The self-developed stress relaxation-dynamic disturbance test apparatus was used to measure the axial stress

axial strain and acoustic emission of rock subjected to loading and stress relaxation

dynamic disturbance. From the experimental results

it was found that the stress of rock specimen declined and its strain increased after the dynamic disturbance. In addition

the characteristics of sandstone were more obvious than that of granite. The preliminary study suggests that one reason for this phenomenon is likely related to the irreversible damage in the rock during the stress relaxation-disturbance process. Another reason is related to residual strain induced by the dynamic disturbance. During initial compaction and elastic phase

it is found that AE hits seldom occurs

while in the peak near the peak stress

AE hits instantly increases; during stress relaxation phase

the AE hits decrease

and it may increase instantly when triggered by dynamic loading. Clearly

the acoustic emission signal is induced by the damage evolution of rock

thus the AE data may reflect that the induced rock damage is one reason for the phenomenon of stress decline and strain increase. In addition

the quasi-static cycling loading and unloading test is conducted to quantify the residual strain of rock under the different loading levels. The residual strain in sandstone specimen is much larger than that in granite specimen

which corresponds well with the obvious phenomenon of stress decline and strain increase. In addition

the residual deformation increases with the rising initial unloading deformation both in stress relaxation-disturbance testing and quasi-static cycling loading and unloading test. Also

it should be mentioned that

the damage in rock is closely associated with residual strain

thus the both the rock and residual deformation may contribute to the phenomenon of stress decline and strain increase of rock specimen during stress relaxation-dynamic disturbance test of rock.