Question

Which of the following is not required in the drainage system of highways?
1. The highest level of the underground water table should be placed above the level of the sub-level
2. The side drain should have sufficient capacity and longitudinal slope so that all the water collected on the surface can drain out.
3. Surface water from the carriageway and shoulder must be drained efficiently as it does not allow subgrade
4. Special care should be taken in aqueous areas, especially when it contains harmful salts.

Answer 1

Correct Answer - Option 1 : The highest level of the underground water table should be placed above the level of the sub-level

Explanation:

In the drainage system of the highways, drainage consists of removing or controlling surface water and subsurface water away from the road surface and the subgrade supporting it. Part of the rain water flows on the ground or road surface, while the other part percolates into the ground and reaches the ground water table, raising its level. The subgrade soil above the ground water table may raise through the soil pores due to the phenomenon of capillarity. So subgrade preparation is done as much height above the water table that it does not get affected by the rise in water table.

The three principle type of highway drainage is:

• Surface drainage
• Sub-surface drainage
• Cross drainage