Abstract：The underground cavern group of Laxiwa Hydropower Station is one of the largest projects in China at present. When the excavation is completed，a number of splits appear in surrounding rock of busbar tunnels. There are similar phenomena in Longtan，Ertan，Guangxu，Dachaoshan Hydropower Stations. Finding the reason of this phenomenon is helpful for strengthening the stability of caverns. For this instance，Laxiwa Hydropower Station is taken for example to study causes of this phenomenon and get the reasonable reinforced measures. At first，the corresponding characteristics of the splits are found by comparing different projects. Then the process that splits come to being is studied with numerical simulation methods. The results indicate that the especial position of busbar tunnels in the powerhouse can result in stress concentration on parts of surrounding rock of busbar tunnels and then splits come into being. Meanwhile，it can be found that geostress is another important factor for the splits. Finally，several reinforced measures are put forward for similar projects.
