I am in the process of converting a half-walkout basement to a complete basement. The process involves taking approximately 60 cubic feet of dirt/stones and have a picture of the design i would like to make. The picture "A" shows the present situation and would like to make it like picture "B" & "C".
1. how to I move the pillars on which my deck in pic "A" is resting?
2. How will lumber (6 by 6 by 8) hold?, act as a retaining wall ?
1. Do you want to move them or replace them with longer posts to reach the new lower footing? If just longer put temporary braces in while you remove the posts, dig down, pour new footings and put in the new posts. (Don't use the deck while doing this). If you want to move them it looks like you could only go a foot or less wider at each end and still hit the beam. And you would need to verify that the wider support distance between the posts on your beam still meets your codes.
2. I don't know. Retaining wall success has to do with depth, soil type, climate and materials. I would consult local expertise such as building inspector. Be sure to use good soil fabric to keep soil from coming through the joints or you'll always be cleaning up.
I know you didn't ask, and I understand why you want to do this, but the design has a major issue in that you will be collecting rainwater for a fairly large area that must be drained away. It appears that you cannot drain by gravity as the surrounding ground level is higher and you can't drain stormwater into your sanitary sewer so you must use a collection basin and a pump to pump the water up and over to somewhere else on your property for discharge.
This type of design often leads to water in the basement when the drain becomes clogged with leaves or when the pump fails. Leaves always collect in amazing quantities in low areas like this that block wind. So if you're going to do this make sure you design a very good drain system and be very good about keeping leaves out.