Study on calibration method for accurate calculation of water content in sandy soil in western China

The determination of the quantitative relationship between soil permittivity and volumetric water content is an important basis for the development of ground penetrating radar technology to determine soil volumetric water content.The traditional ground penetrating radar (GPR) technology is generally based on the classic Topp formula for calculating soil volume moisture content,but the accuracy of the calculated value is often larger than the actual measured value,and it is difficult to meet the calculation accuracy of soil volume moisture content under different geological conditions.In order to solve this problem,the method of combining ground penetrating radar and shallow drilling is adopted,and the description and depth calibration of the medium layer by shallow drilling are used to accurately calculate the two-way travel time of the radar wave reaching each reflection interface in the radar data section to obtain a more accurate relative dielectric constant above the interface of each layer of media,and through regression analysis of the measured water content values of each medium,a Topp formula form suitable for accurate calculation of volumetric water content of sandy soils of different particle sizes in western China was established modified model.The comparison between the calculated soil volume water content value using the revised model and the original Topp formula shows that the average error of the volume water content obtained by the revised Topp formula calculation model is 42% lower than that before the correction.Sand is reduced by 56%,the average error rate is reduced by 58% compared to the fine sand before the correction,and the sand is reduced by nearly 67%.The accuracy of the volumetric water content calculation of the two particle size sandy soils using the revised calculation model has been greatly improved.This result illustrates the accuracy of the calculation model modified by the Topp formula using the measured water content,and also verifies the accurate calculation method of the GPR wave velocity calibration method based on the combination of ground penetrating radar and shallow drilling for the water content of the sandy soil medium in western China rationality.