Soft clay soil layers are recent alluvial deposits presumably formed through the most recent 10,000 years described by their featureless and flat ground surface. Such clays identified by their low undrained shear strength and high compressibility. These soils are found at high natural moisture content. Soils with such characteristics create serious problems to geotechnical engineering associated with stability and settlements problems. A soft sub grade in construction of roadways is one of the most frequent problems for highway construction in many parts of the world. In addition, existence of soft clay soil which is unsuitable for supporting structures in construction sites, lack of space and economic motivation are considered important reasons for using soil improvement techniques rather than using deep foundation system. Many soil improvement techniques can be applied to increase its shear strength and decrease the consolidation settlement. This paper will shed light on several techniques that are used to improve the soft clay soil, idea about different techniques, how they are applied and work.