IMPORTANCE OF HIGHWAY DRAINAGE
Significance of Drainage
An increase in moisture content causes decrease in strength or stability of a soil mass the variation in soil strength with moisture content also depends on the soil type and the mode of stress application. Highway drainage iS l important because of the following reasons
(i)Excess moisture in soil suberade causes considerable lowering of its stability The pavement is likely to fail due to subgrade failure as discussed in Article 10.1.
(11) Increase in moisture cause reduction in strength of many pavement materials like stabilized soil and water bound macadam.
(1i1)) In some clayey soils variation in moisture content causes considerable variation in volume of subgrade. This sometimes contributes to pavement failure
(iv) One of the most important causes of pavement failure by the formation of waves and corugations in flexible pavements is due to poor drainage.
(v) Sustained contact of water with bituminous pavements causes failures due to
stripping of bitumen from aggregates like loosening or detachment of some of the
bituminous pavement layers and formation of pot holes.
(VI) The prime cause of failures in rigid pavements by mud pumping is due to the
presence of water in fine subgrade soil.
(vii) Excess water on shoulders and pavement edge causes considerable damage.
(viil) Excess moisture causes increase in weight and thus increase in stress and
simultaneous reduction in strength of the soil mass. This is one of the main
reasons of failure of earth slopes and embankment foundations.
(ix) In places where freezing temperatures are prevalent in winter, the presence of
water in the subgrade and a.continuous supplyof water from the ground water can
cause considerable damage to the pavement due in frost action.
(x) Erosion ot soll rom top oF unsurtaced roads and slopes of embankment, cut and
hill side is also due to surface water
