Impact of Igneous Rock Admixtures on Geotechnical Properties of Lime Stabilized Clay

This paper investigates the probable influence of powder from two igneous rocks, namely granite and rhyolite, on the geotechnical properties of lime stabilized clay soil. A clay soil sample was collected from Jhelum, city of the province Punjab in Pakistan, and its major geotechnical properties including particle size distribution, Atterberg limits, Activity, compaction parameters, California Bearing Ratio (CBR) and unconfined compressive strength (UCS) were determined by using standard ASTM procedures. Owing to the presence of clay minerals, the Jhelum soil is classified as CH soil (Fat clays) following the Unified classification system. Lime was added to the soil in the range of 0 – 12 % and the most influential lime percentage, i.e. the one causing the highest possible positive impact on geotechnical properties, was chosen for further stabilization. Following a gradual increase by 8 %, up to 32 % of granite and rhyolite powders were separately mixed with the soil sample showing maximum stabilization with lime, i.e. the sample containing 6 % lime. Each of the resulting samples was tested for all the parameters mentioned above. The results demonstrate that addition of granite and rhyolite powders produces significant improvement in workability and performance of the clay soil previously stabilized with 6 % lime. The improvement is obvious from reduction in Plasticity index, Activity and optimum moisture content, and rapid increase in UCS, maximum dry density and CBR. The principal reason for the observed positive changes is the presence of abundant non-active and denser minerals in granite and rhyolite powders as compared to lime and clay soil. Furthermore, the positive impact of rhyolite on the geotechnical behaviour of soil is relatively higher than granite obviously because of its better petrographic features, physical properties and strength.