Necessity of Road Drainage
Road drainage is necessary because of the following reasons:
1. Variation of the moisture content in the soil causes variation in the volume of sub-grade and leads to the failure of the road pavement.
2. Excess moisture content in soil sub-grade causes a substantial reduction in its stability.
3. If the stability of the soil sub-grade fails due to poor drainage, the pavement structure is likely to fail due to sub-grade failure.
4. The entrance of water causes a reduction in the bearing capacity of soil sub-grades like WBM and stabilized soil.
5. The stagnation of water on the surface of the pavement reduces the strength of the pavement.
6. Due to poor drainage, waves and corrugations are formed in the flexible pavement which causes failure of the pavement.
7. Due to poor drainage of the road, water remains in contact with the bituminous material for a longer time causing the stripping of bitumen from aggregates and the formation of potholes.
8. In rigid pavements failure occurs by mud pumping due to the presence of water in fine sub-grade soil.
9. Poor and improper surface drainage work causes erosion of soil from the top of the un-surfaced road, slopes, hillside, etc.
10. Increased moisture content causes a considerable increase in weight and thus, increase in stress and simultaneous reduction in strength of the soil mass.
11. Due to excess water, the shoulders and the pavement structure get damaged.