## 2 Materials and Methods  
### Geological, Hydrogeological, and Geomorphological Conditions  
The railway link route that is being designed is located in an area that was first formed by the Danube River. The geological structure of the area through which the route passes comprises three types of ground environments: anthropogenic sediments, Quaternary fluvial sediments, and Neogene sediments.  
Quaternary fluvial sediments are found on both banks of the Danube River--at a greater distance from the river--in the form of terraces whose thicknesses decrease toward the slopes of the Little Carpathians. They usually consist of gravel and sandy gravel, which contain a variable proportion of sand. Gravel grains are worn by water as their sizes are largely smaller than 30 mm and, less frequently, even larger, up to 100 mm. They consist mainly of hard quartzite, granite, limestone, and crystalline schist. The occurrence of boulders of 300 to 500 mm in diameter in contact with the Neogene bedrock has been recorded in several exploration works. The thicknesses of the layers of Quaternary sediments found along the route ranges from 8 to 14 m. Quaternary sediments are very permeable; therefore, they form a significant corridor for groundwater flows. They are supplied with rainwater, water that flows down the slopes of the Little Carpathians, and, primarily, water that seeps from the Danube River. Therefore, the fluctuations in the water table level follow, with a time delay, the fluctuations in the water surface of the Danube River [17]. Neogene sediments make up the subbase of the Quaternary sediments, and they are represented by cohesive soils and sands with abrupt and irregular alternations in their layers. Soils originate from sedimentation at the edge of a former Palaeogene sea or in the beds of rivers and streams that end in the sea. The main groundwater aquifer is created by fluvial gravel layers and Neogene sands. The groundwater level in these layers is in direct hydraulic dependence on the level of the Danube River, with a corresponding retardation, that is proportional to the distance from the river bed. Neogene clays are impermeable, but positions of Neogene sands are often water-bearing, mainly with a tension horizon, which, after drilling, stabilizes approximately at the level of the free surface in the Quaternary gravels. According to [19] and previous pumping tests [20], it has been determined that the hydraulic conductivity value \(k\) in the horizontal direction is approximately  
Figure 2: General overview of planned TEN-T track in Bratislava (longitudinal profile) [17; 18].  
to 3 \(\times\) 10\({}^{-2}\) m\(\cdot\)s\({}^{-1}\) for Quaternary gravels. In the case of Neogene sands, the hydraulic conductivity value ranges from \(k\) = 3 \(\times\) 10\({}^{-4}\) to 1 \(\times\) 10\({}^{-6}\) m\(\cdot\)s\({}^{-1}\).  
Based on the regional geomorphological classification [21], the solved territory belongs to the area of the Danube Lowland, which is drained by the Danube River. At the same time, the Danube is the dominant natural factor involved in the formation of the relief. In addition to the natural factors involved in the formation of the relief, anthropogenic interventions have had the greatest impact on the current landscape (Figure 3).