Description

Characterizing the elastic response from body waves propagating through an interbedded shale-sandstone geological formation with multiorientation joints and various interlayer ratios is extremely challenging. A laboratory composite model of three layers, i.e., sandstone-shale-sandstone, with multi-angled joint orientations, i.e., 30°, 45°, 60°, and 90°, provides an expressive approach to evaluate the anisotropic behavior of body wave velocities. In this study, body wave velocities were obtained from tests using the Portable Ultrasonic Non-Destructive Indicating Tester and the Free-Free Resonant Column. The anisotropic dynamic responses of the composite model are characterized in comparison to the intact shale and the intact sandstone. Empirically, as the joint orientation approached a perpendicular angle, both velocities of the P-wave (VP) and the S-wave significantly decreased. In comparison, the wave velocity values were reduced by 35% and 66% for VP and VS, respectively, as were the increment angles of joint orientation from 30° to 90°. The anisotropic behavior of wave velocity for the composite model appears to be influenced by the joint orientation rather than the bedded shale interlayer. The increase in elastic modulus and shear modulus values with respect to the increase in interbedded angles indicates that interbedded orientation has a signifcant influence on the stiffness behavior of the composite model. This result was supported by the decrement of Poissons ratio, measured as the increment of the interbedded angle of orientation. The experimental data is then utilized to develop a semi-empirical model to predict the wave velocity at any angle of joint orientation and at any interlayer ratio. 

Date Conducted

April 2021

Contributors

Hasan Abbas

Owned by organization

Geotechnical and Geological Engineering