Dear Madhav,
The PTS,s Pali-English Dict.:
Vāḷa - [cp. late Sk. vyāḍa, see Geiger, P. Gr. § 54⁶] I. a snake Vism 312 (so read for vaḷa).- 2. a beast of prey [...] vāḷa-miga, a beast of prey, predaceous animal, like tiger, leopard, etc. [...]
When in search for the Elixir of immortality Garuda enters the underworld, he kills two serpents hidden under the [eternally] revolving wheel. (Mbh. I, 29. 3-9).
When the relics of the Buddha are hidden by Ajatasattu in the underground chamber, Vissakamma places over them, for their defence the [eternally] revolving vāḷa–saṅghāṭa–yanta.
If vāḷa would mean "snake, serpent", then this could be one of the tropes linking both the narrations.
Yanta means "contrivance, artifice, instrument, machine, mechanism" - in what way could it be constructed/pegged together - using serpents? Ataching it to serpents? Giving it a serpentine look?
Artur