Does anyone know where to find a design manual for calculating the sectional modulus for a soldier pile wall with a raker for a 14 foot high wall, soldiers at 7 feet on centre, raker about 2 feet from the top with a 50 psf surcharge?
If you want you can place a waler between piles and a raker every 14 feet with a roll chock. This will help excavation activity (more space for excavator).
Are you adjacent to an existing building? Prefer tiebacks over rakers in this situation.
The raker acts as a strut (assuming that you've sized it correctly for the required loads). It's a straightforward problem for a nongravity wall. See FHWA guidance for determining braced wall earth pressures and anchor/strut loads here: