16-04-2013, 04:18 PM
HIGHWAY DRAINAGE
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INTRODUCTION
Highway drainage is the process of remaining and controlling excess surface and subsoil water with in the right of way.
The installation of suitable surface and sub surface drainage system is an essential part of highway design and control.
MCADAM said that “ if water passes through a road
and fill the native soil, the road whatever may be its thickness losses support and goes to pieces”.
IMPORTANCE OF HIGHWAY DRAINAGE
Sustained contact of water with bituminous pavements causes failures due to stripping of bitumen from aggregates .
Erosion of soil from top of un surfaced roads and slopes of embankment .
Excess moisture in soil sub grade causes considerable lowering of its stability.
Excess water in shoulders and pavement edges causes considerable damage.
REQUIREMENTS OF HIGHWAY DRAINAGE
The surface water from the adjoining land should be prevented from entering the roadways.
The side drain should have sufficient capacity and longitudinal slope to carry away all the surface water collected.
Highest level of ground water table should be kept well below the level of sub grade, preferably by at least 1.2MTS.
The surface water from the carriageway and shoulder should effectively be drained off without allowing it to percolate to sub grade.
seepage and other sources of under ground water should be drained off by the surface drainage system.
HYDROLOGIC ANALYSIS
The main objective of hydrologic analysis is to estimate the maximum capacity of water expected to reach the drainage system under consideration.
Various factors affecting the runoff are the rate of rainfall, type of soil and moisture condition, topography of the area, type of ground cover.
Rational formula is widely used to estimate the peak runoff water for highway drainage.
Q = C i Ad
Q = run-off,
C = run-off coefficient,
I = intensity of rainfall,
Ad =drainage area in 1000 sq mts.
ROAD CONSTRUCTION IN WATER LOGGED AREAS
When the problem is one of water logging only without flooding or pressure of detrimental salts , the following methods can be adopted.
Depressing the sub surface water level by suitable drainage system.
Raising the road level by constructing embankment.
Providing a capillary cut off to arrest the capillary rise of water.
Providing sufficient pavement thickness in view of the sub grade conditions.
CONCLUSION
Slope and Chamber should be provided well.
Embankment height should be identified well.
Shoulder height should be less than pavement height.