Abstract
As most rocks are of an anisotropic nature, the measurement elastic modulus of anistropic rocks is of general interest. Nevertheless, uniaxial compression test is common method to measure the dynamic elastic constants of anisotropic rocks; the use of ultrasonic pulse test is attractive, because the test is non-destructive and easy to apply. This study aimed to demonstrate the influence of orientation of foliation planes of banded amphibolite rocks on the compressional (Vp), shear wave (Vs) velocities propagating and elastic modules using ultrasonic pulse test. The result showed that the planes of foliation have a major effect on the wave velocity, where the Vp and Vs were taken parallel to the foliation plane show higher values than those obtained in the other directions (β = 30。, 60。 and 90。). The preliminary conclusions are developed concerning that the elastic modulus is vary continuously as a function of cleavage orientation with respect to the direction of wave propagations, where Poisson’s ratio having the smallest relative change. The highest values of Young’s modulus and shear modulus are observed for foliation dip angles of 0? and the lowest values are for foliation dip angles of 90。. This indicates that the observed intrinsic anisotropy and the close relations of the directional dependent seismic anisotropy to the foliation planes are mainly a result of crystallographic preferred orientation of major minerals (e.g. horn- blende and elongated quarts grains).
Highlights
By adopting both theoretical and experimental approaches, several authors reported that the anisotropy of metamorphic rocks plays crucial role in the planning and design of civil and mining engineering structures [1]-[7]
It is obvious that the planes of foliation have a major effect on the wave velocity, where the Vp and Vs taken parallel to the foliation plane show highest values than those obtained in the other directions (β = 30 ̊, 60 ̊ and 90 ̊)
Precise measurement of compression and shear velocities of anisotropic rocks by ultrasonic pulse test make the basis for the general assessment of static elastic constants in the initial design stage in geotechnical and mining engineering
Summary
By adopting both theoretical and experimental approaches, several authors reported that the anisotropy of metamorphic rocks plays crucial role in the planning and design of civil and mining engineering structures [1]-[7]. In such rocks, preferred orientation of minerals and cracks are highly anisotropic to seismic waves. Twenty-four rock samples were prepared using large size blocks of banded amphibolite, which were collected from varied rock slopes along Chengdu-wenchuan highway in Sichuan province in china for laboratory investigation. These rocks were selected due to their high rock-fabric complexity and their high significance impact in rock engineering design. The density is determined for core specimens following the standard test procedures outlined in [18] (Table 1)
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