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The use of lightweight fill is increasing in the state of Minnesota. This material is used to replace a heavier insitu soil so as to reduce the load burden on the subgrade. There may be several alternative materials to consider for any construction project; however, design engineers might not consider them because of a limited knowledge or unfamiliarity with them. Various materials have been used, but specific design guidelines are not available because this type of construction is still considered experimental. The current selection is generally based on local knowledge. Additional research is required to determine more specific design guidelines for each lightweight fill material. The Local Road Research Board (LRRB) has therefore requested this synthesis to determine what technology and materials are available for the appropriate use of lightweight fill material in road construction.

Following is a synthesis of various reports regarding equipment and methods used to determine frost zones within the soil. Some of the equipment described is used to determine soil strength characteristics, thereby enabling us to determine frozen soil layers. By utilizing temperature and conductivity probes, zones of frozen soil may be directly determined. However, certain chemicals and minerals within the soil may vary these parameters. Heat transfer modeling is a third method of determining frozen zones utilizing local temperature and weather data.