A novel sensor for in-situ thermo-mechanical testing and application to MICP-treated soils

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Microbially Induced Calcium Carbonate (CaCO3) Precipitation (MICP) is an innovative technique for strengthening sandy soils that leads to the binding of soil grains with CaCO3 crystals. These crystals can act as thermal bridges to enhance the soil's thermal conductivity, an important soil thermal property for assessing the efficiency of ground heat exchangers, which are used, for example, in energy geo-structures at shallow depths. The combination of energy geo-structure applications with MICP-treated soils is still in its nascency. While existing studies focus on thermal property changes, the quantification of changes in soil thermal conductivity under the in-situ stress state and during isotropic compression is overlooked due to limitation of current experimental techniques. Thermal conductivity measurements in this application require accurate, fast, and non-destructive sensors. However, conventional steady-state and transient thermal probe methods do not fulfill these criteria. The former suffers from long waiting times required to reach a steady state, making it unsuitable for measuring the thermal conductivity of unsaturated soils due to potential changes in the uniform water content of the sample. By contrast, measurement cycles of less than one minute can be achieved by transient thermal probes, but commercially available sensors are expensive, and can be destructive for some laboratory tests. This research introduces a novel transient sensor by miniaturising the traditional thermal probes into a point measurement with just a resistor and using a thermocouple to measure temperature change. The accuracy of the new sensor is investigated using numerical and experimental approaches. The developed sensor in this work provides an economical and non-destructive solution for in-situ and laboratory thermal sensing and can be used in other applications.

9th International Congress on Environmental Geotechnics (ICEG2023)

Biogeotechnics and Bioremediation