I started what was to be a fairly small project that has turned ugly due
to all the support posts under my back porch deck either being already
rotted through or in various stages of rot. They were rough cedar.
Half were concreted into heavy black clay soil(1 foot or so on top of
the parent material soil which is limestones on top of limestone slabs
with minimal soil), and half were just dug in.

The damage was done, I believe, by very poor drainage due to the builder
leaving the soil in piles in a way that ran the runoff water right into
the posts.

I cannot get post hole diggers or even a standard shovel under the deck
to dig new holes because it is too low and it is also roofed over.

I am thinking that I can place concrete blocks under the rim joist close
to where each rotting post is, cut it out, and then place blocks for
support where the old post was. The old posts are directly below the
posts that support the roof over the deck.

Or I could dig a hole as deep as I can after cutting out the rotted post
and pour a pier with a metal standoff bracket anchored on top and use a
post above that to go up to support the rim joist.

Does anyone out there have any experience with this problem and know of
any other way(s) to address it?

Thanks for any assistance.

RonT