Tailings piles in tropical environments: Risks, evidence and good practices to avoid liquefaction

The liquefaction of tailings stored in stockpiles represents one of the greatest challenges for modern geotechnical engineering in tropical environments. Historically associated with seismic events in saturated soils, the phenomenon has been increasingly observed under static conditions, driven by local climatic, operational, and geotechnical factors. In a scenario where the storage of filtered tailings is becoming increasingly frequent, understanding the mechanisms of destabilization in these materials becomes imperative. This article aims to consolidate the main recent technical advances and propose practical guidelines applicable to real-world conditions.

 

Types of Liquefaction and Mechanisms Involved

• Dynamic Liquefaction (Seismic): Caused by seismic waves in saturated soils, usually sandy, with structural collapse due to the sudden increase in neutral pressure and consequent loss of effective resistance.
• Static Liquefaction: It can occur even in the absence of seismic events. It is induced by factors such as progressive loading, rapid saturation, changes in boundary conditions, loss of metastable structure, or stress redistribution. Shear strength drops abruptly, leading to material fluidity.
• Liquefaction by Water Cycling (“Cyclic Softening“)Cyclic rewetting in partially saturated materials, often observed in piles exposed to seasonal cycles of rain and drought, induces localized restructuring and collapse, even in the absence of full saturation. This cycling alters stiffness and strength properties, favoring the development of weak zones.

 

Critical Characteristics of Tropical Environments

Weathering and Mineralogy

• Tropical soils often present high degrees of lateritization, with a predominance of secondary minerals, iron and aluminum oxides.
• The metastable structure, often associated with the presence of dispersed fines, is particularly vulnerable to rewetting and percolation.

Rainfall and Infiltration Regime

• Tropical regions concentrate intense rainfall in short intervals of time, favoring rapid saturation of surface layers.
• Shrinkage cracks during dry periods can act as preferential flow paths, accelerating vertical percolation.
• Capillary rise also contributes to the creation of partially saturated transition zones, with low resistance and high potential for instability.

Lack of Coverage and Compaction

• Tailings piles often lack protective surface covering, making them susceptible to direct infiltration.
• The lack of technological control during the disposal of waste (e.g., absence of compaction or granulometric segregation) contributes to heterogeneity and the formation of critical water accumulation zones.

 

Evidence and Case Studies

Recent Empirical Studies

• Oliveira & Fourie (2017, 2019): identified that sandy and silty iron tailings, even partially saturated, presented collapse under wet-dry cycling in laboratory tests.
• Vick & Lemos (2021): demonstrated that thickened tailings, when not protected by cover or surface drainage, can develop saturation points and loss of strength over time.

 

Technological Trends and Modeling

Hydromechanical Integration

• The use of software such as PLAXIS, FLAC3D and SEEP/W, with coupled flow and deformation modules, allows simulating behavior in partially saturated conditions, considering loading and infiltration history.

Importance of Matrix Suction

• The apparent undrained resistance in partially saturated soils is directly influenced by matric suction.
• The sudden loss of this suction during rainfall events can cause abrupt transitions in behavior, leading to local liquefaction.

Instrumentation and Monitoring

• The adoption of tensiometers, fast-response piezometers, humidity sensors and inclinometers allows for the anticipation of changes in behavior before rupture.
• The integration of data into digital platforms with predictive analysis based on climate triggers represents an emerging practice in the sector.

 

Practical Guidelines for Design and Operation

Geotechnical and Construction Project

• Prioritize layout using benches with limited height, controlled compaction and humidity control.
• Implement internal drainage systems (vertical and horizontal) to reduce the accumulation of interstitial water.
• Apply surface coverings with granular material or vegetation to reduce direct infiltration.

Stability Assessment

• Perform analyses considering undrained and partially saturated scenarios, incorporating parameters obtained by controlled suction triaxial tests.
• Simulate critical cases of rapid saturation, using historical rainfall data and climate projections.

Monitoring and Governance

• Establish continuous monitoring and feedback programs for geotechnical data.
• Create response protocols based on alert levels linked to accumulated rainfall, neutral pressure variation and displacements.
• Ensure technical governance with active participation of engineers of record (EoR), with technical autonomy and functional independence.

 

Conclusion

Modern understanding of liquefaction in tropical tailings piles requires abandoning simplistic models based solely on total saturation and seismicity. It is a complex, procedural phenomenon, highly influenced by environmental, operational, and structural factors.

The future of geotechnical safety involves the incorporation of advanced hydromechanical models, the valorization of instrumentation and a culture of prevention.