An increase in moisture content causes decrease in strength or stability of soil mass, depending on type of soil and mode of stress application. Following are some of the effects of poor drainage system in Roads and Highways:
- Excess moisture in sub-grade results in lowering of stability, swell and fail under heavy load.
- Due to poor sub-surface drainage waves, cracks, and corrugation develop in flexible pavements.
- Sustained contact of water with bituminous pavement cause failure due to stripping of bitumen from aggregate and formation of pot holes.
- Failure in rigid pavement causes high moisture content in subgrade result in pumping (rise of slurry in cracks).
- Excess water on shoulder seeps and cause damage.
- Highway constructed on embankment slopes may damage due to slop failures the reason for which is excess moisture content which causes increase in weight and thus increases stresses and simultaneous reduction in strength of soil mass.
- In freezing temperature water in pores may freeze and finally damage the pavement by frost action).
- The flowing water on surface cause erosion on the hill side also result in erosion of embankment cut and hillside.
Requirement of good highway
- Adequate cross slop to allow drainage without allowing the water to percolate to subgrade.
- Shoulders paved should have an adequate slope to avoid percolation of water.
- The side slop should not be steep to cause erosion.
- Surface water from the adjoining land should be prevented from entering the roadway. Fro this purpose intercepting drains are provided.
- Side drains with sufficient capacity, and longitudinal slope.
- To avoid seepage of water from underground water sources of water, provision of subsurface drainage system should be provide.
It is more appropriate to take care of drainage at the time of location survey. Ideal location fro a drainage stand point would lie along the divides b/w large drainage areas. Then all streams flow away from the highway, and the drainage problem is reduced to caring for the water that falls on the roadway and back slope. In contrast location paralleling large streams is far less desirable as they cross every tributary where it is largest. Ideal locations avoid steep grades and heavy cuts and fills as they create difficult problems in erosion control.