Assessment of risks is a key task in the project management. In this process, Risk Breakdown Structure (RBS) approach can be utilized to identify project relevant risks. In the previous classical method, only Limited number of attributes is considered in the evaluation that can cause unreliable results. In this paper, an attempt has been made to introduce and involve a relatively comprehensive set of attributes for applying in Multi Attribute Decision Making (MADM) techniques. Using this model, the risks of tunneling construction in the Seimareh dam project, located in South-West of Iran, are assessed and ranked. For the collection of experts' judgments, group decision making method by conducting various decision panels was applied. Also for the risk ranking, Linear Assignment (LA), Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and Simple Additive Weighted (SAW) methods were considered. Final ranking of the risks was computed using integration methods. It was concluded that the risks economical factors and guarantee are the project most and least critical risks, respectively.