Brief
Explore key causes behind the failure of a retaining wall on a slope and discover vital geotechnical lessons for future design and investigation.
Insight
The failure of a retaining wall on a gentle 10-metre-high slope highlights critical geotechnical oversights in slope stability design and site assessment. Despite appearing stable, the slope adjacent to a tower block collapsed mid-construction, damaging nearby infrastructure and disrupting river flow. Post-failure investigation revealed the presence of undetected soft soil layers, which played a major role in triggering the slope failure. This incident underscores the importance of comprehensive site investigation, particularly in transitional or river-adjacent terrains.
Key contributing factors included the absence of dedicated boreholes for the retaining wall, reliance on data from unrelated locations, and the failure to perform overall or global stability checks. While the retaining wall design accounted for sliding, overturning, and bearing capacity, it neglected the interaction between structural loads and subsurface ground conditions—especially beneath and behind the wall.
Inadequate consideration of water-related effects also worsened the situation. Rainfall and groundwater can increase pore pressure, decrease soil strength, and erode slope faces, especially where permeable and impermeable soils intersect. These hydrological influences are often underestimated, particularly under changing climate conditions with more frequent heavy rain events.
Geotechnical standards such as Eurocode 7 and recommendations from the Federal Highway Administration call for slope-specific investigations beyond the immediate wall base, including areas downhill or adjacent to rivers. Unfortunately, these requirements were overlooked in this case. The lesson is clear: visual slope gradients can be misleading, and safety factors must consider subsurface variability and hydraulic conditions.
To prevent similar incidents, engineers should conduct desk studies, investigate geological hazards, and assess groundwater conditions before design finalisation. Rectification measures post-collapse included ground improvement via jet grouting, installation of soil nails, subsoil drainage, and structural enhancement of the retaining wall using tie beams and additional piles.
Ultimately, the failure of retaining wall on slope settings reiterates the need for robust geotechnical practices, proper adherence to codes, and proactive anticipation of adverse ground and weather conditions. Such diligence not only ensures slope stability but also protects public safety and long-term infrastructure performance.
Highlight
- Key contributing factors included the absence of dedicated boreholes for the retaining wall, reliance on data from unrelated locations, and the failure to perform overall or global stability checks.
- While the retaining wall design accounted for sliding, overturning, and bearing capacity, it neglected the interaction between structural loads and subsurface ground conditions—especially beneath and behind the wall.
- Rainfall and groundwater can increase pore pressure, decrease soil strength, and erode slope faces, especially where permeable and impermeable soils intersect.
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