Mineralogy as a Key Parameter for Strength Evaluation of Clayey Subgrades

Abstract

The current pavement design practices do not take into consideration the mineralogy of clays. It was also recommended by researchers in the recent past that current standards should be revised and should take into consideration the clay mineralogy. The major task of this research was to study the soils of same type according to AASHTO classification system, but having different quantities of clay minerals, so the behavior of different quantities of clay minerals on the strength properties of soil can be accessed. During this research, three soils were collected from different sources and having different percentages of clay minerals were studied. Soils were collected from three different regions of Pakistan, Kohat (Soil-A), Islamabad (Soil-B) and Faisalabad (Soil-C). Various classification and strength tests, like Sieve Analysis & Hydrometer Analysis (ASTM D-422), Liquid Limit & Plastic Limit (ASTM D-4318), X-Ray Diffraction Analysis, Modified Proctor Test (AASHTO T 180 B) and California Bearing Ratio Tests (un-soaked condition & soaked condition) were performed and relationship of clay mineral quantity with CBR (Un-Soaked & Soaked conditions) and swelling potential was established. A comparison has also been made between the percentage of clay obtained by X-Ray diffraction analysis and Hydrometer analysis.
Keywords: Mineralogy, Clay, Subgrade, California Bearing Ratio, Hydrometer analysis