Pavement Design for Heavy Oil Tanker Routes in South Sudan:Load Equivalency and Performance Modelling

The rapid expansion of oil extraction and transport operations in South Sudan has intensified demand on road infrastructure designed originally for light mixed traffic. Heavy oil tanker vehicles, routinely exceeding standard legal axle loads by 15 to 40 percent, impose disproportionately large pavement damage expressed through fourth-power load equivalency factors. This study presents a comprehensive framework for pavement design on designated oil tanker routes connecting producing blocks in Unity, Jonglei, and Upper Nile States to the Port Sudan export terminal via Juba. Axle load equivalency factors (ESALs) were computed for single, tandem, and tridem configurations representative of fully laden crude-oil tankers using the AASHTO 1993 empirical model and verified with mechanistic-empirical analysis under the Austroads Pavement Design Guide. A structural number approach was combined with layered elastic theory (BISAR 3.0) to determine optimal layer thicknesses across five critical route segments. Subgrade bearing capacity, evaluated from Dynamic Cone Penetrometer (DCP) surveys along 320 km of existing corridors, revealed CBR values ranging from 3 to 8 percent, characteristic of tropical expansive clays. Performance modelling using the HDM-4 deterioration equations predicted International Roughness Index (IRI) progression and remaining service life under three traffic growth scenarios (2%, 4%, 6% per annum). Results demonstrate that standard pavement sections designed for 3.5 × 10⁶ ESALs are inadequate for oil tanker corridors demanding up to 9.2 × 10⁶ ESALs over a 20-year design life. Structural Numbers between 4.8 and 7.2 are required, implying asphalt concrete layers of 100–150 mm, crushed-stone base of 200–300 mm, and laterite subbase of 150–250 mm. This research pr