For a solid deck for counteract the effects of frost, install steel piles equipped with helical blade.
Vistech company did the work.
You can see, here, the piles under the deck. They support 6" X 6" posts (15 cm X 15 cm).
9' (2,74 meters) between the posts.
Supporting head whose height can be adjusted by rotating the hexagonal bolt.
Very convenient to fit !