The present paper deals with the special problems of consolidation which are met with when vertical sand drains are used in order to accelerate the rate of settlement of clay. Furthermore, certain particular phenomena connected with the consolidation problem as a whole are also treated. Chapter 1 contains a review of some important theories of consolidation. Chapter 2 gives some results of research on pore water pressures and "friction j or rather, "bond", between the ring and the clay in the oedometer test. Chapter 3 deals with the permeability of clay. The results of permeability tests are pre-sented and a new theory of permeability is suggested. A new equation of con-solidation is advanced in Chapter 4. Finally, in the light of the new findings, Chapter 5 gives the results obtained in connection with full-scale investigations in a test field, established in 1957at Skå-Edeby, 25 km west of Stockholm.