Seasonal Changes in Water Content of Subsoil Beneath Old Slab-on-ground Structures in Finland

The objective of this study is to determine the normal level of water content of the subsoil beneath old slab-on-ground structures and discuss the impact of the thermal and moisture conditions. According to measurements, the water content of subsoil beneath a slab-on-ground structure equals or exceeds the hygroscopic equilibrium moisture content of the material in RH 100%. The high water vapor content with warm subsoil temperature can cause moisture damages to the floor covering. In fine-grained soils where capillary action is possible often some excess capillary water is detected at the samples. The amount of capillary bound water and risk for damage is dependent on distance from the ground water table.