I would recommend SIGMA/W by GEP.SLOPE of Calgary, Alberta who also developes SLOPE/W (slope stability) and SEEP/W (seepage analysis). These are Window based softwares with CAD like features and they complement each other. Once you have set the dam geometry, you can use it in all three...
georam
Inciddentally I am looking for the same information for a power plant proejct. Have you have any success so far. There must be something that be co-related based on UCS and/or Point Load Index.