Type pressure and axle load surveys of heavy vehicles and the implications in northern corridor, Rwanda

Abstract

Rwanda, as a country in quick progress to a sustainable development and whose economy is based on infrastructure and the protection of environment has to make regulation on Axle load. Loads are applied to the pavement through contact between vehicle tyres and the surface course. The tyre pressure primarily affects the stresses and strains developed at the surface and within the upper layer of the pavement. In fact, the aim of this thesis is to analyse the tyre pressure and the extent of overloading on the National Road three (NR3) and to evaluate the performance of the pavement. A survey to collect tyre pressure and axle load data on the National Road three (NR3) were carried out where the tyre pressure survey were taken by the use of Tyre pressure gauge at a private station located nearby KABUYE and the axle load were taken by the use of mobile weigh bridge at Gatuna and Nyacyonga stations. The data show that 91% of the tyres surveyed were over-inflation and 9% were under-inflation. The average and recommended tyre pressure were 907kPa and 845kPa respectively. The axle load data show that the maximum overloading were 60.76% found for Heavy Good Vehicle (those with three axles) towards Kigali and 46.3% for Buses towards Gatuna direction. The maximum axle load was 27.18 tons for Heavy Good Vehicle towards Kigali and 21.28 tons for Heavy Good Vehicles towards Gatuna. This thesis presents the results of Mechanistic design where the horizontal tensile strain on the bottom of the binder course, major stresses in the middle of the granular layer and the vertical strain on the top of the subgrade were calculated using Bitumen Stress Analysis in Roads (BISAR3.0) a product of Shell. These parameters were used to calculate the number of axle load repetitions each layer could handle with the use of South African transfer functions. The pavement can survive 2.58 *10 4 standard axle load repetitions and it will first fail due to the shear stress. As the tyre pressure increase by 16% the life of the road decrease 7%. The average maximum axle load exceeds twice the standard axle load limit of 10 tons. It means that the increase of 100% from 10 tons to 20 tons the life of the road will decrease 1500%. Advanced instrumentation as well as the Stress in motion (SIM) within which accurate stress could be measured; this method should be used in the future for the tyre pressure and axle load surveys.