Due to the insufficient research on the stress relaxation characteristics of the nonholonomic hard rock

the stress relaxation tests were carried out on the gabbro specimens with pressure relief holes and rock burst tendency. The tests included the modes of pre-peak loading

relaxation and reloading

and re-relaxation. The pre-peak stress relaxation characteristics

relaxation model and ultrasonic variation law were obtained

and the mechanism of pressure relief hole in the stress relaxation process was revealed. Results showed that the stress relaxation process of hard rock with pressure relief holes experienced three evolution stages of rapid attenuation

attenuation and stability. With the gradual increase of pre-peak loading

the stress relaxation degree generally increased

the energy dissipation increased

and the proportion of energy used for damage and fracture evolution of hard rock increased. The deformation

damage

and fracture of hard rock in stress relaxation process can be reflected by the comparative analysis of the wave velocity

wave amplitude and waveform. The Burgers model can better express the stress relaxation characteristics of hard rock with pressure relief holes. Compared with the stress relaxation testing results of intact gabbro specimens

the hard rock containing pressure relief holes had higher stress relaxation degree

greater energy dissipation

and faster dissipation velocity. The research results provide significant guidance and reference for the long-term stability analysis

rock burst prediction and solution of hard rock with or without pressure relief holes.