AN INVESTIGATION OF THERMAL CONDUCTIVITIES FOR SEVERAL DIFFERENT SOIL TYPES IN SOUTHWEST VIRGINA

The thermal properties of soils play an important role in engineering projects where significant heat transfer is involved. Pipelines, power cables, water pipes, roads, ground-source-heat-pumps, and geothermal systems are all impacted by these thermodynamic characteristics. It is therefore important to have ways of measuring thermal properties in order to help predict their impact on the successful construction and operation of engineered projects. Research conducted by Omar Farouki of Cornell University quantified these characteristics for various soil types and conditions. The Standard Test Method for the Determination of Thermal Conductivity of Soil and Soft Rock by Thermal Needle Probe, ASTM D5334, is the most common method used today. The needle probe is typically a few cm long and uses a heating element and a temperature measuring element to record the rise in temperature over time. Our research takes a different approach by using a cylinder two feet long to house the material for heating at one end and measuring the distribution of heat over time and distance. The soil sample is placed in an insulated stove pipe with a sealed bottom and open top for ventilation. Constant heat is then applied using an electric coil burner modified to have a steel plate on top for even heat distribution. The system is heated and heat flow is measured until it reaches an equilibrium state, after which the decrease in temperature is also recorded until it returns to room temperature. A temperature sensing and data logging system was constructed using Arduino microprocessor technology and sensors to take readings at 10cm intervals from 0cm to 50cm. This presentation is a progress report describing an alternative method for measuring thermal properties of soils and looks to shed new light on the thermodynamic properties of varied soil materials. One goal is to provide information on the suitability of soils found in southwest Virginia for use with ground-source-heat-pumps.