A study of the geostress field of the surrounding rocks of the Baota mountain tunnel and rock burst forecast

In order to determine the stress state of the surrounding rocks of the Baota mountain expressway tunnel , geostress measurements with the hydrofracturing method were carried out. Based on the testing results, the geostress field in the project area is analyzed with finite element and linear multivariable regression methods. The results of regression analyses indicate that the values of the maximum vertical principal stress are larger than the gravity stress along the tunnel axis. Vertical stress field is dominated in this area. Within the measured depths, the maximum horizontal stress ranges from 2.3 to 8.4MPa, and this stress level can be classified as a middle level. The dominant direction of the maximum horizontal stress is about N53°E, the angle between the direction of the maximum horizontal stress and the direction of the tunnel axis is relatively big for this tunnel，and is adverse to the stability of the tunnel and the surrounding rock mass. Based on the data of geostress， rock burst of the surrounding rocks of the tunnel during construction is analyzed and forecast. The results show that the possibility of weak and moderate rock burst in the tunnel exists and the moderate rock burst exists during construction in the complete and hard rock tunnel segments.