Metro Uncovers Rare Geological Formation | October 2025

Unprecedented Rock formation Discovered During São Paulo Metro Line 20 Project

A groundbreaking discovery of an unusual rock formation is prompting a reassessment of engineering plans for São Paulo’s planned line 20 – Pink metro expansion, scheduled to begin construction in 2027. The finding, made during preliminary analyses for the new line, could substantially impact the project’s timeline and budget.

Geological Anomaly found Near Future Portugal station

Geologists working with the São Paulo Metro system have identified an unprecedented type of rock formation located between 46 and 52 meters below ground, in the area of the future Portugal station tunnel in Santo André, part of the greater ABC region. The presence of medium to high-grade metamorphic rocks – including mica schists, gneisses, and mylonites – necessitates heightened caution during excavation.

“This discovery marks a turning point in the region’s underground engineering,” a company release stated, “as it is indeed an unprecedented geological scenario for Metro projects in the São Paulo metropolitan area.”

Mitigation Strategies and Data-driven Approach

To address the challenges posed by this complex geological landscape, specialists have been meticulously mapping the subsoil, analyzing geotechnical profiles, and developing three-dimensional models to mitigate risks. This data-driven approach is crucial for informed decision-making throughout the project.

Variable Terrain Along the 33km Route

According to a geologist with nearly 40 years of experience at the Metro, the Line 20 project will encounter a diverse range of geological conditions. Excavations between Lapa and Vila Madalena will proceed through clay soil,transitioning to a rocky profile near Faria Lima Avenue and intensifying towards the Imigrantes highway as the line approaches the ABC region.

However, the area around Portugal station presents a particularly challenging scenario: a muddy rock formation prone to crumbling. “It’s like driving on a paved road, in fifth gear, and, suddenly, you enter a patch of mud,” the geologist explained.”We need to understand what must happen to program the project and the machine in these transitions.”

unexpected, Yet Not Entirely Surprising, Discovery

While the specific rock formation is unprecedented in Metro excavations, the presence of mica schist was previously indicated on regional geological maps. The discovery wasn’t entirely unexpected, though this marks the first time it’s presence has been confirmed through Metro excavation projects in the São Paulo metropolitan area. Similar formations are known to exist in Minas Gerais.

since the beginning of the year,the state-owned company has conducted approximately 700 surveys,spaced an average of 60 meters apart,to further characterize the subsurface conditions. this ongoing work is being integrated into the basic project design for Line 20.Collected samples are meticulously cataloged and stored in a warehouse beneath Line 3 – Red, in Brás, central São Paulo, awaiting further analysis.

Comprehensive Studies Underway to Define Project Parameters

The basic project, contracted in February, is slated for completion in 20 months and will provide detailed studies to define the technical aspects of Line 20. These analyses will inform the project schedule, contracting process, and economic model. The São Paulo government emphasized that the studies will also define the characteristics of tunnels,roads,stations,and maintenance yards.

The study phase encompasses architectural design, urban integration, finishing details, visual communication, and civil works, as well as electrical, telecommunications, escalator, and elevator systems, according to management officials.

Line 20: Connecting Communities and Anticipating 1.3 Million Daily Passengers

With a planned length of 33 kilometers and 24 stations, Line 20 will connect the municipalities of Santo André and São Bernardo do Campo in the ABC region to the western areas of São Paulo, including Lapa, Pinheiros, Vila Olímpia, Itaim Bibi, and Moema. The government is exploring the possibility of locating one of the line’s two maintenance yards on the site of the former Ford factory in São Bernardo,which closed in 2019.

The anticipated daily ridership for Line 20 exceeds 1.3 million passengers, highlighting the critical importance of addressing the geological challenges and ensuring a safe and efficient transportation system for the region.