Study On Construction Mechanical Behavior And Countermeasures Of Small Distance And Grade Separation Tunnel Under The Condition Of Shallow Buried

For the construction of shallow-buried grade separation tunnels with extremely close distance, there are already some engineering cases at home and abroad. But most of the solutions just take the matter on its merits, there is no unified construction standard to follow. Considering the above situation, this paper takes the project of Luojia 1# tunnel to Zengjialing 1# tunnel in northwestern Changsha as the background, and a systematic study on mechanical behavior and countermeasures of the construction of shallow-buried grade separation tunnel is carried out using the technological means including theoretical analysis and numerical analysis etc..Through the research, the main research achievements are as follows:(1) Based on the project of Luojia 1# tunnel in Hang-Chang passenger railway, this study put forward the construction key technique of grade separation tunnels with extremely close distance under the condition of shallow buried. And the construction sequence, excavation methods, supporting technology etc. are determined.(2) This study put forward the effects partition standards under the criterion of the displacement and lining stress increment in adjacent construction of shallow-buried interchange tunnels. By using the analyze methods including theoretical analysis, three-dimensional numerical analysis, etc., the effects partition standards, i.e. strong impact zone, weak and non-affected zone, are determined under the criterion of displacement and lining stress increment.(3) In selected construction sequence of "down first, up second", this paper analyses the region and degree of influence of "after-constructed tunnel" to "previous-constructed tunnel", and the evolution characteristics of the structure stress. Thus, the critical control steps in the construction process of adjacent tunnel are determined.At present, Luojia 1# tunnel and Zengjialing 1# tunnel have been completed. The supervision units monitored the adjacent construction of the shallow-buried interchange tunnel during the whole construction period. And the monitoring-data show that the surrounding rock is stability and structures dimension meet requirements of the design and technical standard. Practices prove that the advanced support measures, excavation methods, supporting measures presented in this paper are feasible and safe for the construction of small distance and grade separation tunnel under the condition of shallow buried. The successful experience can provide a reference for the future design and construction of similar projects.