Lima, December 22,  2025. During the webinar “Mobility in high-end waste dumps: The role of the runout path,” held as part of the Slope Stability 2026 international conference, geotechnical engineer Marco Arrieta emphasized that runout in engineering is crucial for anticipating mobility and controlling risk in high-end waste dumps.

“When the material is already moving, the path governs the energy. The slope, curvature, and degree of confinement control acceleration, flow concentration, and dissipation,” Arrieta pointed out.

“Therefore, events with similar materials and even with very different volumes can show surprisingly similar or completely different ranges depending on the runout path,” he said.

During his presentation, Arrieta explained that material properties are critical to understanding the onset of instability, while runout and velocity are primarily determined by the path's geometry.

“A flow channeled through a narrow valley tends to concentrate and accelerate; if it opens up over a wide surface, it disperses and loses energy. In high-altitude landfills built in valleys, the shape of the path often acts as the main accelerator or brake,” he said.

Practical tools

For conceptual and pre-feasibility stages, Arrieta proposed a simple and traceable geometric approach: adjusting parabolic cross sections (y = a·x²) based on the topography.

“The parameter a is a direct indicator of openness or confinement: the higher it is, the more closed the section, the greater the concentration of flow, and the greater the potential for mobility; the lower it is, the more open the section, with lower speed and expected range,” he said.

This “geometric screening” is based on DEM and topography obtained with drones, LiDAR, or GNSS, profile extraction in GIS, and quick mechanical checks (H/L for apparent dynamic friction, ru to capture the role of pore pressures, and a Voellmy-type term (ξ) for velocity-associated dissipation). “It is a first filter to prioritize scenarios; in feasibility and operation, numerical modeling is required to capture the flow-groundwater coupling,” he said.

The analysis of 46 waste dump failures allowed mobility to be classified into operable runout ranges: low (<500 m), moderate (500–1000 m), high (1000–1500 m), and extreme (>1500 m). “The case base reduces uncertainty and creates a common language between geotechnics and operations,” Arrieta noted.

Three practical signs emerge for prioritizing risk: more confined trajectories (greater than a), high pore pressure at the foundation (ru ≈ 0.4 or more), and very low basal resistance (f < 0.15 or φd < 10°). “When these coincide, the flow is channeled, maintains higher velocity, and runout can grow disproportionately,” he warned.

Arrieta emphasized the direct translation of technical results into operational decisions, runout envelopes (range, width, times, and speeds) on actual topography, operational maps with exclusion zones and critical corridors, and TARPs with measurable activation criteria and unambiguous actions. “The rule is simple: each threshold must have an owner and an immediate action,” he stressed.

Key recommendations

Among the main recommendations, Arrieta called for defining and maintaining the ‘propagation corridor’ as an operational deliverable (axis, profile, and sections), planning the discharge sequence so as not to “build risk,” managing water in the corridor, especially in confined sections, converting runout envelopes into operating rules, and linking monitoring to clear decisions.

“The corridor must be reviewed with operational discipline, updating topography and recalibrating parameters after geometric changes or water events,” he concluded.