An Experimental Investigation On The Causes Of Flexible Pavement Failures: A Case Study On Tarcha – Yalo Road Section

Abstract

In Ethiopia, recently constructed roads are reported to deteriorate rapidly after being opened to traffic. This may include excessive loads, climatic changes, poor drainage, and inferior pavement materials. This study has been conducted on Tarcha-Yalo Road segment .The objective of this study is to investigate the causes and remedial measures for asphalt pavement distresses. In order to meet the objective a systematic methodology is used to investigate field survey and laboratory tests were carried out. The soil samples were collected using purposive techniques of sampling from three severely damaged and two non-damaged sections. The severely damaged section distresses were corrugation, block cracking, ravelling and stripping. Based on the type failures, the representative samples of soil was collected for the three failed and two non-failed section from the study area. The condition survey has been conducted for the evaluation of pavement performance condition and the average PCI value indicates the pavement performance condition of the total road length (47.4 km) is under category of good (60%) and very good (40%) condition of pavement condition rating. The average thicknesses of each layer of failed sections were measured and Asphalt 2.13cm, base course 10.5cm, and sub-base 11.67cm.And the average thicknesses of non-failed sections were 3.35cm for asphalt, 9cm for base course and 12.5 cm for sub base. From laboratory test result, the soil classification according to AASHTO and Unified Soil Classification of Subgrade A-7 and SC, sub base A-2-4 and GP and base course A-1-a and GW respectively. An average liquid limit (LL), plastic limit and plasticity index(PI) of failed sections of base course are (5%,0%,5%), sub-base(33.33%,25%,8.33%) and subgrade(52.5%,31.33%,21.33%) respectively whereas an average liquid limit (LL), plastic limit and plasticity index(PI) of the non-failed sections are (4.5%,0%,4.5%), (35.5%,25.5%,10%) and (46.5%,33%,13.5%) for base course, sub base and sub grade materials respectively. Compaction(MDD(g/cc),OMC(%)) of base course of failed section are (1.73g/cc,10.92%),sub base(1.67g/cc,12.23%) and sub-grade(1.58g/cc,20.33% whereas the non-failed sections were (1.76g/cc,9.95% ), (1.74g/cc,11.1% , (1.65g/cc,14.4%) for base course, sub base and sub grade respectively .The CBR% of base course 80%, sub-base 60% and sub-grade 9% obtained. The Los Angeles Abrasion test values of sub base and base course were sampled with two trials of tests for each. The result of sub base abrasion resistance loss is 30.97%which is less than 40% that is the standard specification in ERA 2013.Hence it fulfills the requirement. And the result of base course is 28.97% which is less than 35% that is standard specification in ERA 2013.Hence it satisfies the requirements. Based on the laboratory test result and condition survey the pavement failure is due to insufficient thickness design, improper compaction and absence of shoulder. Finally it is recommended that the preventive maintenance is to be applied for failed section in Tarcha-Yalo road section.