关键词: 厚壁圆筒围岩试样, 开挖卸荷, 声发射, 峰值频率, 幅度, b值

Abstract: 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.

Key words: thick-walled cylinder roadway surrounding rock sample, excavation unloading, acoustic emission, peak frequency, amplitude, b value