On the interpretation of the needle probe test results: thermal conductivity measurement of clayey soils

Recently, there is an increasing need for accurate and rapid thermal measurement of soils. Within a variety of available methods a needle probe test is most widely used. The needle probe method was standardized for the measurement of thermal conductivity of soils and soft rocks. In the paper, two different interpretation methods of the needle probe test were used for determination of thermal conductivity of selected soils. The first method (ASTM D5334-05 Standard approach) takes into account only the data which are recorded during heating while the second approach is based on fitting the known analytical solution to the data obtained within both heating and cooling phases. The soil samples used were classified as clayey ones. Laboratory tests were performed using the KD2Pro thermal conductivity meter (Decagon Devices) with a TR-1 sensor. The main goal of the paper is to show that the selection of interpretation method is very important and may lead to significant differences in resulting thermal conductivities.