Research methods: Through making analyses of the geological conditions of tunnel portal in unfavourable geological section, the different construction methods are presented and the brief introduction is given to the characteristics of these methods, the analyses are made for the harms and causes for tunnel collapse, and the relative prevention and treatment measures are proposed.
Research results: When working out construction program far tunnel portal, the geological conditions should be taken in account fully. Before conducting construction, the design and construction program should be adjusted according to tire real site conditions and at the same time the necessary preparation should be done for possible sudden events. The relative measures should be taken in construction.
Research conclusions: Since the geological condition of the tunnel in mountain area is complicated, the available and effective construction technology and method should be adopted according to the different conditions, in order to ensure the construction and service safety of tunnel.
2007, Vol. 24 
