TENTATIVE GUIDELINES FOR STRENGTHENING OF FLEXIBLE ROAD PAVEMENTS.

Tentative guidelines required for strengthening of flexible road pavements for the purpose of design method, the traffic is considered in units of heavy vehicles (vehicles with a laden weight of 3 tonnes or more) per day, in both the directions in the case of two lane roads and in the direction of heavier traffic in the case of multi lane divided highways. Based on the present traffic, the design traffic, ie the traffic expected at the end of the design year should be estimated. In preparing these estimates due consideration should be given to the existing traffic, possible changes in the road net work and land use of the area served, and probable growth of traffic during the period of projection under consideration. It is considered appropriate that major thorough routes should be designed for at least ten years of life. Less important roads may, however, be designed for a somewhat lower period based on growth prospects and judgement. Since the pavement deflection is dependent upon change in the climate season of the year, it is always desirable to take deflection measurements during the season when the pavement in its weakest condition. Since in India this period occurs soon after monsoon, deflection measurements should be confined to this period as for as possible. When deflections are measured during the dry months, they will require a correction factor which is defined as the ratio of the maximum deflection immediately after monsoon to that of minimum deflection in the dry months. The correction factor will depend upon type of surfacing, subgrade soil composition and other factors. Due to large variation in subgrade soil and climatic conditions prevailing in India. It is difficult to give a single value for this factor. It is however, recommended that the clayey subgrade soils the correction factor may be taken as 2 , where as for sandy subgrade it may be taken as 1.2to 1.3 and for intermediate soil types the value may be Interpolated.