India has one of the most extensive highway systems in the world most of the roads built in the country pre-independence era were constructed using John Macadam more than 100 years old principle in which dry pavement structure would be provided on the subgrade having on slope center of the section. Still, some of the last decades have seen a tremendous increase in the volume at the same time three has been increased in the weight of the vehicles and number of axle loads which accelerated the deterioration of the pavements. To overcome this problem the contact surface is changed by asphalt and concrete. There is overwhelming evidence that a larger percentage of the distressed roads sections are poor drainage which clearly speakers of the need to provide effective water drainage which is often neglected.
Various modes of water penetrate into pavement:
Subsurface water from sides of the pavements
Subsoil water from the underside in capillary action.
Intercepted water due to over flooding of drainage.
Groundwater from interrupted aquifers and localized springs.
Percolation through cracks and poor pavement surface.
Sub-soil water from the side of the pavement.
Effect of water pavement (Distress):
Continuous contract causes stripping of asphalt mixture and affects durability and D cracking of concrete.
It reduces the strength of granular materials and subgrade soils.
It causes the pumping of concrete pavement with subsequent faulting and degradation of pavement.
Climatic changes severally damage the surface. In cold countries where freezing action and surface continuously supply of ground pavement damages.
Conventional methods of pavement drainage:
Prevention of roof water infiltration.
Most of the geotextiles presently in use are manufactured from petroleum derivatives such as polymer, polyethylene, and polypropylenes. They are also resistant to wear and tears and to adverse environmental conditions. Fabrics manufactured from wood plum (rayon and acetate) and silica (glass fiber) have also been found in limited use in the civil egg. The term geotextiles are being increasingly used to include such materials as coir and jute netting, which find primary. Application in erosion geogrids, such as tensor and hatch are also considered the larger members of the geotextiles family.
Engineering Characteristics and functions:
Important engineering properties of geotextiles are tensile strength, burst and puncture strength modulus of elasticity, permeability. Pore size distribution, abrasion resistance ultraviolet, stability against a hostile environment. The main functions of geotextiles are reinforcement, filtration, drainage, control separation. Highways on soft or problematic soils, rails roads, reinforced earth embankment and walls, dams drainage control stabilization of soil and rock slopes, erosion control.
Role of Geotextiles in Highway Stabilization:
Whether a drainage system is part of the original road design or remedial measures it must be hydraulically efficient and shouldn't be subject to clogging. It requires course element permits water flow and filter element for restraining soil from piping conventionally, a combination of these requirements are met by the use of well-graded aggregates. Geotextiles changes this approach. In drainage application geotextiles act as filter elements that prevent the drain system from getting clogged. Expensive well-graded aggregate can be replaced with open-graded gravel. Moreover, because of the high filtration efficiency, smaller volumes of aggregates are required and the construction task is very simple.
MECHANISM OF GEOTEXTILES:
Filtration mechanism of geotextiles
The effective geotextiles don't actually filter the water. It acts as a catalyst for the formation of a stable soil filter cake. In the early life of drain, a certain amount of soil fines would pass through the geotextile fabric. Larger soil particles are retained on it a bridge network. Behind this, a layer of finer particles collects from adjacent undisturbed soil. Once the filter cake has been established no soil will pass through the system. While the cake now does the filtering job, the geotextiles hold it in place preventing it from collapsing into the draining aggregate.
Any type of geotextiles will not perform a satisfactory filtration job. An effective fabric should have a large number of openings of fixed size is in woven fabric. Most of the non-woven fabrics meet this criterion. The filter fabric shouldn't trap particles within its pore openings and it shouldn't change porosity being compressed under loads.
As far as any construction project local conditions must be evaluated in order to properly design the drainage system such as soil characteristics, external loads imposed on the system (static or dynamic), and prevailing hydraulic conditions.
Separation mechanism of geotextiles:
There are several drainage-related functions in the construction maintenance and repairs of roads beds. The primary geotextiles functions in roads way applications are separations. It consists of placing the geotextiles fabrics as separation fabrics as a separation barrier between the subgrade and sub-base layer.
Reinforcing effect of geotextile:
Since geotextiles have appreciable tensile strength, the use of geotextiles layers can also be expected to have a reinforcing effect. Depending upon the type of subgrade, type of geotextile layer and anticipated wheel loads, a reduction in the thickness of 10 to 25% is possible. Flexible overlays over distressed rigid or pavements are known to suffer from reflection cracking, leading to an increase in the life of the overlay, which is normally a high-cost asphaltic concrete surface. The use of existing pavements has been found to sustainability reduce the reflection cracking whenever a deteriorated pavement is to strengthened by providing an overlay with geotextiles cracks if any are to be filled with asphalt and asphalt sealant is supplied on the existing deteriorated pavement. The fabric is then placed on the sealed by hand or mechanical device.
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