Highway pavement failures can occur due to defects in materials or construction methods, inadequate drainage, excessive traffic loads, environmental factors like rainfall, or poor subgrade stability. Flexible pavement failures present as potholes, cracks, ruts, and depressions. The most common type of failure is alligator cracking caused by repeated loads or moisture damage. Other failures include consolidation of layers forming ruts, shear cracking, longitudinal cracks from frost or settlement, and reflection cracks from overlays not bonding to the lower layer. Maintaining adequate subgrade strength, drainage, and pavement thickness can help prevent failures.

1. HIGHWAY MAINTENANCE

2. Causes of Pavement failure
• Defects in quality of materials used.
• Defects in construction methods and quality control
during construction.
• Inadequate surface or sub surface drainage resulting in
stagnation of water.

3. • Increase in magnitude of wheel loads and the number of
load repetitions due to increase in traffic load.
• Settlement of foundation of embankments of the fill
material itself.
• Environmental factors including heavy rainfall, soil
erosion, high water table, snow fall, frost action etc.,
• Poor workmanship
• Improper design

4. Flexible pavement failures
• A flexible pavement failure is defined by formation of pot holes,
ruts, cracks, depressions and settlements.
• Failure of any one or more pavement layers develops waves and
corrugations on pavement surface or longitudinal ruts and
shoving.
• Pavement unevenness itself is considered as failure.
• Various factors contribute to pavement distress or failure like,
aging and oxidation of bituminous film causes failure in
bituminous pavements.

5. Failure in Flexible Pavements

6. Failures in Subgrade
• One main cause of flexible pavement failure is excessive
deformation in subgrade.
• Failure can be noticed in the form of undulations or
waves and corrugations in pavement surface and also
depressions followed by heaving of pavement surface.
• Lateral shoving of pavement near edge along the wheel
path of vehicles is due to insufficient bearing capacity or
a shear failure in subgrade

7. • Failure of subgrade is due to two basic reasons:
– Inadequate stability
– Excessive stree application.
• Inadequate stability may be due to inherent weakness of soil or
excessive moisture or improper compaction.
• Stability is the resistance to deformation under the stress.
Excessive stress application is due to inadequate pavement
thickness or loads in excess of design value.
• Deformation of soil subgrade and other pavement materials is
increased with increase in number of load repetitions.

8. • If the applied stress on the subgrade or pavement is very low
when compare to its bearing capacity, the deformation due to
load would be elastic or fully recovered when load is released.
• If compaction of layers is not adequate and after loading, part
of the deformation may be permanent due to compaction of
soil, this may be called as consolidation deformation.
• If applied stress is excessive with respect to stability and if
plastic flow takes place as in the case of wet clayey soil,
deformation is called as plastic deformation and is not partly
recoverable.

9. Soil deformation under loads

10. • Damage in flexible pavement caused by traffic to
subgrade failure or inadequate compaction of subgrade
and other pavement layers can be seen in below fig.
Failure due to improper compaction of subgrade and pavement layers

11. Failures in Sub-base or Base Courses
• Chief Failures:
– Inadequate stability or strength.
– Loss of binding action.
– Loss of base course materials.
– Inadequate wearing course.
– Use of inferior materials and crushing of base course
materials.
– Lack of lateral confinement for granular base course.

12. TYPES OF FLEXIBLE PAVEMENT FAILURES
• Alligator (map) cracking.
• Consolidation of pavement layers.
• Shear failure.
• Longitudinal cracking.
• Frost heaving.
• Lack of binding (keying) to the lower course.
• Reflection cracking.
• Formation of waves and Corrugations.

13. Alligator Cracking:
• This is the most common type of flexible pavement failure
and occurs due to relative movement of pavement layer
materials.
• This may be caused by repeated application of heavy wheel
loads resulting in fatigue failure or due to moisture
vibrations resulting in swelling and shrinkage of subgrade
and other pavment materials.
• Weakness in underlying course also causes a cracking of
surface course.

14. Alligator or Map cracking

15. Consolidation of Pavement layers:
• Ruts are mainly formed due to consolidation of one or more
layers of pavement.
• Repeated application of loads along the same wheel path
cause deformation resulting in consolidation deformation or
longitudinal ruts.
• Shallow ruts on surface course can also be caused due to
wearing along wheel path.
• Depending on depth and width of ruts, it can be estimated
whether the consolidation deformation has been caused in
subgrade or in subsequent layers.

16. Formation of ruts

17. Shear failure and cracking:
• Shear failures are caused due to inherent weakness of
pavement mixtures and shearing resistance being low due
to inadequate stability or excessive heavy loading.
• Shear failure causes upheaval of pavement materials by
forming a fracture or cracking.
Shear failure cracking

18. Longitudinal Cracking:
• Due to frost action and differential volume changes in
subgrade longitudinal cracking is caused in pavement
traversing the full pavement thickness.
• Settlement of fill and sliding of side slopes also would
cause longitudinal cracking.

19. Frost heaving:
• Frost heaving is often misunderstood with shear or other
types of failures.
• In shear failure, the upheavel of portion of pavement is
followed with a depression. In this case, there is mostly a
localized heaving-up pavement portion depending upon
ground water and climatic conditions.
Failure due to frost nature

20. Lack of binding with lower layers:
• Slipping occurs when surface course is not keyed/bonded
with the underlying base. This results in opening up and loss
of pavement materials forming patches or pot holes.
• This will occur when bituminous surfacing is provided over
existing concrete base course or soil-cement base course.
• This can be caused when there is lack of prime/tack coat in
between two layers.

21. Reflection Cracking:
• This type of failure is observed when bituminous overlays
provided over existing concrete pavements.
• The crack pattern as existing cement concrete pavements
are mostly reflected on bituminous surfacing in the same
pattern.
• These allow surface water to seep through and cause
damage to the soil subgrade or result in mud pumping.