- 2082 Baisakh · 8 marks
Flexible pavement failures: causes and remedies
Short answer
Typical failures: alligator cracking (fatigue, thin layers; remedy overlay), rutting (weak base; levelling course), potholes (water entry; patching), ravelling, bleeding, shoving. Main causes: traffic overloading, poor drainage, weak subgrade, design/materials deficiencies. Remedies include drainage improvement, patching, structural overlay or reconstruction.
Explain the failure of flexible pavement with cause and remedies.
Failures of flexible pavement: causes and remedies
A flexible pavement fails when it can no longer give a safe, smooth ride or carry traffic. Common failures:
| Failure | Description | Main causes | Remedy |
|---|---|---|---|
| Alligator (fatigue) cracking | Interconnected cracks like a crocodile skin in wheel paths | Repeated loading, thin layers, weak subgrade or base, poor drainage, aged binder | Patching or removal and replacement, overlay, drainage improvement |
| Rutting | Longitudinal depressions in wheel paths | Weak subgrade/base, insufficient compaction, overloading, soft mix in heat | Fill with levelling course, overlay, reconstruct if deep |
| Shoving and corrugation | Waves across the road | Unstable mix, poor bond, braking and starting loads | Remove and replace, scarify and relay |
| Potholes | Bowl-shaped holes | Water entry in cracks, weak mix, traffic wear | Patching with premix |
| Ravelling | Loss of stone from the surface | Poor bitumen, stripping, age, insufficient binder | Seal coat, surface dressing |
| Bleeding | Excess bitumen forms a shiny film | Too much binder, low air voids, heat | Hot sand/chips, remove binder |
| Depression and settlement | Local sinking | Subgrade consolidation, poor compaction, utility trench | Fill and level, reconstruct base |
| Edge failure | Breaking at pavement edge | Poor support, narrow shoulder, water | Strengthen shoulder, drain |
| Longitudinal / reflection cracks | Cracks following joints below | Differential settlement, poor construction joints, old cracks | Seal, overlay with crack relief layer |
| Stripping | Loss of bond between bitumen and aggregate | Water action, hydrophilic aggregate | Anti-stripping agent, replacement |
Alligator cracking Rutting (cross-section)
+--+--+--+--+
|x |x |x |x | ----. .----
+--+--+--+--+ '-------'
small interlocked depressed wheel path
cracks
✓ Answer checked by Claude Opus 5.5 (high effort)
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