Numerical Investigation Of Formation Mechanism And Process On Excavation Disturbed Zone (EDZ) Of Tunnel

In the design and construction of underground laneway, we not only concern the size and direction of ground stresses before the laneway is excavated, but also more pay attention to the state of the stress redistribution of the surrounding rock induced by excavation. In the stress analysis of the surrounding rock of the laneway, theoretical analysis may give the stress distribution at the surrounding rock in circular or elliptical roadway. Finite element method has extensive flexibility, may consider some complex laneway with arbitrary shape, and gives the stress distribution at the surrounding rock. Knowledge of the stress distribution as well as the deformation and failure process of roadway pays an important role in controlling the roadway stability and selecting appropriate support parameters.Theoretical analysis for the rock stress surrounding the roadway of circular or elliptical roadway subjected to different ratios between pressures in horizontal and vertical directions is carried out by using elastic theory. The equation of tangential stress around the roadway boundary is given, and stress distribution around boundary of the circular and elliptical roadway is summarized. The figures of tangential stress distribution around the boundary of elliptical roadway with different lateral pressure coefficient are drawn. According to finite element atlas of underground engineering analysis, the stress distribution of surrounding rock of the arch laneway is calculated. The figures of stress distribution at the surrounding rock of laneway are drawn. The distribution rules of tensile stresses and compressive stresses around the roadway boundary are summarized. When a tunnel or an underground structure is excavated in rock mass, rock disturbed or damaged zone (EDZ) is formed around the tunnel due to the stress concentration resulting from stress redistribution. Recent studies on the rock EDZ revealed its important to structural stability around underground opening. In this study, the fracture and damage mechanisms of rock induced by the accumulation of microcracks were investigated by AE tests.The results of the experiments showed that tensile failure was the major microscopic failure mechanism of rock in excavation damaged and distrubed zone. The damage of tunnel surrounding rock masses usually results from the redistribution of stress indisturbed rock mass in tunnel excavation process. The excavation-disturbed zone (EDZ) is defined as the rock zone where the rock properties and conditions, such as fracture, stress and hydraulic aperture, have been changed dueto the processes induced by excavation.EDZ is considered to be physically less stable and can form a continuousand highly permeable pathway of groundwater flow. The characterization of EDZ will affect tunnel supportstructure design, tunnel construction and tunnel surrounding rock mass stability analysis. Seismic surveytechniques can be, used to examine the nature of EDZ around the tunnel.Based on the concept of EDZ and theprimary factors that lead to the change of rock properties, a methodology is proposed to depict mechanical andhydraulic behavior of EDZ. By using the in-situ data, deformability and hydraulic properties are studied bynumerical analysis. The results show that the excavation damage depends on the excavation method. In addition, the influence boundary of the excavation-disturbed stress zone is smaller than that of the seepage. Therefore, theseepage boundary condition should be emphasized in establishing the coupled fluid-solid numerical models. Theresults will make the establishment of coupled fluid-solid model more reasonable.