Numerical Simulation Study on the Construction and Bearing Characteristics of Soft Rock Tunnel-Type Anchorages

To explore the impact of soft rock tunnel-type anchor construction and main cable tensioning on surrounding rock and surface deformation, relying on the tunnel-type anchorages project of BDC Yangtze River Bridge, Numerical modeling was employed to analyze the mechanical effects under the conditions of anchor hole excavation, anchorage plug body casting, and anchor bearing using FLAC3D. The results show that: (1) After the anchor hole excavation, part of the rock body yielded, resulting in the appearance of a tensile stress zone in the vault and bottom plate at the catwalk. Surface deformation primarily occurred during the catwalk excavation stage. (2) The casting of the anchor plug body caused the surrounding rock to have clamping effect on the anchor plug body, and the anchor plug body had little effect on the surface buildings. (3) The displacement and surface deformation of the anchor plug body increase with the increase of the tension in the primary cable; under the same tension, the displacement of the measuring point which is farther away from the horizontal distance of the anchorage plug unit is smaller, and the displacement between the two anchors by the superimposed stress is the largest. (4) Under the main cable design load (1P), the adjacent rock is in a condition of compression. The tensile stress is mainly distributed in the structure of the anchor body, and the nearby rock is almost not damaged; as the load progressively increases, the adjacent rock in contact with the tunnel anchor arch and sidewall gradually appears in the area of shear damage zone. Until the 11P load, the shear damage zone of surrounding rock between the two anchors is penetrated.