Effect of Fly Ash on Geotechnical Properties of Expansive soil

Abstract

This paper investigated the effect of fly ash addition on geotechnical properties of expansive soil. Classification tests, consistency limits test, specific gravity test, compaction test, direct shear test, swell percentage, and swell pressure tests, were conducted on specimen of expansive soil. Results of tests showed that soil was a clay high plasticity (CH) soil, according to the Unified Classification System (USCS) classification system. Liquid limit reduced from 74 % at 0 % fly ash to 56 % at 20 % fly ash content by dry weight of soil, the plastic limit reduced from 31 % at 0 % fly ash to 25 % at 20 % fly ash content, the plasticity index reduced from 44% at 0% fly ash to 31 % at 20% fly ash. The maximum dry density reduced from17.3 kN/mᵌ at 0% fly ash to13 kN/mᵌ at 20 % fly ash and optimum moisture content increased from 19.2% at 0% fly ash to 29.3% at 20% fly ash. Shear strength parameters c and Ø were measured after the addition of various contents of fly ash on curing days (7, 14 & 21). The value of cohesion (c) increased with increasing the amount of fly ash added to 15% then decreases. The effect of curing time on cohesion increased until 14 days. While c is decreased at various contents of added fly ash at 0 time (no curing or immediately tested). The increased internal friction angles (Ø) with added fly ash in all samples are independent ....