In order to study the mechanical properties and reinforcement mechanism of special-shaped cross-section polypropylene fiber reinforced shotcrete, compressive, splitting tensile, and flexural tests were conducted on benchmark shotcrete and special-shaped cross-section polypropylene fiber reinforced shotcrete, and SEM micro scanning tests were carried out. The results showed that the addition of special-shaped cross-section polypropylene fibers can improve the compressive strength, splitting tensile strength, and flexural strength of sprayed concrete. The most significant improvement was observed when the fiber content was 6 kg/m³, the compressive strength at 1 day, 3 days, and 28 days, splitting tensile strength at 28 days, and flexural strength at 28 days were increased by 13.9%, 5.8%, 5.1%, 26.8%, and 8.1%, respectively, compared to the benchmark concrete group. The toughness of sprayed concrete is enhanced by adding special-shaped cross-section polypropylene fibers, and the failure mode changes from brittle to ductile. Special-shaped cross-section polypropylene fibers can reduce the proportion of large pores in the concrete matrix, improve the compactness of the matrix, and reduce the width and number of microcracks at the interface between coarse aggregates and matrix, provide a bridging effect to absorb destructive energy, and enhance the strength and toughness of sprayed concrete. The research results can provide a theoretical basis for the application of special-shaped cross-section polypropylene fiber reinforced shotcrete.

To study the influences of the underpass tunnel proximity construction on the settlement of overlying suspension bridge tunnel anchor plug body, taking the Baishiyan tunnel Ⅰ under the tunnel anchorage of Lyuzhijiang bridge of Yuxi-Chuxiong Expressway as an example, model test and numerical analysis methods are used to analyze the deformation evolution characteristics of surrounding rock during the proximity construction, investigate the influence distance between plug body and tunnel and the burial depth of tunnel on the settlement of the plug body. The results show that: The settlement of plug body mainly occurs during the advance tunneling of the tunnel. The settlement of plug body and tunnel arch and disturbance area increase with the decrease of surrounding rock grade, the decrease of distance between plug body and tunnel and the increase of buried depth. The settlement of tunnel arch and the bottom settlement of plug body are the most sensitive to the change of tunnel buried depth, the least sensitive to the distance between plug body and tunnel. The change of the distance between plug body and tunnel has little effect on the settlement of tunnel arch, but has a greater effect on the settlement of plug body. The research results can provide important reference for the construction design and stability control of tunnel-type anchorage and underpass tunnel.