---
title: "Typical failures of flexible pavement"
subject: "Transportation Engineering II"
chapter: 4
key: "semester_7/transportation_engineering_ii:flexible-pavement-failures-causes"
source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/flexible-pavement-failures-causes
site: BCT Engineering
---

# Typical failures of flexible pavement

Transportation Engineering II · Chapter 4: Highway Maintenance, Repair, and Rehabilitation

- Asked in: 2073 Shrawan, 8 marks; 2072 Chaitra, 8 marks (asked 2 times)
- Video: [Failures in Flexible Pavement - Transportation Engineering - I](https://www.youtube.com/watch?v=xAFZohikrUo) — Ekeeda
- 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-failures-causes
- Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-4

## Question

Explain the typical failures of flexible pavement with neat sketches?

## Short answer

Typical flexible pavement failures: alligator cracking from repeated loading, rutting from weak subgrade, potholes from water entry, ravelling from binder loss, bleeding from excess binder, shoving from unstable mix, and edge failure from poor shoulder support. Each requires specific repair like patching, sealing, or overlay.

## Answer

#### Typical failures of flexible pavement
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. Interconnected crocodile-skin cracks in wheel paths are called:
   A. Rutting
   B. Alligator (fatigue) cracking
   C. Ravelling
   D. Shoving
   Answer: B. Alligator cracking comes from repeated loading, thin layers and weak subgrade, in wheel paths. (Key point: Alligator cracking)

2. Rutting is:
   A. Waves across the road
   B. Longitudinal depressions in wheel paths due to weak subgrade/base, poor compaction or overloading
   C. Loss of stone from the surface
   D. Excess bitumen forming a shiny film
   Answer: B. Rutting is a longitudinal depression in the wheel path from weak layers, poor compaction or overloading. (Key point: Rutting)

3. Bleeding is mainly caused by:
   A. Too little binder
   B. Too much binder, low air voids and heat
   C. Water stripping the binder
   D. Subgrade consolidation
   Answer: B. Excess bitumen with low air voids rises in heat and forms a shiny film. (Key point: Bleeding cause)

4. Stripping is:
   A. Loss of bond between bitumen and aggregate by water action
   B. A step at joints
   C. Cracks at the pavement edge
   D. Local sinking from trench settlement
   Answer: A. Water action on hydrophilic aggregate breaks the bitumen-aggregate bond; anti-stripping agents are the remedy. (Key point: Stripping)

## Related in Transportation Engineering II

- [Flexible pavement failures; deflection overlay design](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-failures-deflection-overlay) — Transportation Engineering II, chapter 4
- [Flexible pavement failures: causes and remedies](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-pavement-failure-cause-remedy) — Transportation Engineering II, chapter 4
- [Repair vs rehabilitation; rigid pavement failures](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Arepair-vs-rehabilitation-rigid-failure-types) — Transportation Engineering II, chapter 4
- [Flexible pavement design with 8 CBR values](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-design-eight-cbr-340-cvd) — Transportation Engineering II, chapter 2
- [Flexible pavement life with 140 cvpd traffic](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-design-life-years-140-cvpd) — Transportation Engineering II, chapter 2
- [Pavement classification; flexible layer functions](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Apavement-classification-flexible-layer-functions) — Transportation Engineering II, chapter 2