The frost susceptability plays an essential role in the design of foundations placed above the freezing front. Each superstructure may be subject to frost heave due to freezing of a frost-susceptible soil having capillarity access to water. The risk of frost heaving is determined from correlations with grain-size-distribution and other soil-parameters or from frost heave tests in the laboratory. Newly fashioned frost heave tests were indroduced and the correlation between fines content, the amount of course grains and frost susceptability is investigated. Also the risk of thaw weakening is investigated with CBR-testing series.