when doing the consolidated undrained test, first we apply the chamber pressure and let the pore pressure develop in the specimen to dissipate, so it drains. and THEN we close the drainage line at the top and bottom and apply axial load, so the name "consolidated undrained". I understand this overall. but for the steps in between i have questions...

my question is, why do we do the drainage by the chamber (horizontal) pressure and not vertical pressure? the consolidation is a vertical thing, so i am confused why we apply the horizontal to do drainage first.

and how do we know how much to apply the radial pressure to make the drainage, and how do we know at which point to stop when it drains (pore water dissipates, i mean how do we know how much it should dissipate to stop drainage process)?

after that we apply the axial load in undrained condition. but for the steps before this, as i wrote, i have those questions.