--- title: "Pavement evaluation; flexible failure types and causes" subject: "Transportation Engineering II" chapter: 4 key: "semester_7/transportation_engineering_ii:pavement-evaluation-flexible-failure-causes" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/pavement-evaluation-flexible-failure-causes site: BCT Engineering --- # Pavement evaluation; flexible failure types and causes Transportation Engineering II · Chapter 4: Highway Maintenance, Repair, and Rehabilitation - Asked in: 2076 Chaitra, 8 marks - Video: [Flexible Pavement Failures & Their Repairs | Types, Causes & Maintenance | Highway Engineering](https://www.youtube.com/watch?v=iGu8lRDTKZI) — Engr. DANISHWAR KHAN - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/pavement-evaluation-flexible-failure-causes - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-4 ## Question Define pavement evaluation. Explain the types of failure & its causes in flexible pavement. ## Short answer Pavement evaluation collects and analyzes condition data to decide maintenance. It includes functional evaluation (roughness, skid resistance, distress surveys) and structural evaluation (deflection tests like Benkelman beam, FWD, and destructive tests). Flexible pavement failures are alligator cracking (repeated loading), rutting (weak subgrade), shoving (unstable mix), potholes (water), ravelling (binder loss), bleeding (excess binder), and others. ## Answer #### Pavement evaluation **Pavement evaluation** is the systematic collection and analysis of data on the present condition of a pavement (surface and structure), so that the need for maintenance, strengthening or reconstruction can be decided and priorities set. **Functional evaluation** (ride quality and safety) - **Roughness** - measured by bump integrator, MERLIN, Roadroid (smartphone) or profilometer, and expressed as the International Roughness Index (IRI, m/km); IRC:SP:16 gives evenness limits, and Nepal DoR uses roughness in its road maintenance management system. - **Skid resistance** - pendulum tester (British Pendulum Number), skid trailer. - **Surface distress** - visual condition survey of cracks, potholes, rutting, ravelling, bleeding and patching (IRC:82 and the Nepal DoR condition survey). **Structural evaluation** (load capacity) - **Deflection tests** (non-destructive) - Benkelman beam (IRC:81), Falling Weight Deflectometer (FWD), Lacroix deflectograph. - **Destructive tests** - test pits and cores to find layer thickness, density and subgrade CBR; Dynamic Cone Penetrometer (DCP) for in-situ strength. - **Other tests** - Ground Penetrating Radar (layer thickness, non-destructive), plate load test on exposed layers, and back-calculation of layer moduli from FWD data. **Use**: the results give a condition index, which is combined with traffic to select the treatment: routine maintenance, periodic maintenance, overlay (strengthening) or reconstruction. #### Types of failure and causes in flexible pavement A flexible pavement fails when it can no longer give a safe, smooth ride or carry the traffic. Common failures: | Failure | Description | Main causes | Remedy | |---|---|---|---| | **Alligator (fatigue) cracking** | Interconnected cracks like crocodile skin in the 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 the wheel paths | Weak subgrade/base, insufficient compaction, overloading, soft mix in hot weather | Fill with a levelling course, overlay, reconstruct if deep | | **Shoving and corrugation** | Bulges and waves across the road | Unstable mix, poor bond, braking and starting loads | Remove and replace, scarify and relay | | **Potholes** | Bowl-shaped holes | Water entering through cracks, weak mix, traffic wear | Patching with premix | | **Ravelling** | Loss of stone from the surface | Poor bitumen, stripping, ageing, insufficient binder | Seal coat, surface dressing | | **Bleeding** | Excess bitumen forms a shiny film | Too much binder, low air voids, heat | Spread hot sand/chips, remove excess binder | | **Depression and settlement** | Local sinking | Subgrade consolidation, poor compaction, utility trench | Fill and level, reconstruct base | | **Edge failure** | Breaking at the pavement edge | Poor support, narrow shoulder, water | Strengthen shoulder, improve drainage | | **Longitudinal / reflection cracks** | Cracks that follow joints or cracks in the layer below | Differential settlement, poor construction joints, old cracks | Seal, overlay with a crack relief layer | | **Stripping** | Loss of bond between bitumen and aggregate | Water action, hydrophilic aggregate | Anti-stripping agent, replacement | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Pavement evaluation is: A. Systematic collection and analysis of data on present condition so that maintenance, strengthening or reconstruction needs can be decided B. Only the visual survey of signs C. Construction of a new pavement D. Measuring traffic volume Answer: A. Evaluation sets priorities and treatment by assessing the present surface and structure. (Key point: Definition) 2. Which is a structural evaluation test? A. Pendulum skid test B. Bump integrator roughness C. Benkelman beam or FWD deflection D. Visual crack survey Answer: C. Deflection tests (Benkelman beam, FWD) measure load capacity; roughness, skid and distress are functional. (Key point: Functional vs structural) 3. Roughness is expressed as: A. CBR B. IRI in m/km C. Penetration in mm D. BPN Answer: B. International Roughness Index (IRI) in m/km is used for ride quality; BPN is for skid resistance. (Key point: Roughness) 4. Alligator cracking is caused by: A. Repeated loading, thin layers, weak subgrade/base and poor drainage B. Excess binder C. Blocked expansion joints D. Oil spillage Answer: A. Repeated wheel loads on weak or thin layers fatigue the bituminous layer, forming interconnected cracks. 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