Evaluation and Validation of the Causes for Cobblestone Road Failures in Hawassa City

Tigist Assefa¹*, Tigist Guracha, Erste Telila, and Temesgen Aynabeba

Abstract

       Cobblestone road failures are a process of decreasing the serviceability of the cobblestone road by causing potholes, poor bonding, and poor drainage conditions. The present cobblestone road condition of Hawassa city shows high failures. The severity of the cobblestone road is even more critical in the study area because of the significant problems of the construction process, clogged ditches, and poor crossectional slope. Similarly, the effect of failures in this area that is shown on the vehicles that use the road is also the main effect that affects the life span of the road since there is no legal load limit and freight vehicles use this road. This research mainly focuses on the assessment of cobblestone road condition by studying the causes of cobblestone road failure in relation to the sub-grade strength, traffic volume currently handled by the cobblestone road in Hawassa city with relation to standards, studying the drainage condition of the study area based on the availability and functionality of ditches and putting the remedial measures that should have to take through having a primary and secondary data collection method. For this study, different analysis methods are used such as descriptive, laboratory, and exploratory using the purposive sampling method. From this, the analysis of cobblestone road condition assessment is done by taking the weighted average of high failure of the study area based on various measurement and visual methods such as capturing the picture of road condition and measuring the deteriorated route length and width. In another way, cobblestone road failures concerning subgrade soil strength and the analyses were carried out using laboratory tests by taking representative samples from study area route segments. The test integrates density, maximum dry density, and CBR (California bearing ratio) determination. Based on the study the condition of the study area road segments taken as moderate and poor condition, handle higher traffic volume than the recommended standard  for route that connects the main road to the public area, have poor crossectional slope compared to the standard manuals and taking visual inspection onsite but the soil strength of study area route segment attain the recommended standard so the cause of the failures are due to unavailability of the ditch and poor functionality, lack of timely maintenance, lack of legal load limit for low volume roads especially for those routes that connect main road with public areas and poor construction experience and the city municipality have to do scheduled survey condition, maintenance, construct ditches and put legal load limit  to control the city low volume road to not deteriorate without attaining the service life year

Keywords: Cobblestone road failures, survey condition, Subgrade strength, California Bearing Ratio (CBR), Traffic volume