Strength Weakening Effect of High Prestatically Loaded Marble Subjected to Low-Frequency Dynamic Disturbance under Point Load

Abstract

The deep high prestatically loaded rock is often subjected to low-frequency dynamic disturbance and exhibits unusual strength characteristics, and thus, it is important to investigate the strength characteristics under the coupling effect of prestatic load and low-frequency dynamic disturbance loading conditions. In this study, a series of point load tests were conducted on the high prestatically loaded marble subjected to low-frequency disturbance by the MTS system, focusing on exploring the role of prestatic load level and low-frequency disturbance frequency in the process of rock strength change. Based on the average static failure load (Fmax) of samples under the static point loading, the high prestatic load levels (Fp) were selected as 70%, 80%, and 90% of Fmax, the corresponding low-frequency dynamic disturbance was loaded by sinusoidal waves with amplitudes of 60%, 40%, and 20% of Fmax, and the low-frequency dynamic disturbance frequencies (f) are 1, 2, 5, and 10 Hz. The change curve of the point load strength with the prestatic load level or the disturbance frequency was analyzed, which indicates that the point load strength under the coupled high prestatic load and low-frequency dynamic disturbance load was significantly lower than that under the pure static loading, presenting a significant point load strength weakening effect. Only when Fp or f reaches a certain level, the point load strength decreases significantly as f or Fp increases. Moreover, the point load strength weakening rate was proposed to characterize the degree of strength weakening. The comprehensive analysis demonstrates that Fp has a greater effect on the point load strength weakening effect than f, which is mainly reflected in the point load strength weakening level dominated by the Fp, and the weakening degree is affected by f.