Geosynthetic are evolving as a material choice in the field of civil engineering because of the extensive advantages. They are reliable, durable, eco-friendly and cheaper. There are six types of geosynthetic material available. The main function includes providing the surface with drainage, separation, filtration, reinforcement, stiffening, barrier and protection. A lot has been researched on how geosynthetics improve the durability of the unpaved roads but not a lot has been researched on which is the best choice among the six materials for unpaved roads. The purpose of this paper is to answer that question with the help of research that is done already and methods used to reach the said answer. The existing work will show how the geosynthetic material will increase the strength of the subgrade; where and how to place the material in the subgrade during the testing to maximize the result and get the best of them. Geosynthetics have been known to increase the life of the pavements when placed at the correct depth, angle, position and the type of subgrade in the question.  This paper will also help in determining which particular material provides the maximum strength, durability in the unpaved roads. Geosynthetics are efficient in soaring the load carrying capability and degrading rut depth. (Gali & M Nair 2014)

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 Geosynthetics’ most important application is to increase the CBR of the soil by providing the reinforcement the soil needs. CBR value is very important in determining the type of material to be used to strengthen it. A subgrade with low CBR value allows for geosynthetics to have better benefits than the subgrade with high CBR in terms of improved strength. (Singh, Trivedi & Shukla 2019a)

The modulus of base course is increased of geosynthetic materials when the interlocking with aggregates interaction minimizes lateral movement of the particles. This leads to reduction of vertical subgrade deformation.(Calvarano et al. 2016)

This interlocking can be seen in geocells, geogrids and geotextiles. A common test used to check the durability of the unpaved roads is California Bearing Ratio or CBR test. This test is carried out in laboratory using a sample of the subgrade and testing it after and before using the various types of geosynthetic materials.(Singh, Trivedi & Shukla 2019a)

Geosynthetic materials have found to have reduced the thickness of the road and proves to be cost and performance effective.(Gali, M Nair & S. Hemalatha 2010)

Many things need to be checked for a geosynthetic material to be suitable for an unpaved road; like, binding property, drainage, strengthening of the non-bituminous, CBR results etcetera.

Apart from the reinforcement used to strengthen the unpaved roads, the thickness of the unreinforced road needs to be acknowledged and be of the correct thickness to provide the maximum strength.

Given by
log⁡N=hCBR0.630.19
     (Hufenus et al. 2006)

In the CBR mould, a geosynthetic material is placed at the bottom half of the height of the specimen or near the load. While some researchers believe that the maximum effect of reinforcement is obtained by placing it at the centre of the CBR mould. (Singh, Trivedi & Shukla 2019a)

The maximum strength of the subgrade is increased or is at its maximum when a geosynthetic reinforcement is kept at the middle of the CBR mould. (Singh, Trivedi & Shukla 2019b)

The geosynthetic material can be added in either single layer or double layer depending upon the need of the pavement, which increases the CBR value of the subgrade. With the single layer reinforcement, the CBR value is increased by 5-60% and double layer increases it by 112-325%. This increase depends upon where the material is placed and which reinforcement is used. (Singh, Trivedi & Shukla 2019b)

Geosynthetic materials lose about 30% of their strength in the first 20 years. Geogrids are thicker and may lose less strength than others. (Barksdale, Brown & Chan 1989)

As you can see, the research shows the various tests done on unpaved roads using different geosynthetics but there isn’t a clear answer as to which material is best suited for the unpaved roads, of course a lot depends upon the type of subgrade, moisture content, thickness of the road, drainage capacity and the material of geosynthetic used. What the previous research has shown is that CBR test is done to check for the penetration value before and after using geosynthetic material.

What this paper will do differently is choose a subgrade, prepare a CBR mould, check the CBR value of the subgrade. Place the geosynthetic material at the most appropriate position as shown by the research done, measure the CBR value for each of the material and compare the result. Whichever provides the maximum result is best for that type of subgrade and soil in question. This test can be done with different soil types and different unpaved subgrades. This can save valuable time and effort in choosing which material is best for which type of soil and the subgrade.

Reference:

Barksdale, RD, Brown, SF & Chan, F 1989, Potential benefits of geosynthetics in flexible pavement systems, Transportation Research Board, National Research Council, Washington, D.C.

Calvarano, LS, Palamara, R, Leonardi, G & Moraci, N 2016, ‘Unpaved Road Reinforced with Geosynthetics’, Procedia Engineering, vol. 158, 2016/01/01/, pp. 296-301.

Gali, M, M Nair, A & S. Hemalatha, M 2010, ‘Performance of geosynthetics in unpaved roads’, International Journal of Geotechnical Engineering, vol. 4, 04/01, pp. 337-49.

Gali, M & M Nair, A 2014, ‘Geosynthetics in unpaved roads’, Indian Journal of Geosynthetics and Ground Improvement, vol. 3, 07/01, pp. 3-12.

Hufenus, R, Rueegger, R, Banjac, R, Mayor, P, Springman, SM & Brönnimann, R 2006, ‘Full-scale field tests on geosynthetic reinforced unpaved roads on soft subgrade’, Geotextiles and Geomembranes, vol. 24, no. 1, 2006/02/01/, pp. 22-23.

Singh, M, Trivedi, A & Shukla, SK 2019a, ‘Strength enhancement of the subgrade soil of unpaved road with geosynthetic reinforcement layers’, Transportation Geotechnics, vol. 19, 2019/06/01/, pp. 54-57.

Singh, M, Trivedi, A & Shukla, SK 2019b, ‘Strength enhancement of the subgrade soil of unpaved road with geosynthetic reinforcement layers’, Transportation Geotechnics, vol. 19, 2019/06/01/, pp. 54-60.