Task 1 : Ground investigation methods
This task concerns the thermo-hydro-mechanical behaviour of the ground around thermoactive geostructures.
The thermal properties of the ground around a shallow geothermal energy installation determine the heat fluxes in the system and its overall performance. The temperature variations induced in the ground due to the exploitation of a thermoactive geostructure can affect the geotechnical behaviour and the stress state of the soil/rock around it, as well as at the structure-soil interface, which in turn can affect the geostrucutre itself.
Different approaches will be studied :
- in situ tests, namely TRT : Thermal Response Tests
- laboratory tests
- numerical modelling.
The proper design of the GSHP requires the knowledge of the soil thermal properties. For this aim TRT are often adopted, especially in vertically oriented loops.
The thermal conductivity and the specific heat can be evaluated in the laboratory submitting the test specimen to a specific thermal flux. Numerous effective methods exist today. The comparison of ground investigation and laboratory tests for the evaluation of soil thermal properties is the first issue to be addressed. The different techniques and practices currently used in Europe will be identified and compared. The main problems concern the scale effect (from micro to macro), the saturation conditions, the spatial scatter of soil properties and the sampling effects.
An integrated methodology aiming at the definition of a geological and geotechnical model including the relevant properties of soils for the design of thermoactive geostructures could arise. Hydro-thermo-mechanical behaviour of soils is also to be addressed. An extensive study on this subject is to be carried out. Numerical models have been used to simulate the observed behaviour in laboratory tests and in case studies of energy foundations. Several constitutive models and numerical analysis for describing the hydro-thermo-mechanical behaviour of soils have been proposed in the last two decades.
This task aims to analyse them, creating a comprehensive summary of their features, capabilities and limitations.