When a mineral transport corridor passes through a water-rich karst cave, fluctuations in pore water pressure are highly likely to induce deformation and instability of the surrounding rock of the cavity-corridor. To study the effect of fiber-reinforced shotcrete support on the stability of the cavity-gallery system, mechanical tests were first conducted on shotcrete with different dosages of coarse polypropylene fiber (CPF), and the optimal dosage of CPF was proposed. Subsequently, considering the fluid-structure interaction, a numerical analysis model of the cavity-gauge under pore water pressure was established to systematically study the deformation of the surrounding rock and the stress characteristics of the sprayed layer structure under different spraying ranges and thicknesses. The results indicate that: (1) The CPF dosage significantly affects the mechanical properties of the shotcrete; the peak tensile strength initially increases and then decreases as the dosage rises. Considering the overall compressive strength, residual compressive strength, and tensile performance, 8 kg/m is the optimal CPF dosage. (2) Expanding the scope of shotcreting can effectively mitigate surrounding rock deformation and local stress concentration; among the approaches, the combined shotcreting scheme targeting the "solution cavity, arch crown, and left sidewall" demonstrates superior effectiveness in controlling surrounding rock stability. (3) As the thickness of the shotcrete increases, the displacement of the surrounding rock and the maximum shear stress in the support structure generally decrease; at a thickness of 350 mm, the maximum shear stress drops by 58.9%, but further increases in thickness yield only marginal improvements in support performance, indicating the existence of an optimal range for the thickness. (4) Considering the effects of material properties, shotcrete coverage, and shotcrete thickness on the mechanical response of the surrounding rock-support system, an integrated shotcrete support scheme with a CPF dosage of 8 kg/m3, a thickness of 350 mm, and a support range covering the cavity, crown, and left haunch was determined. The field monitoring results align well with the numerical calculation results, demonstrating that the optimized support parameters effectively improve the stress state of the surrounding rock-support system and provide a reference for support design and stability control in similar projects involving water-rich karst cavities.