Initial characterization of subgrade soils and granular base materials at the Minnesota road research project

This research was conducted on the behavior of materials at the Minnesota Road Research Project (Mn/ROAD), the construction of which was completed in 1994. Falling-Weight Deflectometer (FWD) tests were conducted on the test sections at all stages of pavement construction (pre-base, post-base, and post pavement). Deflection values were highly variable due to variability in surface condition, soil moisture content, density, and stressdependent effects.

In general, backcalculated subgrade moduli tended to increase with increasing FWD sensor offset (decreasing stress). Post-base and post-pavement testing also indicated an apparent increase in subgrade modulus relative to pre-base values. Moduli values were also determined for granular base results.

These results were compared to Dynamic Cone Penetrometer (DCP) penetration index values as well as to resilient moduli values from tests conducted on subgrade and granular base materials in the lab. The backcalculated subgrade soil modulus values compared well with the laboratory resilient modulus values, but no correlation was seen between backcalculated moduli and penetration index values.

The results of this testing will provide a baseline for future analysis of the test sections at Mn/ROAD.