The term reinforcing in road paving means the ability to distribute a concentrated load over larger area of the subgrade , thus avoiding local over- loading of the bearing capacity . A closer analysis of reinforcing function of geotextiles in road construction reveals the presence of two types of reinforcement, the membrane reinforcement and horizontal reinforcement.
In practice, both functions acts simultaneously to improve the load- bearing capacity of the structure.
- Membrane reinforcement
Membrane reinforcement is mobilized when the subgrade is deformed by rutting. As subgrade deforms under loading , the geotextile stretches like a hammock, as shown in figure (I-11) .The loading is thus distributed over a wider area , as a result of the vertical component of the tension developed in the geotextile. Rutting and resulting spread of the load by geotextile continues until an equilibrium is reached.
Thus , with geotextile’s membrane reinforcement , a road can be constructed on a subgrade with low load – bearing capacity. In areas , where the sub- soil has a strongly varying load- bearing capacity, the use of geotextiles can relieve stresses at weaker points and thus promote a more uniform deformation of the subgrade.
- Lateral restraint
Horizontal reinforcement , often referred as lateral restraint, reduces the horizontal deformation of base course and subgrade material where they are in contact with the geotextile. The geotextile holds the base material and subgrade together by developing frictional forces between itself and the material.
The positive result of lateral restraint is that there is better load distribution in the base course material , for a particular vehicle load, the subgrade is less heavily loaded . In addition the subgrade tends to be less deformed because some of the
Fig (I-9) Separation function
Fig (I-10) Drainage and filtration function
Fig (I-11) Reinforcement mechanism with geotextiles
deformation is taken up by the geotextile itself. The overall effect of using geotextiles in road construction, therefore , is less rutting , a higher allowable vehicle load and a more solid road structure. (22)