Research purposes: During construction, the serious collapse happened to the Baizicun No. 1 Tunnel, and the cracks of tunnel lining on the vault were repaired after the completion of construction. However, in the initial operational stage, the new cracks were found in the tunnel exit section, and the cracks developed to the tunnel entrance section rapidly. In the serious disease section, the vault of the tunnel was fractured longitudinally and crushed out block, and the arch springing, side wall and hance of tunnel were fractured longitudinally and dislocated for intrusion. Also the cracks happened to the mountain body. Therefore, there was no condition to keep the railway in good operation, even there was a risk of interruption of the railway for a long time at any time if the disease further developed. It was necessary to do the research on the tunnel disease. Research conclusions: The disease of the Baizicun No. 1 Tunnel was caused by the activity of ancient landslide. The stratigraphic inversion and obvious ancient sliding zone are direct and deterministic evidences of this ancient landslide existence, and characteristic of special topography and slipping slope displacement are indirect and complementary evidences. Through comprehensive survey researching, the material basis (internal cause) and causative factor (external cause) of the activity of this ancient landslide were found. The analysis method of main orientation of similar landslide which has the same direction with the maximum slope of landform and the orientation of the maximum tendency of flabbiness layers of valley, generally with the sliding direction of the ancient landslide, with the major principal stress of underground structure, such as tunnel lining, with the direction of the major plane displacement horizontal vector, was summarized. Because of the obvious pushing, the landside was at the creep stage and comprehensive measures, dominanted with anti-sliding pile, were figured out in this article. It will be of significance to similar landslide and ancient landslide engineering survey, treatment designing and construction.
