Comparison of Construction Schemes for Small-Space Tunnels with Large Sections and Shallow Depth in Jointed Weak Rocks

The small-space tunnels on city expressways have high requirements on the tunnelling deformation, construction period and budget control. Therefore, the selection of a reasonable construction scheme is quite important. Based on a specific small-space tunnel project in Suzhou, China, the differences of central diaphragm (CD) method, bench cut (BC) method, and BC method with feet-lock pipes on the construction of small-space tunnels in jointed weak rocks are examined using the plane strain finite element method. The anisotropic constitutive behavior of jointed rock is considered, and the crown settlement, ground surface settlement, rock horizontal deformation, middle rock stress, and construction safety are investigated. The results show that the bench cut with feet-lock pipes can effectively limit the crown settlement, lower the stress in the surrounding rock near the side wall of the tunnels, improve the safety of surrounding rock than the traditional bench cut method, and is more convenient in construction process and budget control than the CD method. The numerical simulation matches relatively well with the field monitoring, showing the effectiveness of the numerical simulation. The results can provide reference for the design and construction of other similar tunnel projects in future.