Abstract: The position relationship between tunnels and karsts is summarized, so as to avoid or reduce the mud bursting risk in tunneling in karst areas. The mud bursting mechanisms and the major influencing factors are studied by means of mechanical analysis method. The causes, treatments and prevention and control methods of mud bursting are discussed, with the mud bursting in Jiutiaolong tunnel on GuiyangDuyun highway as an example. Conclusions drawn are as follows: 1) The position relationship between tunnels and karsts can be divided into 3 types, i.e., there are karsts around the tunnel, the entire tunnel crosses karsts and part of the tunnel crosses karsts. 2) The mechanisms of mud bursting in tunneling in karst areas are studied in macroscopic and microscopic manners. The macroscopic mechanisms of mud bursting refer to different mud bursting types, and the microscopic mechanisms of mud bursting refer to the small scale physical and mechanical effect of the ground water on the ground. 3) The engineering investigation and the advance prediction during tunnel construction should be emphasized, rational excavation methods and advance support measures should be adopted and the construction process should be standardized on basis of the geological characteristics of tunnels in karst areas, so as to avoid mud bursting. 

Key words: tunnel, karst, mud bursting mechanisms, prevention and control