Occurrence mechanism of slope crack at the bias highway tunnel entrance

Deformation problems of tunnel entrance construction has been a technical problem puzzled the large-scale tunnel construction, especially in bias section, this paper has been a special research on the problem relying on the subject of `Comprehensive Technical and Engineering Application of Disaster Prevention and Treatment of the North Tunnel Groups Engineering´, and combining with the Beikou tunnel entrance project of Zhang Jiakou-Shi Jiazhuang Expressway in Hebei Province. Based on the summarization of the main factors those affected the deformation and failure of slope in Beikou tunnel entrance, and its failure modes, with the methods of surrounding rock pressure, broken-rock circle, plasticity and deformation theories when the tunnel excavated, through combining support structure characteristics curve with wall rock support demand curve, the slope deformation occurrence mechanism in bias tunnel entrance was proposed, which provided a theoretical basis for solving the problems in the project and similar projects.