Waveform Effect on Fatigue Properties of Intact Sandstone in Uniaxial Cyclical Loading: Fid-Bau Portal

Waveform Effect on Fatigue Properties of Intact Sandstone in Uniaxial Cyclical Loading

Bagde, M.N. / Petros, V.

Rock formations as well as rock structures are subjected to both static and dynamic loads. Static loads result from such sources as tectonic and gravity forces. Small dynamic loads are continually propagated through natural vibrations of the earth's crust. Large dynamic forces are intermittently applied through major earthquakes, rock bursts, rock blasting, drilling, traffic etc.. The mechanical behaviour of rock under static loading has been thoroughly investigated. However, rock reaction to the cyclic, repetitive stresses resulting from dynamic loads has been generally neglected with the exception of a few rather limited studies. The effect of loading waveform and amplitude on the fatigue behaviour of intact sandstone was investigated using uniaxial cyclic loading conditions in the laboratory. In the first set of experiments sinusoidal, ramp and square waveforms were used at loading frequency of 5 Hz and peak amplitude of 0.05 mm. In another set of experiments, tests were conducted at a range of amplitudes varying from 0.05 to 0.3 mm at 5 Hz frequency using sinusoidal and ramp waveforms. It was found that loading waveform as well as amplitude is of great significance and affects the rock behaviour. It was found that fatigue behaviour is a function of the cyclic energy of the load and the shape of the waveform. Damage accumulated most rapidly under square waveforms with a high energy requirement. A ramp waveform was the least damaging of those considered. The loading waveforms strongly influenced the damage accumulation under cyclic loading conditions. Finally, it is concluded that machine behaviour in terms of amplitude affected the rock behaviour. This study has practical significance to the behaviour of rock and rock masses within the excavation systems subjected to cyclic loading.