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Energy Foundations and Other Thermo-Active Ground Structures

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Abstract

Energy foundations and other thermo-active ground structures, energy wells, and pavement heating represent an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimised maintenance. The paper focuses on earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. Absorber pipes filled with a heat carrier fluid are installed within conventional structural elements (piles, barrettes, diaphragm walls, basement slabs or walls, tunnel linings), forming the primary circuit of a geothermal energy system. The natural ground temperature is used as a heat source in winter and for cooling in summer. Hence no additional elements have to be installed below surface. The primary circuit is then connected via a heat pump to a secondary circuit within the building. 'Free cooling' may even run without a heat pump. The paper describes heat transfer in the ground, and between absorber fluid and concrete/soil. Temperature-induced changes of soil properties or of foundation behaviour are also discussed, and recommendations for design and operation are given. Pilot research projects and case histories bridge the gap between theory and practice, and special applications reveal the wide field of geothermal geotechnics.

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... Previous research has studied the effects of C&D materials on geotechnical and environmental properties [25][26][27][28][29][30]. However, research on the influence of C&D materials on geothermal systems is limited to date. ...
... In addition to the energy collection, an asphalt solar collector system can effectively reduce pavement surface temperatures. The pipe system of an asphalt solar collector is commonly installed at a shallow depth in the pavement in order to prevent cracks in the asphalt layer due to the stress concentration around the pipe [25][26][27][28][29][30]. ...
... Based on the published literature [27][28][29][30], the pipe system of a geothermal pavement system can be installed in the base layer to minimize construction and maintenance costs. A geothermal pavement system, comprising a pipe system formed by a number of pipe circuits (for redundancy) in the base layer to collect the thermal energy, is an advancement in renewable energy resources for generating electricity as an alternative to the conventional power generation for both heating and cooling systems. ...
Article
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Geothermal pavements have the potential to reduce the pavement surface temperature by circulating fluid in pipes within the pavement structure. This research investigated an innovative geothermal pavement system with multiple benefits, such as reducing the surface temperature and harvesting heat energy for power generation. This research aimed to provide an understanding of the mechanical properties of geothermal pavements constructed with construction and demolition (C&D) waste materials through large-scale physical testing, experimental testing, small-scale prototype testing, and numerical simulation. The mechanical properties of the geothermal pavement system were assessed under long-term traffic loading conditions using a prototype test system. The repeated load triaxial and repeated-load California bearing ratio tests were also undertaken to evaluate the effect of pipe inclusion on the permanent deformation, stiffness, and strength of the pavement base. A numerical model was subsequently developed and calibrated using the data from small-scale prototype testing. In addition, the effects of the flow rate and pipe materials on the thermal performances of the geothermal pavements were also investigated in this research. The inclusion of pipes in the pavement base layer was found to have negligible detrimental effects on the deformation behavior of RCA. The resilient moduli of recycled concrete aggregate (RCA) samples slightly decreased with the inclusion of pipes. An HDPE pipe reduced the stiffness of the RCA + HDPE mix. On the other hand, a copper pipe’s high stiffness improved the mix’s strength. The numerical simulations indicated that for the HDPE pipe, increasing the flow rate from 500 mL/min to 2000 mL/min reduced the surface temperature by approximately 1.3%, while using the copper pipe resulted in an approximately 4% further decrease in the surface temperature compared to the HDPE pipe.
... Several studies have shown that thermal conductivity increases with dry density and water content of the material [10], [11] as does the thermal capacity [12]. Meanwhile the impact of water content and moisture transfer in soil is not widely discussed in the literature. ...
... These properties are dependent on soil properties: density, water content, mineralogy, size, and grain arrangement. Several studies have shown that thermal conductivity increases with dry density and water content [10], [11], as does thermal capacity [12] [93]. References [13], [14] showed a proportional relationship between soil moisture content and soil thermal conductivity. ...
... HAMLab model [127] includes 2D and 3D geometries, heating, ventilation, and air conditioning systems' description, and TBs. TB models are based on Eq. (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). HAMLab is effective in predicting heat, air, and mass transfer in the building envelope. ...
Thesis
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The building sector is the highest energy-consuming sector in France. Hence, renovation should be considered to overcome high energy consumption. Naturally, heat rises and escapes through roofs, windows, and walls rather than the ground, acting as a natural insulator and thermal reservoir. Ground heat loss has been considered negligible compared to heat losses from other building surfaces for a long time. Therefore, heat transfer at this level should be included in the whole energy simulation for slab-on-grade buildings. In this context, the thesis describes significant ground physical phenomena to understand ground behavior, boundary conditions and soil thermal parameters. This is followed by the presentation of different studies evaluating heat transfer phenomena through the soil and the thermal bridges. In addition to that, a detailed three-dimensional analysis of ground heat transfer using WUFI Plus software is presented. Considering ground thermal bridges in whole building calculations is strongly highlighted in this analysis. Several boundary conditions, climates, insulations, slabs materials, and soil thermal properties are widely compared and discussed. Finally, the thesis concludes with an optimization study. The last chapter compares and validates a 2D heat transfer model (KIVA) in EnergyPlus to the 3D model in WUFI Plus. Several insulations or renovation solutions are proposed, and other thermal and economic parameters are described in an optimization work using GenOpt and EnergyPlus (KIVA) software.
... A GSHP system is used to minimize the capital cost of cooling and heating geostructures. The GHE loops are embedded inside the pile foundations, and the heating and cooling process is shown in Figure 1 [16][17][18]. ...
... A GSHP system is used to minimize the capital cost of cooling and heating geostructures. The GHE loops are embedded inside the pile foundations, and the heating and cooling process is shown in Figure 1 [16][17][18]. Piles are structural foundation components that are relatively long and usually slender and transport loads from superstructures to deep layers of soil. ...
... The high-density poly-ethylene/poly-propylene (HDPE/HDPP) plastic pipes with a U shape that carry the heat carrier fluid (HCF) within the geothermal energy pile (GEP) are utilized in the energy pile design, which have been called the energy loops or absorber pipes, and have a diameter of 40 mm. The soil type was stated to be of a clayey nature and the heat carrier fluid (HCF) in the tubes was stated to be pure water [48] or water mixed with an antifreeze-or biocide (ethylene or propylene glycol)-based solution [17]. The freezing point is decreased by ethylene glycol, whereas its viscosity increases, which results in higher input energy for pumping [49]. ...
Article
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The present study focused on the design of geothermal energy piles based on cone penetration test (CPT) data, which was obtained from the Perniö test site in Finland. The geothermal piles are heat-capacity systems that provide both a supply of energy and structural support to civil engineering structures. In geotechnical engineering, it is necessary to provide an efficient, reliable, and precise method for calculating the group capacity of the energy piles. In this research, the first aim is to determine the most significant variables required to calculate the energy pile capacity, i.e., the pile length (L), pile diameter (D), average cone resistance (qc0), minimum cone resistance (qc1), average of minimum cone resistance (qc2), cone resistance (qc), Young’s modulus (E), coefficient of thermal expansion (αc), and temperature change (ΔT). The values of qc0, qc1, qc2, qc, and E are then employed as model inputs in soft computing algorithms, which includes random forest (RF), the support vector machine (SVM), the gradient boosting machine (GBM), and extreme gradient boosting (XGB) in order to predict the pile group capacity. The developed soft computing models were then evaluated by using several statistical criteria, and the lowest system error with the best performance was attained by the GBM technique. The performance parameters, such as the coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), mean biased error (MBE), median absolute deviation (MAD), weighted mean absolute percentage error (WMAPE), expanded uncertainty (U95), global performance indicator (GPI), Theil’s inequality index (TIC), and the index of agreement (IA) values of the testing data for the GBM models are 0.80, 0.10, 0.08, −0.01, 0.06, 0.21, 0.28, −0.00, 0.11, and 0.94, respectively, demonstrating the strength and capacity of this soft computing algorithm in evaluating the pile’s group capacity for the energy pile. Rank analysis, error matrix, Taylor’s diagram, and the reliability index have all been developed to compare the proposed model’s accuracy. The results of this research also show that the GBM model developed is better at estimating the group capacity of energy piles than the other soft computing models.
... An energy pile is a set of heat exchange pipes buried in the foundation, which is combined with the building structure. By using the relatively stable temperature underground, the circulating fluid in a closed loop (through heat exchanger pipes) can bring heat/cold energy from the underground to the building [1,3]. It is a dual-purpose foundation system that incorporates heat exchangers inside the pile and provides foundation support for the building, thus making it possible to use shallow geothermal while withstanding the load of the superstructure. ...
... As a practical alternative to the BHE, energy pile has been used more and more globally since they were first adopted in the 1980s [3]. Although an energy pile may provide less heat/cold energy than BHE, it can cover the basic heating/cooling needs of a building and show many advantages over BHE [4,5]. ...
... Hence, compared with BHE, an energy pile can provide a higher heat transfer capacity [6,7]. Moreover, in the past few decades, considerable efforts have been focused on energy piles through full-scale tests [3,8], model tests [9,10] and numerical modeling [11,12]. ...
Article
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The underground energy geostructure represented by the energy pile is one of the key paths for the cooperative development of underground space and geothermal energy. Because of its advantages of low cost, high efficiency and no extra occupation of underground space, it has become a feasible alternative to the borehole heat exchanger. The change in the temperature field of the energy pile and its surrounding ground not only affects the geological environment but also influences the thermomechanical performance and the durability of the structure. However, the temporal and spatial unsteady-state temperature distribution of piles and surrounding rock under typical intermittent and unbalanced thermal load conditions is still unclear. In this paper, a finite element model was applied to analyze the unsteady-state temperature distribution, and the thermomechanical behavior of the energy pile group was developed and verified. The temperature field distribution of pile and surrounding rock under typical intermittent working and unbalanced thermal load conditions were determined. Moreover, the thermomechanical behavior characteristics of the energy pile group were investigated. Finally, the influences of pile layout on the thermomechanical behavior of the energy pile group were identified by designing six different scenarios. The results indicate that under typical intermittent operation conditions, the temperature of the energy pile and surrounding ground near the heat exchange pipe varies periodically. For areas with unbalanced cooling and heating loads, long-term operation of energy piles leads to thermal accumulation, and the maximum temperature of energy piles occurs in the first daily cycle. In summer/winter working conditions, the increase/decrease in pile temperature induces axial compression/tensile stress. When the pile group is partially used as the energy pile, the non-energy pile acts as the “anchor pile”, and it generates the added tensile stress.
... To reduce primary energy consumption and greenhouse gas emissions, ground source heat pumps (GSHPs) are among the effective technologies to utilize shallow geothermal energy sources to meet energy demands (Gao et al. 2009). As an extension with good potential, a pile heat exchanger (so-called energy pile) combines shallow geothermal energy exploitations and pile foundation utilizations (Brandl 2006). The geothermal energy extracted by energy piles can be used for cooling/heating buildings or deicing bridges (Kong et al. 2019;Wu et al. 2020) while bearing the load of the superstructure or upper bridges. ...
... An improved understanding of the load transfer mechanisms and restraints at both ends provides a greater understanding of the behavior of the equal-diameter energy pile. Field tests have been conducted to investigate the axial stress/strain behaviors (Brandl 2006;Bourne-Webb et al. 2009;Murphy et al. 2015), the degree of freedom along with the pile depth (Mimouni and Laloui 2015), radial deformation of the pile (Luo et al. 2019;Lv et al. 2020), and the pile interaction in a group (Fang et al. 2020;Wu et al. 2020). Bourne-Webb et al. (2019) summarized many published experimental and numerical results to analyze the thermomechanical behavior of energy piles under different constraints and load conditions. ...
Article
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This paper demonstrates the influence of pile head freedom on the thermomechanical performance of a belled pile. Field tests on the belled pile response to a cooling-heating cycle and incremental structural construction are carried out. The temperature changes, axial strain profiles, and pressures at the pile toe are recorded through the buried instruments. The variation in the degrees of freedom, tensile forces, and inferred pile head settlements along the pile depth for different test procedures are analyzed using the measured data. The degree of freedom close to the pile head calculated from strain rates decreases with the structure mass with a gradient of −2.8 × 10 −5 =kN. The reducing effect of the incremental superstructure on pile freedom decreases along with the orientation of the pile depth. Compared with the inferred thermal displacement of the pile without an applied structural load, the values decrease by about 10% when the pile was subjected to in-cremental floors, and an elastic recoverable characteristic response to cooling-heating-recovery phases is observed. Compared with the equal-diameter pile, the belled pile showed a significant constraint close to the toe. Mechanical loads can decrease the cracking risk because of a possible tensile force under cooling conditions.
... The exploitation and utilization of geothermal energy are receiving increasing attention due to advantages in terms of abundance, cleanliness, and sustainability (Moore and Simmons 2013). Energy piles, as a new type of underground heat exchanger, are increasingly and widely applied for the exploitation of shallow geothermal energy in actual engineering projects (Brandl 2006;Hamada et al. 2007). In winter, the ground is generally used as a heat source, and energy piles are used as the medium to transfer the heat from the ground to the buildings, thus heating the buildings. ...
... Researchers have conducted many investigations on the thermomechanical behavior (Laloui et al. 2006;Bourne-Webb et al. 2009;Amatya et al. 2012;Fang et al. 2020;Lv et al. 2020) and the thermal performance (Hamada et al. 2007;Gao et al. 2008a;Ghasemi-Fare and Basu 2019;Bodas Freitas et al. 2021;Nazmabadi et al. 2022) of energy piles. Energy piles are perceived to be reliable owing to their outstanding economic and heat exchange performance (Brandl 2006;Park et al. 2013). ...
Article
Energy piles, having the dual roles of exploiting geothermal energy and providing structural stability, are creating large worldwide interest. This paper aims to provide knowledge on the potential effects of pile and soil properties on the thermally induced mechanical behavior of energy piles. It presents the results from in-situ experimental investigations conducted on an energy pile. Three-dimensional numerical models were developed and validated to evaluate the behavior of energy piles equipped with various U-pipe configurations from the viewpoint of energy efficiency and structural safety. The results indicated that although increasing the pipe length could improve the thermal exchange capabilities of energy piles, it introduced more significant mechanical effects on the piles, which should be considered during the design. Moreover, parametric studies were performed to explore the potential effects of the soil thermal expansion and elastic modulus on the thermomechanical response of energy piles. The comparative analysis showed that the soil thermal expansion after heating would reduce the thermal compressive stress induced in the energy piles. The soil thermal expansion effects were time-variable and became more significant with the operating time of the energy piles. The thermal stress increased and approached the theoretical maximum value as the soil elastic modulus increased.
... High density polyethylene pipes, in which a heat carrier fluid circulates, installed within the concrete structures extract the geothermal energy from the ground [4]. ...
... According to [4,5], the ground temperature tends to be constant below approximately 10 -15 m with the magnitude depending on the location (10 -15 o C in Europe and 20 -25 o C in Africa). These temperature ranges are sufficient to allow heating and cooling of buildings in winter and summer respectively. ...
Article
Shallow energy piles are these days internationally being implemented for serving as heat exchanging media between the ground and the building in addition to supporting structural loads. This research aims at providing the basic concepts for the application of energy piles for a portion of the total demands of high-rise buildings in Ethiopia, specifically heating and cooling demands. Preliminary estimation of the number of energy piles to cover a certain portion of the total heating and cooling demands of a selected building in Addis Ababa showed the potential for its application in the future. Investigation of the behaviour of energy piles due to the action of cycling heating and cooling loads by using finite element software TOCHNOG were also performed by employing the appropriate hypo-plasticity constitutive model for the soil layers. The measured values of the thermo-mechanically loaded pile were reasonably simulated by the finite element model. The coupled thermo-mechanical cyclic thermal and mechanical loads were found to reduce the settlements of the foundation significantly, which can be considered as an additional advantage of this foundation technique for high rise buildings.
... Parmi les géostructures thermiques, les plus développées à l'heure actuelle sont les pieux géothermiques (Fig. 2). Relativement répandus dans des pays tels que l'Autriche, pionnier dans ce domaine 1 (Brandl, 2006), ou le Royaume-Uni, où de nombreuses recherches les ont rendus populaires, ils restent peu utilisés en France par manque de connaissance. Toutefois le recours aux tunnels et parois moulées thermoactifs se développe également. ...
... Le transfert de charges en toute sécurité de la structure au sol restant le rôle principal des géostructures thermiques, l'impact des variations de température sur le comportement des sols est un sujet d'attention particulier. Les variations thermiques induisant une migration de l'eau vers les zones plus froides (Brandl, 2006), cela peut provoquer une contraction dans les zones chaudes en particulier dans le cas des sols fins. De plus, l'augmentation de température accroît la pression de l'eau interstitielle et par conséquent diminue la contrainte effective du sol. ...
Article
Alors que nous consommons toujours plus d’énergie pour le chauffage et la climatisation de nos lieux de vie, les impératifs de lutte contre le changement climatique et la croissance de la population urbaine mondiale rendent crucial le recours à des sources d’énergies renouvelables. Parmi elles, les géostructures thermiques associent au rôle mécanique pour lequel elles sont conçues un rôle énergétique en captant l’énergie du sol de faible profondeur à l’aide de tubes échangeurs de chaleur connectés à une pompe à chaleur. Elles apparaissent donc comme une solution décarbonée, non intermittente, locale, à faible risque pour l’homme, aisément intégrable dans le mix énergétique et au taux de retour sur investissement raisonnable. Pourtant, certaines questions quant à leur dimensionnement thermomécanique, notamment en présence d’un écoulement souterrain en freinent toujours le développement à large échelle. Après avoir dressé un état de l’art détaillé pour rappeler les points d’achoppement subsistant, un groupe de pieux géothermique au sein d’un écoulement est étudié sous l’angle de la modélisation numérique et de la modélisation physique centrifugée. Les différents outils à disposition de la communauté scientifique pour lever les verrous restant sont présentés.
... Temperature variations inside the soil mass may create threat to the geotechnical performance of sub-structures. In extreme cases, it can result in soil failure, e.g., differential settlement of buildings due to operation of geothermal piles [3,4]. Thermal changes in soil mass may cause alteration in shear strength, consolidation, pore pressure and stiffness of the soil. ...
... As a result, they further move apart from each other and results in thermal expansion. The flow of atoms, molecules or mineral particles in a new Geothermal heat exchange applications -10 to 10 [3,4,53] In situ burning of oil spill 60 and higher [54,55] Nuclear waste disposal 20 to 120 [56][57][58] Explosion on or inside the soil 300 to 500 for the duration of the blast [59,60] Forest fire 550 for 1 min and [ 100 for 10 min* [61] High temperature and pressure oil recovery 350 (water temperature) [62] Deep geothermal power plant 150-300 [63] * Here minutes refer to the temperature residence time at the soil surface stable position causes an elastic distortion of mineral particles which can be recovered by the same magnitude of temperature reduction. The thermal expansion of pore water is much higher than that of soil minerals. ...
Article
Temperature changes in saturated soils may result in volume change and consequently the stress–strain behavior of soils may undergo alterations. These alterations may impose implications on geotechnical stability of soils. Temperature-dependent behavior of soils has been studied in the literature, both experimentally and theoretically. Based on the experimental studies from the literature, this paper aims to review the thermo-mechanical behavior of saturated soils. First part of paper attempts to provide a conceptual insight on the thermally induced volume change behavior of saturated soil and second part reviews the experimental investigations from the literature, for a temperature range of 5–100 °C for clay and 5–600 °C for sand. These experimental studies confirm the irreversible contraction of NC clay at OCR = 1 and quasi-irreversible volume change of normally consolidated and overconsolidated clay with a low overconsolidation ratio (< 2), during drained heating. Similar behavior is also observed for loose to medium dense sand. The parameters like pre-consolidation pressure, secondary consolidation, permeability, drained and undrained shear strength also show temperature dependence.
... Thermo-active geo-structures have been shown to have the potential to efficiently harvest shallow geothermal energy. At depths below 5-7 m, the temperature of the ground is relatively stable, which allows the ground to be reliable and efficient as a heat source in the winter and a heat sink in the summer [1]. The soils adjacent to the structure are typically subjected to annual and daily cyclic temperature variation, depending on the operation mode of the ground source heat pump (GSHP) system. ...
Article
Full-text available
The effect of temperature on the monotonic and cyclic shearing response of a soil–structure interface is of critical importance for the application of thermal-active geo-structures. To investigate this, soils and soil–concrete interfaces were comprehensively tested with a temperature-controlled direct shear device under both fixed temperatures and thermal/mechanical cycles within the range of 2–38 °C. Monotonic and cyclic shearing with various boundary conditions, including constant normal load (CNL), constant normal stiffness (CNS) and constant volume (CV), were conducted to resemble the conditions that thermal-active-geo-structures may experience. The strength properties of the sand, clay, and sand–concrete and clay–concrete interfaces were partially influenced by heating and cooling under all boundary conditions. However, several effects were observed which could affect the performance of thermo-active structures. Heating cycles caused the clay–concrete interface to be overconsolidated, implying a lower excess pore pressure would be generated during shearing. The cyclic CNS tests suggested that the interface strength could degrade due to (thermally induced) cyclic shear displacements, with this effect strongly related to the state of the soil rather than the temperature directly. In these tests, the medium-dense sand–concrete interface degraded to almost zero shear strength after 5 cycles, whereas the clay–concrete interface asymptotically degraded to around 60% of its strength after 10 cycles.
... Clayey soils are widely distributed in the sedimentary layers around the world and are related to a lot of geohazards and geotechnical problems such as slope instability, excessive settlement, embankment failure, etc., which have been extensively studied in the past decades. In more recent years, the thermal effect on clayey soil behaviour has been another concern for various engineering practices, such as the thermoboosted soil improvement (Abuel-Naga et al., 2006a;Chen et al., 2022), marine pipeline engineering (Scheiner et al., 2006;Shahrokhabadi et al., 2020;Thusyanthan et al., 2011), buffer of nuclear waste (Cui et al., 2009;Houston et al., 1985;Romero et al., 2005), energy piles (Brandl, 2006;Guo et al., 2020), tunnel fire (Chen et al., 2016), etc. Since the middle 20th century, researchers have experimentally investigated the temperature effects on the mechanical properties of different types of soft soils, the main findings from which can be summarized as follows. ...
Article
The thermal effects on geomaterials, especially on clayey soils are getting increasing concerns in many geotechnical applications. To study the effects of temperature on the stress-strain behaviour of Hong Kong marine deposits (HKMD), a series of temperature-controlled experiments were carried out. Oedometer and constant-rateof-strain consolidation tests under temperatures from 10 °C to 60 °C were conducted on both intact and reconstituted HKMD considering different temperatures and stress paths. The effects of temperature history on the compression curves, thermally induced strain, and the characteristics of creep are revealed and discussed. The concept of virgin heating is proposed for interpreting the thermal plastic deformation. With increasing temperature, the creep coefficient is found to decrease while the creep strain rate increases. Consolidated undrained triaxial tests were performed on intact and reconstituted HKMD under different strain rates and temperature conditions. Under constant temperature, the undrained shear strength of HKMD is not significantly influenced by temperature. In triaxial tests subjected to step-changed temperature, the undrained heating causes a significant reduction of effective stress and rise of porewater pressure in HKMD. Finally, microscopic investigations with mercury intrusion porosimeter and scanning electron microscope are presented and discussed in this paper. It is found that the micropores of HKMD are evolutional with temperature.
... Geothermal energy is considered as an energy source, which has many advantages over than the conventional energy sources (concerning cost, reliability and environmental). Thermally active structures such as diaphragm walls, piles, tunnel linings, and basement walls present a promising and sustainable way for buildings heating and cooling as cited by Fromentin et al. [1], Laloui et al. [2] and Brandl [3]. The functioning of thermo-active geostructures are based on variations of the surrounding soil temperature (about 12 °C) over a range from 4 to 30 °C as discussed by Peron et al. [4]. ...
Article
Full-text available
In geotechnical engineering, geostructures with thermo-active functions establish a direct thermal exchange between the ground and buildings. They can transfer energy from or into the ground to heat or cool a building. However, adapting foundation piles, completely or in part, to produce energy piles results in heat exchange with the soil, which changes the temperature of the soil and could thereby and affects the geotechnical properties and load bearing capacity of the geostructure. Most calculations of the bearing capacities of deep foundations conducted in France are currently based on in-situ testing results using a pressuremeter. Using the finite element method to model the pressuremetric behavior of compacted soil subjected to thermo-mechanical variations is the main motivation for this work. In this study, several pressuremeter tests were conducted on compacted illitic soil in a laboratory tank at temperatures between 1° and 40°C. The impact of temperature variation on the limit pressure (Pl), the creep pressure (Pf), and the Ménard pressuremeter modulus (EM) were determined. The results showed a significant decrease for both limit pressure (Pl) and creep pressure (Pf) with the increase in temperature. Numerical simulations of these tests were used to calibrate a bilinear constitutive model, taking into account temperature effects on soil compressibility within a coupled thermo-mechanical framework. Thereafter, a case study of a heat exchanger pile was simulated using the proposed approach.
... In recent years there has been an increasing interest in the study of EP systems by different research groups (de Moel et al., 2010;Brandl, 2006;Olgun, 2013), but more research to optimize their design, construction and operation is still needed. Table 1 summarizes the main features of energy pile projects around the world (found in the scientific literature). ...
Article
A novel application of retaining wall anchors as heat exchangers is proposed as an alternative or complement to pile geothermal exchangers. A fullscale in-situ study using anchors and piles was performed. Thermal response tests (TRT) were carried out in both types of systems. The installation process of the heat exchanger anchor is shown and results of the in-situ tests are compared in terms of their thermal parameters and performance. We demonstrate that the installation of required pipes is possible in the anchors with no mechanical interference during its installation and after anchor tensioning. The results show that the use of heat exchanger anchors is a valid alternative, with thermal performance similar to more common energy piles.
... However, with little additional cost, vertical GHEs could be used for the dual purpose of thermal provision as well as structural stability (Hepbasli et al., 2003 [62]). That's why geothermal systems have recently become more useable and feasible with the different structural elements (See Figure 10), as reported in several case studies, such as foundation piles (Brandl, 2006 As explained before, GSHP systems have several benefits, but their high installation costs prevent them from being extensively used. Moreover, the implementation and design of GHEs extremely depend on the geometry of the underground structures and site layout. ...
Article
Full-text available
Particularly for asphalt pavement, where the temperature is a crucial driver in selecting construction materials, premature infrastructure failure and higher maintenance costs might be highly expected with the recently witnessed dramatic changes in climate. Numerous studies highlighted how the recent climate change might result in hazards to transportation infrastructure and affect all types of transportation modes. On the flip side, flexible pavement also contributes to global warming; various studies referred to the significant emissions percentages released by asphalt pavement upon subjection to solar radiation. With that in mind, several studies showed that the environmentally-friendly geothermal systems that mainly depend on heat exchanging with the soil have positive influences on reducing energy consumption, melting the ice on roadways in cold climates, or reducing the ambient temperature and the induced latent heat from the pavement in hot climates. However, very limited studies explored the influence of those geothermal systems on the structural behavior of the pavement concerning the associated distresses with extreme climate changes. In this paper, a critical review concerning climate change has been performed to investigate the structural performance and the associated distress of both conventional and geothermal asphalt pavement. This review underlines several advantageous physical and mechanical characteristics of geothermal pavement, which may recommend this system as a worthwhile alternative to conventional asphalt pavement. The paper also identified future research needs to overcome the shortcomings associated with the structural performance of the geothermo-electrical asphalt pavement.
... 土中的热传导一直是岩土工程领域的热点问题, 地下高压输电线设计 [1] 、油气管道的埋设 [2] 、核废料 存储 [3] 、 冻结法施工 [4] 以及冻土区地基的承载力 [5] 都与 土中的传热过程密切相关。近年来,浅层地温能开发 中能源地下结构 [6] (能源桩、地下连续墙等)的设计 更是基于土体的传热能力。热导率作为研究土体传热 过程中的关键参数,直接影响了土体温度分布计算与 土体换热能力评估。 现阶段土体热导率测试方法主要采用现场取样室 内测试的手段,分为瞬态法和稳态法 [7] 。稳态法测试 的基本原理是用仪器在土样两端施加一定的温差,待 土样内形成恒定的一维热流后,测得其热流与温度梯 度,即可根据傅里叶定律计算热导率。但土体一般为 三相体,形成稳定的热流需要的时间较长(30~40 min) , LOW 等 [8] 的试验表明温度作用下土体内部的水 分迁移和相伴的热固结 [9] 会影响测试结果。瞬态法则 主要为热探针法 [10] ,已写入 ASTM [11] 、IEEE [12] [20] ,测试时间往往大于 50 h [21] , 成本较高,且测试得到的是一个综合地层热导率,不 能精确反映不同土层换热能力的不均匀性,造成地埋 管、能源地下结构的换热能力设计的不精确 [22] 。目前 有研究 [23] 采用光纤对换热管内的温度进行分布式测 量并用非线性回归法估计各土层的热导率分布,但其 对测试设备与数据分析要求较高, 尚未得到广泛应用。 热探针也有用于现场测试 [24] 中的先例,因为其尺寸较 小易于折断,且需须在现场预钻孔后再插入热探针进 行测试,此方法操作复杂,测试深度有限,仅能用于 表层土。Akrouch [25] ...
Article
The thermal conductivity is the key parameter to the design of many projects, such as energy structures, high-voltage buried power cables and permafrost embankment, related to estimating the heat transfer capability and temperature field in the soil. However, at present there is no effective in-situ testing method. Based on the theory of instantaneous heat release along a line source, a heat conduction cone penetration test (CPT) probe for thermal conductivity evaluation of in-situ soil is developed. According to the theoretical assumptions and the sizes of CPT system, the length, diameter, internal structure and positions of the temperature sensors are introduced. Then, the corresponding test procedure and the method for thermal conductivity are proposed. The test process is simulated in COMSOL to verify the method, and the results validate that the actual heat transfer conforms to the line source theory. The interpretation method yields reasonable values within a general range of conductivities. For less conductive soil (<0.6 W/ (m∙K)), longer duration of heat dissipation may be required. The field test results show that the in-situ soil conductivity is higher than that from laboratory tests on undisturbed samples, indicating the sampling disturbance may be responsible for this reduction. Finally, some suggestions on laboratory thermal conductivity tests and engineering designs are given.
... Geothermal energy piles (GEPs) are the most useful energy geostructures because of their simultaneous role in structural stability and energy supply (Batini et al., 2015;Fadejev et al., 2017;Gashti et al., 2014;Luo et al., 2016;Mohamad et al., 2021). In these cost-effective systems, heat is exchanged between the pile and the soil due to the relatively constant temperature several meters deep in the ground (colder than ambient during winters and warmer during summers) (Abdelaziz et al., 2011;Batini et al., 2015;Brandl, 2006;Lee, 2013). The operation of heat transfer in an energy pile occurs via the ground and the convective water flow in the ground, conduction in the energy pile and heat exchanger tubes, and convection in the fluid at the interface with the internal tube surface (Abdelaziz et al., 2011;Mohamad et al., 2021). ...
Preprint
Considering groundwater flow in the soil, the amount of energy extracted from an energy pile is still vague. Therefore, this paper has examined the energy produced considering different design parameters in the presence or lack of groundwater flow by employing the finite element method (FEM). The results illustrate that increasing groundwater flow velocity is ineffective in energy extraction from the ground in some conditions. Moreover, lengthening the pile height after a certain height has a negative effect on the average output power. Porosity has negligible influence on the energy output; however, changing the pipe diameter shows two different behaviors
... As a novel application of GSHP, energy piles are capable of sustaining structural loads while also harvesting geothermal energy through the integration of a heat exchange system into the pile foundation (Laloui et al., 2006). They have gained significant interest due to their environmental benefits, reduced land occupation, low cost, and high efficiency (Brandl, 2006;Han et al., 2021). Since energy piles have been employed as a group in major construction projects, an increasing number of studies on energy pile groups, including full-scale field tests (McCartney and Murphy, 2012;Mimouni and Laloui, 2015;Murphy et al., 2014Murphy et al., , 2015Rotta Loria, A. F. and Laloui, L., 2017;Wang et al., 2020), laboratory experiments (Ng and Ma, 2019;Peng et al., 2018;Yin et al., 2022), numerical simulations (Di Donna and Laloui, 2015;Di Donna et al., 2016;Jeong et al., 2014;Salciarini et al., 2015;Suryatriyastuti et al., 2016;Yang et al., 2022), and analytical models (Fei et al., 2020;Ravera et al., 2020;Rotta Loria and Laloui, 2016;Rotta Loria, Alessandro F. and Laloui, Lyesse, 2017;Rotta Loria et al., 2017, have been reported. ...
Article
Energy piles have attracted increasing interest for bearing structural loads and providing energy for space conditioning by employing geothermal energy from a ground source heat ena pump system. Although energy piles have demonstrated promise for geothermal energy exploitation, the insufficient energy supply resulting from geotechnical design prohibits their broad deployment. To address the incompetency of energy piles, we propose an innovative design of high-energy efficiency energy pile group by incorporating microencapsulated Phase Change Material (microPCM) into energy piles. With experimental measurement and numerical simulation, a systematic evaluation of the microPCM energy pile group is carried out, from property characterization to energy performance analysis. In addition, the influences of GHE configurations (U shape, W shape, and double U shape) and microPCM addition ratios on energy-saving potential and optimal design of the microPCM energy pile group in cooling mode are investigated. The results reveal the great potential of adding microPCM to facilitate more energy extraction for the energy pile group. However, because the addition of microPCM degrades the compressive strength of the energy pile, it is recommended to increase the concrete design grade when employing microPCM energy piles in engineering practice. In addition, the energy pile with double U shape GHE and 1% wt. microPCM addition is identified as the optimal design in the study, which contributes to 6–49% more energy extraction with a tolerable loss in compressive strength. Meanwhile, the separation spacing between adjacent piles should be greater than 3D to prevent thermal interactions and ensure stable energy performance. This study aims to provide support for the optimal design of the microPCM energy pile group and guide its engineering application.
... The heat exchange rate comparison between the precast and cast-in-place piles is a factor of many items, including the number of loops inside the piles, loop configurations (U-loop, W-loop, spiral loop, etc.), ground thermal conductivity and heat capacity, ground temperature, soil type, and groundwater table. However, in general, precast and cast-in-place piles can provide 70-80 kWh/m 2 over a period of 180 days [37]. ...
Article
Full-text available
Geothermal energy piles are increasingly luring attention in the construction industry as a cost-effective and environmental friendly solution for heating and cooling buildings. Energy piles are used as the primary unit in the ground source heat pump systems, which exchange heat with the ground. Energy piles are generally categorized into driven (displacement) and cast-in-place (non-displacement) piles. The present paper aims to review the available methods of design and construction of driven precast concrete energy pile foundations and provides a clear understanding of its construction challenges. Additionally, precast and cast-in-place energy pile foundations are compared. This paper found that precast concrete-driven energy pile foundations are a competitive alternative to cast-in-place energy piles. Driven concrete energy piles have higher quality control and quality assurance in the construction process; they have an easier, faster, and more reliable installation. Several other advantages and limitations related to the technical, economical, and environmental aspects of such piles are discussed in detail. The driven precast concrete foundations have a large worldwide market; however, there is a lack of guidelines, design standards, and experience for using such foundations as energy piles.
... It is noteworthy to point that heat process such as micro-scale radiation between particles, convection in the pores, phase change processes depending on the season, condensation and vaporisation take place on the surface of the asphalt surface. However, in this study these processes are not taken into consideration because it takes place in small scale processes thus negligible in relation to the volume of the structure under consideration [23]. ...
... Thermal-related geotechnical engineering have received widespread attention with the development of energy-and environment-related infrastructure constructions, such as nuclear waste disposal [19,25], buried high voltage cables [55,62], geothermal energy piles [9,17,33], thermo-active tunnels [31,40,44], landfill treatment [29,48,77], highway pavements [32,41], geological CO 2 storage [3,50], and biomineralization [39,70,72,74,75]. The thermomechanical characteristics of geomaterials are key factors affecting the safety and stability of thermal-related geotechnical infrastructures. ...
Article
Full-text available
The deformation and strength of soils change significantly under thermal loading, which affects the safety and stability of thermal-related geotechnical infrastructures. Although laboratory tests have been performed on pure clay or sand, few studies were conducted on binary sand–clay mixtures. To enhance the understanding of the mechanisms for thermally induced volume change behavior of sand containing plastic fines, a series of drained heating tests and temperature-controlled isotropic consolidation tests were conducted. The results of the drained heating test demonstrate that the sand–clay mixtures generally exhibit plastic volumetric contraction deformation at temperatures ranging from 20 to 60 °C. The thermal volumetric contraction increases with increase in stress level or fine content. With isotropic consolidation tests, it was found that the compression curves gradually moved downward with an increase in temperature. The compression and swelling indexes change slightly with temperature variation, which can be considered independent of temperature. The yield stress of sand–clay mixtures decreases with increase in temperature, and the thermal softening phenomenon becomes more obvious with an increase in fine content. The proposed equation for yield stress accurately predicted the temperature- and fines-dependent behavior of sand–clay mixtures.
... Brandl [1] and Yuan et al. [2] applied ground source heat pump (GSHP) to tunnels in cold areas and improved the energy efficiency of GSHP by absorbing the geothermal energy of surrounding rocks, so as to serve the heating of tunnels and nearby buildings. Some scholars [3,4] even found that the subway tunnel structure can obtain an annual average heat of 175 MWh and an annual average refrigeration capacity of 437 MWh. ...
Article
Full-text available
For tunnels in cold or serious cold areas, the problem of leaking in the spring thawing period is very frequent, which will cause various tunnel diseases due to freezing. By using the surrounding rock geothermal energy in the tunnel project, especially the tunnel project below the permafrost layer, the cold area tunnel heat pump system is able to improve the overall heating energy efficiency as the side temperature regarding the heat pump evaporation increases, that furtherly serves the surrounding supporting building facilities. Inspired by this system and the active and passive coupling building technology, a heat recovery type of heat storage wall model is proposed in this research. By describing the heat transfer process regarding the heat recovery type of heat storage wall and carrying out the experimental research, its feasibility and effectiveness are verified. The results show that when the outdoor ambient temperature in Urumqi is −7~−15°C and the instantaneous total solar radiation reaches the range of 0~1108 W/m2, this kind of wall can create hot wall-near air whose temperature is 11.89°C higher than the ambient temperature for providing a high-quality air heat source for the air source heat pump when the temperature is low, thereby significantly improving the air source heat pump heating system efficiency. Without the photovoltaic and photothermal equipment, the heat recovery type of heat storage wall can make the utilization rate of solar energy reach 13% to 20%, even up to 36%.
... For instance, Lai et al. [10] adopted an electric heating method to treat frost heaving in a high-altitude tunnel in China, where the measured tunnel lining temperature was maintained above 0 • C. Gao et al. [11] developed a solar collection system to address the problem of snow accumulation on asphalt pavements. Brandl [12] and Wang et al. [13] proposed the underground energy engineering concept, in which heat exchange tubes are buried underground, thereby promoting the use of geothermal energy in deep rock formations. To address the frost damage problem, Adam et al. [14] and Fordl et al. [15] established frost mitigation and heat preservation system for tunnels using ground source heat pumps; they used geothermal energy to actively supply heat to frost circles in tunnels during winter. ...
Article
Full-text available
The primary objective of this study is to address the embankment frost heave issues in cold regions with an active heating method. The applicability of various heat sources was compared with the heating demands of embankments, and the results demonstrated that the seasonally frozen areas of China are rich in solar energy resources. A specialized device for heating embankments, comprising a solar collector section and an embankment heater section, was developed. The device integrates energy conversion, storage, and transfer with no moving parts and can therefore be used for self-driven operations on an “isolated island”. Performance tests showed that the maximum heating temperature exceeds 60 °C with an average range of 20–40 °C, which increases with solar radiation. The effective heat utilization rate of the soil is approximately 26%. A predictive model that considers latitude and the daily ordinal number was proposed for heating temperature. The long-term heating performance of the embankment was numerically simulated. The results revealed that the heating mode in all seasons is capable to overcome the limitations of existing insulation measures and effectively enhance the potential of frost-resistant embankments in winter.
... Energy piles with embedded geothermal heat exchangers (GHEs) can not only withstand structural loads, but also harvest geothermal energy to meet the building's heating and cooling requirements [1]. Compared to typical geothermal heat pump systems, energy pile technology can reduce expensive borehole drilling costs, conserve subsurface space resources, and achieve higher energy efficiency, thanks to the concrete's superior thermal properties [2]. Therefore, as green building technology, energy pile can significantly reduce a building's reliance on fossil fuels, hence reducing CO 2 emission [3]. ...
Article
Energy piles utilize geothermal energy via integrated geothermal heat exchangers (GHEs), which can sustain structural loads while also harvesting geothermal energy to meet the building's heating and cooling requirements. In the study, we report a systematic investigation of the Microencapsulated Phase Change Material (MicroPCM) C50 energy pile, from characterizing the material properties of the MicroPCM C50 concrete to analyzing the energy performance of the MicroPCM C50 based energy piles. Through integrating the MicroPCM into structural concrete, MicroPCM C50 concrete is manufactured and its properties, such as mechanical compressive strength and thermal conductivity, are characterized. With measured material properties implemented into a numerical model of the MicroPCM C50 energy pile, the energy performance when the energy pile works in the cooling mode is assessed. Our results suggest that (1) incorporating MicroPCM into C50 concrete specimens (up to 5 wt.%), will dramatically reduce the compressive strength of C50 concrete; (2) Thermal conductivity and heat capacity of C50 concrete specimens are improved as mass fraction increases from 1 to 3 wt.%, while reduced as mass fraction increases from 3 to 5 wt.% (maximum at 3 wt.%); (3) When considering both the mechanical and thermal performance of the energy pile, the energy pile with W shape GHE and 1 wt.% MicroPCM addition is the best option for this scenario, followed by the energy pile with U shape GHE and 1 wt.% MicroPCM, which will collect around 5% more geothermal energy, compared to normal concrete energy pile, and meanwhile retain a high level of mechanical strength. Our results will provide support for the design and optimization of the MicroPCM C50 energy piles toward real-world applications.
... Determination of the thermal properties [viz., thermal conductivity (λ), thermal resistivity (R T ), volumetric heat capacity (C v ), and thermal diffusivity (α)] of soils in cold regions/permafrost is essential for the safe execution of various industrial and infrastructure projects. Some of these applications are the design and construction of the foundations of roads, embankments, airfields (Yang et al. 2010;Xu et al. 2011;Flynn et al. 2016;Liu et al. 2019;Kurz et al. 2020;Lijith et al. 2021), buried pipelines (Moya et al. 1999;Oswell 2011;Li et al. 2020), and structures for harnessing geothermal energy (Brandl 2006;Adam and Markiewicz 2009;Saaly et al. 2019). Moreover, they are discerned to be essential for multiphysics models to simulate heat, liquid water, vapor, and solute transport in unfrozen/frozen soils (Bitteli et al. 2008;Wu et al. 2018;He et al. 2020), land-atmosphere interaction (Zhang et al. 2008;Steeves et al. 2019), freezing-or thawing-front migration in the active layers (Overduin et al. 2006), and recovery of methane gas from hydrate-bearing sediments (Waite et al. 2002(Waite et al. , 2006Dangayach et al. 2015;Lijith et al. 2019;Malagar et al. 2019), among others. ...
Article
Accurate measurement of the thermal properties (viz., thermal conductivity, thermal resistivity, volumetric heat capacity, and thermal diffusivity) of soils in cold regions necessitates the development of techniques that are robust and efficient and that can incorporate different heat migration mechanisms under the influence of complex initial and boundary conditions. However, devices or the numerical procedures employed to determine them are scanty. In such a scenario, here, a methodology that facilitates the determination of thermal properties of soils in cold regions has been developed based on their heat-pulse migration characteristics (HPMC). To control the temperature of the soil specimen, a temperature-controlled environment chamber has been employed and HPMC was established by using the dual-probe heat-pulse sensor. Furthermore, a technique to estimate the thermal properties of the soil specimen by employing the measured HPMC, which facilitates solving an inverse transient heat conduction problem by using the conjugate gradient method, has been developed. Subsequently, the thermal properties of fine sands corresponding to different initial moisture contents and low temperatures have been determined and the results were compared with those predicted from the HPMC by utilizing interpretation techniques such as the single-point method and nonlinear fitting.
Chapter
One of the greatest challenges society faces today is the provision of clean and renewable energy to both meet the over-growing energy demand and reduce our carbon footprint. Ground source heat pump (GSHP) systems can efficiently heat and cool buildings using shallow geothermal energy and can therefore contribute towards the above goals. Significant attention has been given to energy geo-structures in the last few years, that is, using subsurface structures to exchange heat with the ground. Thus, these geo-structures provide structural support and thermal energy. The majority of literature relating to energy geo-structures focuses on piles, but only limited research exists on geothermal pavements. This work developed a detailed 3D finite element (FE) model to explore the thermal performance of geothermal pavement systems. This 3D FE model has been successfully validated against a full-scale experimental test undertaken in Adelaide, South Australia. The validated model is then used to evaluate the long-term performance of geothermal pavement systems under both a traditional system configuration and as a hybrid system configuration. The performance of the geothermal pavement system is analysed under three thermal loading cases including balanced, heating dominated and, cooling dominated cases, showing the potential and identifying possible limitations for geothermal pavements.
Chapter
Jordan is located in the western region of Asia. It has limited conventional energy resources such as oil and gas: and is reliant on imported oil and gas. Although, it lies nearby a tectonically active border. Therefore, Jordan could have a potential for utilizing the available geothermal energy resources, however, all previous studies and reports showed that a wide range of temperature applications, such as space heating and power generation would be utilized. Nevertheless, it would not be possible at prevailing conditions to utilize high-temperature applications.This work reviewed all published official reports pertinent to geothermal energy in Jordan, including techno-economic studies for utilizing such resources. At present some of these sites are used as thermal spa. Since the economics of available geothermal energy recovery processes and environmental controls are still not attractive under the present conditions. Hence, the utilization of such resources in the future will be strictly limited by eco-technical feasibilities. Comprehensive scientific research, feasibility studies, legislation, and best practice codes should be addressed as main parts of a national energy strategy for future utilization.In this chapter, a short introduction about the country, location, demography, economy, and energy sector is presented to provide the readers with a simple background of Jordan. Then a review of local geothermal sources with previous studies investigating the occurrence and possible utilization of such resource were assessed. Also, the current uses for space heating and cooling are presented and finally recommended future actions and essential scientific research studies are pointed out.KeywordsGeothermal resourcesGround source heat pumpJordanThermal springsUtilization
Conference Paper
Full-text available
The paper presents a condensed description of BTES, TTES and PTES technologies and the potential use of thermally active ground structures (i.e. energy foundations and thermal piles) that can be used as heat exchangers in future Smart Cities. The technologies mentioned were presented in the context of national programmes for the development of geothermal energy use in Poland and the Polish Energy Policy until 2040. The role of the geologist in the investment process in determining the geothermal potential and thermal properties of soils and rocks and the experience of PGI-NRI in this field were presented.
Article
Energy piles have been recently utilized as ground heat exchangers in ground source heat pump systems to improve the energy efficiency in the heating, ventilation and air conditioning (HVAC) systems for residential and commercial buildings. On top of the structural role of energy piles to transfer the mechanical loads of buildings to the ground, they are used to dissipate heat energy into the soil to reduce the consumption of energy and hence lower greenhouse gas emissions. In this study, eight factors affecting the thermal conductance of the energy piles are investigated to maximize the thermal performance of energy piles. These eight factors are the number of U-tubes, pile diameter, tube diameter, tube thickness, pile thermal conductivity, tube thermal conductivity, soil thermal conductivity, and velocity of circulated water in U-tubes. The significance of these factors is statistically evaluated, and the optimal values of the significant factors are obtained using response surface methodology. The results reveal that tube thickness, water velocity, and soil conductivity have an insignificant impact on thermal conductance of the energy piles, while other factors have a significant effect. This research may lay a foundation for future research in optimizing the thermal performance of energy piles and promoting their applications in practice.
Article
Full-text available
The efficiency of shallow geothermal energy recovery has been constrained by both the short-term temperature anomaly around heat exchangers and the long-term ground heat depletion. This study presents numerical investigations of significant improvement in the thermal performance of energy piles by using microencapsulated phase change materials (mPCM) and metal fins in the ground. A three-dimensional hydrothermal FEM model of an energy pile embedded in the ground is developed, validated, and extended to consider phase change and latent heat in the ground to evaluate the thermal performance of the energy pile under various ground conditions. The results show that both the energy harvest amount and efficiency can be evidently improved by mixing small proportions of mPCM in the ground to utilize its latent heat. The recovery energy from the sand–mPCM mixture is twice that of just sand and thrice that of the pure granular mPCM ground during seasonal operations. Moreover, the temperature influence zone is significantly shrinked in the sand–mPCM mixture ground. In addition, installing metal fins around the energy pile can accelerate heat conduction with the far field and furtherly improve the heat recovery efficiency. This study sheds light on efficient and environmentally friendly geothermal energy recovery using phase change materials.
Article
A ground source heat pump (GSHP) system provides efficient space heating and cooling and thus is regarded as a contributor to achieve net-zero emissions targets. This study focuses on an economical type of GSHP system – energy walls where earth retaining walls are equipped with pipes to act as geothermal heat exchangers in addition to being geotechnical structures. A detailed numerical investigation is performed to study the long-term heat exchange mechanism between the walls and the surrounding ground. The work highlights the significance of the existence and magnitude of groundwater flow on the temperature distribution of the ground and the thermal performance of energy walls. Compared to the case when there is no subsurface flow, the energy retaining wall can offer up to a 6 % better coefficient of performance (COP) or provide up to 1.3 times higher thermal yield for relatively slow groundwater flow velocities of 0.013 m/d. The COP can improve up to 93 % and thermal yield up to 23 times for high velocities of 2 m/d, even in extremely cooling-dominant thermal demand cases. The study also shows that the ground thermal conductivity plays a crucial role on performance when groundwater flow is minimal, however, as the convective heat transfer resulting from the groundwater flow becomes more dominant, the influence of thermal conductivity gradually diminishes. It is also found that the absorber pipe flow rate has a rather small effect on the system thermal performance, of less than a 10 % COP difference in all studied cases. This suggests that obtaining reliable hydrogeological information specifically on the groundwater flow velocity and direction are crucial for accurate predictions and optimal design for energy retaining walls and large scale GSHP installations. The insights from this study can improve the design and enhance the uptake of retaining walls for efficient heating and cooling of above/underground spaces - critical components in achieving a clean energy future.
Article
As a new carrier for collecting shallow geothermal energy, energy piles have been widely used around the world. However, the existing methods are limited by different factors, and they do not further improve the heat transfer efficiency. In this article, the preparation of a new high-thermal conductivity SiC concrete (HCSC) pile is described. Primarily, a study on the properties of HCSC is conducted, and its thermal conductivity properties are tested. Second, indoor model tests of HCSC piles are conducted, and the influences of the pile material, heat exchange pipe material, inlet and outlet water temperatures, and thermal exchange fluid flow rate on the efficiency of energy piles are analyzed. The results show that SiC particle gradation strongly influences the thermal conductivity of concrete, with an average thermal conductivity of 2.87 W/(mk); additionally, the maximum thermal conductivity reaches 3.72 W/(mk), which is three times higher than that of conventional concrete. The working efficiencies of SiC piles increase to 261%, which is greater than that of the conventional piles, with a maximum energy of 189.51 W/m. The inlet water temperature of 32 °C has an acceptable energy consumption ratio, and the maximum temperature difference between the inlet and outlet reaches 0.357 °C/m, with an average value of 0.255 °C/m. Within the first 10 h, the energy obtained by the new energy pile is 128.2 W/m, while that of the conventional group is only 60.45 W/m.
Article
The energy diaphragm wall (EDW) attracted increasing attention due to its high energy exchange rate and low space occupation. The current research on EDW primarily focused on its heat exchange capacity and performance. The elastoplastic effects on thermal-induced mechanical behavior caused by soil were neglected, which might underestimate the wall deflections in deep EDW due to the asymmetrical surrounding pile height pressure on both sides. This paper investigated the thermal performance and the induced mechanical behavior in deep energy diaphragm wall (EDW) based on the finite element analysis method (FEA) by the COMSOL Multiphysics software. Firstly, the thermal performance of varied pipe configurations (e.g., single U-shaped; W-shaped; double-U shaped; horizontal arrangement) was studied. Then it was followed by a study of a single heating–cooling cycle with a single U-shaped pipe, where the elastoplastic impact of the soil in the deep EDW was observed. Moreover, a parametric analysis with a long operation period (30 years) perspective was proposed regarding the heat load modes, the pipe buried locations, the air temperature of the adjacent underground space, and the excavation level. Results revealed that the heat transfer process caused an obvious impact on thermal-induced mechanical behavior. Higher levels of heat injection (Case 3) and extraction (Case 2) both led to a relatively large wall deflection after 30 years. The horizontal displacements at the top of the wall under Case 3 and Case 2 were up to 30.5 mm and 25.9 mm, respectively, while 22.9 mm under balanced case (Case 1) and 21.1 mm under the no heat load case (Case 0). When the pipe was close to the side of the excavation, the plastic deformation was about 1.25 times greater than that on the soil side, where the thermal contraction effects were emphasized. Besides, the air temperature in the underground space caused a small impact on the plastic strain in the soil domain. Because of the enhancement in the heat transfer process from the air to the wall while the air temperature increased, resulting in the average wall temperature raised. In addition, the influence caused by the excavation levels was quite evident. The deeper the excavation level, the easier the plastic strain to occur. This paper proposed a new perspective for understanding thermal-induced mechanical behavior in deep EDW, especially the long-term soil elastoplastic effects, which exerted a complex impact on the deformation variation of the diaphragm wall.
Article
Using energy piles with cap foundations under 3.0 m of backfill, four tests with different heat exchanger tube types (U&W) and operation modes (continuous and intermittent heating) were carried out. The temperature and stress changes of the energy pile and its adjacent structures were measured, and the experimental results were compared with those without buried depth conditions. The heat exchange rate per pile length with W-type heat exchanger tubes was approximately 1.39 times that with U-type tubes. The heat exchange rate per pile length during intermittent heating operation was approximately 1.30 times that during continuous heating operation. The overlying backfill showed a certain insulation effect, and the heat exchange rate per pile length was approximately 1.13 times that without burial. The soil above the pile was less susceptible to seasonal variations, and after 192 h of heating, the temperature rise at the pile top under the 3.0 m of backfill was 5.10 °C less than that without burial. The overlying 3 m of backfill also exhibited some restraining effects: this inhibited the thermal relative displacement of the pile top, with thermal expansion coefficients of 0.027 mm/°C and 0.037 mm/°C with and without burial, respectively. The corresponding thermal dissipation coefficients were 2.55 °C/m and 3.43 °C/m. The null point appeared at 0.78 times the pile length, and there were slight differential deformations in the cap with/without burial.
Chapter
This paper investigates the behavior of a single energy pile with three different mechanical head loads (65, 115, and 185 N) and also the effect of pile temperature on its bearing capacity by conducting 1g physical model tests. Thermal loading is comprised of over ten heating-cooling cycles with amplitude of ± 6 ℃, provided by circulating temperature-controlled water through a steel U-tube placed inside the pile. The pile is a closed-end aluminum tube of 60 cm length with an outer diameter of 2 cm and a wall thickness of 1.2 mm which is filled with water to facilitate thermal interaction between the U-tube and the pile. The model ground is dry silt which is placed in a 100 × 100 × 80 cm3 container using the dry tamping method. Thermal cycling started with the heating phase during which the pile showed different settlements for different surcharges: the larger the mechanical surcharge, the larger the observed settlements are. The increment of pile head displacement follows an asymptotic trend with the number of cycles in all three cases. In the case with 65 N head load, a slight upward pile head movement is observed during the last few heating phases due to the more contribution of the pile tip resistance as the thermal cycling goes on. This is also supported by the results of total pressure cells. Pile temperature was found to affect its bearing capacity; heating caused an increase while cooling caused a more noticeable decrease in its bearing capacity.KeywordsEnergy pilePhysical modelingShallow geothermal energyHeat exchangerDeep foundation
Article
A geothermal energy pile is a revolutionary piling technique that combines a pile foundation with a ground source heat pump system that not only supports the structure but also provides heating and cooling for buildings and bridges. The thermo-mechanical behavior of long energy piles in soft clay has rarely been investigated, despite their increasing utilization. A long floating energy pile with a length-to-diameter ratio of 66.7 was evaluated on its own and monitored in service of the supported structure in the city of Kunshan, China. With vertical mechanical loads, the experiment involved alternate cooling and heating cycles, allowing for careful analysis and assessment of the pile’s temperature, stress, and displacement. Temperature-induced stress, axial force, and friction resistance of the pile shaft, as well as the change in displacement of the energy pile throughout building, were all studied. The field observations revealed without any surprise that a longer energy pile outperformed a shorter one in terms of heating exchange capacity with a more homogenous temperature distribution along the pile. Following a quasi-linear relationship with the temperature variation, the thermo-induced additional axial force soared with the larger length-diameter ratio of the pile and may even reach four times that of the pile under pure mechanical loads. Important additional settlements were also observed especially in cooling conditions. The shaft frictions along the long bored energy pile were found to have a complicated distribution, which requires further investigations.
Article
Energy pile foundations play the dual role of providing structural support to buildings and acting as heat exchanger units. Thus, they are subjected to different mechanical loads from the buildings and the cyclic temperature changes encountered in optimized hybrid systems. However, the effects of mechanical loading levels on the thermo-mechanical behaviour of energy piles under cyclic temperature changes are still to be investigated fully. This paper fills this knowledge gap through a series of model scale tests where the effects of different mechanical loading levels were investigated over multiple cooling-heating cycles in over-consolidated saturated clay. In this respect, ten cooling-heating cycles were applied while the pile's head load was maintained at 0, 25%, and 50% of the pile's ultimate bearing capacity, respectively. After ten thermal cycles, the pile's normalized settlement reached 0.05%, 0.37%, and 1.19%, respectively. The ultimate bearing capacity was 555 N, 535 N, and 520 N, respectively. The results indicate that the increase in load levels exacerbates the irreversible settlement while reducing the bearing capacity of the piles. Moreover, it also affects the stress distribution within the pile and further develops internal tension. The results from this study can be used for qualitative analysis of energy pile design.
Article
Frictional energy piles have been emerging as a proenvironmental means in the industry to exploit shallow geothermal energy. A growing concern for energy piles is their bearing capacity typically subjected to temperature variations. To better understand the temperature-dependent behavior involving bearing capacity, herein a series of direct shear tests were carried out to examine the effects of temperature and thermal cycles on the frictional behavior of the pile–soil interface for energy piles. The pile–soil interface consisting of fine-aggregate concrete and kaolin clay was tested under four normal stress levels, i.e., 50, 100, 200, and 300 kPa. The results suggest that: (1) a positive correlation may exist between temperature and the shear strength of the pile–soil interface; (2) the adhesion of the interface may vary with temperature in terms of a nonmonotonic function; and (3) the shear strength of the interface appears to decrease with an increasing thermal cycle and/or an increasing fluctuation amplitude of temperature within a temperature cycle. The experimental data obtained here may help enrich the understanding of the complex behavior of the shear strength of the pile–soil interface for energy piles and related soil–structure interaction.
Conference Paper
In many cases, structural problems occur during and after the construction of the building due to the lessening of the importance of conducting geotechnical investigations. This study was prepared for a hotel building in the construction phase consisting of eight floors without a basement within the boundaries of the old city of Karbala (the camp area). The concrete structure was built on a land of approximately 207 m2 (81 × 11.5 m) in a crowded building area. There was a differential settlement between the four corners of the building in the finishing phase ranging between (10–40) mm when starting the finishing work. These reasons led to the occurrence of the building’s tilt (rotation due to tilting) with a differential settlement of (170) mm from the top of the structure compared to its lower projection in its front facade, which contains the large protrusions (cantilever equal to 3.0 m) on the side of the main street. This was accompanied by a settlement of (60) mm on the side of the secondary street. This study suggests giving importance to the role of the specialized geotechnical engineer in the initial and detailed design stage of the building and encouraging conducting simultaneous soil investigations. The official authorities’ weak application of control and follow-up controls by the official authorities related to the issue of construction and stabilization of the construction work are also reasons for such failures.
Conference Paper
Full-text available
A continuous flight auger (CFA) pile is a cast-in-situ concrete pile made with a hollow stem auger that is fully flighted. Its application and constructability have greatly extended as a result of technological advancements. CFA piles with diameters ranging from 300 mm to 1200 mm, as deep as 50 m or more, and in subsurface conditions are now increasingly frequent. Several projects have successfully used continuous flight auger piles as a technically viable and cost-effective deep foundations technique in Iraq for the past ten years. The background of CFA piles, technical concerns, and case examples in Iraq are presented in this study. Several experimental and working piles were tested according to the American Standard ASTM D 1143. Some of these piles were tested under the working load, and others were carried to the maximum load, and the settlement values were recorded in all cases. It was concluded that the CFA piles used in Iraq have lengths 16–18.7 m and diameters of 0.5–0.8 m. The average settlement of piles doesn’t exceed 2% of the pile diameter, indicating that the piles were far from a failure under the design loads. CFA piles in Iraq are usually constructed in clays, so they will be subjected to negative skin friction (i.e., shear stress reversal) when the soils in contact with the upper portion of the pile move downward relative to the pile.
Article
Sequentially coupled thermal-stress finite element analyses were performed to investigate the mechanical behaviors of an energy pile group subjected to non-uniform thermal loadings. The group effect was highlighted by comparing the thermo-mechanical responses with those of the single pile case. Due to the thermal interactions between piles, the group piles’ temperatures were higher than that of the isolated single pile. If only part of the piles served as heat exchangers, i.e., the pile group was thermal loaded unevenly, there were differential deformations between the heated and the non-heated piles. Due to the pile-raft-pile interaction, the axial forces of the piles changed significantly. The location of the heated pile had an important influence on the thermally induced axial force, while the effect of the soil’s coefficient of thermal expansion was not significant. Inspired by the numerical result, a simplified method was proposed to capture the main characteristics of energy pile groups and to facilitate the design. The proposed method was developed in the framework of the traditional load transfer approach, and the pile-raft-pile interaction was included. By applying different temperature increments to different piles, the non-uniform thermal loading was modeled. The proposed method was verified by comparing with the finite element analysis results and the data collected from the literature.
Article
Soil thermal conductivity (λ) is an important parameter for determining the thermal properties of rock and soil materials. In this study, multivariate probability distribution (MPD) models were established based on the factors influencing λ. The performance of the MPD models was evaluated by testing parameters and comparing them with the traditional empirical relationship model of λ to verify the effectiveness of the MPD models. According to the research results, MPD models can accurately predict λ. With the increase in influencing factors considered by the MPD models, the prediction accuracy significantly improved, the correlation coefficient (R²) increased from 0.7125 to 0.9248, the E(ε) value was reduced to 1.0208, and the COV(ε) value was reduced to 0.2336. Among the established MPD models, the performance of the λ-{w, ρd, n, Sr, c, sa, qc} model was the best, and the prediction accuracy of the MPD models was better than that of the traditional empirical relationship model. The results of this study suggest that different types of MPD model should be chosen to estimate the thermal conductivities of different types of soil with significant differences in engineering properties and complex sedimentary environments.
Article
Full-text available
This study presents the specificity of the Silesian Botanical Garden (SBG) and its importance in protecting biodiversity in the Silesia area in Poland. Due to the special socio-ecological nature of the SBG and the request of the Garden’s Director, various types of renewable energy sources (RESs) installations were considered. These installations were intended to fulfill an educational function for society and meet the energy demands of the SBG. The concepts of on-grid and off-grid, including wind turbine, a system of photovoltaic panels (PVPs), and pumped storage hydropower plant (PSHP), were taken into account in the geoengineering analysis. The guidelines of the RESs device manufacturers do not consider complex soil–water conditions, the value of the loading forces (including influences from wind, temperature, snow, and soil pressure) related to a specific location (e.g., insolation), etc. The preliminary analysis of possible solutions showed that the energy from renewable energy sources meets the demands of the Garden on an annual cycle. In addition, the proposed conceptions take into account the specificity of the Silesian Botanical Garden (for example, a set of photovoltaic panels looks like a solar tree) and interfere with the landscape and ecosystem as little as possible. The selection of specific devices and materials and the accurate design of the proposed solutions may take place in a larger group of specialists in the field of geotechnics, mechanics, energetics, electricity, aerodynamics, etc., after obtaining financing by the SBG authorities.
Article
The use of geothermal energy piles (GEPs) associated with ground source heat pump systems is a sustainable and cost effective technology to heat and cool buildings, based on the efficient application of available resources found at the building site. Currently, a new building with GEPs is under construction at the University of São Paulo campus in São Paulo City, Brazil. Part of the building loads will be supported by steel pipe piles equipped with single U-type absorber pipes for heat exchange. To find the optimum solution of pile backfill material in terms of cost, constructability, sustainability and thermal performance, field thermal response tests were conducted on 4 instrumented piles filled with different materials: water, saturated sand, grout, and steel fiber grout. Both analytical and numerical models were used to evaluate the tested alternatives. The results showed that the thermal performance of the 4 piles is similar; however, the costs and sustainability aspects (low CO2 emissions) of the solutions using water or saturated sand imply that they are more advantageous than those using grout. Additionally, the experiments showed that for the pile backfilled with water the convection effects have improved the heat transfer to the soil.
Article
Many ongoing tunnel projects provide a favorable opportunity for the investigation and application of tunnel lining ground heat exchangers (GHEs). Tunnel lining GHEs can be connected to a heat pump to extract geothermal energy for heating and cooling buildings. Numerous studies have focused on the thermal performance of tunnel lining GHEs; however, the studies on the interaction between heat pumps and tunnel lining GHEs are relatively rare. In this study, a coupled heat transfer model of heat pumps and tunnel lining GHEs was proposed and then calibrated based on in situ test results. The model was used to evaluate the energy efficiency of a heat pump with tunnel lining GHEs under different conditions. The results show that the energy efficiency ratio (EER) increases exponentially with the absorber pipe length and thermal conductivity of the surrounding rock. The EER is governed by the convection heat transfer coefficient, which varies exponentially; meanwhile, the EER decreases approximately linearly with the annual average air temperature in the tunnel. Different types of heat pumps affect the EER significantly, and the EER of a Type-3 heat pump is higher than that of a Type-1 heat pump by 27.1%. Based on the aforementioned results, an empirical formula for the EER and absorber pipe length was established. Moreover, a preliminary design method for the absorber pipe length based on this empirical formula was developed. The method was employed to determine the appropriate absorber pipe length for the tunnel lining GHEs in the Shapu tunnel in Shenzhen, China. Finally, groups of absorber pipe layouts with a pipe spacing of 0.5 m, area of 135 m², and length of 293.5 m were preliminarily determined.
Article
In this study, a hollow steel ball (HSB) is used to macro-encapsulate the phase change materials (PCM) to obtain PCM-HSB aggregates. Furthermore, the PCM-HSBs were incorporated with steel fibres to improve the thermal and mechanical properties of concrete. The effect of the volume content (0.35, 0.7, and 1.05 vol%) of the steel fibre and the thickness of HSB (0.3 and 1 mm) on the thermal and mechanical properties of the steel fibre reinforced PCM-HSB concrete was evaluated. The test results demonstrated that the thermal conductivity and compressive strength of the PCM-HSB concrete significantly increased with an increase in the steel fibre content and HSB thickness. The addition of 0.35% steel fibre improved the thermal conductivity of the PCM-HSB concrete by 71% due to the bridge function of the scattered steel fibres in the concrete matrix. However, the thermal conductivity decreased when the high steel fibre content was increased to1.05 vol% due to fibre agglomeration. Moreover, compared with that of the plain PCM-HSB concrete, PCM-HSB concrete with 0.7 vol% steel fibre increased the compressive strength of the concrete by 63%. The proposed fibre reinforced PCM-HSB can significantly improve the heat capacity and bearing capacity of concrete, which can ensure potential applications of energy piles.
Article
Full-text available
The effect of bulk density and moisture content on the thermal conductivity of some Jordanian soils was investigated through laboratory studies. The soils used were classified as sand, sandy loam, loam, and clay loam. The hot wire method was used to perform the experiments. Heating and cooling methods were used to evaluate thermal conductivity for the soil types and the results obtained by the two methods were compared. Thermal conductivity increased with increasing soil density and moisture content. It was found that the soil containing higher percentage of clay particles had lower thermal conductivity. Graphical comparisons of thermal conductivity obtained by both methods, cooling and heating, for each soil type are presented. In general, the heating data yielded thermal conductivities that were slightly higher than those derived from the cooling data.
Article
Comprehensive laboratory tests and field observations have shown that not only grain size distribution but also mineral composition of fine grain functions is of decisive importance for frost-thaw characteristics of soils. The influences of metal hydroxides and organic components, as well as soil chemistry, were also examined. There are no clear-cut limits in nature between ″frost-resistant″ and ″frost-susceptible″ . Consequently, the distinctions required for construction purposes must be defined on the basis of field and laboratory investigations. Guidelines have been established for a mineral criterion, concerning the admissible grain fraction less than 0. 02 mm in connection with the mineral composition and the colloidal clay content.
Book
Ludwig Prandtl hat mit seinen grundlegenden Beiträgen zur Hydro-, Aero-und Gasdyna­ mik die Entwicklung auf dem Gebiet der Strömungsmechanik entscheidend geprägt und mit seinen bahnbrechenden Arbeiten in der ersten Hälfte des letzten Jahrhunderts die moderne Strömungsmechanik begründet. Sein 1942 erschienenes Buch Führer durch die Strömungs­ lehre hatte seinen Ursprung in den vorangegangenen Buchveröffentlichungen 1913 Lehre von der Flüssigkeit und Gasbewegung und 1931 Abriß der Strömungslehre. Der Titel Führer durch die Strömungslehre bringt Prandtls Absicht zum Ausdruck, den Leser auf einem sorgfältig angelegten Weg durch die einzelnen Gebiete der Strömungslehre zu führen. Dabei dringt der Verfasser, ohne umfangreiche mathematische Ableitungen, intuitiv zum Kern des physika­ lischen Problems vor. Die Beschreibung der grundlegenden physikalischen Phänomene und Begriffe der Strömungsmechanik, die zur Ableitung der vereinfachten Modelle erforderlich sind, haben Vorrang vor der Behandlung der Methoden. Prandtls Führer durch die Strömungslehre war bei seiner Erstauflage das einzige Buch über die Strömungsmechanik und zählt bis heute zu den wichtigsten Büchern auf diesem Gebiet. Nach seinem Tode haben es seine Schüler Klaus Oswatitsch und Karl Wieghardt übernom­ men sein Werk fortzusetzen und neue Erkenntnisse der Strömungsmechanik in der bekannten anschaulichen Darstellungsweise einzufügen. Nach dem die neunte Auflage vergriffen war und der Verlag eine Neuauflage anstrebte, ha­ ben wir diese Aufgabe gerne übernommen. Unter dem neuen Titel Prandtl - Führer durch die Strömungslehre wird, in den ersten vier Kapiteln, der von Prandtl vorgezeichnete Weg der ersten Auflage von 1942 beibehalten.
Article
This paper presents a case study of a piling contract undertaken in Chichester in 2003. Unusually, the piles contained a network of plastic pipes, which were subsequently connected to the heating and cooling system for the new building. The plastic pipes cast in the piles facilitate the transfer and storage of geothermal energy between the structure and the underlying ground mass, allowing the building to be both heated in winter and cooled in summer economically and in an environmentally friendly way. The philosophy of the geothermal pile technology is presented, together with the modified pile construction techniques used on the site.
Article
This paper presents results of a study on the effects of high temperature (up to 90°C) on undrained shear characteristics of clay in both normally consolidated (NC) and overconsolidated (OC) states. The study is based on isotropically consolidated undrained triaxial tests carried out using a temperature controlled triaxial apparatus. Several sequences of heating and consolidation were used to gain insight into the effects of temperature on clay. The study reveals that : (1) in NC state, both the initial secant modulus and the shear strength increase with increasing temperature, and (2) in OC state, only the initial secant modulus increases with a temperature rise, but the shear strength is not affected by heating. This paper further explains these experiment results in terms of micro-resistance and macro-resistance of the clay structure.
Article
This paper is concerned with modeling of thermomechanical failure of triaxial specimens of saturated clays of low porosity. Thermomechanical failure manifests itself in undrained conditions as a development of advanced irreversible strains due to heating under constant total stress. In experiments on two clays the failure occured at temperatures from 70° to 90°C. The observed failure is associated with a pore water pressure buildup. Models of thermoplastic behavior of skeleton and of thermal volume changes of adsorbed water are employed to interpret and numerically simulate the test results. Using these models, thermomechanical failure was found to occur when the effective stress is brought to the critical state by expansion of pore water and thermoplastic compressive strain in skeleton.
Article
A summary is given of some of the main features associated with the thermal properties of soils in cold regions as described in a USACRREL monograph and report. The main effects of the freezing process in soils are noted and its analogy with the drying process is emphasized. It is shown that the unfrozen water present in frozen fine-grained soils plays an important and effective role in facilitating heat transfer. The influence of the degree of saturation is described and the concept of a “critical” degree of saturation introduced.The methods for calculating the thermal conductivity of frozen soils are compared and some of their trends indicated. The results of an evaluation of these methods show which gives the best agreement with measured thermal conductivity values under certain conditions.
Article
Ten successive in situ experimental investigations of hot water storage by a single well and a pair of wells (doublet) were conducted in 1976-1977 at Bonnaud, Jura, in a confined aquifer 2.5 m thick. The injected volumes ranged from 500-1700 m3. Temperature profiles were measure daily in 12 boreholes distributed along two perpendicular axes within 13 m of the injection well. Individual temperatures were measured by ten thermistors placed in the caprock. The results are discussed and used to calibrate two mathematical models. An axisymmetric model allows the calibration of average values of the parameters, while a three-dimensional model is used to determine their spatial variation in the horizontal plane. The latter model leads to the identification of a nonhomogeneous transmissibility field which fully accounts for both hydraulic and thermal contour curves. The models, which were matched against particular experiments, proved accurate when simulating other periods. Evidence is given of the importance to the recovery ratio of thermal dispersion in the aquifer and of the water content of the caprock. In a final section, experimental results of single well storage at Bonnaud, Campuget, and Auburn are compared with general type curves derived in the companion paper. They prove to yield adequate predictions of water temperature during the production phases.
Article
This work is concerned with the nonreactive transport of solute materials in groundwater, or hydro-dispersive transfer. Several types of flow fields are considered: linear (or uniform) flow with one- and two-dimensional dispersion and radial flow under diverging and converging conditions. The analysis includes the two main possibilities for introduction of solutes into an aquifer: continuous and instantaneous (or slug) injection. Different solutions from the literature plus some original solutions for dispersion in a linear flow field have been unified by transposing the solutions into dimensionless variables of concentration (CR), time (tR), and the Peclet number (P). This permits an analysis of the errors committed in some commonly used approximations for dispersion as a function of P. In the case of radial flow, a numerical method using finite differences has been developed that can be applied to either diverging or converging flow problems. Results in dimensionless form when compared to the only analytical approximations that could be found (for continuous injection in a diverging flow field) indicate that the approximate solutions are in error when P ≤ 10. The radial flow results are also compared to those for linear flow fields to demonstrate that in most cases either approach can be used as long as P > 3. A series of dimensionless type curves has been developed showing CR versus tR for practical ranges of P. A simple method of interpreting tracer tests is proposed using these type curves. One is able to directly determine dispersivity and kinematic porosity using curve matching techniques. Results from some recent field tests in France are analyzed using this approach. There is definite confirmation from these investigations that the apparent (macroscopic) dispersivity can vary depending on the distances used in the field.
Article
A review of ground heat transfer effects on the thermal performance of earth contact structures is presented. The fundamental heat transfer processes relevant to the problem are described along with methods of determining thermal properties of soils. An overview of the many analytical, semi-analytical and numerical methods available to solve the heat transfer problem is also provided, followed by a brief summary of design guides. The review also considers the influence of changes in ground water content on the heat transfer properties of soils. A description of the processes that give rise to changes in ground water conditions is provided. The bulk thermal conductivity of a soil is shown to be strongly related to its water content. An overview of methods of analysing changes in soil moisture content is then presented. Methods of estimating the relevant hydraulic properties of soils are also considered. The final part of the review provides a brief outline of the theoretical approach required to analyse coupled heat and moisture migration in soils. Notwithstanding the fact that there are many practical design tools available, it appears that further work is necessary to clarify the circumstances in which more sophisticated analysis is warranted. Recent studies indicate that geometric simplification can lead to quite significant errors in heat loss calculation. Full three-dimensional treatment appears to be necessary in some cases. Thermal properties of soils vary according to the properties and proportions of the constituent phases (air/water/solid). Soil moisture content variations occur naturally or as a result of anthropogenic activity. The influence of such variations on the thermal conductivity of the ground is significant. The review outlines some simplified methods of accommodating this feature of the ground heat transfer problem. However, this aspect of the problem appears to need further consideration.
Energy piles for heating and cooling of buildings
  • H Brandl
Brandl, H. (1998a). Energy piles for heating and cooling of buildings. Proc. 7th Int. Conf. Exhib. Piling and Deep Foundations, Vienna, 3. 4. 1-3. 4. 6.
Numerische und experimentelle Untersuchungen zur Nutzung von geothermischer Energie mittels erdberührter Bauteile und Neuentwicklungen für den Tunnelbau. Doctoral thesis
  • R Markiewicz
Markiewicz, R. (2004). Numerische und experimentelle Untersuchungen zur Nutzung von geothermischer Energie mittels erdberührter Bauteile und Neuentwicklungen für den Tunnelbau. Doctoral thesis, Institute for Soil Mechanics and Geotechnical Engineering, Technical University of Vienna.
Jahrbuch Erneuerbare Energien. Radebeul: Bieber- stein-Fachbuchverlag
  • F Staiß
Staiß, F. (2001). Jahrbuch Erneuerbare Energien. Radebeul: Bieber- stein-Fachbuchverlag.
The exploitation of energy extracted from ground-contact concrete members
  • R Ferrari
Ferrari, R. (1998). The exploitation of energy extracted from ground-contact concrete members. Nägele Reports, Röthis, Austria.
Utilization of geothermal energy from railway tunnels
  • D Adam
  • J Hofinger
  • N Ostermann
Adam, D., Hofinger, J. & Ostermann, N. (2001). Utilization of geothermal energy from railway tunnels. Proc. 15th Int. Conf. Soil Mech. Geotech. Engng, Istanbul 3, 2029-2034.
Engerieanlage mit Saisonalem Thermospeicher
  • A Ennigkeit
Ennigkeit, A. (2002). Engerieanlage mit Saisonalem Thermospeicher, Mitteilungen des Institutes und der Versuchsanstalt für Geotechnik der Technischen Universität Darmstadt, No. 60.
Erdwärmenutzung und Ausführung auf der U-Bahnbaustelle U2/1
  • N Von Der Hude
  • R Völkner
von der Hude, N. & Völkner, R. (2003). Erdwärmenutzung und Ausführung auf der U-Bahnbaustelle U2/1, 'Schottenring' in Wien. O ¨ sterreichische Vereinigung für Beton-und Bautechnik 54, 15–11.
Erfolgskontrolle Energiepfahlanlage Pago, Zwischenbericht, Grabs
  • U Lippuner Energie
  • Metallbautechnik
Lippuner Energie-u. Metallbautechnik (1996). Erfolgskontrolle Energiepfahlanlage Pago, Zwischenbericht, Grabs. Unpublished report.
Einsatz von Energiepfählen am Beispiel des Main Tower in Frankfurt am Main. Reports of the Institute for Geotechnics
  • N Von Der Hude
  • Chr Kapp
von der Hude, N. & Kapp, Chr. (1998). Einsatz von Energiepfählen am Beispiel des Main Tower in Frankfurt am Main. Reports of the Institute for Geotechnics, Technical University of Darmstadt, Vol. 39, pp. 15-28.
Degree-days and heat conduction in soils
  • F J Sanger
Sanger, F. J. (1979). Degree-days and heat conduction in soils. Proc. 1st Int. Conf. Permafrost, Purdue Univ., Indianapolis, 253–262.
Ground heat storage: thermal analyses of duct storage systems I. Theory. Doctoral dissertation
  • G Hellström
Hellström, G. (1991). Ground heat storage: thermal analyses of duct storage systems I. Theory. Doctoral dissertation, Lund Institute of Technology, Department of Mathematical Physics, Lund University, Lund, Sweden.
Nutzung von Verkehrstunneln als Absorberbauwerke für die Gewinnung geothermischer Energie
  • H Brandl
  • D Adam
  • R Markiewicz
Brandl, H., Adam, D. & Markiewicz, R. (2004). Nutzung von Verkehrstunneln als Absorberbauwerke für die Gewinnung geothermischer Energie, Research Report. Vienna: Federal Ministry for Transport, Innovation and Technology.
Thermal properties of soils Clausthal-Zellerfeld
  • O T Farouki
Farouki, O. T. (1986). Thermal properties of soils, Series on Rock and Soil Mechanics, Vol. 11. Clausthal-Zellerfeld: Trans Tech Publications.
Energy savings with concrete: Heating and cooling with energy from subsoil
  • R Preg
Preg, R. (1997). Energy savings with concrete: Heating and cooling with energy from subsoil. Nägele-Reports, Röthis, Austria.
Thermoaktive Fundamente
  • Enercretnägele
Enercretnägele (2004). Thermoaktive Fundamente. Nägele-Reports, Röthis, Austria.
Geothermische Energienutzung mittels Pfählen
  • H Brandl
  • D Adam
  • F Kopf
Brandl, H., Adam, D. & Kopf, F. (1999). Geothermische Energienutzung mittels Pfählen, Schlitzwänden und Stützbauwerken. Pfahl-Symposium 1999, Braunschweig, 329-356.
Fluid-to-ground thermal resistance in duct ground heat storage
  • G Hellström
Hellström, G. (1994). Fluid-to-ground thermal resistance in duct ground heat storage. Proc. Calorstock '94, Espoo, pp. 373-380.
Effect of ground water flow on the performance of long-term pipe heat storage in the ground
  • P Lund
Lund, P. (1985). Effect of ground water flow on the performance of long-term pipe heat storage in the ground, Report TKK-F-A586 (1985). Helsinki University of Technology Finland.
Geothermische Nutzung von Bauwerksfundierungen ('Energiefundierungen'). O ¨ sterr
  • H Brandl
  • R Markiewicz
Brandl, H. & Markiewicz, R. (2001). Geothermische Nutzung von Bauwerksfundierungen ('Energiefundierungen'). O ¨ sterr. Ing. Archit. Z 146, No. 5–6, 216–222.
Environmentally friendly geothermal piles at Keble College
  • T P Suckling
  • P E H Smith
Suckling, T. P. & Smith, P. E. H. (2002). Environmentally friendly geothermal piles at Keble College, Oxford, UK. Proc. 9th Int. Conf. Exhib. on Piling and Deep Foundation, Nice, 445-452.
Oberflächennahe Nutzung der Geothermischen Energie: Analyse ihrer Umweltauswirkungen und der rechtlichen Rahmenbedingen im internationalen Vergleich
  • M Brauner
Brauner, M. (2002). Oberflächennahe Nutzung der Geothermischen Energie: Analyse ihrer Umweltauswirkungen und der rechtlichen Rahmenbedingen im internationalen Vergleich. Master's thesis, Institute for Soil Mechanics and Geotechnical Engineering, Technical University of Vienna.
Energie aus Erdwärme
  • M Kaltschmitt
Kaltschmitt, M. (ed.) (1999). Energie aus Erdwärme. Stuttgart: Deutscher Verlag für Grundstoffindustrie.
Thermal response test: In situ measurements of thermal properties in hard rock. Division of Water Resources Engineering
  • S Gehlin
Gehlin, S. (1998). Thermal response test: In situ measurements of thermal properties in hard rock. Division of Water Resources Engineering, Department of Environmental Engineering, Lulea University of Technology, Sweden.
Nutzung geothermischer Energie und Umweltwärme auf niedrigen Temperaturniveau mittels erdberührter Bauteile
  • J Hofinger
Hofinger, J. (2002). Nutzung geothermischer Energie und Umweltwärme auf niedrigen Temperaturniveau mittels erdberührter Bauteile. Master's thesis, Institute for Soil Mechanics and Geotechnical Engineering, Technical University of Vienna.
A comparison of two methods used to evaluate thermal conductivity for some soils
  • N Abu-Hamdeh
  • A Khadair
  • R Reeder
Abu-Hamdeh, N., Khadair, A. & Reeder, R. (2001). A comparison of two methods used to evaluate thermal conductivity for some soils. Int. J. Heat Mass Transfer 44, No. 14, 1073-1078.
Geothermische Nutzung von Bauwerksfundierungen ('Energiefundierungen'). Ö sterr. Ing. Archit
  • H Brandl
  • R Markiewicz
Brandl, H. & Markiewicz, R. (2001). Geothermische Nutzung von Bauwerksfundierungen ('Energiefundierungen'). Ö sterr. Ing. Archit. Z 146, No. 5-6, 216-222.
Cool thinking. European Foundations, Spring
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