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From the word flexible, it is very clear that in this category pavement that come are those that deflects under the applied load. Flexible pavements are very dependent on the underlying layers, these underlying layers (surface layer, base, subbase, subgrade layer) are composed of different materials like silt, clay, gravels, stones etc…)
The design of flexible pavement is based on the principle that for a load of any magnitude, the intensity of a load diminishes as the load is transmitted downwards from the surface by virtue of spreading over an increasingly larger area, by carrying it deep enough into the ground through successive layers of granular material. Top most layer that is the pavement layer with highest bearing capacity and most expensive layer takes the load and bears load up to the bearing capacity limit. When load crosses the limits, then a deflection occurs in the top most layer and as a result load transfers the base layer which is underlying the top most layer. Now in the same manner base layer bears only that much load of which it is being capable and when limit exceeds then remaining load transfers to the subbase layer. In the same manner subbase layer carry loads and transfer loads to the subgrade layer if any load left to distribute. After that finally load reaches the underlying earth where remaining load distribute. |
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Flexible Pavement Design:
The flexible pavement design is made in such a way that the structure basically deflects under load. The structure is designed in such a way that each layer comprising of materials receives load from the upper layer and passes on the load to the next layer. This way the load in different layers is reduced to a great extent. The design is made in such a way that the maximum load bearing layer (i.e. the top layer) will comprise of the most expensive materials and the lowest load bearing layer (i.e. the lower/bottom layers) would be made up of the least expensive materials. While making a design for the flexible pavement two major factors that needs to be considered i.e. determination of the approximate thickness of the layer and the composition of the materials that is required for each layer. The composition has a significant impact on the structure of the flexible pavement because of the impact of traffic loads and variations in the temperature. |
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AASHTO 1993 Specifications:
The AASHTO 1993 flexible pavement design emphasizes on the particulars involved in designing the pavements meticulously so that they can bear the traffic load and the impact of the temperature variation at the same time. AASHTO 1993 flexible pavement designs were established on the basis of the specifications of the AASHTO road test which in turn considers the specifications of the pavement materials and the roadbed soil. In case of AASHTO 1993 flexible pavement design, the load can be segregated to mixed traffic in order to reduce the burden on layers to certain extent. But it should also be kept in mind that the load capacity as per AASHTO 1993 flexible pavement design, considers the vehicle that were operating on the road with axle loads and configurations that were identical to each other.
AASHTO 1993 flexible pavement design considers a number of inputs regarding the structure of the pavement, the subgrade support available and the maximum bearable load. The inputs emphasized on the maximum load that the pavement would be able to bear over its lifetime, the performance of the pavement design with an increase in the traffic load over the pavement and changes in the environmental conditions. Another important consideration in the AASHTO 1993 flexible pavement design is the subgrade support which is great contributor in determining the structure of the pavement AASHTO 1993 flexible pavement design also considers the serviceable life of the structure of the pavement.
The AASHTO 1993 flexible pavement design emphasizes on the particulars involved in designing the pavements meticulously so that they can bear the traffic load and the impact of the temperature variation at the same time. AASHTO 1993 flexible pavement designs were established on the basis of the specifications of the AASHTO road test which in turn considers the specifications of the pavement materials and the roadbed soil. In case of AASHTO 1993 flexible pavement design, the load can be segregated to mixed traffic in order to reduce the burden on layers to certain extent. But it should also be kept in mind that the load capacity as per AASHTO 1993 flexible pavement design, considers the vehicle that were operating on the road with axle loads and configurations that were identical to each other.
AASHTO 1993 flexible pavement design considers a number of inputs regarding the structure of the pavement, the subgrade support available and the maximum bearable load. The inputs emphasized on the maximum load that the pavement would be able to bear over its lifetime, the performance of the pavement design with an increase in the traffic load over the pavement and changes in the environmental conditions. Another important consideration in the AASHTO 1993 flexible pavement design is the subgrade support which is great contributor in determining the structure of the pavement AASHTO 1993 flexible pavement design also considers the serviceable life of the structure of the pavement.