USAGE OF GEOGRIDS IN FLEXIBLE PAVEMENT DESIGN

As on 31^st March 2018, estimates the total road length in India 6,603,293km (4,103,096 mi) making the Indian road network, the second largest road network in the world after the united states. But the roads are not giving the desired result due to poor CBR value.

Roads in India have mostly the problems like the formation of potholes, ruts, cracks and localized depression and settlement, especially during rainy season. These are mainly due to the insufficient bearing capacity of the subgrade in water saturated condition. The subgrade soil mostly yields low CBR value 2-5%. In the CBR method of pavement design (IRC:37-2012) the total thickness of pavement increases exponentially with a decrease in the CBR value of subgrade soil which in turn increases the cost of construction. So, it has been tried to use the geogrid material for increasing the bearing capacity of the subgrade. Laboratory and simulated field CBR tests are conducted on soil samples with and without the inclusion of geogrid layer and also by varying the position of it in the mould. Use of geogrid increases the CBR value of the subgrade and thereby reduces the pavement thickness considerably up to 40%.

This study will have a positive impact on cost as it will reduce the Project as well as maintenance cost of the road. Our project will discuss in detail the process and its successful applications.

One of the major problems faced by the engineers in highway construction in plains and coastal areas of India is the presence of soft/ loose soil at ground level.  Roads constructed over this loose soil demands higher thickness of granular materials resulting in the high cost of construction. Alternately attempts of reducing the thickness of pavement layer to make an economic construction will lead to early damage to the pavement which in turn will make the road unserviceable within a short period after construction. This condition may be further worsened if supplemented with poor drainage or lack of it. Some states of India is situated in a region of high rainfall area suffers from poor drainage as well as weak subgrade condition. This is one of the major causes of deplorable road condition in those states.

Looking at the poor road condition of some states of India use of geogrid is thought for road construction to improve the performance of roads. Geogrid a geosynthetic manufactured from polymers is selected for this purpose. 

Geogrids used within a pavement system perform two of the primary functions of Geosynthetics: separation and reinforcements. Due to the large aperture size associated with most commercial geogrid products, geogrids are typically not used for achieving separation of dissimilar material. The ability of a geogrid to separate two materials is a function of the gradations of the two materials and is generally outside the specifications for typical pavement materials. However, geogrids can theoretically provide some measure of separation, albeit limited. For this reason, separation is a secondary function of geogrids used in pavements. The primary function of geogrids used pavements in reinforcement, in which the geogrid mechanically improves the engineering properties of the pavement system. The reinforcement mechanisms associated with geogrids

Tension Membrane Effect

This mechanism is based on the concept of vertical stress distribution. This vertical stress is from the deformed shape of the membrane as shown in the figure below. This mechanism was initially considered as the primary mechanism. But later studies proved the lateral restraining mechanism is the major criteria that must be taken into consideration