Road is the most commonly and widely used means of transportation. So what is road? Road is a wide way connecting one place to another and specially made surface for vehicles use. Road has 2 major components
Pavement is the top surface of road on which the vehicles travels. Pavements are of two types’ rigid pavement and flexible pavement. Subsurface is the portion which is below the earth surface.
When pavement is filled with water, heavy vehicle loads causes severe damage such as erosion, disintegration on cement, stripping of asphalt coating.
So it is important to have a proper drainage of water and there should no water logging, for that subsurface drainage is required. The subsurface drainage deals with removal of water and percolate through the sub grades. It may leads to rise in water table and also reduce the problem of water logging. The percolation of water is done through gravity. Due to high pores in subsurface the water from surroundings percolates due to gravity action.
The rate of percolation depends upon the voids content, higher the voids higher the rate of percolation. So in design of subsurface drainage we have to select the size and grading of material to be used to get optimum void ratio so to percolate the required water.
C & D waste: it means the construction and demolition waste. The major material in c&d waste is concrete and brick bats. Due to increase in construction and demolition this c&d waste is being generated is huge quantity.
And it may pollute the environment so to protect the environment and make this waste useful we will use this construction and demolition waste as a filter material.
Fig4. Construction and demolition waste
India is developing country so the construction is increasing day by day. And at the end of structure life it has to be demolished so demolition waste will be generated in huge mass so to reduce that waste we will use that material.
Due to increase in road construction the water logging problem has been raised so to overcome this problem we will design sub surface drainage.
Due to increase in construction of roads the water does not percolates into ground due to which the ground water level is reducing so we will percolate the water into ground through sub surface and do ground water recharge.
Highway pavements are very susceptible to the damaging effects of waterwhich enters the pavement as surface water through cracks, joints, pavementinfiltration and as groundwater from an intercepted aquifer. Edge drains systems thatallow water to filter down through shoulder gravel into trenches and pipes that carrythe water away have been a preferred method for managing subsurface drainage. These systems keep moisture from softening subgrades and reducing the structuralstrength of pavement. Longitudinal drains are placed parallel to the pavementcenterline in both the horizontal and vertical alignments. This type of drain consists ofa trench with a perforated collector pipe surrounded by a protective filter. Thesedrains are usually placed under the pavement edge joints or under shoulders wheremost water infiltrates the pavement; but, on wide pavements such as runways theymight also be placed at the center and intermediate points to draw down the watertable.
The unsaturated zone is located above the water table. Within this zone, thepore spaces are usually only partially filled with water. Hence, porosity of soil islarger than volumetric water content. Due to the fact that water in this zone is held inthe soil pores under surface-tension forces, negative pressures or suction pressures aredeveloped. Rainfall on pavement runs off and infiltrates through the base, subbase, and subgrade soils. Infiltration of any layer depends upon its porosity, thickness and quantity ofwater present. Water that has entered into the pavement can be carried to edge drainsthrough permeable layers and then drained out of pavement through outlet pipes.
Road drainage system concerned in study consisted of pavement layerplaced on granular base layer (sub base) of 30cm thickness, assumed to be initiallysaturated, laid above a sub grade layer. The water table assumed to be 0.5m below thegranular base. The subsurface drainage system consisted of 10cm radius edge drain,edge drain laid below road shoulder and along road length through 40cm x 40cm highpermeability gravel trench. The finite element mesh optimized and discredited usingthe auto-run mesh routine EasyMesh.
Time required to reach saturation of 85% is same in subbase A and subbase B while time required for subbase C is less.
Water drain through subbase C is more, subbase A is less compare to subbase C and subbase B has least drainage.
Pavements designed without rapid internal drainage can remainfilled with water a number of days or weeks after each saturatingrainfall, adding up to several months of damaging environmentalconditions each year. When good internal drainage is provided,however, the water-related damages can be eliminated or at leastgreatly reduced. The main source of moisture in a pavement structure is surfacewater infiltrating through cracks, transverse and longitudinal joints, granular shoulders, and interconnected voids in the pavement. Surface water infiltration can account for as much as 90 to 95 percent of the total moisture in a pavement system.
Generally the drainage layer is a minimum of three to four inchesthick, highly permeable material that extends under the full widthof the roadway exposed to traffic loads. The drainage layer, alsoreferred to as a drainage blanket, horizontal drainage blanket, ora drainable layer, uses highly permeable material to allow quicklateral drainage even though the cross slope of the layer is verylow and the thickness of the layer is limited.
Generally, the gradations of these materials limit the permeability to very low values (less than 2 ft/day); an ideal drainage layer should have permeability in excessof 1000 feet per day.
Some general specifications/guidelines for permeable base aggregateare as follow:
use crushed aggregate since crushed material is more stable than natural, rounded aggregate;
limit maximum size aggregate to prevent material degradation from high inter-particle contact stress; do not use degradable materials, which over time decrease the permeability of the drainage layer; and
Use caution with crushed recycled concrete and certain slag-type materials that may produce a precipitate which can plug drainage systems.
In order to protect the drainage layer from intrusion of fines the supporting layer must satisfy certain filter criteria. If these criteria are not satisfied by the existing support layer, then a protective filter must be designed and placed between thefine and coarse soils to prevent intrusion and clogging.
Filter material, whether granular or fabric, must meet threegeneral requirements:
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