Model test on the bearing behaviors of the tunnel-type anchorage in soft rock with underlying weak interlayers

Abstract

The stability of tunnel-type anchorages is related to the stratum lithology and geological conditions of the anchorage sites. The bearing behavior of tunnel-type anchorages in soft rock with underlying weak interlayers is analyzed in this work using a field model test. Using FLAC3D, we investigate the effects of the geometric parameters (i.e., base angle, β, length, L) of plug bodies and the distance, D, between the right and left plug bodies on the stress states of weak interlayers. The results show four stages of surrounding rock deformation. Furthermore, the vertical displacement of the surrounding rock is less than that in the main cable force direction. In dealing with tunnel-type anchorages in soft rock with underlying weak interlayers, focus should be directed towards controlling the surrounding rock deformation in the main cable force direction. The surrounding rock in the postmedian plug body is the main bearing part of a tunnel-type anchorage. The final failure mode of tunnel-type anchorages in soft rock with underlying weak interlayers is similar to that of an inverted wedge body. Moreover, this final failure mode is slightly related to the plug body’s geometric parameters and the distance between the right and left plug bodies. The maximum tensile stress, tmax, inside the weak interlayer decreases as the distance, D, between two plug bodies (or length, L) increases, and it increases as the base angle, β, of the plug body increases. The parameter sensitivity of the plug body to tmax is ranked as β > L > D.