I beleive that PVR stands for Potential Vertical Rise and relates to situations where you have expansive clay material below the slab.
Geotechnical Engineers will evaluate the soil conditions for your building and estimate the potential for the soil to swell under varying moisture conditions. This gives you, the structural engineer, an understanding of the degree to which the swelling may damage your structure AND...provides you with an idea of how to detail to either avoid the damage or accommodate it.
Usually, in high PVR conditions, you will want to avoid the swelling by:
1. Designing a structure that is supported on deep foundations with a crawlspace and suspended slab so that future swelling has little effect on your structure. The PVR value is used in this case to determine the amount of void space below suspended grade beams and slabs.
2. Over-excavating the "bad" soil to a recommended depth (usually recommended by the geotech) and filling with "good" soil that has little swelling potential.
