--- title: "Flexible pavement failures: causes and remedies" subject: "Transportation Engineering II" chapter: 4 key: "semester_7/transportation_engineering_ii:flexible-pavement-failure-cause-remedy" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/flexible-pavement-failure-cause-remedy site: BCT Engineering --- # Flexible pavement failures: causes and remedies Transportation Engineering II · Chapter 4: Highway Maintenance, Repair, and Rehabilitation - Asked in: 2082 Baisakh, 8 marks - Video: [Flexible pavement failures and maintenance](https://www.youtube.com/watch?v=kKmG5qMZcAc) — lohit talawar - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/flexible-pavement-failure-cause-remedy - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-4 ## Question Explain the failure of flexible pavement with cause 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. ## Answer #### 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 | ```text Alligator cracking Rutting (cross-section) +--+--+--+--+ |x |x |x |x | ----. .---- +--+--+--+--+ '-------' small interlocked depressed wheel path cracks ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A suitable remedy for alligator cracking is: A. Sprinkling sand B. Patching or removal and replacement, overlay and drainage improvement C. Tack coat only D. Ignoring it Answer: B. Fatigue-cracked areas are patched or replaced, overlaid, and drainage is improved. (Key point: Alligator remedy) 2. Ravelling (loss of stone from the surface) is treated by: A. Seal coat or surface dressing B. Hot sand C. Full reconstruction always D. Dowel retrofit Answer: A. A seal coat or surface dressing re-binds and covers the raveled surface. (Key point: Ravelling remedy) 3. Shoving and corrugation are caused by: A. Unstable mix, poor bond and braking/starting loads B. Excess drainage C. Weak subgrade only D. Ageing of sealant Answer: A. Unstable mix, poor layer bond and braking/starting loads push the surface into waves. (Key point: Shoving cause) 4. Potholes mainly develop from: A. Water entering cracks, weak mix and traffic wear B. Over-compaction C. Wide shoulders D. Cold weather alone Answer: A. Water enters cracks and weakens the mix, which traffic wear then breaks out into bowl-shaped holes. 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