​A novel geotechnical solution for a tailings storage facility in central Chile

In this series, we’ll explore the power of collaboration and co-creation with our clients. These partnerships showcase how we rise to the world’s greatest challenges together.

​“It’s all about building trust.”

​That’s Johanns Pfannschmidt, geotechnical engineer and our construction quality assurance (CQA) supervisor, based in Santiago, Chile. He oversees the construction of tailings storage facilities (TSF), helping to see that the embankments, foundations, drainage systems and geotechnical instrumentation are constructed in accordance with design criteria, project technical specifications, and construction quality controls.

​Properly constructed TSFs are essential to provide the facility’s physical and hydraulic stability. In this context, close technical coordination with the client allows for validating construction decisions based on field findings, managing unforeseen geotechnical deviations, and overseeing the correct execution of each stage. This provides compliance with the Global Tailings Management Standard applicable to tailings storage facilities in Chile.

​Pfannschmidt works with Codelco, Chile’s main state-owned copper producer and one of the most important in the world. His on-site management through CQA helps construction to be carried out in accordance with design and quality standards, promoting the protection of the environment and communities.

​"It’s why I do what I do,” he says. 

​Strategic support in the technical management of tailings storage facilities 

​“In our TSF projects, we always look for a partner that brings geotechnical expertise in tailings storage facility construction and helps us make strategic decisions based on field findings. Working with Johanns and Stantec feels like they’re part of our team and aligned with our TSF construction and management objectives. Together, we develop solutions to geotechnical challenges that arise during construction and from site conditions,” says Marlene Lopez Chavez, senior engineering manager at Codelco.

​According to Pfannschmidt, being visible on site is the key to this relationship. “It’s all about putting the time in, face-to-face, solving problems together,” he says. “I’m always talking to members of the client team. I analyze what they need, and I’m hands-on through every step.”

​A novel tailings storage facility solution

​A critical aspect in TSFs is to verify the stability of the foundation, as the integrity of the embankments and drainage systems depends on it. Geotechnical characterization helps see that the base of the TSF is constructed and remains stable over time, reducing the risk of instability and contributing to its overall safety.

​The Andina copper mine, in central Chile, has used the Ovejeria tailings storage facility to store its mining waste for over 25 years. 

​During the construction stage, while inspecting an excavation at the toe of the embankment, plastic clay strata were identified that had not been considered in the initial geotechnical profile. As a result, the foundation soil characterization did not align with the properties assumed in the original design. 

​“High-plasticity clay strata pose a critical geotechnical challenge: If not completely removed during the construction stage, they could compromise the stability of the embankment, increasing the risk of future failures in the TSF,” Pfannschmidt says. 

​The presence of these high-plasticity clay strata had not been considered in sufficient detail; as a result, in some areas, what was observed in the field during the excavations did not match the profile foreseen for the construction of the drainage system at the toe of the embankment.

​To address discrepancies between the original geotechnical profile and the field observations, Pfannschmidt called for the development of a new geotechnical profile of the foundation soil to accurately characterize the high-plasticity clay strata to be removed and verify the stability of the TSF. 

​“Based on an exploration campaign by means of test pits, the high-plasticity clay strata were identified, and the necessary removal measures for the construction of the TSF were defined. These findings were supported by soil characterization and on-site laboratory tests, providing technical evidence,” Pfannschmidt says. 

​“Johanns and Stantec developed and thoroughly characterized a new geotechnical profile of the foundation soil through an exploratory campaign and evaluation of the high-plasticity clay strata, identifying their critical properties and the mitigation measures required to ensure the long-term stability of the embankment and drainage system,” Lopez says. “This approach was implemented in coordination with the construction, ensuring that each stage responded correctly to the geotechnical conditions encountered in the field.”

Reviewing mining waste storage

​Every year, the International Tailings Review Board (ITRB) reviews the safety, stability, and management of tailings storage facilities. Codelco presented the updated geotechnical profile of the foundation soil, based on the new characterization and removal measures of the high-plasticity clay strata identified by Pfannschmidt, which was well received by the committee. This recognition reinforces the best practices and safety and stability standards for TSFs globally. 

​“Updating the geotechnical profile of the foundation soil and removing the high-plasticity clay strata reduces the risks of foundation instability and the potential impacts on the drainage system efficiency, helping protect the embankment and foundation stability and mitigating the geotechnical risks identified during the field characterization,” Pfannschmidt adds.

​Putting in that extra effort was noticed. “It’s rewarding working with Stantec because I know when we’re faced with a technical problem, they’ll be there to help deliver a technical solution,” Lopez says.

​Collaboration is key

​Regarding his relationship with Codelco, Pfannschmidt doesn’t think of himself as a typical consultant. 

​“It’s more than just getting the job done,” he says. “My work has a direct impact on the safety of the TSFs and, with it, a significant commitment to communities and the environment. Helping these facilities operate safely is what really motivates me.” 

​Lopez agrees: “Without highly committed people like Johanns and an exceptional level of collaboration, we wouldn’t have achieved what we did. It’s much more than a regular working relationship.” 

​With every community, we redefine what’s possible. Through collaboration with our clients, together we will unlock outcomes neither could achieve alone.