Applications of Bamboo as a Sub Grade Soil Reinforcements (Ziway-Hawassa Road), Ethiopia

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Addis Ababa University


Road construction on fine grained soils are challenges to geotechnical engineers and designers because of its low bearing capacity which results in cracks in the pavement structure as well as increase in the thickness of the pavement. Use of natural fiber in geotechnical engineering for improving soil properties is advantageous because they are cheap, locally available, biodegradable and eco-friendly and causes significant improvement in tensile strength, shear strength, and other engineering properties of the soil. This thesis work is aimed to evaluate the applications of bamboo as a subgrade soil reinforcements. The soil samples was collected from Ziway town and Bamboo sample was collected from Hagere selam. Two test pits of soil samples were collected for the investigation purposes but tests on reinforced soil were conducted on only one selected test pit. The preliminary investigation of the soil on index properties shows that it belongs to A-4 class of soil in the AASHTO soil classification system and ML under USCS system. Compaction, direct shear and CBR tests were used to evaluate properties of bamboo reinforced soil. The soil was reinforced with bamboo in percentages of 0.25%, 0.5% and 1% by dry weight of the soil and length of 15mm, 30mm and 45mm with a maximum thickness of 3mm to 5mm.Certain percentages of bamboo with varying lengths are used for the experimental investigations. All bamboo samples were treated by a certain amounts of kerosene by mixing it with kerosene to avoid the absorption of moisture. Water absorption test shows that the water absorption of bamboo coated by kerosene was decreased by about 20%.Soil samples were prepared at its MDD corresponding to its OMC to conduct direct shear and CBR tests with and without reinforcements. Analysis of test results shows that bamboo reinforcements of soil reduces MDD very slightly while OMC remains more or less the same. Bamboo reinforcements of sandy silt soil has no significant effects on shear strength parameters (C and Ø) but significantly increases CBR (i.e.CBR increases by about more than 200% of that unreinforced soil) at 1% of 45mm. Generally the CBR value of sub-grade soil increases significantly with the inclusion of bamboo but different factors such as removal of bamboo (environmental cost), transporting of bamboo (transportation cost), preparation of bamboo (technical cost), decomposition of bamboo makes the design un-economical and as the sub-grade soil is sandy silt it is better to improve its engineering properties by compaction only.



Geotechnical Engineering