Soil suitability card — Settlement sensitivity

Building on weak soil requires insight into the prevention of “slap” layers in the subsoil. Sagging layers are defined as layers that have a low carrying capacity. In particular, the thickness of the peat layers is important. In addition, (thick) clay layers also play a role. In order to determine the degree of suitability of the subsurface for construction, the 3D subsurface model looked at the shares of peat, clay and sand in the soil profile. Only the Holocene package has been taken into account. The Pleistocene units are consolidated in such a way that they cannot be expected to have a substantial impact on ground level setting. Based on the variation in common soil profiles, a classification was then drawn up which represents a gradual course of soil settlement sensitivity. Only in class 9 areas will hardly be set. In the other classes, the setting sensitivity towards class 1 is steadily increasing and therefore a certain degree of setting and associated costs for prevention (funding) and management and maintenance costs (compensation of ground level differences resulting from setting differences) must always be taken into account. The presence of peat layers is the most determinant of the sensitivity to set. In the legend, a thin peat layer is more unfavourable to the setting than a thick clay layer. The holocene package therefore initially looked at the total thickness of the peat package. Then we looked at the thickness of the clay package, whether or not in combination with peat. The variation in sand thicknesses in the province of Utrecht is almost entirely reflected in the combination of peat and clay thicknesses, and therefore does not form a separate column in the final classification. For the municipality of Vijfheerenlanden, which has been part of the province of Utrecht since 1 January 2019, no data is yet available.