Wave Propagation in Rocks – Investigating the Effect of Rheology

Authors

  • Tamás Fülöp
    Affiliation

    Department of Energy Engineering, Faculty of Mechanical Engineering, Budapest University of Technology and Economics, Bertalan Lajos 4–6, 1521 Budapest, Hungary

https://doi.org/10.3311/PPci.16096

Abstract

Rocks exhibit beyond-Hookean, delayed and damped elastic, behaviour (creep, relaxation etc.). In many cases, the Poynting–Thomson–Zener (PTZ) rheological model proves to describe these phenomena successfully. A forecast of the PTZ model is that the dynamic elasticity coefficients are larger than the static (slow-limit) counterparts. This prediction has recently been confirmed on a large variety of rock types. Correspondingly, according to the model, the speed of wave propagation depends on frequency, the high-frequency limit being larger than the low-frequency limit. This frequency dependence can have a considerable influence on the evaluation of various wave-based measurement methods of rock mechanics. As experience shows, commercial finite element softwares are not able to properly describe wave propagation, even for the Hooke model and simple specimen geometries, the seminal numerical artefacts being instability, dissipation error and dispersion error, respectively. This has motivated research on developing reliable numerical methods, which amalgamate beneficial properties of symplectic schemes, their thermodynamically consistent generalization (including contact geometry), and spacetime aspects. The present work reports on new results obtained by such a numerical scheme, on wave propagation according to the PTZ model, in one space dimension. The simulation outcomes coincide nicely with the theoretically obtained phase velocity prediction.

Keywords:

rocks, Poynting–Thomson–Zener rheological model, wave propagation, phase velocity, group velocity

Published Online

2020-09-28

How to Cite

Fülöp, T. “Wave Propagation in Rocks – Investigating the Effect of Rheology”, Periodica Polytechnica Civil Engineering, 65(1), pp. 26–36, 2021. https://doi.org/10.3311/PPci.16096

Issue

Section

Research Article