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Abstract Wenxiang tunnel is a shallow large-span loess tunnel in Zhengzhou—Xi′an Special Passenger Railway；and the mechanical behaviors of big pipe-roof are studied. The longitudinal deformations of the pipe-roof before the underpass section are monitored by strain gauges fixed in the pipe-roof. Based on the monitoring results，the mechanical behaviors and function mechanism of long scale pipe-roof are thoroughly analyzed. Furthermore，a new double-parameter elastic foundation beam model of pipe-roof in shallow tunnels is build and its boundary condition gets analyzed. By model calculating with deflection curve equation and calculation of longitudinal strain，the evaluation of mechanical behaviors of the pipe-roofs in Wenxiang tunnel is performed successfully. The measured values and the calculation results are consistent well. The research results show that：(1) In front of the excavating face about 15m，the pipe roof starts to bear the load；and after the excavating face about 15 m，its force tends to be stable. The longitudinal deformation of the whole pipe-roof is groove-shaped distribution and its largest force is at the excavating face. (2) Simultaneously，the results also indicate that the mechanical behaviors of pipe-roof relate to the location of the excavation face，the footage of the tunnelling cycle，the mechanics parameter of both pipe-roof itself and surrounding rock，and so on. (3) The conclusions from calculation model can be used as theory basis in the design parameter optimization of construction and the construction scheme selection of pipe-roof；and the application effect has been verified in deformation monitoring at underpass section.
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Received: 20 May 2010
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2011, Vol. 30 
