Pavement-Transportation Computer Assisted Structural Engineering (PCASE) Implementation of the Modified Berggren (ModBerg) Equation for Computing the Frost Penetration Depth within Pavement Structures

The design of pavement structures in cold climates must account for the changes in soil properties due to the influence of freezing and thawing cycles. The calculation of the frost penetration depth is a fundamental step in the design and evaluation of pavement structures by the U.S. Department of Defense DoD. To compute the frost penetration, the DoD currently uses the modified Berggren ModBerg equation. The Unified Facilities Criteria UFC 3-130-06 includes a methodology to manually compute the frost depth. The Pavement-Transportation Computer Assisted Structural Engineering PCASE software incorporates a more accurate numerical solution of the ModBerg equation, which in some instances provides slightly different values than the manual solution described in the UFC. Researchers from the U.S. Army Engineer Research and Development Center ERDC realized the need to explain why the same procedure results in different values of the frost depth, and sought to reaffirm the importance of advanced numerical tools in pavement design and evaluation. The objective of this report is to present the solution of the heat equation applied to a one-dimensional homogeneous and isotropic layer, which is currently implemented in the PCASE software. The report also explains the differences between the UFC- and PCASE-computed solutions.