Abstract
As a common method applied in the construction of tunnels with Grade IV and Grade V surrounding rock, the center diaphragm (CD) method has the advantage of resisting the inward horizontal convergence of the tunnel. However, due to the small lateral earth pressure of the shallow tunnel, the curved center diaphragm would have an unstable stress state and cannot provide sufficient support to the surrounding rock. Based on the CD method, this study presents a vertical center diaphragm (VCD) method with an axisymmetric structure. The application condition of the VCD method relies on the comparison of the surface settlement and tunnel deformation with the two methods in different surrounding rock grades and buried depths by using a three-dimensional finite-difference code. Based on the Shenzhen Eastern Transit Expressway Connection Line Tunnel, which has six lanes of double lines, the deformation regularities and mechanical characteristics of the VCD method, including the surface settlement, tunnel deformation, internal force of the center diaphragm, surrounding rock pressure, and steel arch stress, are investigated by numerical calculations and a field comparative test. The results obtained in this study provide several suggestions for constructing shallow tunnels. Furthermore, the construction efficiency and economy of the VCD method are evaluated.
Highlights
With the fast development of the economy and the continuous improvement of synthetic national power, the infrastructure construction space is vigorously expanded in China
The deformation depends on the location of the disturbance area. For both the vertical center diaphragm (VCD) and center diaphragm (CD) methods, if the buried depth changes from 0.5D to 4D, the surface settlement will increase first and decrease, the crown settlement will increase first and remain constant, the arch springing convergence will increase first and decrease, and the side-wall convergence will remain constant; In different surrounding rock, the deformation depends on the scale of the disturbance area
For Grade V2, the surface settlement, crown settlement, and horizontal convergence will increase rapidly; The VCD method could be an appropriate choice for tunnel construction when the buried depth is less than 4D and the surrounding rock is Grade IV1 –V1
Summary
With the fast development of the economy and the continuous improvement of synthetic national power, the infrastructure construction space is vigorously expanded in China. The above researches play a guiding role in underground the primary support of the first excavation part, which can transfer the vertical earth pressure engineering constructions, but lack improvement or innovation of the CD method. This study presents a new method applied in shallow tunnel engineering, called the vertical is investigated by numerical calculations and a field test, and is compared with the traditional CD center diaphragm (VCD) method, which alters the shape of the center diaphragm based on the CD. Based on the Shenzhen Eastern Transit Expressway Connection Line Tunnel, the VCD effect,method construction efficiency, and economy are evaluated, and several construction suggestions are is investigated by numerical calculations and a field test, and is compared with the traditional given.CD. Shenzhen Eastern Transit Expressway Connection Line Tunnel is a crucial project in
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