## 3 Results and Discussion
### Surface Resistivity Measurements--Recognition of Subsoil and Hydrotechnical Structures
In conclusion, geophysical surveys have not recorded the presence of sealing in this area, which gives the opportunity to evaluate the range of the problem and related detailed research on a given section of the embankment. Figure 13: Geoelectrical cross-section through the embankment compared with cone resistance from the CPTU test. Similar observations were also made by other researchers [10] at a small earthen dam in Colorado where anomalous seepage was observed. The resistivity anomalies were used to delineate three seepage zones within the dam. Another example illustrates the resistivity investigations of a ground under an earth dam where the alluvial deposits, with resistivity reach 150 \(\Omega\)m, overlay the resistive hard limestones bedrock (more than 1100 \(\Omega\)m). The appearance of anomalies in geoelectrical cross sections indicates opened cavity filled with alluvial deposits (40 to 150 Wm). These discontinuities in the bedrock form additional possible pathways for water leakage from the dam reservoir [11]. The proposed approach could be easily practiced in other similar objects suffering from leakage's problems. The next two examples include geophysical surveys, which were carried out in order to complete the geotechnical investigations. Previous research showed a high diversity of the geological structures; in particular the depth of the top of Pliocene deposits and its physical parameters in the analyzed area, e.g., [35, 49]. The properties of these deposits determine the geotechnical design of the above ground and underground structures. These formations require a detailed analysis before their use as building foundation. The first one--the Vistula slope area--shows the use of electrical resistivity measurements to determine the top of undisturbed clay deposits. For this purpose, several electrical resistivity profiles were carried out. Figure 16 shows a geoelectrical cross-section in combination with cone resistance qc and dilatometric index I\({}_{\text{D}}\) values obtained during CPTU and DMT (flat dilatometer test) tests. Figure 14: Geoelectrical cross-section across the embankment body after installing the sealing system. Figure 15: Geoelectrical cross-section across the embankment after installing the sealing system (view of vertical sealing and hydraulic window in the embankment body). CPTU and DMT tests showed a diversified structure of the colluvial-delluvial deposits in the slope area. The change in cone resistance and dilatometric index indicates the top of clay deposits at 6 \(\div\) 6.5 m below ground level (DMT-2, CPTU-2) in the western and middle part of the cross-section. The cone resistance values obtained during CPT-3 testing (eastern part of the cross-section) showed diverse parameters and thus significant diversity of strength and strain parameters due to numerous lenses in colluvial-delluvial deposits in the slope area. Two zones: one at 7.5 to 11 m--cone resistance 1 \(\div\) 2 MPa (clay in the colluvial area) and one below 11 m--cone resistance of approximately 3 MPa, were observed during the analysis of cone resistance during CPT-3 testing. The difference in measured cone resistance indicates 11 m as the depth of the undisturbed top of clay deposits and the bottom of colluvial-delluvial deposits. High electrical resistivity up to 200 \(\Omega\)m, specific for non-cohesive formations in the area can be observed in the electrical resistivity cross-section used in the analysis up to 2 m below ground level. With depth increase, the values decrease to several \(\Omega\)m, which indicates the presence of cohesive soils. The decline in the resistivity isoline towards the east, corresponding to the terrain slope, can be observed on the right side of the cross-section. Changes in electrical resistivity of the subsoil and their detailed analysis have allowed to determine the top surface of clay deposits, assuming that the boundary of the top of Pliocene deposits runs along the 20 \(\Omega\)m isoline.