Failures of Flexible Pavements

1. Alligator(Map) cracking
2. Shear Failure
3. Frost Heaving
4. Longitudinal cracking
5. Consolidation failure
6. Wearing of the Surface
7. Reflection cracks

• Alligator Cracking: 

Alligator or map cracking occurs on the surface of the flexible pavement due to the relative movement of the material or failure of the materials of the pavement layers. This may be caused by the repeated application of the heavy wheel loads resulting in fatigue failure due to the moisture variations resulting in swelling and shrinkage of sub-grade and other pavement materials. The localized weakness of the underlying base course would also cause cracking of the surface course in this pattern.

Shear Failure

Shear failure of the flexible pavement occurs due to the weakness of the pavement mixtures, the shearing resistance being low due to inadequate stability of excessive heavy loading. The shear failure causes upheaval of pavement material by forming a fracture or cracking. 

Frost Heaving

Areas having cold climates are prone to frost heaving. When the water present in the pores of the layers turns into ice, it causes swelling of the ice and therefore results in the upheaval of the area affected by the frost. 

It must be remembered that the difference between the frost heaving and the shear failure is that in shear failure the depression is followed by the upheaval of the adjacent area but in case of the frost heaving, there is no depression.