Ground source heat storage and thermo-physical response of soft clay

Abstract

Ground source heat storage can condition buildings with reduced consumption of fossil fuels, an important issue in modem building design. However, seasonal heat storage can cause soil temperature fluctuations and possibly deformation of soft clays. This thesis evaluates the thermo-mechanical response of soft clays to seasonal heat storage and associated temperature fluctuations. A literature review reveals that, in normally consolidated to lightly overconsolidated clays, increases in soil temperature can lead to significant plastic strains and a reduction in soil strength. This behavior can be modeled through constitutive formulations that include thermal strain within the elasto-plastic framework of the well-known Modified Cam-Clay Model. The current research uses the MCC Picard (1994) model to study the ground response to a buried heat exchange pipe. The spacing of the pipe was found to govern the effectiveness of ground heat storage. With only one pipe in semi-infinite soil, heat transfer to the ground dissipates quickly and thermal-mechanical interaction is negligible; however, seasonal heat storage is not possible. Closely spaced heat pipes would permit effective seasonal heat storage, but could undergo significant thermally induced consolidation deformations.