This paper made a research about the change rule of elastic wave velocity with stress applied on rock from theoretical and experimental aspect. Firstly, a mathematical model of P-wave velocity and confining pressure of rock was set up from the point of acoustoelastic character. Effect of axial stress on P-wave velocity in granite and sandstone during uniaxial compression process was studied experimentally by using GAW-2000 rock mechanical testing system and RSM-SY5 ultrasonic wave testing system, and the relation curves of axial stress with P-wave velocity were obtained. Based on test data, acoustoelastic theoretical formulas of granite and sandstone were established and the best empirical formulas were fitted by using regression method. Meanwhile, a comparative analysis of the empirical and theoretical calculated values was carried out. Finally, the reliability of applying acoustoelastic theoretical formula in hard rock range was further verified based on the experimental data of granitic gneiss. The results show that the P-wave velocity experiences a rapid increase, gentle increase and then a sharp fall during the uniaxial compression process. The B-value in acoustoelastic theoretical formula (proportion coefficient determined by elastic modulus and third-order elastic constant) decreases exponentially with axial stress. The acoustoelastic theoretical formula can effectively reflect the relationship between rock acoustic velocity and stress within the allowable error, which can be the theoretical foundation of acoustoelastic geo-stress measurement of subsurface rock mass. 相似文献
Accurate characterizations of rock strengths under higher loading rates are crucial in many rock engineering applications. The split Hopkinson pressure bar (SHPB) system has been used to quantify the dynamic compressive strength of rocks using the short cylindrical specimen and the dynamic tensile strength of rocks using the Brazilian disc (BD) specimen. However, SHPB is a standard tool that is suitable for metal testing; there are some fundamental issues that need to be carefully visited in applying SHPB to rock dynamic tests. This paper addresses several such critical issues, including the choice of slenderness ratio of the compressive specimen, the effect of friction between the sample and bars on the measured results of compressive strength, the necessity of dynamic force balance on the dynamic BD test, and the validity of using the standard BD equation in the data reduction. We show that with proper experimental designs that address these issues, the dynamic compressive strength and dynamic tensile strength of rocks measured using SHPB are valid and reliable. 相似文献
Pre-conditioning by hydraulic fracturing is a vital work in block caving mining of hard-rock metal mine, and breakdown pressure is one of the important parameters in rock hydraulic fracturing process, which determines the equipment selection and job-parameter control. Based on numerical simulation method, a pre-holed cylindrical hard rock sample was built for simulation of hydraulic fracturing process to investigate the effect of stress condition, rock properties and water injection rate on breakdown pressure. The results show that the breakdown pressure is increased with the confining stress, and the breakdown pressure is 2.28 times confining stress based on rock tension strength. The variation of rock tension strength affects the breakdown pressure and a positive linear relation exists. Pre-formed notch could obviously reduce the breakdown pressure and control the orientation of hydraulic fracture. And the borehole diameter has a reverse influence on rock breakdown pressure.
The nonlinearty of rock deformation results mainly from closing, opening, and propagation of microcracks or microviods inside rock. Taking the influence of microdefects into account, a new constitutive relationship of damage is developed, and applied to different models of rock with different porosities. The theoretical curves consist with the experimental ones. 相似文献