How Geosynthetics work in Construction on Soft Soils?

Geosynthetics are mainly used in stabilisation applications to facilitate the construction work. Even if the finished pavement can be supported by the subgrade, it may be difficult or sometimes impossible for the initial construction work to be started without some sort of stabilisation in the beginning. Geosynthetics offer a cost-effective alternative to other expensive stabilisation methods such as dewatering, excavation and replacement with a thick layer of selected granular material, or chemical methods such as lime stabilisation. The geosynthetic reinforced layer also enables contractors to meet required deflection criteria beneath the subbase layer. Geosynthetics provide long-term benefits and improve the performance of the road over its design life.

Using geosynthetics in road construction provides various benefits which includes: reducing the stress on the subgrade, preventing the aggregate from penetrating into the subgrade and preventing subgrade fine particles from pumping up into the granular layer (separation and filtration), preventing contamination of the granular layer which allows open-graded draining aggregates to be used in the road design and construction (filtration), reducing the depth of excavation required for replacing the unsuitable and soft subgrade materials and also providing a stiffer subgrade or working platform (separation and reinforcement), increasing the stiffness of the granular material (reinforcement), and reducing differential settlements (reinforcement).

The main mechanism for geogrid reinforcement is called lateral confinement. In fact, the loads applied to the road surface create lateral spreading of the aggregates. Tensile lateral strains are created at the aggregate-geogrid interface as the aggregates move down and spread away due to the applied load. Interlocking of the aggregates into geogrid apertures provide lateral confinement and prevents the aggregate from spreading. Through shear interaction of the aggregate with the geogrid, the aggregate is laterally restrained and tensile forces are transmitted from the aggregate to the geogrid. The stiffness of geogrid (tensile strength of the geogrid at very low elongation) plays an important roll in providing higher lateral confinement.

Lateral confinement of the aggregate layer due to geogrid reinforcement results in higher layer stiffness and so higher load distribution angle which leads to reduction in the normal stress on the subgrade directly beneath the applied load.

When used in flexible pavements, geosynthetics reinforcement provide two main benefits through the mechanism described above: reducing the pavement thickness ( Base Course Reduction-BCR), and/or increasing the serviceability and design traffic and reducing the maintenance works and costs (Traffic Benefit Ratio-TBR). In the case of a very weak subgrade, geosynthetics can provide a thinner and stiffer working platform or semi-infinite subgrade for road construction. This will again lead to a reduction in the pavement thickness or increase in the design traffic indirectly, as the pavement will have a stiffer subgrade.

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