deck replacement/repair and soil preparation

I have a large redwood deck that my other half destroyed this summer (don't ask).
I need to replace or repair two thirds of the deck and all of the railing, steps, and built in benches.
The soil under the deck is clay.
I've decided to go ahead and stick with redwood and I'll stain it to match the surviving deck.
I'm wondering about soil preparation as well. The clay shrinks and cracks during the hot dry summer months and swells and softens during the wet months.
I want the pier and post supports to be rock steady under the deck and was thinking that some soil prep might be necessary.
Also, any good how to deck books to help me with protecting the house where the deck attaches?
Any thoughts?
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