COMPUTER AIDED DESIGN OF FLEXIBLE PAVEMENT OVERLAYS BASED ON IRC : 81, 1997

Abstract

The primary object of the flexible overlay design is to determine the thickness of the upper most layer of the payment so that it has adequate stability to withstand the design traffic under prevailing climatic and subgrade conditions. Due to unexpected economic development in the given region, the loading conditions may become severe and alternative would be either to divert the traffic on some adjacent routes or to strengthen the existing pavements. Strengthening may be done by providing additional thickness of the pavement of adequate thickness in one or more layers over existing pavement, which is called overlay. The flexible overlays in India are designed using Benkelman Beam ac-cording to lRC:81, 1997 (first revision). The method given in this code of practice is lengthy and thickness of overlays are determined by repetitive use of curves drawn for the purpose. The scenario of the computer applications in civil engineering is at drastic veer and it is more true in relation to CAD. The use of CAD has many advantages like easy display, increased accuracy, large storage facilities, quick retrieval and easy modification to old design. Many software related to overlay design are available in interna-tional market. There are difficulties in adopting these softwares in India due to different conditions prevailing here. Therefore, the solution lies in indigenous development of packages in a number of modules to be finally integrated. Keeping in view the above aspects, a generalised and user-friendly package for the design of flexible overlay, based on IRC:81, 1997, has been developed. Program OVERLAY, written in 'C' designs the flexible overlay III based on IRC:81, 1997 and includes the features of interactive data entry, checks for invalid inputs and displays warning messages for the data exceeding their maximum or minimum limits. It provides the values of all the relevant parameters which affects the overlay thickness e.g., Vehicle Damage Factor (V.D.F.), Moisture Correction Factor, Traffic Distribution Factor etc. the deflection data collected on to validate the software. The package has been validated by applying it on a typical road.