I Am In The Planning Stage Of Building A "soldier And Pile" Retaining Wall. I Only Need It To Be 4' High And 56' Long. I Want To Use Steel I-beams But With The Price Of Steel So High Im Thinking Of Using 4x4's With 2x8's Bolted On Each Side To Form An I-beam. my Question Is Will The Stregth Of Wooden I-beams Be Strong And Efficiant Enough For What I Am Using It For?. The Wall Is Being Built More To Keep Back A Hillside Of About A 45% Grade. I Do Plan To Bury The Post 36" In The Ground.
4' is about the limit for an ordinary wall with with a level area retained with no engineering. With a 45 degree sploe you have much higher loads and can expect movement.
You are fooling yourself if you think you are creating wood "I beams". You just have posts with onle layer or wood retaining the large load and the outer layer doing little but not rotting as fast since it is not in the soil. The way wood shrinks and dries nails will noy create a wall the acts like a big I beam.
Your 4x4s are too small anyway, especially at 36" deep.
you need either tie-backs to dead men or a segmental concrete block retaining wall (not footings) with geo-grid soil reinforcement. Another option is the big Mafia blocks of concrete, but usually there is no guarantee for a site like yours.
A good, long rain could level the 4x4 and 2x8 wall.
I agree with our fly fisherman freind. Making and I beam out of wood - well I don't see the reasoning. Why are you thinking of an I beam at all? I recently built these 2 retaining walls - these are 3' high at the tallest point. One important point in retaining walls is to add good drainage.