The excavation damaged zone (EDZ) is an areas around an excavation where in situ rock mass properties, stress condition, displacement and groundwater flow conditions have been altered due to the excavation itself. In this study, the ‘hydraulic EDZ’ is defined as the rock zone adjacent to the excavation where the hydraulic aperture has been changed due to the excavation. Fundamental principles of distinct element method (DEM) were used in the analysis. In the same groundwater level, the behavior of hydraulic aperture near the cavern was analyzed for different stress rations, initial apertures, fracture angles and fracture spacing by using a two- dimensional DEM program. And hydraulic EDZ (hydraulic aperture changed zone) was considered in a three- dimensional DFN model. According to the numerical analysis, the hydraulic aperture change induced by the hydraulic- mechanical interaction becomes one of the most important factors influencing the hydraulic behavior of jointed rock masses.
The excavation damaged zone (EDZ) is generally defined as the zone beyond the excavation boundary where the rock has been significantly disturbed and/or damaged due to the excavation and re- distribution of stresses (Winberg 1991). Various studies have investigated EDZ (Sato 1998; Shen etal. 1997), with most studies focusing on the mechanical behavior of EDZ using in situ experiments. Even though the EDZ could potentially form a highly permeable pathway for groundwater flow, only a few studies have analyzed groundwater flow in EDZ. In the following, we shall examine the zone adjacent to the excavation where the hydraulic aperture changes by using hydraulic- mechanical coupling analysis. In order to investigate the influence of the hydraulic aperture change, we have employed a numerical analysis using a discrete fracture network (DFN) which can simulate groundwater flow through three-dimensional discrete fractures. DFN approach is widely used in flow monitoring to evaluate the groundwater flow. In the DFN model, however, fracture aperture does not change as time and stress re-distribution after excavation. In view of this, H-EDZ was considered in a three- dimensional DFN model in this paper.
We define a ‘hydraulic excavation damaged zone (H-EDZ)’, the zone adjacent to the excavation where the hydraulic aperture has been changed due to excavation. This hydraulic aperture (e) can be obtained from the flow tests using the modified form of Darcy's law and determined both from laboratory fluid- flow experiments, and bore-hole pump tests in the field (Olsson et al. 2000).
(Equation in full paper)
Shen & Barton divide the EDZ into three zone by using distinct element method; (1) the failure zone, where loose rock blocks are falling into the tunnel; (2) the open zone, where joints open up; (3) the shear zone, where joints experience a certain shear displacement (Shen et al. 1997). In a view of this study, we completed a numerical analysis that investigated the behavior of the hydraulic aperture near the cavern for different stress rations, initial apertures.
