While it has been established that temperature can change the preconsolidation pressure of clays, the current understanding is limited to specific ranges of temperatures, with temperatures above freezing being studied entirely independently of temperatures below freezing. However, as temperature is a continuous domain and clays may be subjected to both above- and below- freezing temperatures over the course of an engineering application, a unified view is necessary. The first goal of this thesis is to develop a single model which can be used to predict the preconsolidation pressure of a normally consolidated clay at any temperature over a wide range which includes both frozen and elevated temperatures. To do so, consolidation tests were run at various temperatures between -7 °C and 50 °C, and the yield stress at each consolidation temperature was determined. As previous studies have established that the temperature response of clays is dependent upon their mechanical stress history, the specimens were consolidated initially at a reference temperature until they reached the normally consolidated state. Subsequently, the temperature of the specimens was changed and the volume changes during the temperature change stage were recorded. Once the specimens stabilized at the new temperature, they were consolidated once again and the preconsolidation pressure determined at the new consolidation temperature. The volumetric strains and changes in preconsolidation pressure for each temperature used in this study align generally with the previous data published for each temperature domain. Heating led to a decrease in the volume of the specimens, cooling to minimal strain, and freezing to an increase in the specimen volume. Changing the consolidation temperature by either heating, cooling, or freezing the specimen led to various degrees of increase in the preconsolidation pressure. A mathematical model was developed to fit the observed preconsolidation pressures at each consolidation temperature. This model can be used to predict the yield stress of NC kaolinite at any temperature within the tested range, and captures the smaller magnitude increases in yield stress which occur upon heating and cooling as well as the large increases which occur upon freezing the clay. With the effects of unidirectional thermal paths having been treated in the previous portion, a second investigation was also undertaken to assess how much of the temperature history of the soil might influence the behavior at its final consolidation temperature. In particular, the impacts of previous freezing on the preconsolidation pressure at elevated temperatures were investigated. The same clay material was first consolidated to the NC state and then frozen to -15 °C. Subsequently, the material was thawed or heated to various final temperatures and consolidated further to determine the preconsolidation pressure. The results of these tests indicate that the preconsolidation pressure was independent of the consolidation temperature for previously-frozen soil. While increasing contractive axial strains were recorded with increasing temperature, there was no accompanying increase in the preconsolidation pressure. These results indicate the thermal history of the clay can alter its behavior at the current temperature, overriding the effects of the most recent thermal path. / Master of Science / Temperatures around the globe are becoming more extreme every year due to global warming. The warming climate has destabilized permafrost. Additionally, new energy applications, such as heat exchange piles, and existing energy infrastructure, such as oil and gas pipelines, also constitute extreme thermal environments. The settlement of soils in these conditions must be well understood so that engineers can predict and mitigate potentially damaging conditions. One engineering parameter which is necessary to predicting the amount of consolidation settlement in clays is the overconsolidation ratio (OCR), and the preconsolidation pressure of clays is required in order to compute OCR. Previous studies have established that preconsolidation pressure is a function of temperature. However, in addition to changing soil temperatures due to climate, soil temperatures between in situ and laboratory settings where preconsolidation pressure is determined are often different as well. Therefore, in order to develop resilient foundations and structures in areas with thermal variations, a thorough understanding of how the preconsolidation pressure changes with temperature is necessary. The goal of this study is firstly to develop a mathematical model which can be used to predict the preconsolidation pressure of a clay over a wide temperature range which includes both frozen (<0 °C) and heated (>20 °C) temperatures. Consolidation tests were run on kaolinite clay specimens to determine the preconsolidation pressure at various temperatures within the chosen range. Then, a single expression was developed to allow the user to predict the preconsolidation pressure at any temperature within this range. While the mineralogy and stress state of the clay impact the parameters of this equation, the general form models the expected change in yield stress for a given change in temperature. The second goal is to assess whether the thermal history of the clay, in particular a prior frozen state, affects the preconsolidation pressure determined following subsequent thawing and heating.

Les pieux énergétiques représentent une solution alternative intéressante, face à l’accroissement des besoins mondiaux en énergie et à la réduction de l’utilisation des énergies fossiles. L’objectif principal de la thèse est d’identifier et de quantifier les principaux facteurs influençant le dimensionnement des pieux géothermiques, qui sont impactés par les changements de température des pieux lors de leur activité. Pour ce faire, ce travail de thèse a été dressé en 3 campagnes expérimentales, dont deux à échelle réelle : (i) une première campagne à chargement thermomécanique contrôlé (Marne La Vallée), (ii) une seconde campagne en conditions d’utilisation réelles sous une station d’épuration (Sept Sorts) et (iii) une troisième campagne à l’échelle du laboratoire grâce à une nouvelle machine de cisaillement direct d’interface permettant l’étude du comportement thermo mécanique des interfaces sol-structure. Ces trois campagnes expérimentales ont pour but de quantifier l’effet de la température et des cycles de température sur le comportement des pieux énergétiques. Les premiers résultats expérimentaux de la campagne de Sept Sorts ont ensuite été simules dans le code LAGAMINE via la méthode des éléments finis, afin d’adopter une approche complémentaire permettant de mieux appréhender la réponse thermomécanique de ce type de pieu lors de l’activation géothermique. et (iii) une troisième campagne à l’échelle du laboratoire grâce à une nouvelle machine de cisaillement direct d’interface permettant l’étude du comportement thermo mécanique des interfaces sol-structure. Ces trois campagnes expérimentales ont pour but de quantifier l’effet de la température et des cycles de température sur le comportement des pieux énergétiques. Les premiers résultats expérimentaux de la campagne de Sept Sorts ont ensuite été simules dans le code LAGAMINE via la méthode des éléments finis, afin d’adopter une approche complémentaire permettant de mieux appréhender la réponse thermomécanique de ce type de pieu lors de l’activation géothermique. / Energy piles, also called thermo-active piles, are an alternative solution to the increase in the global energy demand as well as in mitigating socio-economical stakes concerning the increase of energy costs due to fossil fuels. Energy piles are double purpose structures that allow transferring the loads from the superstructure to the soil and that integrate pipe circuits allowing heat exchange between the pile and the surrounding ground. The objective of this thesis is to identify and quantify the principal parameters involved in the geotechnical design of pile foundations impacted by temperature changes associated with geothermal activation. For this purpose, this research work was organized in 3 experimental campaigns: (i) A full scale load controlled test at Ecole des Ponts Paris-Tech, (ii) Full scale energy piles monitoring under real exploitation conditions at Sept Sorts, (Seine et Marne, France), (iii) Laboratory tests in order to assess the effect of temperature and temperature cycles at the soil-pile interface. The experimental results are used to estimate the effect of geothermal activation of a pile foundation, on its bearing capacity as well as on its long-term exploitation. Finally, preliminary numerical simulations were performed using a thermo-hydro mechanical model, using the finite element method code LAGAMINE able to capture the main phenomena.

Abstract. The circadian locomotor (walking) rhythms of forager honeybees (Apis mellifera ligustica L.) were entrained to eight different 24 h light‐dark cycles. The phases of activity onset, peak activity, and offset were correlated with the lights‐off transition, suggesting lights‐off as the primary zeitgeber for the rhythm. Further support for this hypothesis was provided by LD 1:23 experiments, in which entrainment occurred when the light pulse was situated at the end, but not at the beginning, of the subjective photophase. Steady‐state entrainment of the locomotor rhythm was achieved with square‐wave temperature cycles of 10oC amplitude under constant dark: most of the activity occurred within the early thermophase. Smaller amplitude temperature cycles yielded relative coordination of the rhythm. Interactions of temperature and light‐dark cycles resulted in entrainment patterns different from those elicited in response to either cycle alone or those formed by a simple combination of the two separate responses. Furthermore, temperature cycles having amplitudes insufficient for entrainment of the rhythm nevertheless modified the pattern of entrainment to light ‐ dark cycles, suggesting a synergism of light and temperature effects on the underlying circadian clock system.

Distributed power generation through renewable sources of energy has the potential of meeting the challenge of providing electricity access to the off-grid population, estimated to be around 1.2 billion residing across the globe with 300 million in India, in a sustainable way. Technological solutions developed around these energy challenges often involve thermal systems that convert heat available from sources like solar, biomass, geothermal or unused industrial processes into electricity. Conventional steam based thermodynamic cycle at distributed scale (< 1 MWe) suffers from low efficiency driving scientific research to develop new, scalable, efficient and economically viable power cycles. This PhD work conducts one such study which provides a database of thermal power blocks optimized for the lowest initial investment cost to developers of distributed power plants. The work is divided in two steps; a) feasibility study of various thermodynamic cycles for distributed power generation covering different operating temperature regimes and b) perform their detailed thermo-economic modelling for the heat sources mentioned above. Thermodynamic cycles are classified into three temperature domains namely, low (< 450 K), medium (< 600 K) and high (< 1000 K) T cycles. Any fluid whose triple point temperature is below the typical ambient temperatures is a potential working fluid in the power cycle. Most of the organic and the inorganic fluids satisfy this criterion and can be perceived as potential power cycle fluids. The general notion is that organic fluids are more suited for low or medium temperature cycles whereas inorganic fluids for high temperature ones. Organic fluids can further be classified into hydrofluorocarbon and hydrocarbon. While the former has high global warming potential (GWP), the latter is flammable in nature. Their mixture in certain compositions is found to obviate both the demerits and perform equally well on thermodynamic scales for low T cycles. On the similar lines, mixture of HCs and inorganic fluids, such as propane+CO2 and isopentane+CO2 are found to be more appropriate for medium T applications if the issues like pinch temperature in the regenerator arising due to temperature glide are taken care of. In the high temperature domain, high efficiency Brayton cycle (supercritical CO2) and transcritical condensing cycles are studied with the latter being 2 % more efficient than the former. However, application of the condensing cycle is limited to low temperature ambient locations owing to low critical temperature of CO2 (304 K). In the same cycle configuration, mixture of CO2 and propane (52 and 48%) with a critical temperature of ~ 320 K is observed to retain the thermodynamic performance with the increased heat rejection temperature matched to the tropical ambient conditions. However, these cycles are plagued by the high operating pressures (~300 bar) calling for high temperature steel making the power block uneconomical. In this regard, the advanced CO2 cycles are developed wherein the optimum operating pressures are limited to 150 bar with an increased cycle efficiency of 6 % over the S-CO2 cycle. Feasibility study carried out on these cycles in the Indian context indicates the low and medium T cycles to be better suited for distributed power generation over the high T cycles. In the second part of work, a comprehensive study is performed to optimize the low and the medium T cycles on a thermo-economic basis for the minimum specific investment cost ($/We). Such a study involves development of component level models which are then integrated to form the system of interest, thus, following a bottom-up approach. A major emphasis is given on the development of scroll expander and low cost pebble bed thermal energy storage system that are the reported in the literature as the areas with high uncertainties while connecting them to the system. Subsequently, the key design parameters influencing the specific cost of power from an air-cooled ORC are identified and used to formulate a 7-dimensional space to search for the minimum costs for applications with a) geothermal/waste or biogas heat sources and b) solar ORCs. Corresponding maps of operating parameters are generated to facilitate distributed power engineers in the design of economic systems within constraints such as available heat source temperatures, maximum expander inlet pressures imposed, etc. Further, the effect of power scaling on these specific costs is evaluated for ORC capacities between 5 and 500 kWe.