Abstract: To study the influence of concealed karst caverns on the stability of metro shield tunnel, the karst caverns distribution of a metro shield tunnel on Lianda Street StationWujiaying Station of Kunming Rail Transit Line 4 located in the plateau karst Development area are explored using borehole geophysical prospecting and electromagnetic CT methods. The threedimensional finite element numerical simulation method is adopted to study the influence of lower karst caverns on stability of shield tunnel with different burial depths and that of karst cavern radius, state of karst cavern filling, position of karst cavern and spacing between karst cavern and tunnel on the stability of shield tunnel. Then the stability of tunnel structure in karst development area during construction process is analyzed as well. The results show following. (1) The karst caverns distribution can be well explored using borehole geophysical prospecting and electromagnetic CT methods. (2) When the size and position of the karst cavern remain unchanged, the plastic zone and deformation of the surrounding rock of the shield tunnel increase with the increasing burial depth of karst cavern. (3) With the increase of karst cavern radius, the stress concentrated area between tunnel and karst cavern becomes dispersed, and the deformation of tunnel surrounding rock decreases. (4) The materials and amount of filler in the karst cavern has no effect on the deformation of surrounding rock of tunnel. (5) The influence degree of karst cavern at the both sides of tunnel on the deformation of tunnel surrounding rock is greater than that of karst cavern below tunnel, and that of karst cavern below tunnel is greater than that of karst cavern above tunnel. (6) The karst cavern would affect the tunnel construction within a certain spacing between tunnel and karst cavern.

Key words: karst development region, concealed karst caverns, metro shield tunnel, stability, numerical simulation