In Situ Measurement of Soil Thermal Properties: a New Prototype

Abstract

As part of the THERMALTUNNEL R&D, partially funded by Centro para el Desarrollo Tecnológico e Industrial (CDTI), a Spanish Ministry of Science and Innovation agency, PRO GEO has developed a soil penetration prototype that measures soil temperature and the thermal properties of the ground (thermal conductivity and specific heat) at different depths. The prototype is the size of a conventional CPT and contains an internal heat source with local thermocouples. A data acquisition system measures the temperature both in the prototype itself and in the surrounding ground through a penetration needle protruding from the main body of the prototype. The thermal parameters are determined by analyzing the measured heating and cooling temperature curves using the finite element codes CODE_BRIGHT (Olivella et al., 1993) and G-PFEM (Monforte, 2018). In this later numerical code, a thermal analysis module has been incorporated within the framework of the project. The operation of the prototype has been satisfactory in laboratory tests through a calibration chamber setup with granular soil under different controlled conditions of water saturation and porosity to assess the impact of those variables on the obtained values of soil thermal conductivity and specific heat. The back-analyzed parameters from the calibration chamber results have been compared with point tests (thermal conductivity and specific heat tests). The project has been developed with the cooperation of CIMNE – International Centre for Numerical Methods in Engineering.

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