# Control and Analysis of Layered Soil Structure to Ensure Railway Roadbed Stability
## 3 Results  
During the experiment, the drill was inserted into different soil layers beneath the railway track. The control zone was a specially artificially organized section of the railway roadbed, for which dry sand (specific electrical resistance \(\rho\approx 300\) kOhm\(\cdot\)m) or a sand and gravel mixture (5 in the figure) was used as the upper ballast layer (cushion). The following parameters of the measuring setup and experimental conditions were used: a temperature of the near-surface part of the geological environment of +18 \({}^{\circ}\)C; pH of 6.5; frequencies of probing electrical signals of 166 Hz; amplitudes of the probing electrical signals of 80 V; a sampling frequency of the analog-to-digital converter of the receiving path of the measuring system of 10,101 Hz; the type of geoelectric setup--radial (consisting of two emitters and six receivers); a distance between emitters of 12 m; and a distance between receivers of 3 m.  
The diagram of the measuring setup is shown in Figure 2, where A and B are emitters, and M and N are field receivers. The immersion process was conducted in stages, starting from the 80 s mark and continuing at 50 s intervals, with a drill penetration step of 10 cm. Voltage changes on the receiving electrodes were recorded with a sampling frequency of 10,101 Hz. The phase shift of the output signals (see Figures 3 and 4) was monitored during the drill's passage through various soil layers. Observations showed that the phase of the electrical signals varied as the drill moved through layers with distinct electrical characteristics, which is crucial for assessing the impact of different soil layers on railway track stability. Figure 1: Experimental setup diagram. Figure 2: Layout of electrodes in measuring setup (A,B—input signal electrodes, M\({}_{1}\)M\({}_{2}\)M\({}_{3}\)N\({}_{1}\)N\({}_{2}\)N\({}_{3}\)—output signal electrodes). Studies have demonstrated that the extent of phase change in the signal is strongly influenced by the depth and electrical characteristics of the soil layers. This information is critical for assessing the operational reliability of the railway roadbed, as variations in soil properties can lead to differential settlement and track misalignment. Accurate identification of different soil layers helps in understanding how they interact with railway loads and how they respond to changes in moisture content, density, and other factors. This understanding is essential for predicting potential issues and implementing effective reinforcement measures to prevent track failures. For railway infrastructure, where maintaining precise alignment and stability is crucial for safe and efficient operations, this capability significantly enhances the management of soil-related risks [18,19]. The experimental data demonstrate that the phase-metric probing method is effective in detecting variations in soil composition, including moisture content and density. For  
Figure 4: Output signal phase change (experiment 2). Figure 3: Output signal phase change (experiment 1). example, soil with a lower density or higher moisture content will have a different effect on the phase of the probing signal, which allows for the identification and localization of such layers. The figures show that as the drill penetrated the soil and passed through different layers, the angle of the phase signal changed. Thus, in Figure 2, starting from the 410 th second, the probing drill reached a layer with a lower moisture content. In Figure 3, starting from the 290 th second, the drill also hit less wet soil. These changes in the phase signal confirm the possibility of using the method to detect and characterize different soil layers. Thus, the phase-metric probing method has proven its worth in identifying and analyzing the layered structure of the soil, which is important for ensuring the stability and reliability of the railway roadbed.