Potential Vertical Rise and Differential Soil Movement in Post-Tensioned Slabs-on-Ground: Why They Are Not Relatable or Interchangeable

Using PTI DC10.5-19, geotechnical engineers can provide recommendations and design parameters which do not require extensive site work (such as removal and replacement) of expansive clays that result in cost-effective designs. Extensive site work is often a significant cost and time-consuming operation. The increasing use of the PTI DC10.5 method and post-tensioned reinforced designs demonstrate that post-tensioned slabs are an economical solution to building foundations. PTI DC10.5-19, Standard Requirements for Design and Analysis of Shallow Post-Tensioned Foundations on Expansive and Stable Soils is an IBC-referenced standard for the design of slab-on-ground foundations. Misconceptions exist regarding whether the potential vertical rise (PVR) index often determined in site investigations can be used in place of the value of differential soil movement, (y_m) defined in PTI DC10.5-19. This paper will outline the requirements of relevant IBC sections, explain the differences between PVR and y_m, discuss why they are not interchangeable or relatable, and review the geotechnical aspects of design of a post-tensioned slab-on-ground foundation using PTI DC10.5.