Back Board for Back to Back Handball Courts

This design cannot be done over the Internet.

Hire a structural engineer to design the wall.

You need to hire a structural engineer. You have to do this if you want sealed documents, a necessity in the few prisons that I have done work for.

My guess is that he will simply thicken the slab for a foot or two on either side of the wall.

The main considerations are wind velocity in the area and frost depth and soil properties.

Might not hurt to get a Geotech Contractor involved to see what the underlying soil will support. This will help in the design of the footer.

This is your customer's specification. Build it to his specification. Make him give you one.

If a potential customer did not provide me with STAMPED documents from the office of a LICENSED and INSURED architect or engineer, I would most certainly reject the project. The responsibility for design is on your customer. If the prison system is run by the government, there are most certainly engineers on staff who can handle this.

Do not stick your neck out. It is not necessary.

It could be a "Design Build" job.

Could you run cable stays from the upper corners of the vertical slab, the four cables sloping 45° downward and outward?

I would cast the entire wall 27' high x 40' long. The lower 7' would taper from 12" to 6' wide at the base, 3' on each side of the wall. This tapered portion would be buried in the ground. A structural engineer would have to approve it. The slab need only be 4" thick.

If this is intended to be a Design-Build, with your firm responsible for the complete installation including the design, you will need to sub-contract the design to a Structural Engineer as a consultant to take that liability off of your company (consider a microburst out of a storm-front pushing that 22-ft wall over?)

One solution I have seen employed for weight-savings and speed of installation of large surface-area walls, typically in mining applications, has been a structural truss wire "mattress"-like 3D panel with a rigid foam core.

These are ordered to height desired, then stood on end vertically in 4-ft sections, wire-tied together (over and secured-to the rebar extended up from the footer), and then at least 2" of high-strength shotcrete (gunnite) is applied and trowelled-smooth from a scaffolding setup. If thicker concrete really needed, you could form it and pour in sections from bottom to top, then skim-coat it when finished for a flat surface. Top of wall could be a poured-cap of waterproof high-strength concrete, and likely paint the whole she-bang with one of the concrete-sealant products.

Full height rebar can also be wire-tied to the wire truss panels up both sides to form columns for greater rigidity at the edges without creating wings that would block sight lines.

Highly impact resistant and lighter weight by far than a solid pour or precast slab, but only a structural SE can take the resulting weight and wind-loading and give you an accurate required depth and reinf, and possibly give you a best-case orientation for the angle based on prevailing winds...then he`ll stamp and seal it for the records.

Try this mining provider for info on that system above: pmri95.com

We`ve specified their system on various design projects, and would not hesitate to recommend you look into it as an option.

Heck, I wish I had the money to build myself a new home right now, I`d do my house with it and end up energy-efficient, pest-proof, hurricane-tornado-fire and likely earthquake "resistant" as well as sound proof.