The AWWA M45 calculation provides assurance that the pipes will perform under the traffic loads indicated on a sustained basis provided that the parameters used in the calculations are respected, such as the native soil strength and type, the backfill type, and the compaction level. Therefore, under ideal scenarios where the parameters are 100% matching the design ones, the pipe will perform.

• The workmanship of the backfill placement and compaction may not be perfectly following the design parameters in the AWWA M45 calculation. Some locations may receive less than ideal compaction which could lead to joint failure requiring quick repair work to be executed.
• The design values of the wheel and traffic characteristics may change over time. Highways and busy roads may carry at times heavier traffic than the one stipulated in the AWWA M45 calculation. Military vehicles and/or emergency heavy construction vehicles may pass over pipe locations in certain emergency situations.

Hope this is may be useful for some one. i am not able to upload calculations here, may be this is my first post. if needed any one please ask.