Average full-trailer truck equivalency factors for uphill flexible pavements in developing countries

Abstract

ABSTRACT This paper presents the average truck equivalency factors for four types of full-trailer trucks on uphill flexible pavements. Rising grades of 6%,12% and 18% are considered in addition to level flexible pavements. To arrive at each truck equivalency factor for the 254 full-trailer trucks studied, the axle loads were obtained from an axle load survey using permanent weighing stations. Assuming uniform motion, the axle loads on uphill pavement were calculated for different relative height of the centre of gravity of truck above pavement taking into consideration the pull force in the hook connecting both units of each full-trailer truck. The effects on average truck equivalency factor of uphill gradient, type of full-trailer truck, relative height of centre of gravity of truck, pavement structural number and terminal level of serviceability, were thoroughly studied. The paper reveals that an increase in uphill slope causes a significant increase in flexible pavement thickness especially for steep rising grades in developing countries. For rough estimation of standard single axle load applications on uphill pavements from level pavements, overall average uphill slope factors were developed. The uphill slope factor of unity for level pavement increases by about 0.038 per each 1% increase in uphill slope.