I've done a fair amount of concrete work, but I'm not an expert or even close. Retaining walls fail on a regular bases because of the amount of pressure put on them by the soil when it gets saturated with water and even more so when the soil freezes.
An 8 foot wall is way above where I'm comfortable designing or engineering. How deep will your footings be? Will you have posts along the wall? What size rebar will you be using and at what spacing? Will you incorporate a deadman? What thickness will your wall be? How will you brace your forms to deal with blowout?
Instead of pouring a concrete retaining wall that tall, I would go with retaining wall blocks engineered for an 8 foot wall and allow for drainage behind the wall. Then I would cap it with concrete to give it that smooth finish on the top that you are wanting. This is very common.
I am certain you have done more concrete work than I Eddy and am glad you chimed in.
Couple things to note about the wall and to answer your questions.
Footings are already poured. 27" wide - 18" deep in undisturbed heavy clay soil.
The top of the retaining wall footing is a few inches below the footing on the house.
1/2" rebar every 2ft horizontal and vertical.
The soil on the back side of retaining wall actually will slope away from the wall which will chase runoff down the hill and away from the wall.
Will not have posts along the wall.
Deadman are likely not going to be used but I could certainly do so.
Wall is going to be 10" thick.
The steel-ply forms come with adjustable turnbuckle braces and of course the form ties really are what hold the forms together.
Now as far as drainage behind the wall, I plan to fill rock/gravel about 3' back and up about 4-5' as well as run corrugated tube in at least 2 spots to chase water. I have not planned for any spillways or seepage through the wall. I will also be using geotextile fabric to keep the rock from being filled with dirt/mud.
One of the main reasons I want to do a poured wall is time. I am running out of time this year to get my outside projects done due to abnormal rainfall. I still have 100yds of flatwork to do and this retaining wall needs done before some of that can be done.
Let me know your thoughts. I have some time to change my mind on certain things.
