IMPROVEMENTS OF THE GEOTECHNICAL PROPERTIES OF SUBGRADE SOIL USING LIMESTONE DUST

Abstract

The cost of improving the geotechnical properties of road subgrade in the Niger Delta using traditional chemical stabilizers such as Portland cement is partly responsible for the poor development of road network in the region. Lime stone dust (LSD), a by-product of the limestone crushing processes has not been fully utilized as a soil stabilizer in Nigeria. In this study, LSD was employed as a stabilizer to improve the geotechnical properties of Calabar South subgrade soil. The soil was stabilized by adding LSD at 0%, 5%, 10%, 15%, 25%, and 50% by weight of soil.  Test conducted include, Atterberg Limits and indices, particle size distribution, specific gravity, compaction, California bearing ratio, unconfined compressive strength (UCS) and Shear strength. The subgrade was classified as inorganic clay with low plasticity under the Unified Soil Classification System and A-6 soil under the AASHTO classification. The specific gravity was 2.73 with a maximum dry density of 1.74 kg/m3 at an optimum moisture content of 24.5%. The soaked value of the California bearing ratio (CBR) was 6.92%. Atterberg Limits and indices were improved by a reduction in the plasticity of the soil. Compaction characteristics showed improvement by 11.5% as MDD increased from 1.74kg/m3 to 1.94kg/m3 at 10% optimal LSD level with a corresponding reduction in OMC. CBR increased by 75.86% from 6.92% to 12.12% while unconfined compressive strength (UCS) increased by 28.2% from 103.66KN/m2 to 132.89KN/m2.  Shear strength increased by 24.1% from 58.83KN/m2 to 72.31KN/m2. The soil stiffness also improved with the addition of LSD as Secant modulus increased with stabilizer content. It was concluded that limestone dust is a good sustainable stabilizer to the soil. 

KEYWORDS Soil stabilization, limestone dust, Atterberg Limits, Maximum Dry Density, California Bearing Ratio