<p>The construction of urban metro systems in Southwest China is invariably challenged by adverse geological conditions characteristic of water-rich karst formations. This study investigates the damage evolution mechanisms in the cavern-containing stratum and the extent of stratum damage through a comprehensive analysis of the shield tunnel construction in the Shenzhen-Huizhou double-line project. Firstly, the ground surface settlement curve was calculated by numerical modeling and theoretical calculation, and the results were verified by on-site monitoring data. The analysis confirmed that the tunnel construction simulation employed a synchronized excavation method for both parallel tunnels. Subsequently, the stratum dissolution rate (<i>δ</i>) and fissure surface roughness (<i>f</i>) were introduced, and PFC^2D was utilized to study the damage evolution mechanisms in the cavern-containing stratum. The data were then compared with the actual monitoring data to ensure the accuracy of the numerical simulation. It was found that the cave-containing stratum under the tunnel was most prone to collapse. Finally, to study the extent of damage to the stratum under such conditions, four factors, namely, fissure width e, fissure surface roughness <i>f</i>, dynamic viscosity of water u, and karst water pressure <i>P</i>_<i>w</i>, were introduced to study and predict the extension of single-cave fissures. Additionally, the degree of connectivity (<i>L</i>*) between multiple caves was introduced to obtain the law between the <i>L*</i> and karst water pressure and caved location. The results of the study provided some guidance for the prevention and control of water inrush disasters in karst areas.</p>