ABSTRACT
The research was performed to assess the effects of loading frequency on mechanical characteristics of the Khao Ya Puk Formation sandstone in the northern part of Thailand. The aims of this research are to assess fatigue behaviour and compare stress-strain deformation in rocks at varying frequencies. Sandstone specimens were tested using a compressive strength test subjected to cyclic loading conditions with loads of 50, 60, and 70% of ultimate loads and frequencies of 4, 2, and 1 Hz. The results show that the relationship between the number of cycles and the residual strain can be divided into 3 stages: the first stage with gradually increasing strain rate; the second stage or the stable stage with a constant strain rate; and the last stage or the accelerated failure stage with rapidly increasing strain rate. It was found that, when the rock sample was subjected to compression, the axial strain changed more slowly than the lateral strain and volume strain. In the case of constant frequency, the findings reveal that not only the rising-stress amplitude, axial strain, and lateral strain are increased, but also the volume strain. Furthermore, the result shows that the stress amplitude increases when the number of fatigue cycles decreases.
