Abstract: Based on the shallowburied mined doublearch tunnel project applied in parking lot of Xi′an Metro Line No. 5, the deformation characteristics of doublearch metro tunnel in loess area are studied. The variation rules of surface settlement, lining deformation of new tunnel and hance convergence of superadjacent existing tunnel are analyzed through field monitoring data. The results show that: (1) In the construction, the maximum surface settlement is 19.66 mm and the maximum settlement rate is 2.31 mm/d, both of which are less than the construction control limit. (2) For ultrashallow buried tunnels, influencing factors such as construction uncertainty, soil heterogeneity, soil anisotropy, surface random load, etc. will obviously affect the shape of the surface settlement curves, which may make the Peck formula have a large deviation from the predicted results of the surface settlement. (3) When the surface settlement reaches a stable state, the distance between the tunnel surface and the monitored section is obviously more than 5 times of the tunnel diameter, while the primary support deformation rate is faster, and the corresponding distance is basically 3~5 times of the tunnel diameter when the surface settlement reaches a stable state. (4) Due to the barrier effect of the middle pilot hole, the effect of the construction of the back tunnel on the stress variation and convergent deformation of the primary support of the first tunnel is not obvious. (5) When the distance between the tunnel face and the monitored section is more than 2 times of the tunnel diameter, the convergence of the hance of the existing tunnel basically tends to be stable, and the final convergence value of the hance at all monitored sections is basically within 4 mm.

Key words:  , loess area, doublearch metro tunnel, shallowburied and mining excavation, field monitoring, surface settlement, primary support deformation, existing tunnel