I am doing a research on the techniques by which we can determine the in-situ state of soils, rocks. I found some non-intrusive and intrusive techniques of ground investigations here at https://www.dstgroup.com/services/geotechnical-engineering/ground-investigation-in-situ-testing/ . In non-intrusive technique, they have mentioned about sampling using piston sampler but I have no idea how it is being done. Does anyone know about it? Also what are the techniques used to improve the bearing capacity of soil?