岩溶地区地质条件复杂，在隧道修建中存在溶洞突涌水安全隐患，而顶部溶洞带来的灾害性更加明显，溶洞水压是其重要影响因素。针对隧道顶部溶洞，建立数值模型，将溶洞水压作为工况因素，分析围岩中的孔隙水压力变化规律，揭示隧道开挖过程中突涌水通道的分布情况。基于数值模型中单元孔隙水压力突变最大值判断方法，溶洞与掌子面围岩达到塑性状态后，监测两者之间的单元孔隙水压力随开挖步变化速率，找出每一行单元中的最大值，从而确定不同溶洞水压下的突水通道及安全厚度。研究表明，随着顶部溶洞水压增大，突水通道距离溶洞底部由近及远，而安全厚度也随之增大。

Due to the complex geological conditions of karst area, tunnel construction is often accompanied by potential safety hazard of water inrush from karst caves, especially when the karst cave overlies tunnel (in which condition the water pressure is very important). A numerical model for tunnel under a karst cave is established, and the water pressure of the karst cave is regarded as a construction condition. The variation rules of pore water pressure of surrounding rocks are analyzed, and the distribution of water inrush channel during tunnel excavation is revealed. The water inrush channel and safety thickness of rock under different water pressures of karst cave are decided based on the maximum value estimation method of mutation of the element pore water pressure. The study results show that the distance between water inrush channel and the bottom of karst cave and the safety thickness of rock increase with the water pressure of overlying karst cave increases.