Engineering-geological conditions in the edge zone of the Warszewo Hills

Abstract

Development trends of the modern city imply a reduction in the number of inhabitants in its centre, and thus the construction of dormitory suburbs on the outskirts of the city. One of the potential areas for the development of Szczecin is its northern part, i.e. the so-called Warszewo Hills. This area has both latitudinal and meridional extents of about 8 km, and is characterized by complicated engineering-geological conditions. It lies at altitudes ranging from the sea level (Odra River) to 130.9 m a.s.l. (Wielecka Góra), and has highly varied relief. Its landscape consists of hills and flat plateaux, which are cut by deep small valleys, some of them with streams (e.g. the Warszewiec stream). Geological structure is characterized by the occurrence of glacitectonically disturbed moraine deposits mixed with the Tertiary sands and clays. Taking into account geodynamic processes and their intensity, the wide edge zone of the Warszewo Hills can be divided into three main parts: plateau with the upper edge of slope (area of precipitation infiltration), slope, which is cut by small erosion valleys in places (area of surface water and groundwater flow), slope foot (area of water flow and accumulation of slope deposits). One of the most important tasks of the design-investment process is to take action in such a way as to interfere as little as possible in the natural environment and at the same time to achieve the intended purpose. Predominant occurrence of cohesive deposits in the described area (Oligocene scaled clay mixed with moraine disturbed material) results in a high susceptibility of ground to moisture changes. Strength parameters of stable slopes built of clays considerably decrease under the influence of increasing moisture and thixotropy phenomenon. Then landslide processes are triggered, as well as very slow, hardly noticeable in a short time, soil creep.

The complicated arrangement of deposit layers results in spatial variability of groundwater level, and proper design of building foundation is difficult, even in the case of a small, detached house. Too much interference in the landform features (through macro-levelling, construction of streets and routes in the area with steep slopes), the decrease of water retention and increase of surface runoff contribute to an intensification of some geodynamic processes.