A method of sinking a shaft through wet clay, sand, or mud down to firm strata. Castiron tubbing, attached ring by ring on the surface, is gradually lowered as the shaft is excavated. There is a special airtight working chamber at the bottom of the lining. A cutting shoe at the lower end of the tubbing helps it to penetrate the soft ground. The caisson method is obsolescent, being replaced by the freezing method, etc.