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 (IL) for cohesive soils and the saturation ratio (Sr) 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 IL and Sr values remained within the normal zone. In the synthetic scenario, the response was much stronger in cohesive soils, where IL increased from about −0.55 to 1.8, whereas Sr in non-cohesive soils changed only slightly. The Welch’s t-test indicated significant scenario-related changes for IL (p-value of 1.095 × 10−19) but not for Sr (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.