Jinping I hydropower station is one of the most challenging projects in China due to its highest arch dam and complex geological conditions for construction.After geological investigation into the dam foundation,a few large-scale weak discontinuities are observed.The rock masses in the left dam foundation are intensively unloaded,approximately to the depth of 150–300 m.These serious geological defects lead to a geological asymmetry on the left and right banks,and thus some major diffculties of dam construction are encountered.In this paper,the influences of geological defects on the project are analyzed,followed by the concepts and methods of treatment design.Based on the analysis,the treatment methods of the weak rock masses and discontinuities are carefully determined,including the concrete cushion,concrete replacement grids,and consolidation grouting.They work together to enhance the strength and integrity of the dam foundation.Evaluations and calibrations through geo-mechanical model tests in combination with feld monitoring results in early impoundment period show that the arch dam and its foundation are roughly stable,suggesting that the treatment designs are reasonable and effective.The proposed treatment methods and concepts in the context can be helpful for similar complex rock projects. Jinping I hydropower station is one of the most challenging projects in China due to its highest arch dam and complex geological conditions for construction. After geological investigation into the dam foundation, a few large-scale weak discontinuities are observed. The rock masses in the left dam foundation are intensively unloaded, approximately to the depth of 150-300 m.These serious geological defects lead to a geological asymmetry on the left and right banks, and thus some major diffculties of dam construction are encountered. in this paper, the influences of under the concepts and methods of treatment design.Based on the analysis, the treatment methods of the weak rock masses and discontinuities are carefully determined, including the concrete cushion, concrete replacement grids, and consolidation grouting. They work together to enhance the strength and integrity of the dam foundation. Evaluation and calibrations through geo-mechanical m odel tests in combination with feld monitoring results in early archival period show that the arch dam and its foundation are roughly stable, suggesting that the treatment designs are reasonable and effective. proposed proposed treatment methods and concepts in the context can be helpful for similar complex rock projects.