A Study On Strength Characteristics Of Sub Grade Soil Treated With Fly Ash And Enset Fiber; In Case Of Tarcha Chida Road Section, Southern Ethiop

Abstract

In Ethiopia, Road Pavement Failure Is Becoming A Common Problem And Major Challenge. Such Failures Are Most Likely To Happen Due To Expansive Soil In The Subgrade. This Soil Possesses Low Shear Strength, High Plasticity And Compressibility. To Improve The Property Of Such Soil; Stabilization And/Or Reinforcement Technique Is Commonly Used. Stabilizing Expansive Soil With Available Waste Materials And Reinforcing It With Discrete, Randomly Distributed Natural Fibers Are Recently Getting More Attention In Geotechnical Engineering. Fly Ash Is A Waste Material Which Remains After The Combustion Of Coal. Enset Fibers Are Natural Fibers Extracted From The Pseudostem And Leaf Parts Of Enset Plant. The Soil In Tarcha-Chida Road Project Site Does Not Fulfill The Subgrade Soil Requirements; And Construction Is Going On By Removing The Existing Soils And Replacing Them With Selected Materials Which Bring Additional Cost, May Displace The People And Change The Landscape Of The Area. This Study Aimed To Investigate The Effect Of Fly Ash And Enset Fiber On Strength Characteristics Of Expansive Subgrade Soil. The Soil Samples Were Collected From Tarcha-Chida Road Section. The Experimental Programs Were Carried Out For Soil Alone, Soil-Fly Ash And Soil-Fly Ash-Enset Fiber Mixes. Series Of Laboratory Tests Such As Particle Size Distribution, Atterberg Limits, Specific Gravity, Free Swell, Free Swell Index, Compaction, California Bearing Ratio (Cbr) And Unconfined Compressive Strength (Ucs) Tests Were Performed For Soil Alone And Soil Treated With Fly Ash. The Percentage Of Fly Ash By Weight Of Dry Soil Is Taken As 10%, 15%, 20% And 25%. The Results Show That Fly Ash Reduces Plasticity Index, Swelling And Maximum Dry Density (Mdd); And Increase Observed In Optimum Moisture Content (Omc), Cbr And Ucs With Increase In Fly Ash Contents. A Significant Increase In Cbr And Ucs Value Is Observed For Addition Of 20% Of Fly Ash That Is 3.77% And 177.75kpa Respectively, And Further Addition Of Fly Ash Decreased The Values. Optimum Soil-Fly Ash Mix (I.E. 80% Soil And 20% Fly Ash) Were Reinforced Randomly With Enset Fiber Of 0.5%, 1%, 1.5% And 2% By Weight Of Dry Soil And Length Of 15mm And 20mm To Investigate The Effect Of Fiber On Compaction, Cbr And Ucs. Coating The Enset Fiber With Kerosene Leads To Reduction Of Water Absorption Capacity By 29%. The Results On Soil-Fly Ash Enset Fiber Show That Mdd Is Decreased; And Omc, Cbr And Ucs Are Increased With Increase In Fiber Content And Length. The Optimum Cbr And Ucs Value Obtained At 1.5% Fiber Content And 20mm Fiber Length Was 6.38% And 231.5kpa Respectively. Thus The Optimum Percentage Of Soil-Fly Ash-Enset Fiber Mix Is 78.5% Soil, 20% Fly Ash And 1.5% Enset Fiber By Weight. In General, This Study Showed That A Combination Of Fly Ash And Enset Fiber Can Be Effectively Used To Improve The Expansive Subgrade Soil.