Abstract: The monitoring of bolt strain in the model test is relatively difficult for its small size. To solve the problem, the optical fiber Bragg grating sensing technology is applied to the tunnel model test. By constructing tunnel model test based on the actual working conditions of four typical sections in the metro line 2 in Xi’an, the strain of bolts in different stress states can be monitored by the fiber Bragg grating (FBG) sensors sticked to the bolt surface which are packaged by own design. According to the recorded data of five stress states: before the tunnel excavation, after the tunnel excavation, after lining, crack limit state, destruction limit state, the change law in the loading process of anchors axial force in the tunnel is obtained. Test results show that the anchor force has certain change before and after the excavation.After lining the axial force of anchor is increased with the increase of rock pressure. After lining the bolt pressure near the vault begin to decrease, the bolt tension from spandrel to corner begin to increase; the axial force of bolts in the larger water content loess is higher than in smaller ones. It is shown that the method presented provides a new and reliable approach for monitoring bolt strain in the model test.

Key words: fiber Bragg grating, tunnel model test, strain, temperature compensation