Evaluation Of The Performance Of Gravel Road: A Case Study On Mechare To Arssema Road, Amhara Region, Ethiopia

Abstract

In Ethiopia, gravel road deterioration is becoming a common problem and great challenge, appearing even before the completion of a project in certain road projects. In most areas gravel road problems like rutting, fully erosion and corrugation and loose of materials are common before the design life and it require a lot of maintenance cost. In such case, the main objective of this research was to evaluate the performance of gravel road based on material quality, gravel loss, effects of poor drainage system and present serviceability rate of the road. The study was conduct in Mechare to Arssema existing road found in north wollo zone, Amhara region, Ethiopia. The research designs were follow both experimental and analytical methods using qualitative and quantitative data. The study follows non-probability sampling techniques of purposive sampling methods. In order to examine the properties of subgrade soil and gravel material, disturbed soil samples were obtain from five different test pits in different locations at depth of 1.5-2.0m to remove organic matters for each subgrade soil and gravel materials on the existing route. The data processing and analyzing were conduct using both descriptive and analytical methods thus were Excel for laboratory analysis and Arc GIS for hydrological analysis. In this study moisture content, Atterberg Limits testing, particle size distribution, soil classification, free swell index, specific gravity, compaction and CBR were determined for both subgrade soil and gravel material. Based on laboratory analysis the subgrade soil sample was high liquid limit, low CBR swell value. In gravel material property analysis all soil samples were classified in to A-2-7, the material type is sand with gravel, the material quality is zone B which is corrugated and raveling and the soil samples had 20.85%, 7.19%, 12.57%, 6.98% & 6.14% soaked CBR value, with 0.86%, 1.72%, 1.03%, 1.93% & 2.02% CBR swell respectively. In the case of present serviceability rate study the questionnaire were distributed and filled by road users which found under each section the present serviceability rate was 2.63 and the gravel loss determinations of the road using TRH20 gravel loss deterioration model the average gravel loss were 14.37mm. In condition survey, the existing road was evaluated using road condition rate. The road drainage system was evaluating field observations and peak discharge determination by using rational method to compare design discharge with their return periods. Catchment area of each watershed overall route corridor was delineate from DEM data and the sizes of each catchment area were determined using Arc GIS software. Generally, the laboratory result shows both subgrade soil and gravel materials have poor material quality compared with standard specifications. The gravel loss of existing road does not consider as shown in the design profile, because the design thickness was different from the calculated thickness. During the condition survey evaluations the existing road is little or no roadway crown, moderate to severe wash boarding, severe loose aggregate, and moderate potholing. The design peak discharge calculated and the review peak discharge calculated of the return period is not equal. From this the road around this is damaged by over flooding of the water on the road because the calculated peak discharge for the design were less than the calculated peak discharge for the review at all stations.