Benkelman Beam Deflection

Development of road infrastructure is currently being given high priority by the government of India to meet the requirement of growing travel demand and help the growth of economic activity at a faster rate. It is important to adopt a rational approach for the evaluation of the pavements so that more efficient use of materials can be made to improve the pavement performance and lower the life cycle cost. The Benkelman Beam Deflection method is used to know the deflection of the pavement which is inturn used in determining the overlay thickness for an existing flexible pavement. We have used Temperature data, Soil data and Truck specifications for conducting the test.
Overlay design Calculations: 1. If Dintermediate – Dfinal

Large deflections indicate an over-stressed condition which may cause the pavensnt surface to cracko Repeated deflections may cause the pavement to crack and distort as a result of fatigue, or accumulative plastic deformations.
The performance of the flexible pavement is influenced by many Factors. These include gross load, tire pressure, repetition of load, thickness end durability of the various pavement components, a^d the elastic-plastic properties of the pavement components (particularly the subgrade soil)> Pavement distress may be influenced by a combination of the above fact: Pavement failure may result from excessive shear stresses, consolidation of one or more of the pavement components, lateral shoving, bending or a combination of these
Pavement deflection values can be used in a variety of ways. The method of analysis should depend upon the intended usage of the data. In some cases detailed data are not only unwieldy but are too complicated to handle at the present tlme„ As a general rule, measurements which yield the maximum amount of information with the least amount of effort are

Since it is not possible to conduct the test at the standard temperature, a correction factor has to be applied for the deflection. The correction factor is determined by knowing the temperature at the time of the survey. If the depth of the BT surface is more than 40mm , then correction factor has to be applied. If the depth is less i.e if it is a thin bituminous surfacing like premix carpet and surface dressing, then no correction is required.
2.2 Soil data:
Deflection measurements should be made during the monsoons when the pavement is in its weakest condition. Hence a correction for seasonal variation has to be applied for the deflection which is a function of the soil subgrade. The data required is :a) Average annual rainfall in that area , (b) Soil classification – sandy / gravelly, clayey with low plasticity and clayey with high plasticity. (c) Field moisture content.
Hence the soil tests that have to be conducted are Moisture content test (Standard Proctor test), Sieve analysis (for soil classification) and Atterberg limit tests (for Determination of PI value).
2.3