Strength enhancement of the subgrade soil of unpaved road with geosynthetic reinforcement layers

Abstract

Abstract Geosynthetic reinforcement layers are often used to improve the performance of pavement structures. The performance of an unpaved road is routinely measured in terms of the California bearing ratio (CBR), which is an index of strength of subgrade soil of unpaved road. In the present study, an experimental investigation was carried out to evaluate the performance of the subgrade soil by placing a single layer and double layers of geosynthetic reinforcements (Glasgrid, Tenax 3D grid and Tenax multimat) horizontally at varying depths from the top surface of subgrade soil. Through a series of CBR tests in the laboratory, an attempt was made to determine the optimum depth of the reinforcement layer. The single layer of reinforcement has been placed at the middle, one-third and one-fourth of the height of the CBR specimen from the top surface of the soil in the CBR mould. The double layers of reinforcement were placed at one-fourth of the specimen height from the top surface and the bottom surface. The results show the significant contribution in terms of increased CBR value of the soil, resulting in reduced design thickness of the pavement layers above the subgrade soil. It has been observed that for a single layer reinforcement the Tenax 3D grid performs better than other geosynthetics used in this study while the Tenax multimat performs best for double layers. The results indicate that for the maximum benefit, the Tenax 3D grid reinforcement should be placed in between 0.3H and 0.36H where H is the height of the soil specimen. For Glasgrid and Tenax multimat reinforcements, the maximum effect of reinforcement is obtained when they are placed between 0.41H and 0.62H.