Study on the Evolution of Loose Circle of Tunnel Constructed by Blasting Excavation Considering the Schistose Angles

In order to investigate the evolution law of the loose circle during blasting excavation of schist tunnel, the range of the loose circle of the Niuluan Village tunnel was detected by geological radar method. The numerical simulation method was used to simulate the blasting excavation for several times for different inclination of the schist tunnel model to analyze the distribution range and evolution law of the loose circle. The results show that: The loose circles are not always symmetrically distributed along the contour, and the horizontal and vertical asymmetries are different. Due to the joint action of internal schist structure and external blasting excavation disturbance, the schist is easily damaged along the schist direction, and the loose circles are also easily developed along the schist direction. With the blasting excavation, the loose circles show a non-linear cumulative expansion, and the loose circles are not easily developed after four blasting excavations. After four times of blasting, the influence on the initial loosening ring is no longer obvious, and the cumulative degree of different parts of the tunnel is different. The use of geological radar can effectively achieve the detection of the extent of loose circle after multiple blasting excavation.