Abstract：There are many methods to classify the surrounding rock in highway tunnel construction. They are usually divided into two kinds：single factor classification method and multi-factor classification method. Each of them has advantages and disadvantages. The multi-factor classification method is usually complex and not convenient to use. On the other hand，the adaptability of the single factor classification method is not high because it takes only one factor into account. For the specific or complex geological conditions of surrounding rock，the single factor classification method is not accurate. Based on the probability theory，considering rock mass quality and elastic wave velocity，combining with the value of BQ in Code for Design of Road Tunnel(JTGD70–2004)，the rock mass classification is conducted. Taking the Yunling tunnel as an engineering background，a new kind of method for the classification of surrounding rock is proposed based on the probability theory. Using this method to classify the surrounding rock of Yunling tunnel，the calculated results of the surrounding rock classification agree very well with the practical ones. The successful application of this method not only provides advisement for the design and construction of the present highway tunnel but also gives references to the surrounding rock classification in other similar highway tunnel projects.
