The same technical cooperation has been implemented for the mix-design study of the concrete used for the segments production. The super-plasticizer admixtures DYNAMON NRG 1014 and DYNAMON NRG 1022 and the silica-fume based product MAPEPLAST SF have been selected thanks to their technical performances with the local raw material.


Conclusions

The lot 3 of the project “Desarrollo Sustentable de la Cuenca Matanza-Riachuelo” was one of the most critical tunnel projects in the world because of the technical challenges of its design and location.
A profitable cooperation between the Contractor’s staff and the MAPEI UTT international team allowed to profitably manage the various aspects of the projects, from the segments production to the soil conditioning and backfilling grout for the TBM excavation.
Finally, the unique environmental features of POLYFOAMER ECO/100 PLUS gave an additional value to the project in accordance with an innovative and conscious approach for the selection of soil conditioning products, minimizing the conditioned soil impact and promoting its reuse as by-product.