An Experimental Study on the Performance of Highland Bamboo Sawdust for Expansive Subgrade Soil Improvement:-A Case Study of Jimma City

Abstract

Expansive soils are those soils that have undergone significant volume change with the addition or removal of water. Expansive soils cause serious problem in the civil engineering practice due to swell and shrinkage upon wetting and drying. Therefore, these problematic soils when encountered as subgrade should be avoided or treated properly before construction purpose. The aim of this study was to assess the performance of highland bamboo sawdust for expansive subgrade soil improvement in Jimma City. Expansive soil samples were collected from two test pits in Jimma City (Jimma Institute of Technology campus and Ureal sefer). Various preliminary tests for index properties and strength were determined in the laboratory beside this free swell, plasticity, Calforinia bearing ratio swell were done and on failure type criteria, the test results indicate that the soil samples are expansive soils. Highland bamboo sawdust were prepared for this study by manual cutting by axes bamboo into small pieces and grinding by mold and hammer. Then left in an open area for air drying in order to remove its moisture and sieved with different sizes of sieves for different laboratory test depends on standard procedures.The improvements were done 4, 8, 12, 16 and 20% of highland bamboo sawdust by weight. To determine the effect of Highland bamboo sawdust(HBSD) on engineering properties of expansive soil different laboratory tests were carried out which include moisture content, Atterberg limits, grain size, specific gravity, compaction, Unconfined compression strength, Calforinia bearing ratio and Calforinia bearing ratio swell. Tests were performed on natural and treated soil samples as per the Indian standard, American Association state of highway and transportation officials (AASHTO) and American society for testing and materials (ASTM) laboratory test standards. The selected soil samples were characterized and were found A-7-5 category of soil based on the AASHTO soil classification system and High plasticity clay(CH) as per Unified soil classification system(USCS), which is clay soil of poor engineering properties. The results from the analysis show improvement of the geotechnical properties of expansive soil with HBSD. Maximum Dry Density (MDD) increased from 1.45g/cm 3 at natural soil to 1.57g/cm 3 at 16% HBSD treated soil. The CBR values increased from 1.31% at natural soil to 9.8% with highland bamboo sawdust and the optimum values are achieved at 16% HBSD. Unconfined Compressive Strength increased from 68.15 kN/m 3 at remolded natural to 2179.7 kN/m 3 with HBSD at 16% at optimum values. The Free swell index, Liquid limit, Plastic index, Optimum moisture content, Calforinia bearing ratio swell is decreased. Better improvement was found in strength parameters than index parameters when using Highland bamboo sawdust. After improvement the soil categorized under A-2-7 as per the AASHTO soil classification system and MH as per the USCS system. It can be concluded from the present study that expansive soil could properly be improved for use as subgrade material. Adequate strength was achieved with 16% and which is found to be the optimum Highland bamboo sawdust contents for improving the engineering properties of the expansive soils.For the practical applicability, it recommended for further plantation of highland bamboo because from time to time its signifance increasing engineering field and do mineralogical anayisis and durability tests.