Abstract: To explore the support effect and applicability of system bolt in moderatelyweathered mudstone tunnel, field comparative tests with and without system anchor are conducted by taking a deepburied largespan tunnel project as an example. The variation patterns of surrounding rock deformation, surrounding rock pressure, shotcrete stress, axial force of anchor bolt, and contact pressure between primary support and secondary lining are analyzed under different working conditions. Further, the support effect of the system bolt is examined from the aspects of construction safety and economy. The results show the following: (1) The system bolt slightly affects the deformation of surrounding rock and the mechanical properties of lining structure in moderatelyweathered mudstone formation. (2) The application of the system bolt prolongs the closing time of the surrounding rock, thus the deformation of the monitoring section of the surrounding rock with system bolt is greater than that without system bolt. (3) The maximum axial force of the bolt monitored on site is only 3.40 kN, which fails to give full play to its bearing capacity under such formation. (4) The monitoring results of various indexes show that the support effect of system bolt is limited, and the removal of system bolt can reduce the secondary disturbance to surrounding rock, shorten the closing time of surrounding rock, and effectively control the deformation of surrounding rock. (5) In the case of ensuring the safety of the tunnel, the economic benefits of removing the system anchor are also significant.

Key words: highway tunnel, moderatelyweathered mudstone, system bolt, field test