Subgrade Stabilization using Lime and Wheat Straw Ash

Abstract

Subgrade is the bottom most layer of road pavement and acts as foundation for the road structure. Weak subgrade in pavement can result in premature failure and deterioration of road surface. Engineering properties of weak subgrade soil is improved using chemical or mechanical means. Replacement of weak subgrade material with high strength material is not possible many times due to more cost or unavailability of material. Another economical and efficient way to enhance weak subgrade soil properties is stabilization using different materials. The present research is to examine effect of lime and wheat straw ash on different engineering properties of weak subgrade soil. Lime is a white crystalline oxide produced by heating limestone. Wheat straw is naturally occurring material obtained from wheat crop. Ash obtained by burning wheat straw is a natural pozzolan and used in this research along with lime. Clayey soil was used. Atterberg’s limit, compaction characteristics, unconfined compressive strength test and California bearing ratio of natural soil and soil treated with lime and wheat straw ash was determined. Soil treated with lime exhibit decrease in plasticity index and liquid limit with addition of lime and wheat straw ash. Decrease in MDD and increase in OMC was observed for both soil lime mix and soil lime WSA mix. UCS of natural soil increased by addition of lime and WSA. Soaked UCS increased 16 times with addition of lime and 22 time with addition of lime along with WSA. 2 to 3 times increase in soaked CBR was observed for optimum lime and optimum WSA content. Reduction in layers thickness of pavement was observed due to increase in CBR. There was significant economic benefit as per cost analysis conducted by use of lime. There was no significant cost saving in use of WSA along with lime however there was more improvement in geotechnical properties of soil. Keywords: Subgrade Stabilzation, Lime, Wheat Straw Ash