10 DIFFERENT TYPES OF FAILURES OF FLEXIBLE PAVEMENT
TYPES
OF FAILURES OF FLEXIBLE PAVEMENT
TYPES OF FAILURES OF FLEXIBLE PAVEMENT
Flexible pavement consists of
different layers such as,
§ Sub-grade
§ Sub-base
course
§ Base
course and
§ Surface
course
If any one of the above
mentioned layers becomes unstable or weak then it will result in failure of
flexible pavement. Therefore, it is very important to design and construct each
layer with utmost care.
Different types of failure
encountered in flexible pavements are as follow.
1. Alligator
cracking or Map cracking (Fatigue)
2. Consolidation
of pavement layers (Rutting)
3. Shear
failure cracking
4. Longitudinal
cracking
5. Frost
heaving
6. Lack
of binding to the lower course
7. Reflection
cracking
8. Formation
of waves and corrugation
9. Bleeding
10.
Pumping
This is a common type of failure of flexible pavements. This is also
known as fatigue failure.
Followings are the primary causes of this type of failure.
§ Relative movement
of pavement layer material
§ Repeated
application of heavy wheel loads
§ Swelling or
shrinkage of sub grade or other layers due to moisture variation
Fig-1 shows a pavement with fatigue cracking.
2. CONSOLIDATION
OF PAVEMENT LAYERS (RUTTING)
Formation of ruts falls in
this type of failure. A rut is a depression or groove worn into a road by the
travel of wheels.
This type of failure is
caused due to following reasons.
§ Repeated
application of load along the same wheel path resulting longitudinal ruts.
§ Wearing
of the surface course along the wheel path resulting shallow
ruts.
Fig-2 shows a pavement with
Rutting.
3. SHEAR
FAILURE CRACKING
Shear failure causes upheaval
of pavement material by forming a fracture or cracking.
Followings are the primary
causes of shear failure cracking.
§ Excessive
wheel loading
§ Low
shearing resistance of pavement mixture
Fig-3 shows shear failure
cracking of pavement.
4. LONGITUDINAL
CRACKING
This types of cracks extents
to the full thickness of pavement.
The following are the primary
causes of longitudinal cracking.
§ Differential
volume changes in subgrade soil
§ Settlement
of fill materials
§ Sliding
of side slopes
Fig-4 shows a pavement with
longitudinal cracking.
5. FROST HEAVING
Frost heaving causes upheaval
of localized portion of a pavement. The extent of frost heaving depends upon
the ground water table and climatic condition.
Fig-5 shows a pavement with
frost heaving.
6. LACK
OF BINDING WITH LOWER LAYER (POTHOLES & SLIPPAGE)
When there is lack of binding
between surface course and underlying layer, some portion of surface course looses
up materials creating patches and potholes. Slippage cracking is one form of
this type of failure.
Lack of prime coat or tack
coat in between two layers is the primary reason behind this type of failure.
Fig-6 shows a pavement with
potholes & Fig-7 shows a pavement with slippage cracking.
7. REFLECTION
CRACKING
This type of failure occurs,
when bituminous surface course is laid over the existing cement concrete
pavement with some cracks. This crack is reflected in the same pattern on
bituminous surface.
Fig-8 shows a pavement with
reflection cracking.
8. FORMATION
OF WAVES & CORRUGATION
Transverse undulations appear
at regular intervals due to the unstable surface course caused by stop-and-go
traffic.
Fig-9 shows a pavement with
corrugation.
9. BLEEDING
Excess bituminous binder
occurring on the pavement surface causes bleeding. Bleeding causes a shiny,
glass-like, reflective surface that may be tacky to the touch. Usually found in
the wheel paths.
Fig-10 shows a pavement with
corrugation.
10. PUMPING
Seeping or ejection of water
and fines from beneath the pavement through cracks is called pumping.
Fig-11 shows a pavement with
pumping.
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