The landslide in the slope and side of the Warta River valley in the village of Wronki – process analysis, exploratory research, preventive measures, monitoring

The landslide is located in Wronki. It covers the southern side on the bank of the Warta River and occupy an area of 500 m in length. The landslide was once again activated on August 22-23, 2018, causing numerous failures. The Warta River slope in the area of mass movements is built by non-construction embankments, under which the Poznan Miocene–Pliocene of quasi-layered structure lie. There are horizontal interlayers of sandy silts in these clays. The Warta drains water from a large area, and the runoff takes place mainly on the roof of clays. The slide surface of the landslide was precisely the roof of the Poznan clays. Bearing in mind the properties of the Poznan clays, such as relaxation, block disintegration, expansiveness features, the following were considered the direct causes of the failure: heavy rainfall that occurred after a drought, loading of the slope with indiscriminate cubature buildings, construction of a linear sewage system and periodically repeated vibrations caused by the implementation of neighboring investments. In order to identify the area, test boreholes were made, samples were taken for laboratory tests, and geodetic measurements were taken. Based on the obtained results, slope stability calculations were made and a measurement network was developed for systematic monitoring of geodetic displacements of control points. It was recommended to perform drainage to drain the slope and side of the Warta River, plant bushes, and make changes to the land development plan in order to prohibit further development of the area in the endangered zone.