Abstract: As a special rock type, the expansive rock is widely distributed in all over the world. The physical and mechanical properties usually change with moisture content. When the expansive rock is developed in between the strength rock layers, the existence of the expansive rock is often ignored and might impose a geo-hazard to the engineering projects. The expansion and contraction in these rock masses change with the adjacent environment and the strength of the rock masses gradually reduce. Due to the difference of mineral composition, structure and sedimental environment, embedment depth and variation of the rock mass thickness, the properties of expansive bedrock are different. The repetitive contraction and expansion characteristics of the expansive rock and their associated fissures are likely result in the damage of building structures above. The study of the engineering properties of expansive rock and their classifications for the engineering purposes are very impotant.

Key words: Expansive Rock, Nanjing Fourth Yangtze River Crossing Bridge, Free Expansion Ratio, Smectite