Development and Research on the Vertical Center Diaphragm Method Applied in Shallow Tunnel Construction

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.

Study on early-warning System of Karst Tunnel Collapse

During the construction of karst Tunnel, tunnel collapse often occurs. The establishment of early-warning system of tunnel collapse can effectively ensure the construction safety, but the research is insufficient. Based on the combination of theoretical analysis and engineering practice, this paper puts forward to early-warning system for karst tunnel collapse. (1) The evaluation index system of karst tunnel collapse is composed of anchor axial force, displacement, anchor pull-out force and steel arch stress. (2) The relationship between evaluation index and warning level is determined, and the early-warning system of tunnel collapse is established. (3) The model applied to Chong’anjiang tunnel collapse warning, and achieved good results.

The Numerical Analysis of Gradient Material Replacement on Arch Dam of Stress Concentration Area

During operation, due to change of outside temperature, edge of abutment and central part of concrete arch dam is prone to stress concentration, Concrete of tensile stress concentration area appears too large tensile stress easily, which results cracks to affect dam safety. This paper, by changing the material properties, that obtained high strength low elastic modulus of concrete, replaced arch rings with gradient material replacement method, to improve the stress state of dam and enhance strength for dam safety. By comparing the temperature rise with drop of the arch stress distribution area, the relationship of changing elastic modulus and stress has got. Using the VT technology acquire critical values of mutation elastic modulus.