Abstract:Classification of weathering intensity of rocks and research on their engineering features are important to the selection of foundation elevation and the utilization of engineering environment or materials. The present classification of the weathering intensity of rocks is based on qualitative geological evaluation and is optional. Therefore it is necessary to establish the method for quantitative analysis and assessment. Fissures due to weathering action are in uncertain direction and irregular development,which are basically different from fine fissures due to tectonic process. Weathering fissures are important indicator of weathering intensity. Weathering action changes the mineral composition of rocks,and the periods of weathering process reflect weathering intensity. Based on qualitative analysis of the development of fine fissures of weathered rocks and the characteristics of secondary fillings,erosion of feldspar and variation of clay minerals,quantitative statistics is carried out and the criteria are established for classifying of weathering intensity of rocks. The quantitative indexes given can clearly reveal the change of the quality of weathered rocks,and agree well with the indexes of the physical and mechanical properties of rocks.