Soils of hydraulic facilities and foundations are basically in the unsaturated state. Strength properties of these soils inside of each building area may be extremely various and should be carefully studied. It especially applies to tropical and arid areas. Soils that are above ground waters can remain in the unsaturated state in the areas with temperate climate. Research results of the dependence of the soil strength on its physical state (density and moisture) are presented. It was found that increase in the soil density brings to increase in the angle of internal friction and cohesion, but increase in the moisture, on the contrary – to its decrease. Collapse mode of specimens tested in stabilometer depends on how the value of the effective vertical stress relates to preconsolidation pressure, determined by compression test.