• Geomechanics and Engineering
• /
• v.17 no.6
• /
• pp.573-581
• /
• 2019

Excavation of underground cavern and shaft was proposed for the construction of a ventilation facility in an urban area. A shaft connects the street-level air plenum to an underground cavern, which extends down approximately 46 m below the street surface. At the project site, the rock mass was relatively strong and well-defined joint sets were present. A kinematic block stability analysis was first performed to estimate the required reinforcement system. Then a 3-D discontinuum numerical analysis was conducted to evaluate the capacity of the initial support and the overall stability of the required excavation, followed by a 3-D continuum numerical analysis to complement the calculated result. This paper illustrates the application of detailed numerical analyses to the design of the required initial support system for the stability of underground hard rock mining at a relatively shallow depth.

• Tunnel and Underground Space
• /
• v.20 no.1
• /
• pp.28-38
• /
• 2010

In order to investigate the tendency of general displacements and behaviors with respect to each construction process as well as the applicability of numerical analysis schemes, this research has focused on not only analyzing a variety of field observations made in a NATM tunnel, such as displacement of top and side, stress of shotcrete and axial strength of rock bolt, but also carrying out a series of numerical analyses. It was established from the investigation that the 2-dimensional continuum numerical analysis was the one which could more accurately predict displacement of crown and side in the area of one step excavation (patten, P1-P3), while the 2-dimensional discontinuum analysis was the most suitable scheme to study that of two step excavation (patten, P4-P6). In addition, the 2-dimensional continuum analysis enabled to appropriately predict the axial strength of rock bolt and stress of shotcrete in all the area of the tunnel. Finally, it has been possible to conclude from the study that the 3-dimensional continuum analysis should be applied to inspect the behavior and tendency with respect to each stage of the construction as well as in the case of joints, such as large turnouts where relaxation loads in both of horizontal and vertical direction are piled up.