There is no definitive answer to the question of where is the best geotechnical engineering PhD program in the world, as it depends on the specific criteria you use to evaluate the programs. However, some universities known to have strong geotechnical engineering programs include the University of California, Berkeley, University of Cambridge, University of Tokyo, National University of Singapore, Delft University of Technology in the Netherlands, and the University of Leeds. in the UK, the University of Hong Kong and the Technical University of Munich in Germany. We encourage you to thoroughly research the geotechnical engineering PhD programs offered at these and other prestigious universities based on your specific criteria such as faculty quality, available resources, research opportunities, university reputation, professional opportunities, etc.

Choose a good supervisor not a "good university". Most rankings are a scam. Reputation as most things in life is bought.

thank you for the suggestion, actually I'm currently applying for a doctoral program, but I want to find a doctoral program according to my wishes to study rock mechanics or mining geotechnical, any suggestions on which department and university?