Application of High-Vesicularity Cinder Gravels to Railway Earth Structure in Ethiopia

Abstract

The Addis Ababa–Djibouti Railway in Ethiopia extends across the Rift Valley, where cinder gravels (scoria) occur widely. Considering its abundance and environmental benefits, these cinder gravels are an enormous resource for earth structure fill. However, the gravels usually fail to comply with aggregate specifications for ballasted railways, primarily due to the high vesicularity of their particles. Nineteen cinder gravel samples from different locations were tested for their grain-size range, porosity, specific gravity, dry density, morphology, Los Angeles abrasion loss, and geochemistry. The results confirmed that the high void ratios of the gravels limit their direct use in railway construction. The cinder gravels therefore were blended with local silty sands to improve their suitability as aggregates. The blended material was assessed for consolidated undrained shear strength, breakage potential, and California bearing ratio. The field compaction performance of a trial railway section was evaluated and combined with the laboratory test results to produce a guideline for applying the cinder gravels as railway earth structure. Adopting interparticle porosity as a replacement for the original porosity in evaluating the quality of the compacted cinder gravel is recommended. Field dynamic measurements performed at two railway subgrade sections constructed using the stabilized cinder gravel or traditional geomaterials demonstrated that the stabilized-aggregate subgrade performed better under various train speed conditions. This study improves knowledge of aggregate stabilization techniques and facilitates wider use of cinder gravel in railway construction.