Abstract: In this paper, three cases have been presented that may have general meaning in geotechnical engineering: (1) The engineering properties of schistous sands along middle and lower Yangtze river valley. They are quite different from that of silicious sands, so that those experiences based on the research works of silicious sands can not be applied to them without modification. (2) The “critical depth” of deep foundation. (3) The “scale effect” of loading plate testing. The phenomena of critical depth and scale effect of bearing capacity problems could not be explained with traditional soil mechanics theory. The author suggests that it must be emphasized to enhance the fundamental research works on the engineering properties of regional soils and on the behaviour of the foundation in soil layers. It will provide the scientific bases for the development of soil mechanics theory and practice.