Abstract: Based on the Jialiang No. 3 Tunnel project of the Guiyang-Nanning High-speed Railway, a treatment plan utilizing an arch bridge-tunnel integrated structure to span a large karst cave section was proposed, targeting the large karst cave revealed during tunnel excavation. Numerical simulation results and field measurement data were analyzed to study the deformation patterns of surrounding rock and support structures during the construction of the arch bridge-tunnel integrated structure. The study indicates that, due to the uneven distribution scale of the karst cave on both sides, the horizontal deformation on the right side of the tunnel is greater than that on the left. The measured stable settlement value at the arch crown is 6.03 mm, accounting for 12.06% of the settlement control value,and the horizontal convergence value is 3.05 mm, representing 6.10% of the convergence control value, indicating that the tunnel deformation meets the requirements. Excavation and support of the foundation pit at the tunnel bottom are critical stages in the treatment process. Field monitoring data showed that the maximum axial force of the steel support was 277.15 kN, the final convergence value of the steel support was 4.97 mm, and the maximum vertical displacement of the foundation pit was 2.50 mm. Upon completion of the arch bridge-tunnel integrated structure construction, the maximum vertical displacement of the arch structure was 7.14 mm, all within the monitoring alert values. These results demonstrate that the deformation of the surrounding rock and support structure during the karst cave treatment is controllable, validating the safety of using the arch bridge-tunnel integrated structure to span the large karst cave section.