I would suggest you to read "DIPRA" publication on the design of ductile iron pipe. It may give you some guidance on what you are looking for. Following link is for the thrust restraints, and you may find other chapters valuable to read on the same website.

http://www.dipra.com/pdf/thrustRestraint.pdf

Regards,

Ibrahim Demir
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Peace at Home, Peace in the World.
M.K. Ataturk