Rock ultrasonic wave velocity and static deformation were measured simultaneously under triaxial loading to investigate the difference and correlation of rock static/dynamic elastic parameters. The results show that rock dynamic Young' s modulus is higher than the static one. The correlation of static/dynamic Young' s moduli is good. The static and dynamic Young' s modulus is about 0.6. The static and dynamic Poisson's ratios show some extent of positive dependence but the correlation is more discrete. There is also a difference of static/dynamic Bior's coefficients. The static one is higher than the dynamic one. They are all descrease with confining pressure. The inherent cause of static/dynamic difference is the crack-like pores and the pore fluid in rocks. the external cause is the strain amplitude and its frequency difference under static. And dynamic loading.
Rock elastic parameters, such as Young's modulus, Poisson's ratio and Biot's poroclastic coefficientare the primary input for rack engineering design and analysis. There are two kinds or measurement method of rock elastic parameters: dynamic and static method. Static test gives the static elastic parameters by measuring the rock deformation under compression, and the dynamic one gives the dynamic elastic parameters by measuring the elastic wave velocities through rocks. According to the real loading condition, usually static properties should be used in the analysis of rock engineering. But the static test needs rock samples cored from interested zone and special test apparatus sophisticated technology arc necessary for good result. The dynamic method has the advantage of simplicity, timesaving and cost saving. It can give us a continuous elastic parameter profile Under in-situ condition by acoustic logging or seismic. Rock is a multiphase composite medium. Its heterogeneity makes it response differently to dynamic and static load. To Study the correlation of rock static/dynamic elastic parameters and to find the way to determine rock elastic parameters by acoustic logging are very important. Evans (1973) conducted a group or static/dynamic simultaneous triaxial tests of oil and brine saturated Lueders limestones and Pecos sandstones. He found that static and dynamic Young's moduli show the similar regularity of variation with confining pressure.
In order to simulate the in-situ stress condition, the tests should be conducted under triaxial stress condition. At the same time, since rock elastic parameters are the function of stress history, so rock dynamic and static parameters comparison should be done under the same stress history. We built tip a set of test apparatus, which can achieve static/dynamic simultaneous measurement under triaxial stress condition. Triaxial cell is the core of this apparatus (Fig. I). Sample was scaled with rubber sleeve and installed in the triaxial cell. The axial stress, confining pressure and pore pressure can be continuously and separately controlled. The ultrasonic transducers were put on the top and bottom faces of the sample. The central frequencies of the ultrasonic transducers are 850 KHz (P-wave) and 450 KHz (S-wave).
