According to the Department of Transportation for the State of Ohio, proof rolling is a process where compacted soil is checked for soft areas in order to supply a balanced support system for the structure of pavement. If soft subgrade spots are located during construction, they are corrected so that the density of the subgrade is maintained.
According to Ohio's DOT, one trip with a proof roller is usually sufficient for locating soft spots. However, the agency warns that an overloaded proof roller, regardless of the soil type, may cause subgrade instability during the rolling process. On the flip side, soft areas may not be found if the roller is too light for the type of soil.
The Ohio DOT says that a 35-ton roller with a tire pressure of 120 psi should be used on soil classified as A-3, A-4, A-6 and A-7. The aforementioned tire pressure and load is indicated for use on Ohio soils. For granular soils, the DOT suggests using a 50-ton roller with 150 psi of tire pressure.
Some soft soils may be 3- to 5-feet deep. Only in rare cases is a soft spot be deeper than 5 feet. The agency adds that insufficient stability is marked by cracking, rutting or deflection on a subgrade's surface.