An implicit Heat-Pulse-Probe method for measuring the soil ice content

Abstract

• Ice content measurement in soil is essential and challenging, and the thermal response of frozen soil mainly depends on the pore ice content. • The pore ice content can be measured by its thermal response. • An implicit heat-pulse method is proposed to measure soil ice content. • T rela characterizes soil thermal response upon heating. • Ice content θ i affects soil thermal properties and thermal response T rela . • A standard calibration is proposed to determine the relation between T rela and θ i . • The average errors of θ i from the new method are around 3%. Soil ice content increases with time during the freezing process, thus frequently causing severe frost heave of subgrade or foundation in the cold region. It is a lasting challenge to implement real-time monitoring of soil ice content. In this study, a new heat-pulse method with an average accuracy of around 3% was proposed to measure soil ice content. This method was implemented by the following steps: (1) A heat pulse method with a double-probe sensor, i.e., one heating probe and one measurement probe was used; (2) In the calibration, the relation area after a heat-pulse action was measured on four samples with different initial water contents and at eight negative environmental temperatures. (3) On the calibrated data, an approximate function was fitted to characterize the monotonic relation between the relation area and soil ice content; (4) In application, the relation area value and environmental temperature were measured for each frozen sample, and the measurements were substituted into the approximate function to calculate the soil ice content. The effectiveness of the new method was verified by the test on three types of soil, including a silty clay, a sand loam, and a sand.