Utilization of low-cost water content sensors in compaction tests

The common practice of measuring the water content of any soil mass involves a gravimetric methodology by obtaining the dry and wet mass of a soil-water mixture. In terms of execution, this procedure is simple but time-consuming since it requires at least 12 hours to be completed. Therefore, other measuring techniques could be applied, including devices such as sensors to obtain the water contents of soil. There are plenty of sensors in the market whose purpose is to obtain volumetric water content, which is a fundamental parameter of unsaturated soil mechanics. In the present research, three conventional low-cost volumetric water content sensors were evaluated (capacitive-based and resistive-based) in one of the most basic and common geotechnical tests: the Proctor compaction test. This test is appropriate for this assessment given the fact that its objective is to analyze how the dry density of soil varies regarding different water contents when using a specific compaction energy. The soil used in this work corresponds to sandy soil, with fair amount of gravel and fine material (SM). The interface of the sensors was done via an Arduino UNO board, and the data was processed and displayed using Python code. The findings of this research are presented in terms of calibration curves and linear correlation coefficients, and furthermore, a sensor repeatability test was performed in order to evaluate the accuracy of these types of sensors. The results obtained indicate that these low-cost sensors may not be the most recommended devices to use within the context of this specific geotechnical application.