Predicting fatigue strength of rocks by its interrelation with the acoustic quality factor

• Studies of interrelations between rock strength and acoustic quality are scarce.
• Such interrelations provide prediction of geomaterial strength without destruction.
• Interrelations “strength – acoustic quality” of rocks can be got by fatigue tests.
• Fatigue rock manifest both softening and hardening.

This paper presents findings regarding the interdependence of acoustic quality Q-factor and fatigue strength studies for specimens of sedimentary (limestone and travertine), eruptive (gabbro), and metamorphosed (marble) rocks. Test techniques included measurements of Q by resonance spectroscopy through sonic test, damage by mechanical load/unload cycles of number N, and measuring ultimate strength under uniaxial compression. Upon Q-factor measurement, the first specimen of each series was loaded to destruction to determine ultimate strength. Subsequent specimens underwent cyclical fatigue loading. Thereafter, Q-factor and residual strength of the rocks were measured. For sedimentary and eruptive rocks, strength and Q-factor reduction with an increase of load cycle number is observed. For metamorphosed rock their further increase with subsequent N increase is observed. The experimental results enabled establishment of regressional relationships between Q-factor and strength described by logarithmic function. The relationships may be used for predicting rock residual strength without their destruction by Q-factor measurement.