Physical model test on the mechanical behavior and progressive failure of tunnel-type anchorages

This paper presents the results of tensile load tests performed with instrumented model of a tunnel-type anchorage (TTA) installed in a rock mass simulated model material in a rectangular chamber with digital image correlation (DIC) capability. Digital images of the model were captured during the test; the processing of these images using the DIC technique yielded the surrounding rock displacement and strain fields. The data from local sensors and DIC indicated the following: The horizontal displacement field of the surrounding rock undergoes an evolution from trumpet-shaped to spindle-shaped, whereas the vertical displacement field experiences an evolution from an inclined layered to the vertical stripe in the upper part of the plug body and an approximate arc distribution in the lower part of the plug body. The progressive failure of the TTA can be divided into four main stages according to the following: stable bearing stage I, failure stage II of shear crack initiation in the surrounding rock at the back end of the plug body, double failure stage III of compression-shear (and tension-shear) failure of the surrounding rock and slip failure of the interface, and failure stage IV of the crack in the surrounding rock extending to the ground surface and interface debonding. The progressive failure of the TTA changes from early rock mass failure to double failure, which includes rock mass and interface slip failure. During the progressive failure of the TTA, the interface undergoes elastic deformation, plastic slip, and debonding state in turn. The shape of the interface stress distribution gradually shifts from a double-peak shape with two large ends and a small middle to a double-peak shape with the peak at the rear end shifting forward, and finally into a trapezoid-like shape with an overall decrease in stress.