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Abstract In order to precisely understand the rock pressure variation laws of three-arch metro tunnel and its supporting system in construction period in loess region，a large scale field testing relying on the route No.2 of Xi?an metro construction site is conducted. The variation laws of contacting pressure of surrounding rock and initial supporting system，contacting pressure of initial supporting and secondary lining，and surrounding rock pressures of each construction stage are monitored. The research results show as that：(1) The surrounding rock pressures of each part of initial support in earlier excavation chamber are larger than that of later excavation chamber. (2) The pressures in vault and in bottom of invert are larger with the excavation span. (3) The stress of bottom of mid-partition between left and right lines is the largest due to the upper soil load. (4) The stress of the initial supporting system increases after the secondary lining construction. (5) The loading proportions of the initial support and secondary lining are 52.81% and 47.19% respectively，and they can be adopted as 50% in the design stage. (6) The surrounding rock pressure of each part in earlier excavation is increasing with the other chamber′construction later.
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Received: 25 June 2010
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2011, Vol. 30 
