Aiming at the insufficiency of hard rock stress relaxation characteristics and rock burst research

we carried out cyclic loading and unloading tests on stress relaxation process of straight-wall-top-arch roadways (tunnels) under low

medium and high loads

derived the stress relaxation law

established the stress relaxation model

and explored the stress relaxation mechanism. The test results show that the stress relaxation process of the straight-wall-top-arch roadways (tunnels) subjected to cyclic loading and unloading under a low load presents three evolution stages: rapid decay

gradual decay and stability

and the stress relaxation trends are consistent;

the time required for stress relaxation increases

and the degree of stress attenuation loss decreases as the number of cycles increases; the stress relaxation process under low load is a process of simultaneous attenuation of tensile and compressive stresses in the surrounding rock of roadway(tunnel)

with no internal damage and no overall rupture. Under a medium load

the stress relaxation process of straight-wall-top-arch roadway (tunnel) subjected to cyclic loading and unloading also presents three evolutionary stages similar to those under the low load; compared with low load scenario

the stress relaxation process lasts longer under the medium load and internal damage occurs

but subsequent cycles do not lead to surrounding rock failure. Under a high load

the surrounding rock of the straight-wall-top-arch roadway (tunnel) presents a continuous increase in tensile stress and a continuous decrease in compressive stress

the roadway (tunnel) continues to damage and rupture

and the side walls produce stratified burst

eventually forming a V-shaped burst crater

overall

two significant burst failures can be observed. The fractional-order calculus theory is used to describe the stress relaxation process under cyclic loading and unloading. A fractional-order model

namely the stress relaxation equation

is established

and the fitting effect is basically basically satisfactory. Furthermore

we define the degree of stress relaxation that fully can depict the whole process of stress relaxation and the degree of relaxation. Based on the findings of this paper

engineering measures should be taken to stop the deformation of the relaxation process of the rock explosion rock mass from developing to a critical state in engineering practice.