In order to obtain the relationship between the characteristics of acoustic emission (AE) and the unloading state of surrounding rock during roadway excavation

AE monitoring test was carried out during excavation unloading with three different unloading rates using thick-walled cylinder roadway surrounding rock samples made of cement mortar. The self-developed tunnel test system of excavating and unloading of small roadway surrounding rock is equipped with AE system and deformation monitoring system to collect AE time-frequency signals and deformation information of samples during the unloading process. In addition

the b values were also studied. The results show that: 1) The test process has four stages: loading stage

maintenance stage I

unloading stage and maintenance stage II. These four stages correspond well to the cumulative ringing curve. 2) In the loading stage

there are many high frequency and high amplitude signals

and the distribution range is wide. The original crack in the sample is obviously compacted under the pressure of three-direction. After that the high frequency and amplitude signals reduce obviously and the distribution range is also reduced

the sample continues to be compacted under three-direction

and the deformation is small. In the third stage

the signals with high and low frequency and their amplitude increase. The strain rate is high and the deformation increases rapidly

the unloading effect is more significant accordingly. In the maintenance stage II

the high-amplitude signals continue to increase

and the deformation of the inner and outer sides increase continuously with lower speed

when the unloading speed is slow. 3) The bigger the unloading speed is

the higher the amplitude of "steep rise" appears in the ring cumulative curve of the unloading stage

the earlier the amplitude of "steep rise" appears in the ring cumulative curve of maintenance stage II

the smaller the amplitude is. 4) With the increase of unloading rate

the magnitude of b value tends to decrease and varies steadily as a whole

which indicate that the proportion of big AE events are increased

and the fracture scale is larger.