Geological hazards without warnings such as roof collapse and mud-bursting are frequently encountered during the construction of tunnels under complex terrain and geological conditions

especially in the western mountainous areas of China. How to take efficient measures and reasonable technology to evaluate and detect the disposal effect of these geological hazards is very important to insure the quality of the project.This paper discusses in details the detection technology of detecting the collapse hazards in tunnel by Ground Penetrating Radar（GPR） through the case study of collapse hazards of Dulongtian-Tunnel（zk207+300～240） of Changde-Jishou Freeway in Hunan province.Based on the integrated analysis of the basic data collected and disposal measures

the detection technology of GPR can be used with local construction records to accurately detect the degree of saturation of the grout

the possibly existing cavities

and the number or space of the steel structure of reinforced shot Crete ring.A case study shows that GPR

combined by collected data

can not only detect the effect and quality of the disposal of the hazards without damage rapidly and exactly

but also offer scientific guide for the effect evaluation of the hazard disposals.All these are of practical values to reduce hidden hazards

insure the quality of construction and to provide guidance for the tunnel construction.