Types Of Failures In Flexible Pavements

Flexible pavements, commonly found on roads, experience various types of failures that impact their integrity and smoothness. Let’s delve into three major types of failures and understand their causes, effects, and outcomes.

Subgrade Failure

Subgrade failure occurs when the soil beneath the flexible pavement undergoes excessive deformation, leading to undulations and corrugations on the pavement surface. The causes of subgrade failure include inadequate stability, poor road drainage, and excessive stress application.

Causes of Subgrade Failure:

• Inadequate Stability: When the subgrade lacks the necessary stability, it becomes prone to deformation.
• Poor Road Drainage: Inadequate drainage can weaken the subgrade, contributing to its failure.
• Excessive Stress Application: Overloading or applying excessive stress on the pavement can lead to subgrade failure.

Base Course Failure

Base course failure involves excessive deformation in the base or foundation course, resulting in potholes, waves, and corrugations on the pavement surface. Causes range from insufficient strength to inadequate quality control and drainage issues.

Causes of Base Course Failure:

• Insufficient Strength: When the base course lacks the required strength, it is susceptible to deformation.
• Loss of Binding Action: Failure in the binding action between materials contributes to base course failure.
• Crushing of Base Course Material: Physical breakdown of base course material leads to deformation.
• Lack of Lateral Confinement: Insufficient lateral confinement of the granular base course contributes to failure.
• Inadequate Wearing Course: The uppermost layer needs to be sufficient for protection against wear and tear.
• Poor Quality Control: Inconsistent quality control measures can result in base course failure.
• Inadequate Road Drainage: Proper drainage is crucial to prevent water-related issues.

Surface Failure

Surface failure, or wearing course failure, occurs when the wearing course of the flexible pavement experiences excessive deformation, leading to ruts, potholes, and cracks. Causes include improper mix design, inferior binder, poor quality control, and binder volatization.

Causes of Surface Failure:

• Improper Mix Design: The absence of a suitable mix design contributes to surface failure.
• Inferior Binder: The use of low-quality binders impacts the wearing course, leading to deformation.
• Poor Quality Control: Inconsistent quality control measures can result in surface failure.
• Volatization and Oxidation of Binder: Changes in binder properties can lead to pavement deformation.

Results of Flexible Pavement Failure

The failures mentioned above manifest in various ways, each with distinct characteristics and implications.

Ruts : Ruts are longitudinal depressions formed due to repetitive traffic wheel loads on the same location, particularly under wheeled traffic.

Potholes : Potholes, circular depressions, result from the disintegration of road metal or a lack of binding between the surface course and the underlying base.

Frost Heaving : Frost heaving, localized pavement upheaval caused by water freezing in cold climates, can lead to cracks in the pavement surface.

Shear Failure Cracking : Shear failure cracking occurs when a fracture or crack forms due to pavement upheaval, often caused by localized weaknesses in the pavement.

Longitudinal Cracking : Longitudinal cracking, the formation of cracks in the road pavement’s longitudinal direction, results from frost action, volume changes in the subgrade, settlement of filling material, or sliding of side slopes.

Map Cracking : Map cracking, irregular cracks typically found on bituminous surfacing, arises from excessive wear or localized weaknesses in the underlying base course.