To investigate the mechanical properties of segments in sand and cobble strata and their influencing factors, based on a subway tunnel project, numerical simulations were conducted using FLAC^3D software and combined with field construction monitoring data to systematically analyze the surface displacement, stratum deformation, and segment internal force changes during shield tunneling. The influence of different water head heights on the tunnel structure and surrounding stratum was stu-died. The results show that, compared with the case without considering the fluid-solid coupling effect, the final settlement of the surface increased by 49%, the crown settlement of the segment increased by 61.3%, the lateral convergence increased by 51.45%, the maximum stress of the segment increased by about 37%, and the numerical simulation results considering the coupling effect were closer to the actual engineering than the results when the coupling effect was ignored. The water head height is positively correlated with the crown settlement and lateral convergence and negatively correlated with the crown bulge. The bending moment of the segment is positively correlated with the water head height, and the maximum positive bending moment occurs at the crown waist. The axial force distribution is symmetrical, with the axial force at the crown waist being greater than that at the crown shoulder, crown foot, crown top, and crown base. The fluid-solid coupling effect has a significant impact on the deformation of the stratum and the bearing capacity of the tunnel structure when a shield tunnel passes through a water-rich sandy pebble stratum.