Influence of subsurface courses materials on pavement performance: a case study of yebu-agaro road

Abstract

The properties of subsurface material differ from place to place. The same is true the performance of pavement along the route which also varies. The research study is focused in Yebu-Agaro road section. The main objective of this research work is to determine the Influence of subsurface courses material on pavement performance along Yebu-Agaro road section. In order to get the desired objective, a systematic methodology was adopted which includes field investigation, field test and laboratory tests was carried. While the purposive techniques was used to collect Soil samples from portions of the road that are severely damaged showing different road failures types and nondistress surface. These severe types of failures observed along the Road section, Such as Reflective crack, Pothole, Rutting, Alligator crack and Block crack. Based on the failures types, five representative samples was collected at different locations along the failures section and one nondistress pavement of road section with manual hand auger and these samples were air-dried before taken to the Laboratory test for determination of geotechnical Properties of existing embankment of a road. The soil samples collected were analyzed based on the geotechnical analysis: wash gradation, Atterberg limit, Modified proctor test, California bearing ratio (CBR), field test and traffic analysis has been carried out. For subgrade soil the liquid limit varies from 33% -60.5% and Plasticity index from 20.3% -30.1% and increase moisture at the field more than that of OMC in laboratory due to distress of pavement water infiltrate through cracks, this reduce dry density. The soaked CBR values of subgrade soil materials are between 8% -13% compared with 15% minimum specified by ERA manual; therefore the CBR values of the subgrade soils are poor for pavement structures. The soils were classified by ASSHTO under the A-2-6 and A-7-6 category which showed that the soils was fair to poor as a sub-grade material while USCS classification showed that the soil falls into SC group. Therefore, the failures frequently observed on the road surface are significantly influenced by subgrade soil; the sub-base layers materials satisfies minimum requirements with insufficient thickness provided during construction but base courses materials along Yebu-Agaro Road section did not satisfied the standard requirements set by ERA The overall results showed that, heavy vehicles or traffic loads are one of the major causes of road failure along the study road section. Hence, the influence of other factors such as poor drainage courses, level of ground water table, variation of geologic materials along the road route and poor construction materials should be thoroughly addressed before beginning the rehabilitation of the road section in the future. Finally a possible remedial measure had been recommended for every observed failures or distress on the pavement condition of the study area in order to sustain the design life of the Pavement.