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Abstract Construction process of mountain tunnel often encounters tunnel collapse，and collapse of arch springing has characteristics of large destructiveness and difficult detection，which is often neglected in actual project. In the Gaobao tunnel of Yongning express way，arch springing collapsed during construction. The cause of arch springing collapse and its reinforcement measure are studied. The displacement and stress of tunnel section near collapsed zone and collapsed zone after reinforcement are monitored to make sure that the surrounding rock is stable and the construction process is safe. The results show that：consolidation measure of arch springing is practicable，surrounding rock deformation and stress are well controlled，ductile injecting method is good. In the construction of tunnel making up of sand soil，much attention should be paid to the accidents caused by expansion of surrounding rock induced by rising up of ground water and rainfall infiltration. When accident of arch spring collapse occurs，surrounding rock of collapsed zone should be sealed up as quickly as possible，and surrounding rock within limits near collapsed zone should be reinforced. Excavation method of one side-surrounding pilot tunnel with short-line short-dig should be applied after monitoring result being stable near collapsed zone. The experience and conclusions presented can provide reference to design，construction and monitoring research of similar tunnels.
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Received: 10 June 2010
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2011, Vol. 30 
