Abstract: Time domain reflectometry (TDR) has been widely used in geotechnical engineering field as a reliable method to measure the volumetric water content of soils. In this study, TDR measuring of moisture content was calibrated. Loess samples from Yan’an New Area and Wuqi County were selected for test. The test error in the TDR measurement was analyzed, and the effects of dry density and plasticity index of loess on the calibration of TDR test were discussed. Results revealed large error of measurement before the TDR moisture sensors were calibrated. Given the same mass moisture content, the volumetric water content of loess measured by TDR moisture sensor was in a linear growth relation with dry density. For loess samples from Yan’an New Area with a plasticity index less than 10, the volumetric moisture content (θ_v) measured by TDR moisture sensor was greater than that (θ_w) measured by drying method, and the results were all below the contour line (θ_w=θ_v). For loess samples from Wuqi County with a plasticity index between 10 and 17, when the mass moisture content w was smaller than 12%, θ_v was greater than θ_w, and the test results were below the contour line (θ_w=θ_v); on the contrary when w was larger than 12%, θ_v was smaller than θ_w, and the test results were above the contour line (θ_w=θ_v). By comparing and analyzing the relations between θ_w and θ_v, a modified formula for TDR moisture measuring results was established. The research results offer reference for the application of TDR to measuring moisture content of loess in the loess area of north Shaanxi Province.

Key words: loess, TDR, moisture measuring, volumetric water content, dry density, plasticity index