The Effects Of Mechanical Damage And Temperature On Flow And Transport Behaviors Of Rock Fractures

Deep underground projects,such as underground disposal of high-level radioactive wastes,enhanced geothermal systems,and CO₂ geological sequestration commonly involve the complex coupled deformation/damage-temperature-flow-transport processes in fractured rock masses.A better understanding of the space-time evolution of the coupled flow-transport processes in fractured rock masses is the important theoretical basis for the safety assessment of deep underground projects.In this thesis,Beishan granite in the preferred preselected area for high-level radioactive waste geological repository,Gansu,China,was studied.Characteristics of shear-induced asperity degradation and effects of temperature on fracture permeability and solute transport were experimentally studied.The main results achieved are as follows:?1?The characteristics of shear-induced asperity degradation on fracture walls were revealed,and a new fracture damage coefficient was proposed.During shear an instantaneous asperity failure first occurs at the peak shear stress,and then the produced fragments are seriously crushed with increasing shear displacement.The asperity degradation factor is found to increase with the normal stress.The size distributions of the sheared-off fragments under different normal stresses can be fitted by the Weibull distribution.?2?The effect of temperature on fracture permeability is revealed.The results showed that creep has a certain influence on fracture permeability,and temperature has a great influence on fracture permeability.Under cyclic temperature,the change of fracture permeability decreases with the increase of the number of cycles.?3?The effects of fracture asperity degradation and temperature changes on the flow-transport processes were quantitatively examined in fractured rock.The shear-induced asperity degradation significantly increases the values of the solute retardation coefficient,by offering more sorption surfaces in factures owing to sheared-off fragments,thus effectively preventing the solute migration.As the temperature rises,the hydraulic aperture of the fracture decreases,so that the fracture permeability decreases,and the solution flow rate and the solute migration velocity decrease consequently.