Advanced thermo-hydro-mechanical interactions in underground structures

This project aims at characterising the effect of thermo-hydro-mechanical interactions between different components of underground structures and the surrounding soil, and the subsequent impact on their design. Two sources of temperature changes are explored using a combination of 2D and 3D finite element modelling: the activation of structures using heat exchanger pipes and the hydration of concrete. Concerning the former, building upon work carried out by researchers on simplified modelling of thermo-active structures, such as retaining walls and pile foundations, this project will analyse the impact on the temperature fields across the pile section of modelling the thermal loading by explicitly simulating heat exchanger pipes. This will also enable a first-of-its-kind analysis of thermal fluxes in these structures, demonstrating where heat is being stored in different time-frames, as well as characterising the efficiency of such storage, providing further indication of these systems' capabilities as a providers of low-carbon heating and cooling to buildings. Lastly, it is expected that a simplified, yet accurate, modelling approach that yields estimates of pile forces due to temperature changes without the need for computational expensive 3D finite element analysis is produced in order to render their design more approachable by industry practitioners. The second heat source to be considered is the hydration of concrete. These structures are characterised by very large quantities of concrete poured into excavated cavities within the ground. Subsequent chemical reactions are extremely exothermic, producing large quantities of heat that flows from the structure into the ground, triggering a complex interaction mechanism which this project will analyse. A new practical model for simulating this process in geotechnical finite element analyses will be formulated and implemented into the bespoke code ICFEP. Temperature fields around underground structures will be characterised and, where possible, results will be compared to field data for validation purposes (e.g. temperature fields from thermal integrity testing). Lastly, implications from temperature fields generated during hydration to the safe operation of thermo-active structures will be investigated.