- Email: [email protected]
Hydro-mechanical modelling of tunnel excavation in fractured rock masses by a 3-D discrete fracture network approach
ARTICLE IN PRESS
International Journal of Rock Mechanics & Mining Sciences 41 (2004) 482
SINOROCK2004 Paper 2B 29
Hydro-mechanical modelling of tunnel excavation in fractured rock masses by a 3-D discrete fracture network approach S.D. Leea, H.K. Moonb,* a
The Research Institute of industrial Science, Hanyang University, Seoul 133-791, South Korea b Geoenvironmental System Engineering, Hanyang University, Seoul 133-791, South Korea
Abstract This study presents a discrete fracture network (DFN) approach in order to investigate the groundwater and grout flow in fractured rock masses by taking into account the mechanical deformation of fractures due to excavations. Using a statistical method developed in this study, DFN models have been generated, and fracture normal deformation has been calculated from the relation between fracture normal stiffness and stress change, which can be determined by stress transformation before and after excavation. Then, flow calculations have been performed by adopting a finite difference method assuming the groundwater to be a Newtonian fluid, the grout to be a Bingham fluid, and the cubic relation between the flow rate and aperture size to be valid. Through numerical analyses on 2- and 3-D DFN models under various stress conditions (K ¼ 1:022:0) and joint roughness (JRC ¼ 10214), it is shown that flow anisotropy due to excavation does exist (Fig. 1) and that the flow rate into the openings tends to increase parallel to the direction of major initial stress, so that the position of major inflow around the excavation boundary changes with different stress conditions. Also, the groundwater flow into the tunnels tends to increase as the vertical stress increases. Contrary to the results of groundwater flow, the range of grouting propagation does not seem to be highly dependent on the mechanical deformation of fractures, indicating that the effect of grout property and grouting technique on the groutability needs to be investigated in fractured rock masses. However, the need for 3-D grouting simulation has been emphasized by observing the grout propagation beyond the excavation face. As a result, it is concluded that the mechanical deformation of fractures with respect to the fracture geometry significantly influences the hydraulic behaviour of fractured rock masses together with the hydraulic properties and boundary conditions.
Keywords: Discrete fracture network; Fracture deformation; Aperture change; Hydro-mechanical process; Fluid flow; Grout flow simulation
(a)
(b)
Fig. 1. Normalized flow into a circular opening as a function of the ratio of horizontal stress to vertical stress (K). (a) 2-D circular opening with radial factures; (b) 3-D circular opening with statistically generated fracture network.
*Corresponding author. Tel.: +82-2-2290-0413; fax: +82-2-2281-7769. E-mail address: [email protected] (H.K. Moon). For full length paper see CD-ROM attached. doi:10.1016/j.ijrmms.2003.12.015
International Journal of Rock Mechanics & Mining Sciences 41 (2004) 482
SINOROCK2004 Paper 2B 29
Hydro-mechanical modelling of tunnel excavation in fractured rock masses by a 3-D discrete fracture network approach S.D. Leea, H.K. Moonb,* a
The Research Institute of industrial Science, Hanyang University, Seoul 133-791, South Korea b Geoenvironmental System Engineering, Hanyang University, Seoul 133-791, South Korea
Abstract This study presents a discrete fracture network (DFN) approach in order to investigate the groundwater and grout flow in fractured rock masses by taking into account the mechanical deformation of fractures due to excavations. Using a statistical method developed in this study, DFN models have been generated, and fracture normal deformation has been calculated from the relation between fracture normal stiffness and stress change, which can be determined by stress transformation before and after excavation. Then, flow calculations have been performed by adopting a finite difference method assuming the groundwater to be a Newtonian fluid, the grout to be a Bingham fluid, and the cubic relation between the flow rate and aperture size to be valid. Through numerical analyses on 2- and 3-D DFN models under various stress conditions (K ¼ 1:022:0) and joint roughness (JRC ¼ 10214), it is shown that flow anisotropy due to excavation does exist (Fig. 1) and that the flow rate into the openings tends to increase parallel to the direction of major initial stress, so that the position of major inflow around the excavation boundary changes with different stress conditions. Also, the groundwater flow into the tunnels tends to increase as the vertical stress increases. Contrary to the results of groundwater flow, the range of grouting propagation does not seem to be highly dependent on the mechanical deformation of fractures, indicating that the effect of grout property and grouting technique on the groutability needs to be investigated in fractured rock masses. However, the need for 3-D grouting simulation has been emphasized by observing the grout propagation beyond the excavation face. As a result, it is concluded that the mechanical deformation of fractures with respect to the fracture geometry significantly influences the hydraulic behaviour of fractured rock masses together with the hydraulic properties and boundary conditions.
Keywords: Discrete fracture network; Fracture deformation; Aperture change; Hydro-mechanical process; Fluid flow; Grout flow simulation
(a)
(b)
Fig. 1. Normalized flow into a circular opening as a function of the ratio of horizontal stress to vertical stress (K). (a) 2-D circular opening with radial factures; (b) 3-D circular opening with statistically generated fracture network.
*Corresponding author. Tel.: +82-2-2290-0413; fax: +82-2-2281-7769. E-mail address: [email protected] (H.K. Moon). For full length paper see CD-ROM attached. doi:10.1016/j.ijrmms.2003.12.015