Prototyping a Compact Moisture Profiling Probe for Detecting and Zoning Hidden Subsurface Waterlogging

Hidden waterlogging of subsurface soils may develop without clear external signs, while still deteriorating the hydro-physical state of foundation soils. This proof-of-concept study demonstrates a compact monitoring and interpretation workflow for identifying such zones through moisture profiling and subsequent engineering interpretation using the liquidity index (I_L) for cohesive soils and the saturation ratio (S_r) for non-cohesive soils. The developed prototype comprises a modular immersion probe, Arduino-based transmitter and receiver units, 433 MHz ASK wireless communication, and data logging. Using geotechnical survey data from a representative site in Astana, a baseline hydro-physical state and an intentionally constructed synthetic risk-waterlogging scenario were analyzed through vertical profiles and horizontal interpolation maps. Under the baseline state, moisture content varied mainly from about 6 to 23%, while most I_L and S_r values remained within the normal zone. In the synthetic scenario, the response was much stronger in cohesive soils, where I_L increased from about −0.55 to 1.8, whereas S_r in non-cohesive soils changed only slightly. The Welch’s t-test indicated significant scenario-related changes for I_L (p-value of 1.095 × 10⁻¹⁹) but not for S_r (p-value of 0.147). The results show the methodological potential of the proposed workflow for engineeringly interpretable zoning of hidden waterlogging; however, site-specific calibration, metrological characterization, and field validation are still required before practical deployment.