Highway maintenance and causes of pavement failure

Highway maintenance

Highway maintenance is the work done to keep a road, its pavement, shoulders, drainage, structures and furniture in a safe and serviceable condition and to preserve the investment, without changing the original design standard.

Classification (Nepal DoR practice and IRC:82):

1. Routine maintenance - small, regular, yearly works such as patching potholes, cleaning drains and culverts, clearing slips, cutting grass, repairing shoulders and signs.
2. Recurrent maintenance - works repeated at intervals within a year or two, such as resealing cracks and shoulder re-gravelling, drain repair.
3. Periodic maintenance - works at intervals of several years (3 to 8) like resealing, regravelling, surface dressing and thin overlay to restore the surface.
4. Urgent (emergency) maintenance - immediate works to reopen the road after landslides, floods or accidents.

General causes of pavement failure

1. Traffic factors - overloading, more repetitions than designed, high tyre pressure, channelised traffic.
2. Poor drainage - the main cause. Water in the subgrade and base reduces strength, causes pumping, ravelling, potholes and edge failure; blocked side drains and culverts, high water table.
3. Weak subgrade - low CBR, expansive or soft soil, poor compaction, inadequate sub-base.
4. Design defects - thin pavement, wrong assumed traffic or CBR, no allowance for climate, poor geometric and drainage design.
5. Poor materials and workmanship - inferior aggregate or binder, wrong mix proportions, segregation, low compaction, poor joints and bond between layers, low temperature during laying.
6. Climate and environment - temperature extremes (bleeding, cracking), rainfall and floods, freeze-thaw in hills, landslides.
7. Ageing - oxidation and hardening of bitumen with time.
8. Lack of timely maintenance - small cracks and potholes grow rapidly into major failures when not repaired.
9. Utility cuts and other external causes - trenches, spillage of oil.