Abstract: During the tunnel boring machine (TBM) excavation of tunnel engineering, the soft-hard composite strata are widely encountered. Under the action of TBM cutters, the failure characteristics of soft-hard interbedded rock mass are clearly different from those of the homogeneous rock mass. By using the RMT-301 rigidity testing machine, fracture tests were carried out on rock-like specimens with various combinations of soft-hard interbeds. The monitoring data by acoustic emission (AE) and a high-speed camera were recorded as well during the testing process. Furthermore, we discussed the effects of the soft-hard interbed on rock breaking by the TBM cutter along its axial direction. Testing results show that the degree of rock fragmentation by TBM cutters was not only affected by properties of the cutter-acting layer but also strength ratio of the cutter-acting layer to the pressure-bearing layer. The spalling zone found in the plate specimen revealed the compressed plastic zone under the action of cutters. When the cutter-acting layer was the same but with a softer pressure-bearing layer, a greater crushing scope was observed in the cutter-acting layer along the direction perpendicular to the tool penetration. The characteristics of aggregation distribution were found on the plane localization point in the AE events of the plate specimen. In the aggregated area, the cutter-acting also exhibited a tendency to perpendicular to the loading direction of the cutter, when materials of the pressure-bearing layer changed from relatively hard to soft. Thus, it is proved that the distribution of the AE plane location to great extent reflects the damage degradation inside the specimen.

Key words: tunnel boring machine (TBM), acoustic emission (AE), high-speed photography, soft-hard interbed, stress distribution