I recently had the opportunity to do a similar analysis and ended up recommending 44" deep trusses spanning 50' and spaced at 8' c/c across 40' wide bays (40'x50' column grid). The bay geometry was also sized for repetition of a number of panels compatible with the downstream electrical devices...
AASHTO 1989-with 1992 and 2002 interim, "Guide specification for structural design of sound barriers" ($60 at the AASHTO bookstore) gives a procedure which 'may be used'.
Basically you construct the net pressure diagrams for each side (uphill or flat and downhill, using the graphs to determine...
The "Snailz" program, available free from Caltrans's website, has an option to 'apply external force' to a soil nail wall. Adjust the (user-input) force until the desired factor of safety is achieved.
[An upper limit of the force should be <=(FS)x(ka)x(gamma)x(H^2)/2, because the soil mass...
Try
http://www.mabeysupport.co.uk/superprop.asp
for design info in both horizontal and vertical applications.
Axial/bending interaction is important for long spans.
- PR
