The engineering behavior of rock materials depends not only on stress state and stress history but also on the physical and chemical change of the rock materials due to weathering. Changes in index properties such as dry density void ratio, clay content and seismic velocity caused by weathering processes is representing strength and elastic properties of rock materials. The changes caused by weathering processes in rock material may be mainly considered under the two topics; the mineralogical change and the physical change. Because the elastic wave velocity measurement is a non-destructive test, and this measurement is applied easily to repeat and be sensitive to the change of the related engineering properties. One of these parameters is Weathering State Index based on Mineralogical Change Parameter and Physical Change Parameter. Although the unconfined compressive strength of weathered rocks materials are highly important parameters for engineering geology projects, the necessary core samples cannot always be obtained from these rock materials.. For this reason, the predictive models are often employed for the indirect estimation of mechanical parameters.