Effect of Joint Characteristics and Geometries on Tunnel-Type Anchorage for Suspension Bridge

In this study, the pull-out behavior of a tunnel-type anchorage was examined by considering both geometric and rock joint characteristics. Three-dimensional finite element analyses were performed with reference to the tunnel-type anchorage cases designed and constructed in Korea. The factors influencing the anchorage response were analyzed: the enlarged part, anchorage spacing, joint orientation, spacing, and the shear strength of the rock joints. According to the numerical studies, the size of the enlarged part influenced the failure shape of the tunnel-type anchorage. It was found that the anchorage spacing, the relationship between the tunnel-type anchorage, and the joint orientation and spacing greatly influenced the pull-out behavior of the anchorage. Additionally, the friction angle had a larger impact on the anchorage’s pull-out resistance than the cohesion between the rock joints.

Unloading Effect of the Shear Resistance of Rock Joints

To investigate the stress path dependent of rock joints, a comparative experimental study was conducted using cement mortar replicas of artificially split rock joints. In total, 32 replicas were casted and divided into four groups by joint roughness coefficient (JRC). The effects of morphologic characteristics, normal stress levels and stress paths on the shear strength of joints were investigated through tangential loading tests and normal unloading tests. The comparative analysis on the test results indicated that the shear resistance has a distinct unloading effect. The variation trend of shear/normal stress ratio against the normal stress and JRC of the two test conditions were identical. However, under low normal-stress condition, the stress ratio of the joints under normal unloading stress is the higher one; while under higher normal stress, the relationship becomes converse. Compared to that of the tangential loading condition, shear/normal stress ratio of the unloading stress path reduces rapidly as the increasing of normal stress, and the influence of the morphology is masked under lower normal stress. The comparative study revealed a previously unknown unloading effect on the mechanical behavior of rock joints and will aid the estimation of the rock joints’ stability in a complex stress environment.