Problem:

There seems to be some differences in calculation of the virtual anchor length between V09.06.01.11 and V09.06.00.19. Can you provide me some background as to how AutoPIPE calculates slippage length and virtual anchor length?

Solution:

For calculating the weight of soil on top of pipe value when using ASCE 2001 calculation method for vertical up and vertical down directions, AutoPIPE considers the cylindrical shape of the pipe and subtracts half circular area of pipe from the rectangular area above pipe center-line. This approach, although seemingly more accurate, is not consistent with the published ASCE 2001 + 2005 addenda.

The default method for soil weight on top of pipe calculation was set such that it is consistent with the exact code equations. This calculation has a direct effect on the virtual anchor length. 

See Also

Model Soil Properties with Soil Calculator and Underground Piping

"Soil" sub report using Results> Output Report

Bentley AutoPIPE