Grav shafts are elevators that can direct gravity up and down to allow users to quickly change levels. They appear in adjacent upwards and downwards pairs. They allow Talos I staff and other entities (e.g. mimics, phantoms, operators, etc.) to safely travel vertically within most areas, as the sole traditional elevator on Talos I only links the Talos I Lobby, Arboretum, and Life Support.
It is likely that grav shaft technology is based on the same physics breakthrough that "keeps boots firmly planted on the Italian marble of Talos I lobby," as they essentially manipulate the local artificial gravity.
Within a grav shaft pair, the accessible shaft is covered in pulsing green lights while the inaccessible one is covered in pulsing red lights and a 'Do Not Enter' sign. Deactivated grav shaft pairs are either broken, like the one near the Neuromod Division foyer, locked, like the ones that will lead you to the Executive Suites in Crew Quarters or Alex Yu's Office in the Arboretum, or unpowered due to local power outages.
Broken grav shafts reactivate upon being repaired, locked ones reactivate upon being unlocked with their access codes, and unpowered ones reactivate upon restoration of local power. Alternatively, you can either use your GLOO Cannon to make platforms to scale inside deactivated grav shafts, or mimic an operator and levitate through the shafts. If not removed prior to grav shaft reactivation, GLOO platforms remain where they landed and can be obstacles when in transit. While it is possible to remove them by shooting at them from outside activated shafts, it is easiest to remove them when the shafts are deactivated.
Interestingly, voltaic phantoms, despite their tendency to cause electronics to become and remain inoperable while in their proximity, do not cause grav shafts to malfunction.