Model Test Study on‘Lost’Deformation and Corresponding Control Measures in Soft Rock Tunnels with Extremely High Ground Stress

In order to study the laws of core rock deformation and‘lost’rock deformation in soft rock tunnels with high ground stress, the deformations of core rocks in front of the working face and surrounding rocks are monitored by model test method, and the tunnel excavation process is simulated in detail under different high ground stress levels and working conditions with/without lining. The results show that: (1) the ground stress plays a key role in determining the installation time of soft rock tunnel support; (2) the advance deformation within 0.5D in front of the face accounts for about 2/3 of the total advance deformation; (3) the‘lost’deformation behind the tunnel face has a great impact on the monitoring and measurement. With a certain high ground stress, there is a power function relationship between the‘lost’deformation and the distance from the tunnel face. With the high ground stress greater than 20 MPa,it has little impact on the‘lost’deformation; (4) in order to effectively control the advance deformation in soft rock tunnels with high ground stress, it is necessary to reinforce the core rock mass within 0.5D in front of the tunnel face. For the core rock mass within 0.5D~1D in front of the tunnel face, the reinforcement depends on the actual situation.