10 DIFFERENT TYPES OF FAILURES OF FLEXIBLE PAVEMENT

Flexible pavement consists of different layers like,

  • sub grade
  • sub-base course
  • base course and
  • Surface Course

If any one of the above layers becomes unstable or weakened it will result in the failure of the flexible pavement. Therefore it is very important to design and manufacture each layer with utmost care.

The different types of failures encountered in flexible pavements are as follows.

  1. Alligator cracking or map cracking (fatigue)
  2. Rutting of pavement layers
  3. shear failure cracking
  4. longitudinal crack
  5. frost heaving
  6. Lack of binding to the lower course
  7. reflection cracking
  8. Wave formation and corridor
  9. is bleeding
  10. pumping

1. Alligator or map cracking (fatigue cracking)

This is a common type of failure of flexible pavements. It is also known as fatigue failure.

Following are the primary reasons for this type of failure.


  • Movement relative to pavement layer material
  • repeated application of heavy wheel loads
  • Swelling or shrinking of the subgrade or other layers due to moisture variation

A sidewall with fatigue is visible in Fig-1.

Fig-1 Fatigue breakdown
Fig-1 Fatigue breakdown

2. Rutting of pavement layers

This type of failure leads to the formation of ruts. A rut is a depression or groove worn in a road by the travel of the wheels.

This type of failure occurs due to the following reasons.

  • Repeated application of load along the same wheel path results in longitudinal ruts,
  • as a result of wear of the surface course along the wheel path shallow rut,

Fig-2 shows a sidewalk with routing.


Fig-2 Routing
Fig-2 Routing

3. shear failure cracking

Shear failure results in the formation of a fracture or crack in the pavement material.

The following are the primary causes of shear failure breakdown.

  • excessive wheel loading
  • Low shear resistance of pavement mix

Figure-3 shows the shear failure of the pavement.

Fig-3 Shear Failure Cracking
Fig-3 Shear Failure Cracking

4. longitudinal cracking

These types of cracks extend over the entire thickness of the pavement.


The following are the primary causes of longitudinal cracks.


  • Inter-volume change in subgrade soils
  • filling material disposal
  • side slopes

Fig-4 shows a sidewall with longitudinal cracks.

Fig-4 Longitudinal Cracking
Fig-4 Longitudinal Cracking

5. frost heaving

Frost heaving causes upheavals in a localized portion of a pavement. The extent of frost heaving depends on the groundwater level and climatic conditions.

Fig-5 shows a sidewalk with frost protection.

Fig-5 Frost Heaving
Fig-5 Frost Heaving

6. Lack of bond with the bottom layer (pits and slippery)

When there is a lack of bond between the surface course and the underlying layer, part of the surface course loses the material forming patches and pits. Slippage cracking is one form of this type of failure.

Lack of prime coat or tackle coat between the two layers is the primary reason behind this type of failure.


Fig-6 shows a sidewalk with potholes and Fig-7 shows a sidewalk with slippery cracks.

Fig-6 Pits
Fig-6 Pits
Fig-7 Slippage Cracking
Fig-7 Slippage Cracking

7. reflection cracking

This type of failure occurs when a bituminous surface course is laid with few cracks on the existing cement concrete pavement. This crack is reflected in the same pattern on the bituminous surface.

Figure 8 shows a sidewalk with a reflecting crack.

Fig-8 Reflection Cracking
Fig-8 Reflection Cracking

8. making waves and corridors

Transverse fluctuations appear at regular intervals due to the unstable surface course due to stop-and-go traffic.

Fig-9 shows a sidewalk along the corridor.

fig-9 groove
fig-9 groove

9. is bleeding

Bleeding occurs from excess bituminous binder occurring on the surface of the pavement. The bleeding causes a shiny, glass-like, reflective surface that may be sticky to the touch. Commonly found in wheeled paths.

A sidewalk along the corridor is shown in Fig-10.


Fig-10
Fig-10

10. pumping

Water seeping or pumping out through cracks from under the pavement and is called fine pumping.

Figure 11 shows a sidewalk with pumping.

Figure-11 Pumping
Figure-11 Pumping

Reference

Highway Engineering by SK Khanna and CEG Justo


Er. Mukesh Kumar

Photo of author
Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.