The different types of failures in flexible pavements are described below:
1. Subgrade failure.
2. Base failure or base course failure.
3. Surface failure or wearing course failure.
1. Subgrade Failure:
Excessive deformation in subgrade soil of a flexible failure is called subgrade failure.
This is one of the main causes of failure of flexible pavements. This type of failure causes undulations (ups and downs) and corrugations in the pavement surface.
Causes Of Subgrade Failure:
1. Inadequate stability.
2. Inadequate road drainage.
3. Excessive stress application.
2. Base Course Failure:
Excessive deformation in the base or foundation course of a flexible pavement is known as base course failure.
This type of failure causes potholes, waves, and corrugations in the pavement surface.
Causes Of Base Course Failure:
1. Insufficient strength.
2. Loss of binding action.
3. Crushing of base course material.
4. Lack of lateral confinement of the granular base course.
5. Insufficient wearing course.
6. Inadequate quality control.
7. Inadequate road drainage.
3. Surface failure:
Excessive deformation in the wearing course of a flexible pavement is called surface failure or wearing course failure.
This type of failure causes ruts, potholes, cracks etc in the pavement structure.
Causes Of Surface Failure:
1. lack of proper mix design
2. Use of the inferior type of binder.
3. Inadequate quality control.
4. Volatization and oxidation of binder.
Results Of Flexible Failure:
The longitudinal depressions or cuts in flexible pavement is known as ruts. These are usually formed ion earth or W.B.M roads of one lane width due to repetitive traffic wheel loads on the same location, particularly under wheeled traffic.
2. Pot Holes:
The isolated depressions, more or less circular in shape formed in flexible pavements are called pot holes or patches. These are usually formed in all types of flexible pavements due to disintegration of road metal or lack of binding surface course with the underlying base.
3. Frost Heaving:
A localized heaving up of pavement portion is known as frost heaving.
The water which may find access to pavement structure freezes in cold climates. The expansion accompanying this frost action causes upheaval which in turn may crack the pavement surface.
4. Shear Failure Cracking:
The formation of a fracture or cracking due to upheaval of pavement portion followed by a depression called shear failure cracking. This type of failure occurs due to localized weakness in the pavement.
5. Longitudinal Cracking:
The formation of cracks in the longitudinal direction of a road pavement is called longitudinal cracking.
This failure is caused due to frost action, different volume changes in subgrade, settlement of filling material or due to sliding of side slopes.
6. Map Cracking:
The development of irregular cracks, usually formed on bituminous surfacing is called map cracking.
This type of flexible road failure is due to excessive wear of the road surface or due to localized weakness in the underlying base course.