In the process of tunnel excavation,the surrounding rock of the tunnel is damaged and unsta-ble in the form of block,and the damaged part in the tunnel is called"critical block".This paper takes a tunnel as an example,according to the basic principle of the key block theory,identifies the possible key block by the eradial projection method,and uses the vector analysis method to cite the conclusion,which provides the basis for the stability evaluation of the surrounding rock in the tunnel.The following conclusions are drawn:1.The local blocks composed of combinations 1,2 are movable blocks;2.The results obtained by erector projection method are consistent with those obtained by vector analysis method.
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