The geological conditions of Baozhen Tunnel are complex

such as high geostress

deep-buried

rich groundwater

very weak and cracked rock masses and bias pressure along the rock seam. During construction

intense deformation and serious failure happened very often. Monitoring data showed that deformation is rapid with long duration

at the same time the deformation presented asymmetric and uneven features. Comparing and analyzing with the monitoring data of surrounding rock and geologic sketch of the work face

the weak intercalation is the key factor of provoking intense deformation and serious failure for sandy shale (whose strength is higher) or macker (whose strength is lower). So combined with the conclusion of triaxial test on different rocks in Baozhen Tunnel; some mechanical models are established according to different composite srructures between weak intercalation and surrounding rock to discuss the evolutionary process. The results show that the deformation and destabilization mechanism of surrounding rock provoked by the weak intercalation.