BENKELMAN BEAM DEFLECTION
BBD enables precise and non-destructive measurements of the strength evalutaion of road surface layers, made of asphalt or pavement under a standard wheel load and tyre pressure.
2000 KMNH/SH/ODR Strength Evaluation of Pavement
Structural adequacy is the primary response of pavement to transient loads and consists in deformation, deflection, stresses, strain and permanent deformation at critical points in pavement layers. BBD test are widely used as a tool for structural evaluation.
Benkelman Beam Deflection studies are one of the non-destructive techniques for the structural evaluation of flexible pavements. A well compacted pavement section or one which has been well conditioned by traffic, deforms elastically under each wheel load application such that when the load moves away, there is an elastic recovery or rebound deflection of the deformed pavement surface. This is the basic principle of the deflection method of pavement evaluation.
Mechanistic Design of Overlay Based on Benkelman Beam Deflection Technique
- overlay of Flexible pavement design is carried out as per IRC: 81-1997-Guidelines.
- A pavement is regarded as having insufficient strength if the deflection measured under a test load exceeds a predetermined value related to the traffic expected.
- In case where the structure has to be strengthened, the observed deflection serves as the basis for determining the thickness of the overlay to be applied.
- The maximum deflection under a design wheel load depends on several factors such as sub grade soil properties, moisture in the subgrade, pavement thickness and its composition, temperature of the pavement and loading particulars etc.
- Therefore the amount of pavement deflection under a design wheel load or its rebound deflection on removal of this load is a measure of the structural stability of the pavement system under the prevailing condition of the test. Larger rebound deflection indicates weaker pavement structure.
Design of Overlay for Flexible Pavement