Study On Formation Mechanism Of Excavation Disturbed Zone Of Hard Fractured Rockmass

To explore the means for the determination of excavation disturbed zone (EDZ) of rock slope and its related theoretical problems, multiple methods are used to investigate the EDZ and its rock mechanical behaviors for the high slopes in Three Gorges Project (TGP). Major work and its characteristics are summarized as follows:(1) Based on multiple in-situ tests and field monitoring for EDZ in TGP, in which its zoning models and criteria are established, and weakening extent for its mechanical behaviors evaluated. Based on the engineering geological survey, a probability model of joint network is established in 3 dimensions by using the direct method to generate random number, and the deformation analysis of rock mass under unloading condition is carried out using 3 Dimensional Distinct Element Code (3DEC) to simulate joint opening phenomenon in the middle isolated pier of the permanent shiplock slope in TGP, and it is found that rock mass deformation mainly exhibits joint opening, especially steep dip joint opening. Then, studies on opening characteristics and failure mechanism of steep dip joint are carried out.(2) For the Three Gorges granite specimens, the conventional triaxial compression and the confining pressure reduction test under constant axial strain and stress are carried out. The deformational characteristics and failure model of brittle rock under different stress paths or different loading control modes are studied; and it is found that the crack initiation stress changes at the same extent with confining pressure, and comparing with the peak strength,the crack initiation stress is generally located between 25% and 50% of the peak strength. Through experimental and theoretical analyses, the result shows that the microcosmic failure of Three Gorges granites is mainly induced by tensile cracks under uniaxial and triaxial compressive conditions; and the cracks inside the granite belong to I-mode fracture in stable crack growth stage; In the post-peak strain softening process, the value of c decreases with the increasing of generalized plastic strain, while the value of ? keeps constant.(3) Based on the analysis of the complete stress-strain curves and the damage mechanism of the Three Gorges granite, it is put forward that the brittle rock mainly occurs lateral damage and exhibits the similar damage evolutionary rule under different stress paths and loading control modes; and the critical failure generally occurs at a damage variable level of 0.7 to 0.8. Finally, a damage model considering the unloading effect and a failure criterion in strain space are established, in which the lateral damage variable is seen as a critical variable.(4) One back analysis model of mechanical parameters is established by using orthogonal design theory, least squares support vector machines and particle swarm optimization, and the relative mechanical parameters of damage model are back analyzed. Then, the construction and excavation process of the permanent shiplock slope in TGP is simulated by three-dimensional fast Lagrangian method (FLAC3D).(5) Based on the tests and monitoring of EDZ, critical criteria of shear strain and element safety factor for the permanent shiplock slope in TGP are established. Distribution region of EDZ and mechanical behaviors of rock mass are further evaluated by using damage model, and the result shows that damage variable is 0.6-0.8 for damaged zone (DZ), 0.4-0.6 for affected zone (AZ) and 0.2-0.4 for slight affected zone (SAZ). Finally, the slope excavation softening factor is introduced to Hoek-Brown empirical strength criterion, based on the deficiencies of using Geological Strength Index (GSI) to estimate the rock mass mechanical parameter of EDZ.