Research On Deformation And Acoustic Emission Characteristics Of Dry And Saturated Rock Fractures Subject To Normal Stresses

In recent decades,global warming has been intensifying,replacing part of the use of fossil fuels with renewable energy sources and reducing greenhouse gas emissions are effective measures to slow down global warming.Compared with other renewable energy sources,geothermal energy has the advantages of good continuity,huge resources,zero emissions,and wide geographical distribution,and has huge development potential.The rock fracture network in geothermal reservoirs is in a complex geological environment.Quantitative description of the deformation and failure behavior of rock fractures under various conditions is the basis for various studies related to the mechanical behavior of rock fractures,which is helpful to solve the problem of local problems.Various related problems encountered in thermal energy mining have important theoretical significance for other deep resource development,water conservancy and hydropower and tunnel projects.At present,a large number of studies have been carried out on the deformation and failure behavior of rock fractures,and there have been relatively rich scientific research results.However,the research on the characteristics of deformation and failure of rock fractures under compression lacks in-depth discussion on the combination of macroscopic stress-displacement relationship and micro-contact deformation and failure.At the same time,the impact of rock dry and saturated conditions is less considered,and there are few studies on the application of elastic-plastic contact models.In this study,through uniaxial compression test and elastic-plastic contact numerical calculation,the deformation and failure behavior of two different rock fractures under dry and saturated conditions were studied,and the acoustic emission signal during the test was collected and analyzed.The main conclusions obtained from comprehensive analysis of the data are as follows:(1)The elastic-plastic numerical calculation and test results based on the contact between the fracture surfaces have a higher degree of matching on the normal stress-normal displacement relationship curve.The normal displacement shows a nonlinear growth relationship with the slope gradually decreasing with the increase of normal stress.At the same time,the location of the damage area obtained by the test measurement,the location of the damage area obtained by the numerical calculation and the acoustic emission location are basically the same,indicating that the calculation and measurement methods used in the study have high accuracy.(2)The mean increment of plastic deformation is negatively correlated with the stress,and the magnitude of its decrease decreases with the increase of the stress,indicating that the damage mainly occurs on the sharper contact body at the initial loading stage,and as the contact area increases The stress changes from concentration to dispersion,and the amount of damage gradually stabilizes.Through fitting,a formula between the two is established,and the control effect of fracture mechanics and geometric characteristics on plastic damage is explained.(3)Within the stress range involved in this study,the longitudinal wave velocity and the normal stress show an approximately linear growth relationship.The dispersion of longitudinal wave velocity of granite is smaller than that of red sandstone.After the rock sample is saturated,the dispersion of longitudinal wave velocity will be further reduced.Dislocation fissures reduce to a certain extent the influence of P-wave velocity,its increase and the water content on its dispersion.(4)Due to different factors such as rock structure,porosity,mineral composition and properties,granite is less affected by water softening than red sandstone.The presence of water not only changes the mechanical properties of the rock,but also causes the acoustic emission response to weaken.(5)Although the acoustic emission characteristics of each rock under dry and saturated conditions are different,the overall laws are basically the same.The acoustic emission ringing count,cumulative count,and signal amplitude of granite are higher than those of red sandstone,and the ringing count has a good corresponding relationship with the numerically calculated plastic deformation.Although the peak value of the acoustic emission ringing count of the red sandstone sample is not as obvious as that of the granite,the change trend has the same law as that of the granite.