Predictive Slope Failure Analysis

Retrospective Sentinel-1 InSAR Evaluation of an Active Open-Cast Pit Wall Collapse

Executive Summary

In 2025, a severe quarry wall collapse occurred at an active open-cast mining operation during routine drilling, burying equipment and personnel. InSpectiv Labs performed a retrospective 12-month SBAS InSAR analysis across a 5 sq km footprint leading up to the incident month. The satellite radar data confirmed that the site suffered from widespread, multi-hectare terrain instability, with critical high-velocity failure zones concentrating directly along the upper pit wall crest months prior to the collapse.

The Challenge

Open-cast quarrying continuously alters slope geometry, stress distributions, and bench stability. Slope failures are rarely sudden; they stem from progressive internal stress buildup, bench weakening, and subtle surface displacement over time. Traditional physical inspection and localized survey tools often fail to cover broad, multi-hectare pit faces continuously, leaving slow-developing slope instabilities undetected until structural failure occurs.

InSpectiv Labs Solution & Methodology

Data Engine

Sentinel-1 C-band Synthetic Aperture Radar (SAR) imagery acquired over a 12-month timeframe (~5 sq km area).

Processing Technique

Small Baseline Subset (SBAS) Interferometric Time-Series Analysis.

Measurement Physics

Line-of-Sight (LOS) displacement tracking capable of measuring millimeter-scale surface movement.

Analytical Focus

Mapping deformation trends, velocity changes, and high-risk spatial clustering along active pit slopes.

Predictive Slope Failure Analysis — Figure 1. SBAS InSAR Mean LOS Velocity map showing widespread terrain instability across the site, with concentrated high-velocity red failure hotspots along the active quarry wall crest prior to collapse.

Key Technical Findings

Zone Classification	Observed Satellite Signal	Geotechnical Interpretation & Action
Critical Red Hotspots	High negative LOS velocity / concentrated deep red clusters along pit crest (~50 sq m)	Point of maximum acceleration and slope failure. Serves as a clear, localized early warning indicator directly along the active excavation crest.
Widespread Site Instability	Predominant yellow and orange grid patterns across the broader quarry area	Indicates that the majority of the surrounding site was undergoing progressive surface shift and escalating ground stress rather than remaining stable.

Business Impact

Predictive Lead-Time

Demonstrates that satellite radar can identify subtle slope shifts and broad terrain stress months before physical collapse occurs.

Targeted Geotechnical Intervention

Pinpoints exact high-risk slope sections to prioritize ground checks, instrumentation placement, and bench reinforcements.

Worker & Asset Protection

Provides independent spatial intelligence to adjust excavation schedules and keep workers out of hazardous zones.

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