The construction of underground powerhouses for hydropower stations has always been a focal point and challenge in design and construction due to their large scale

high side walls

extensive spans

and complex geological conditions. This study relies on the Shuangjiangkou hydropower station

known for having the highest geostress globally

to investigate the engineering issues related to hard rock deformation and failure under extremely high stress

along with stability control methods. The research is divided into two main aspects: Firstly

we estimate and adjust the in-situ stress field of underground caverns in deep-cut valley areas using limited geostress test data and the brittle failure phenomena observed in the pilot tunnels. Secondly

we examine the typical failure phenomena of underground caverns under extremely high stress

including global issues from high-stress failure and block instability due to localized rock veins cutting

along with corresponding failure mechanisms and control measures. The findings offer valuable case studies and references for constructing large underground caverns in high-stress hard rock environments.