Performance Evaluation of Arba Minch-Sawla Link Road

Abstract

Failure of pavement surface reduces the speed of vehicles thereby decreasing service delivery of the road. Most of the roads constructed in Ethiopia fail prematurely before serving the design life due to various causes arising from many factors. One of these roads failed before reaching design life is 167.24 kms Arba Minch-Sawla bitumen surface treatment link road. Although the road was constructed in 2017, it failed within three years of its completion. It was constructed in three lots by three different contractors. Lot 1 is from Shelle Junction to Balta which is 59.13 kms. Lot 2 is from Balta to Otolo which is 38.31 kms. Lot 3 is from Otolo to Sawla, 50.68 kms. 19.12 km is asphalt concrete pavement from Arba Minch to Shelle junction which is a part of Arba Minch-Jinka AC pavement and shared by Arba Minch-Sawla road. Currently, vehicles moving to Arba Minch from Sawla prefer the gravel road from Sawla to Wolaita Sodo which is 140 kms and then take the asphalt pavement to Arba Minch which is 110 kms which is 250 kms totally. The difference is 82.76 kms. The research is aimed at identifying the types of distresses with their severity and extents, their causes, forwarding suitable maintenance types and carrying out LCCA for its maintenance. The research is applied, explanatory as well as qualitative and was carried out by doing desk review and gathering the necessary data. Pavement condition survey was carried out to find the most distressed places in the span of the road. Distress types were identified and quantified with their severity and extent by videotaping the whole span of the road. The dominating distresses were found to be rutting, potholes and raveling associated with side slope and drainage failure. Aggregate samples for laboratory tests were collected from most distressed areas by purposive sampling method. Five test pits were selected at stations 21+990, 51+400, 74+490, 150+220 and 159+940 respectively from Arba Minch. Tests of CBR and Atterberg limits were carried out for base course, sub base aggregates and subgrade materials. Tests for ACV and water absorption were carried out for base course aggregates. Gradation analysis was carried out for base course and sub base aggregates. Free swell tests were carried out for subgrade aggregates. All testes were carried out as per their respective AASHTO and ASTM standards. Bitumen extraction, soundness test, water absorption, apparent specific gravity and strip test for bitumen affinity of the extracted aggregates was carried out. Traffic data was gathered at five stations and results showed that distresses are not due to traffic load. The causes of these distresses were analyzed and found to be due to poor quality base course aggregates, side slope and drainage failures, expansive subgrade soil and poor design and construction. Test results showed base course aggregates CBR is below the standard. The gradation result showed base course and sub base aggregate tends to be coarser while that of the sub grade material is finer when evaluated with ERA grading envelope. The free swell of the capping layer and sub grade materials result show high value which shows the subgrade materials are very expansive and not good enough for road construction. The PI of all the layers was found to be as per the standard. Bitumen extraction showed that bitumen content is as per the standard. Bitumen affinity towards aggregate highlighted that the bitumen type is good for cold weather roads. Soundness test results are acceptable. It is concluded that subgrade failures are due to expansive subgrade soil, poor drainage, weak base course material and moisture; pavement materials particularly aggregates are substandard. Drainage failures, which resulted in raveling and potholes, are due to slope failures. It is recommended that base course materials should meet the CBR and water absorption standards and future road design and construction shall avoid subgrade with high swell. The suitable treatment method for each distress type was accompanied with the life cycle cost analysis for eighteen years of the road. Four comparative alternative maintenance options were worked out with corrective maintenance, bitumen single surface treatment, bitumen double surface treatment, slurry seal and microsurfacing every two and three years and double surface asphalt patching every six years was proposed to enable the road function for the coming 18 years.