Study on Structural Stability of Mined Large-Span Tunnels Constructed by Two Arch-Cover Methods in Upper-Soft and Lower-Hard Rock Stratum of Qingdao Area
Abstract：
As for the upper-soft and lower-hard rock stratum with larger stiffness differences in vertical depth, the arch-cover method is developed based on the cover-excavation method and double side heading method. The archcover method includes the arch-cover method with double-layer primary support and the arch-cover method with secondly lining. Taking a mined large-span station of Qingdao metro as an example, a numerical analysis on structural stability of the tunnel constructed by two arch-over methods is conducted in light of the characteristics of the upper-soft and lower-hard rock stratum. The results show that: (1) as for the arch-cover method with secondary lining, when tunnel is constructed at a safe strut dismantling distance of 9 m in longitudinal direction, the "spatial stiffness effect" of shed protection of outer primary support can′ t make up for the "arch" effect of arch-cover, the construction technology of arch-cover method with double-layer primary support is more conducive to tunnel deformation control; (2) the arch-cover structure has significant bearing and protection functions during excavating the lower part of the tunnel, however, the plastic damage of rock mass at arch springing is more obvious during the construction by arch-cover method with secondary lining under the same geological conditions, in other words, the arch springing of secondary lining requires higher strength and rigidity of the rock foundation; (3) the internal force con? trol positions of structure by arch-cover method with double-layer primary support are spandrel and arch springing,and the control position is the arch springing for the structure by arch-cover method with secondary lining, the control internal force of arch springing of the latter is about 1.56 times of that of the former, the "beam" effect of the former is more obvious while the "foot" effect of the latter is more obvious; (4) from the perspective of safety, it is suggested that the arch-cover method with double-layer primary support should be adopted.
SHI Yujing
.Study on Structural Stability of Mined Large-Span Tunnels Constructed by Two Arch-Cover Methods in Upper-Soft and Lower-Hard Rock Stratum of Qingdao Area[J] MODERN TUNNELLING TECHNOLOGY, 2020,V57(2): 117-126
2020, Vol. 57 
