Properties of geot
Properties of geotextiles used in road paving
The properties of a geotextile, used in road construction are very important to its successful use. The geotextile must be capable of withstanding the stresses of installation and of the building and consolidation of the construction of which it is a part. (24)
To improve the load bearing capacity of subgrade soil and the load-distribution properties of base course material , the following properties of geotextiles are relevant to its structural applications :-
In order to continue its functioning in road structure, the geotextile must be able to adjust a large deformation without the breaking strain being exceeded . This means that the geotextile should remain intact under loading. The effect of reinforcement will be greater with high modulus of geotextiles because in that case the load distribution increases and therefore , an equilibrium is reached with less track deformation. (22)
2-Creep and relaxation
All important mechanical properties of a geotextile are related to strength and elongation . For long-term behaviour these properties are represented more or less by stress relaxation and creep. Creep represents the long term elongation behavior (mostly under a constant stress) and stress relaxation is the long-term stress behavior ( generally at a constant elongation). Physically both phenomena are strongly interrelated .(28)
As mensioned ,creep is especially important if a construction is designed for static load. If the geotextile has a limited creep resistance, deformation will continue under the effect of constant load. After a wheel load has passed, the stresses in the material will not be completely removed and the structure will remain to some extent in pre-stressed condition.
If , however ,the geotextiles is relaxation- sensitive , the pre-stressing will be removed.
If the geotextiles for any reason be damaged or torn , the tear should not increase in size under normal loads.
When the base course is loaded the aggregate is pressed against the geotextiles . The geotextiles , therefore , must be strong enough to resist puncturing . It is worth to mension that the heavier geotextiles are more resistant to puncturing and bursting.(22)
A geotextile is ,by definition, permeable , and it therefore exhibits the ability to transmit water in a direction normal to its plane. (18)
Permittivity or cross- plane water flow is an important index test for filtration. The mechanism by which water moves through the geotextile is characterized by the permittivity of geotextiles. (4)
Two vital factors in the performance of geotextiles as filters are the size and distribution of the holes or pores in the geotextile. All geotextiles have pores which allow the transmission of water.
Any water in the base course must be able to drain out through the geotextiles, otherwise, the base may become unstable. That means , the water permeability of the geotextiles should be equal to or more than of the subgrade. (22)