Overlay thickness estimation using falling weight deflectometer and benkelan beam method-A case study

Abstract

Pavements with bituminous surfacing are the most preferred and commonly used type of surfacings in India, because of their lower initial cost, ease of maintenance and subsequent up-gradation through stage construction, if necessary. The high traffic intensity in terms of commercial vehicles, overloading of trucks and significant variations in daily and seasonal temperature of the pavement have been responsible for early development of various kinds of distresses leading to premature failure of bituminous surfacings. Due to the various distresses developed in flexible pavements, strengthening by overlay is sometimes required for improving the structural adequacy of the pavement. The determination of overlay thickness is generally carried out by using Benkelman Beam deflection method as per the procedure given in IRC:81-1997. In this method, a static load is applied to the pavement surface and rebound deflections as measured. However, the limitation of the Benkelman Beam technique is that the measurement of deflection under static load does not simulate loading conditions produced in pavements by a moving vehicle. Other equipment which can also be used for structural evaluation of pavements is Falling Weight Deflectometer (FWD). FWD is an impulse-loading device in which a transient load is applied to the pavement and the deflected shape of the pavement is measured. This data, combined with the measured impact load, may be back-analysed (using layered elastic theory) to determine the stiffnesses of the various layers, and the subgrade. In the present study, the requirement of overlay was determined through Benkelman Beam and FWD methods for a 4.5 km road length in Noida, UP in NCR region. A comparison was made between the overlay thicknesses obtained as per IRC:81-1997 and IRC:115- 2014 and the results are presented herein.