The Study Of Relationship Between Wave Velocities And Hydrostatic Confining Pressure Based On General Acoustoelasticity Of Rocks

Due to the inaccessibility in deep earth,natural or artificial seismic waves have become one of the reliable means to investigate the structure composition and stress state of the earth.Comparing the measured ultrasonic wave velocity under certain confining pressure with the wave velocities from seismic wave yields the composition and structure of deep earth,which relates to the quantitative relationship between rock velocity and hydrostatic confining pressure.At present,this quantitative relationship is mainly from statistical fitting of laboratory measurement of ultrasonic wave velocity data under certain confining,where fitting parameters are lack of clear mechanical significance.The main purpose of this thesis is to investigate the quantitative relation model between wave velocities of rocks and hydrostatic confining pressure based on general theory of acoustoelasticity and nonlinear constitutive relation,where unknown parameters in this model has clear mechanical significance.This study will benefit the composition determination of deep earth and the evaluation of crustal stress.In this thesis,acoustoelastic theory of and thermo-acoustoelasticity for rocks are given firstly.Secondly,general quantitative relationship between longitudinal-and shear-wave velocities and hydrostatic confining pressure are deduced by introduction of nonlinear constitutive law of rocks considering the effects of pore/fracture and general acoustoelasticity of rocks.This general quantitative relationship could be simplified further into a coupled model for the relation between longitudinal-and shear-wave velocities and hydrostatic confining pressure,whose unknown parameters are related to elastic constants of rocks.The application of the proposed coupled model into the fitting of the measured ultrasonic longitudinal-and shear-wave velocities of rock samples under hydrostatic confining pressure of rock and comparison with conventionally uncoupled model verify the validity of the proposed coupled model.The results show that the proposed coupled model could fit better physically the measured wave velocities for ultrasonic longitudinal and transverse waves for most rock samples subjected to hydrostatic confining pressure and give more reasonable parameter estimation.Third,introduction of the influence of temperature into nonlinear constitutive relation of rocks considering the influence of pores/fractures,the general quantitative relationship of longitudinal and shear wave velocity and temperature is deduced based on general acoustoelastic theories of rocks,which could be simplified into the coupled model of longitudinal-and shear-wave velocities and temperature.We verify the validity of this proposed coupled model by the fitting of the measured ultrasonic wave velocities of rock at different temperatures,which shows that the fitting result of the coupled model is better than that of the conventionally linear model.Finally,based on the general quantitative relationship between the longitudinal-and shear-wave velocities of rocks and hydrostatic confining pressure,the elastic constants of rocks and the relevant parameters for cracks or porosity of rocks could be given by the fitting analysis of measured data,where we discuss the applicability of the coupled model by Comparison with the results from the proposed coupled model.In conclusion,the relationship between rock wave velocity and hydrostatic confining pressure based on the genenral theory of rock acoustoelasticity has been investigated in this thesis,which gives the following new results:1)Based on the general quantitative relation between wave velocities and hydrostatic confining pressure from general acoustoelasticity of rocks and nonlinear constitutive of rocks considering the influence of pores/fractures,a new coupled model of longitudal-and shear-wave velocities and hydrostatic confining pressure is given,whose unknown parameters have clear mechanical interpretation and the more explicit statistical significance.2)New coupled model of longitudinal-and shear-wave velocities and temperature are given by introduction of the influence of temperature into nonlinear constitutive relation of rocks considering the influence of pores/fractures and general acoustoelastic theories of rocks.3)A new method for the elastic constants of rocks and the relevant parameters for cracks or porosity of rocks are presented based on general quantitative relationship between the longitudinal-and shear-wave velocities of rocks and hydrostatic confining pressure.