Evaluating the Temperature Sensitivity of a Capacitance Sensor for Measuring Soil Volumetric Water Content and Electrical Conductivity

Climate change and subsequent sea level rise is a global challenge that will have adverse effects on coastal infrastructure. As ocean levels rise, soil water content and pore fluid salinity will change, affecting multiple components of total suction (e.g., matric suction and osmotic suction). This in turn has the potential to change the compressibility and shear strength behavior of soils. Within the realm of unsaturated soil behavior, assessing a soil's volumetric water content accurately is crucial for characterizing the soil's thermo-hydro-mechanical behavior. Traditionally, a soil's volumetric water content can be inferred utilizing sensors that measure the dielectric properties of the soil. Previous studies have shown that the volumetric water content measured based on dielectric permittivity can be influenced by changes in temperature. Therefore, in order to accurately assess a soil's volumetric water content, an experimental study was conducted to develop a soil-specific calibration model that accounts for the effects of temperature, which can be implemented with commercially available soil volumetric water content sensors. To develop the calibration model, several soil samples instrumented with a capacitance sensor were prepared at various levels of bulk density, volumetric water content, and electrical conductivity. These samples were then hermetically sealed and subjected to temperatures changes ranging from 20 degrees C to 50 degrees C in order to assess the sensor's performance under different temperature conditions. Results from this study indicate that changes in temperature affect the sensor's ability to accurately measure volumetric water content and dielectric permittivity. A series of calibration models are proposed to account for these temperature effects, in order to enhance the sensor's performance under changing environmental conditions.