The analysis of a buried piping system requires special modeling consideration. This is because the restraint (support) provided by soil surrounding a buried pipe is continuous. As AutoPIPE analysis is based on discretely defined points, so an accurate model of the soil's restraint capabilities would require the definition of a number of closely spaced piping points. Each soil point would then require a set of support springs which model the stiffness(es) provided by the soil at that point.
In AutoPIPE, user can select a range of pipeline and assign soil stiffness properties in four directions and soil spring spacing for that range. Three sets of soil stiffness values can be assigned per soil identifier, which enables the user to define a low bound, average, and high bound stiffness values. In addition, AutoPIPE also has built in soil stiffness calculator, which automatically calculates soil stiffness values based on soil properties entered by the user. There are 4 methods for calculating the soil properties:
American Lifeline Alliance (ASCE 2001 w/2005 addenda):
This method uses the calculation of soil properties as outlined in the Appendix B, Soil Spring Representation of the "Guidelines for Design of Buried Steel Pipe" by American Lifelines Alliance
Pipeline Research Council Int.
(PRCI 2009): This method uses the calculation of soil resistance and displacements as outlined in the Appendix A, Soil Spring Definition for Analysis of Pipe-Soil Interaction of the "Guidelines for constructing natural gas and liquid hydrocarbon pipelines through areas prone to landslide and subsidence hazard" report published in January 2009 by Pipeline Research Council International.
This method use is based on the calculations as outlined in the AutoPIPE reference information
This method allows the user to manually calculate and enter the soil stiffness properties
Furtherore, a simplified tool for calculating virtual anchor length has also been provided.
AutoPIPE version 9.5, additional capabilities for calculating stresses in a buried piping due to the soil load on top of pipe, soil overburden loads like traffic loads, ring buckling, effect of seismic wave propagation, and building settlement effects. The workflows and additional information for calculating these stresses has been detailed in this tutorial.
For more information on modeling with AutoPIPE, please see the following Modeling Approaches WIKI page.