## 2 Methodology and Interpretation of Dilatometer Tests
#### Geotechnical Conditions of Test Sites
The second layer has a thickness from 6.3 to 10.5 m and represents calcareous gyttja (\(G_{y}\)). Its content of organic parts \(I_{om}\) ranges from 10% to 20% and the content of calcium carbonate CaCO\({}_{3}\) is equal to 65 \(\div\) 75% at moisture \(w_{n}\) between 180% and 220%, and the determined liquidity limit \(W_{L}\) is 100 \(\div\) 110%. The unit density \(\rho\) is 1.25 \(\div\) 1.30 g/cm\({}^{3}\), whereas the specific density \(\rho_{\rm s}\) is 2.20 g/cm\({}^{3}\). The third gyttja (calcareous-organic) (\(G_{y}\)) layer has the following properties: the content of organic parts \(I_{om}\) ranges from 10% to 15% and the content of calcium carbonate CaCO\({}_{3}\) is equal to 70 \(\div\) 75% at moisture \(w_{n}\) between 135% and 140%, and the determined liquidity limit \(W_{L}\) is 105%. The unit density \(\rho\) is 1.30 \(\div\) 1.35 g/cm\({}^{3}\), whereas the specific density \(\rho_{\rm s}\) = 2.2 g/cm\({}^{3}\)[26; 27; 28]. The static ground water level is present in the peat layer at the depth of 0.5 m below the ground surface. The preconsolidation pressure obtained from oedometer tests is higher than the initial values of effective vertical stresses, which shows that organic soils are overconsolidated with an overconsolidation ratio, \(OCR\), in the range of 1.5 \(\div\) 4 [26; 27; 28] (Table 3). The physical properties of the soil at the Nielisz site were determined during previous WULS-SGGW tests. The layer of soft subsoil has a thickness of 3 m to 5 m; the ground is slightly preconsolidated [29; 30; 31]. Two layers of organic subsoil were distinguished at the Nielisz site. In the first layer, the content of organic parts ranges from 20% to 30% at moisture between 120% and 150% and the determined liquidity limit \(W_{L}\) is 130 \(\div\) 150%. The bulk density is 1.25 \(\div\) 1.30 g/cm\({}^{3}\), whereas the specific density is 2.25 \(\div\) 2.30 g/cm\({}^{3}\). In the second layer lying below, the content of the organic part is 10 \(\div\) 20% at a moisture of 105 \(\div\) 120% and a liquidity limit of 110 \(\div\) 130%; the bulk density of the layer is 1.30 \(\div\) 1.45 g/cm\({}^{3}\), and the specific density is 2.30 \(\div\) 2.40 g/cm\({}^{3}\). These layers are separated by sandy silt. Beyond the existing embankment under the downstream sperm and the upstream slope, the soft soils are overconsolidated with an overconsolidation ratio, OCR, decreasing from 3 to 2 with depth [28] (Table 3). Taking into account the physical and mechanical properties of the soils, five geotechnical layers were distinguished in the grounds of the WULS-SGGW Campus (Figure 6). Layer I consists of fluvioglacial layers of the Warta Glaciation (\({}^{\text{6S}}\)Q\({}_{\text{P}}\)W)--medium and fine sands, with relative density \(D_{\text{r}}\) = 0.35 \(\div\) 0.55, and clay sands, sandy clays and silt with \(I_{L}\) = 0.15 \(\div\) 0.20. Layer II represents the meltout sediments of the Warta Glaciation (bQ\({}_{\text{P}}\)W)--medium and fine sands with \(I_{D}\) = 0.3 \(\div\) 0.5, and sandy clay and clay sands with \(I_{L}\) = 0.0 \(\div\) 0.20 and \(I_{L}\) = 0.25 \(\div\) 0.54. Layer III is brown glacial clay from the Warta Glaciation (\({}^{\text{6S}}\)Q\({}_{\text{P}}\)W)--sandy clays with \(I_{L}\) = 0.0 \(\div\) 0.11. Layer IV is grey glacial clay from the Oda Glaciation (\({}^{\text{8S}}\)Q\({}_{\text{P}}\)O)--sandy boulder clays with \(I_{L}\) = 0.0 \(\div\) 0.12. Layers III and IV are similar in terms of plasticity, but clearly differ in the sand fraction content. The sandy clays layer III contains a few percent more of the sand fraction, which together with the analysis of the results of DMT sounding were the basis for the separation of these layers into sublayers. Layer V comprises river sediments of the Mazovian Interglacial (\({}^{\text{4}}\)Q\({}_{\text{P}}\)M)--fine and medium sands, in the roof very compact layers with a relative density \(D_{r}\) = 0.8 \(\div\) 0.9 (Figure 6).