Abstract
Expansive shale has been found extensively all over the world, especially in tropical and sub-tropical regions. The ground heave that results from shale swelling potential is a multi-factorial phenomenon. Remarkably, the expansive shale of Saudi Arabia varies considerably due to variations in its ancient environmental climatic conditions. The studied shale of Bathan Formation at Al-Rehaili northeastern Jeddah is considered a problematic expansive material and classified as clayey shale of high plasticity (CH). Clay mineral species of these lacustrine sediments are composed mainly of smectite, kaolinite, and smectite-illite mixed layered. Exchangeable sodium percentage values of the Bathan Formation, northern Jeddah are very low. Addition of quicklime (up to 3 %) decreases consistency limits. The destructive effect of quicklime addition (up to 3 %) on the swelling potentiality of these clayey-rich sediments is due to the formation of highly swell ettringite. Mechanical properties, such as unconfined compression strength, have been improved due to the cementation effect of lime as well as the creation of new crystalline compounds such as calcium silicates and ettringite. Adding quicklime percent should not exceed 3 % to prevent increasing pH value and to avoid formation of ettringite which has higher ability to swell.