Since each soldier carried two sudis (stake) it is surprising that the only ones I have seen come in the Warlord games plastic Early Imperial Roman Scorpion sprue.
There is debate about how they were used
a. palisade wall: unlikely as their shape means they would be easy to pull out
b. pairs attached in a cross to a beam to make a sort of cheval de frise
c. used as spikes facing out towards the enemy below the palisade.
d. used in threes in the construction of a hedgehog (giant - caltrop)
e. stuck in the ground at an angle toward the enemy as a hasty defence (maybe?)
They probably had a lot of other non battle uses!
The term Pilum Muralis (Wall Spear) implies a use of the sudis as in "d" above rather than the name of the stake itself.