For the purposes of the construction of a new diversion weir on the Nysa Kłodzka River in Nysa, instead of geotechnical investigations required by Construction Law, only geological investigations were performed. The depth of subsoil recognition was too small and the number of boreholes, probing as well as the scope of the laboratory test did not meet the requirements of the third geotechnical category. Consequently, the layers arrangement and geotechnical parameters contained in the engineering – geological documentation were inconsistent with the reality. This caused incorrect design of the weir. In addition, according to the documentation, below the bottom of the wide foundation excavation, the cohesive soils in stiff state were located. In fact, there were suffosive fine and silty sands with a thickness more than 4.5 m with a few interbeddings of cohesive soil. Design based on the incorrect subsoil characteristics caused that sheet piling was ended in the sands only 2.5 m below the weir foundation level. While excavation, at a depth of 6 m, the piping took place. The rapid displacement of the lower end of the sheet piling has occurred, and excavation was filled with soil. It caused the total loosening of soil below foundation of the designed structure.

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