Abstract: This work studies the techniques to deal problems associated with karst caves beneath the pile foundation of Nam Song bridge in the Laos-China railway. Many kinds of factors are considered such as construction safety, quality, work duration, cost, environment and forms of karst caves. Based on data derive from the construction site, comparative analyses are performed in the strengths and weaknesses as well as practicability of the macadam back-filling method (e.g. wall-building by throwing and filling clay and rubble) and follow-up steel casing method and their combination in dealing with karst caves of various shapes. Results show that for small empty caves and moderate caves fully or partially filled caves, the first method can deal with the karst caves rapidly, efficiently and economically. For moderate empty karst caves, large karst caves and caves with big channels of underground rivers, the combination of the two methods permit to solve the problems during construction such as low efficiency, hole collapse risk, concrete over pouring, and steel casing deformation by extrusion, to overcome the construction risk owing to the karst cave in an economical and efficient manner. Based on these study results, this paper proposes the feasible options and key technologies deal with karst caves beneath bridge pile foundation in karst areas.