If this road is only about year old, you should be able to dig out the design document including fill material & information on the original grade. That would help to pinpoint the problem areas, and bring about an feasible yet economical solution.
No direct experience on this. Just a little thought.
1. The pile is critical at driving/construction stage only.
2. Upon completion, the pile wall subjects to axial compression mainly, if properly aligned.
Looks like his method is ok (to me).
A few seem good abstracts/papers on "durability of RCC dam/pavements. The PDF seems in line with the first. The second is quite general.
1. China Experience (DAM - Freeze & Thorw Resistance Study)...
Have you checked RISA? Good and cheap engineering software, but I am not positive it has aspects devoted to bridge. You might consider purchase one main structural program, and add a few small programs with devoted features.
Don't understand your application. Plug weld over tube with 1/16" wall thickness? Maybe you want to post this on "Welding, Bonding & Fasterner Engineering" forum.
Depends on the concrete travel distance down the slope. I would utilize chute or conveying hose to gain better control to avoid aggregate seperation, which may lower the quality of the concrete and cause honeycombs, if not vibrate properly.