Energy Pile Groups Research Articles

Thermo‒mechanical behavior of energy pile group in dry sand subjected to a horizontal load

The energy pile is an innovative structure element designed to utilize geothermal energy while simultaneously supporting building loads by means of integrating heat exchange tubes into the pile foundation. Despite the intricate thermodynamic characteristics of energy pile groups, research on them remains limited. This study investigated the horizontal load transfer mechanism of an energy pile group in dry sand by conducting a model test on a 2 × 2 energy pile group subjected to horizontal loads. Specifically, the impact of heating or cooling a single pile within the energy pile group was examined. The results showed that the bending moment was significantly larger on a single pile subjected to a thermal load than that of the other piles, with the majority of this variation occurring in its upper part. Additionally, the horizontal load had a strong influence on the rotational angle and horizontal displacement of the energy pile group. The rotational angle and horizontal displacement decreased with increasing depth. With rising temperature, the interaction between the pile and the soil intensified, and the soil pressure on the upper part of the pile increased while that in the lower part decreased.

Heat Transfer Performance and Operation Scheme of the Deeply Buried Pipe Energy Pile Group

This paper describes a study on the heat transfer properties of the deeply buried pipeline energy pile group, which is an efficient and convenient geothermal development technology. Through in situ experiments and a simulation algorithm, the research investigated the heat transmission characteristics of the deeply buried pipe energy pile group and optimized different intermittent operation schemes. The findings suggest that prolonged operation of the pile cluster intensifies heat buildup within the pile foundation, thereby adversely affecting the system’s overall heat exchange efficiency. Employing an intermittent operating mode can alleviate this heat accumulation phenomenon, thereby promoting sustained heat exchange performance of the piles over time. To evaluate the comprehensive thermal interaction and energy efficiency ratio of the energy pile heat exchange system, various intermittent operation strategies were compared in the study. Among them, the intermittent operational scheme with a ratio of n = 5 was found to be optimal, with the total average heat transfer rate of the pile set only 0.51% lower than that of the continuous operational mode, but the overall energy efficiency ratio improved by 19.6%. The intermittent operational mode proposed in this study can achieve the goal of saving energy and efficiently extracting geothermal resources, providing theoretical guidance for the extraction and utilization of subsurface geothermal power by energy piles.

Heat exchange performance of an energy-pile group in a hybrid GSHP system and effects of pile spacing

In long-term operations, seasonal imbalance in the thermal load may adversely affect the heat transfer performance of the energy piles, potentially resulting in thermal accumulation within the ground and eventual system failure. The heat transfer performance of energy pile systems during long-term operation under unbalanced thermal loads must be investigated. Moreover, the design parameters of energy piles are usually constrained by the requirements of foundation structural design, resulting in energy piles being densely arranged. Hence, the influence of pile spacing on the heat exchange performence of energy piles must be comprehensively understood. In this study, two- and three-dimensional energy-pile heat transfer models were established and innovatively coupled based on an engineering project currently under design. Numerical simulations were performed to investigate the heat transfer behavior of energy-pile groups subjected to unbalanced thermal loads and the effect of pile spacing on their heat exchange performance. Furthermore, design recommendations regarding the determination of the proportion of thermal loads to be borne by the energy piles in a hybrid GSHP system were provided. The results indicate that the proposed 2D-3D coupled modeling approach is able to simulate the heat exchange performance of large-scale energy pile groups. Pile spacing considerably affects the long-term thermal performance of energy-pile groups, especially in cases with small pile spacings. The influence of pile spacing on the heat exchange capacity of energy piles can be considered in the design phase by incorporating a group effect coefficient η, which are calculated to be 0.165, 0.470, 0.732, and 1 for pile spacings of 2 m, 4 m, 6 m, and 10 m, respectively.

Analytical investigations on thermomechanical behavior of energy pile groups resting on stiff soil strata

Energy piles are increasingly being exploited worldwide because of their dual role of exchanging heat with the ground and providing structural support for buildings. Despite the existing studies, simplified but reasonable methods for estimating the vertical displacement of end-bearing energy pile groups subjected to thermal loads are lacking. To address this challenge, an analytical approach was proposed to analyze the thermomechanical behavior of energy pile groups bearing stiff soil strata. To consider the reduction in soil displacement caused by the presence of a bearing layer, an approximate method where the energy piles comprising solid and mirror-image elements was introduced. The proposed approach was implemented using a self-developed program and validated against the results of existing numerical studies. The results indicated that the thermally induced displacement interaction between the predominant end-bearing piles was more pronounced than that between the floating piles. The displacement interaction decreases with decreasing shaft and base soil stiffness, increasing pile spacing, and decreasing pile slenderness ratio. In addition, a simplified method for estimating the displacement of energy pile groups resting on stiff soil strata was established by superimposing the interaction factor.

The mechanical response of energy pile groups in layered cross-anisotropic soils under vertical loadings

The mechanical response of energy pile groups in layered cross-anisotropic soils under vertical loadings is studied with the aid of the coupled finite element method - boundary element method (FEM-BEM). The single energy pile is simulated based on the finite element theory, which then is extended to energy pile groups. The global flexibility matrix for soils is obtained by considering the coupling effects of vertical and thermal loadings. The coupled FEM-BEM equation for the interaction between energy pile groups and soils is derived based on the displacement compatibility condition at the pile-soil interface. According to the displacement coordination condition and force balance in the rigid cap, the displacement of the cap and axial forces of pile groups can be solved. The presented theory is validated by comparing the calculated results with numerical simulations and field test results in existing literature. Finally, effects of the thermal loading, pile-soil stiffness ratio, pile spacing, cross-anisotropy of Young's modulus and the stratification are discussed.

Thermally induced mechanical interactions of energy pile groups subjected to cyclic nonsymmetrical thermal loading

Prior to this study, the long-term thermally-induced mechanical interactions of cyclic nonsymmetrical thermally loaded energy pile groups in soft clay have not been systematically elucidated, particularly with a limited understanding of the interactions among operating and non-operating energy piles, soil, and caps. Observing such a challenge, this paper presents a three-dimensional (3D) thermomechanical finite-element model (FEM), which considers the thermal-dependent behavior at the pile-soil interface and is validated using typical centrifuge tests reported in the literature. Special attention is given to the influence of soil-pile thermal expansion coefficient ratio, pile-soil stiffness ratio, and slab-soil stiffness ratio on the abovementioned interaction. The results indicate that a larger soil-pile thermal expansion coefficient ratio intensifies the interaction between energy piles and the surrounding soil, causing cyclic variations in thermally mobilized friction. With increasing pile-soil stiffness ratios, the differential thermomechanical responses among different piles within a group are enhanced because the toe and shaft resistances mobilized by the cap through nonoperating energy piles are weakened in the interaction process among energy piles, nonoperating energy piles, and the cap. Moreover, the increase in the slab-soil stiffness ratio exacerbates this interaction, strengthening the integrity of the pile groups.

Numerical Study on Energy Pile Groups with Deep Penetration 1-U-Shape Heat Exchangers under Different Operation Modes

Numerical Study on Energy Pile Groups with Deep Penetration 1-U-Shape Heat Exchangers under Different Operation Modes

Heat transfer performance of large energy pile group in a hybrid system subjected to imbalanced thermal load - A numerical investigation

Introduction
 When a energy pile system is coupled with other heating or/and cooling systems, determining the share of thermal demand that energy piles can meet is crucial in designing the size of each system. In the long term, imbalance in thermal load can affect the heat transfer performance of energy piles, and may also lead to annual accumulation of ground temperature over the years, ultimately causing system failure. Furthermore, the mechanical responses of energy piles are also affected by the temperature changes in the pile body and surrounding soil during operation. While Current researches have predominantly focused on mechanical response under temperature load, understanding the heat transfer performance of energy pile groups is equally necessary. Existing studies on heat transfer largely draw from ground source heat pump (GSHP) systems, despite differences in depth and diameter between energy piles and borehole heat exchangers (BHEs), particularly for closely spaced piles. To address this gap, we conducted a series of numerical experiments based on the Tsinghua Science Museum project to investigate the thermal behavior of energy pile group under annual, imbalanced load and the influence of pile spacing. Based on simulation results, we provide design recommendations on how to determine the proportion of heat load that can be carried by energy piles in hybrid systems.
 Method
 We utilized COMSOL software to conduct three-dimensional modeling of a single pile, and developed a two-dimensional model of a pile group using a self-programmed Matlab program. The accuracy of the model was evaluated by comparing it with the results obtained from energy pile field tests (thermal response tests and thermal performance tests) conducted in Shunyi, Beijing. Subsequently, we established two-dimensional and three-dimensional numerical models for the Tsinghua Science Museum project in Beijing. We performed a series of numerical experiments to investigate the behavior of energy piles under balanced and imbalanced temperature loads for one year. Furthermore, we simulated the thermal responses of energy pile groups with different pile spacings of 2m, 2.85m, and 4m.
 Results
 The cooling load surpasses the heating load causing an imbalanced load. The soil temperature rises noticeably by 2.6 °C compared to the initial state after an operation period of 1 year, indicating an undesirable phenomenon of soil heat accumulation. With continuous running over years, the system will fail due to the excessive soil temperature. Moreover, the heat exchange liquid temperature ranges from -4.35 ℃ to +39.65 ℃, which exceeds the acceptable range of 2 ℃ to 33 ℃. To address this concern, a hybrid system can be utilized where the energy pile system bears a balanced portion of the thermal load, and the auxiliary system bears the remaining load. Simulation under various thermal load proportions reveals a linear relationship between the maximum/minimum outlet temperature and the total heat exchange volume. An energy pile system undertaking 60% heating load and 40% cooling load can run stably for long periods. The soil temperature varies in a range of 8.5 ℃ to 17.9 ℃, while the pile body temperature has a variation range of 4.0 ℃ to 22.8 ℃ (Figure 1).
 The study results for various pile spacings are presented in Table 1. Pile spacing plays a significant role in soil heat accumulation and heat exchange fluid temperature. Despite an invariable pattern in the inflow and outflow temperature curves for varied pile
 spacing, the flow temperature range is significantly influenced. The smaller the spacing, the more prominent is the thermal accumulation in the soil, leading to larger changes in soil temperature and the flow temperature. During design simulation, if the range of flow temperature exceeds the limits of the energy pile system, it may present a safety risk during system operation. In such cases, increasing the pile spacing can render the system more reliable and safe.
 Conclusions
 (1) Whether the system can operate normally can be judged by whether the simulation result of the heat exchange liquid temperature exceeds the limit value. There is a linear relationship between the flow temperature and the total heat exchange. Therefore, the proportion of the load that the energy pile system can bear in the hybrid system can be determined. For the Tsinghua project, the energy pile system can bear 60% of the heating load and 40% of the cooling load.
 (2) The pile spacing affects the magnitude of variation in heat exchange fluid temperature by influencing the degree of heat accumulation in soil. If the range of flow temperature exceeds acceptable limits, it is advised to increase the pile spacing during the design phase to ensure the energy pile system can operate effectively.

Thermo-visco-elastic analysis of thermomechanical behavior of energy pile groups considering time-dependent deformation characteristics of soils

Energy piles are increasingly being exploited worldwide for their dual functions of bearing structural loads and utilizing geothermal energy. However, scarce knowledge is available on the time-dependent thermomechanical behavior of energy pile groups constructed in soft soils. In this paper, an analytical approach was proposed for the thermomechanical analysis of energy pile groups considering the time-dependent deformation of viscoelastic soils and validated against field test data. The impact of the soil creep behavior on the axial load–displacement response and pile-soil-pile interaction of the energy piles was further investigated. Finally, a simplified method and design charts were provided for displacement estimation and design of energy pile groups in soft soils. The results indicated that the displacement of energy piles would change with time until stabilization because of the viscous properties of the soil. The interaction between energy piles was directly related to the pile-soil stiffness ratio, the soil viscosity coefficient, the pile slenderness ratio, the pile spacing, and the number of piles. The soil creep behavior would result in a decrease in the displacement ratio of energy pile groups under thermal loading and an increase under mechanical loading.

Numerical investigations on effects of mechanical and geometrical characteristics on thermally induced group behavior of field-scale energy piles

Energy pile groups generally exhibit different thermomechanical behavior from single energy piles. Aiming to investigate the group behavior of energy piles, three-dimensional numerical models were developed and validated against field test data for a 2 × 2 energy pile-raft foundation. The validated models were subsequently adopted to comparatively analyze the thermomechanical behavior of pile groups operating either partially or fully. The results highlighted that the group action effects would induce lower thermal stress and greater head displacement imposed upon piles. Partially operating grouped piles exhibited differential displacement, thus inducing group tilt in the raft. Besides, parametric studies were made to evaluate the effects of mechanical and geometrical parameters on the group behavior of energy piles. The effects of soil thermal expansion were directly correlated with the heating extent of the soil. Under geological conditions with high soil thermal expansion coefficients, heating-induced tensile stresses and excessive head displacements could occur during the long-term operation of multiple piles. Higher soil elastic modulus resulted in higher restrictions on the thermal movement of piles, thus reducing the head displacement and group tilt, which was considered beneficial in practice. Special attention should be paid to the group action effects for closely-spaced energy pile-raft foundations.

Effects of pile configuration on the group behavior of semi-floating energy piles

To investigate the effects of pile configuration on the group effects of semi-floating energy piles, a series of laboratory tests were performed. The tests include three distinct pile configurations, namely, a single energy pile, a 2 × 2 energy pile group, and a 3 × 3 energy pile group. Different operation modes of energy pile groups, including all energy piles being cooled and partial energy piles being cooled, were considered. The monitoring and analysis of temperature changes in energy piles and surrounding soil, axial load variation, and displacement of energy piles and non-thermally activated piles were performed. The interactions among energy piles, non-thermally activated piles, raft, and surrounding soil within semi-floating pile groups with varying numbers of energy piles and operation modes were discussed. The findings reveal that the group effects of energy piles can be attributed to two aspects, namely pile-soil interactions and pile-raft-pile interactions. Both of these interactions contribute to reduced thermally induced axial loads and increased thermally induced displacements of energy pile groups. Under similar thermal loading, the 3 × 3 energy pile group exhibits a 19% increase in displacement and a 64% decrease in maximum thermally induced axial load compared to a single energy pile. Furthermore, the group effects of an energy pile group were affected by the pile configuration and are more pronounced with an increase in the number of energy piles within a pile group. The findings presented in this paper contribute to a more precise assessment of the thermo-mechanical response exhibited by such pile foundations.

Centrifuge modelling of an energy pile group with groundwater flow

For several decades, energy piles have been developed to extract heat from the ground by using foundation piles as heat exchangers. However, the thermal loading of these piles directly affects their mechanical behaviour. Centrifuge modelling of a thermally loaded pile group within a groundwater flow makes it possible to improve the understanding of the hydro-thermo-mechanical behaviour of this type of foundation. In this study, groundwater flow was established in a centrifuge model to study an energy pile group. The focus of this study was to enhance research findings on energy geo-structures such as foundations, which are very often located in soil with seepage. The groundwater flow allows reduction of thermomechanical effects and therefore plays the role as a stress and deformation stabiliser in addition to favouring the thermal recharge of the soil.

Numerical evaluations on the effects of different factors on thermo- mechanical behaviour of an energy pile group

Energy pile is a kind of economical and efficient underground energy structure. Obtaining the effects of different factors on the performance of energy pile help to improve the working efficiency of the energy pile. However, the thermo-mechanical behaviour of energy pile groups are more complex than that in single energy pile due to the mutual interference of energy pile groups. In this paper, the energy pile group with the layout of 3 × 3 was simulated by a 3-D numerical model. The influences of soil type, pile spacing, pile material performance and pile arrangement form on the thermo-mechanical behaviour of the energy pile group were investigated. The results show that increasing pile spacing can not only improve the thermal performance of energy pile group but also reduce the pile displacement, but it will lead to the increase of pile axial force because of the weakening of pile group effect. The thermal performance of energy pile group is the highest under the rock-soil condition, followed by sand and clay. However, the pile displacement is the largest when the soil type is sand, followed by clay, and the rock-soil is the smallest, and the influence of soil type on pile axial force is just opposite to pile displacement. At the same time, the increase of thermal conductivity of pile material benefits to heat transfer performance of energy pile group, but it also aggravates the heat accumulation and results in a larger top displacement and axial force of pile. As for concrete compression modulus, increasing the concrete compression modulus can increase the axial force of pile, but the change of concrete compression modulus has no effect on the pile displacement. In terms of layout of energy pile group, the per unit soil volume heat exchange rate of energy pile group in the cross arrangement form is larger than that in sequential arrangement form. However, the variation range of soil temperature in the cross arrangement form is larger than that in the sequential arrangement form, thus increasing pile displacement and reducing pile axial force.

Study on heat-exchange efficiency and energy efficiency ratio of a deeply buried pipe energy pile group considering seepage and circulating-medium flow rate

Seepage and circulating-medium flow rate are both primary factors affecting the heat-exchange efficiency and energy efficiency ratio of underground energy structures. In this study, a thermal-seepage coupled model of a deeply buried pipe energy pile group is developed, and the effects of circulating-medium flow rate, seepage velocity, and thermal migration caused by seepage on heat-exchange efficiency and energy efficiency ratio are analyzed. The results show that increasing the circulating-medium flow rate can improve heat-exchange efficiency, but aggravate heat accumulation, resulting in energy efficiency ratio reduction. Seepage can eliminate the heat accumulation as well as improve the heat-exchange efficiency and energy efficiency ratio. The heat accumulated around upstream piles will migrate along the seepage direction, generating thermal disturbance to the downstream piles. An increase in the circulating-medium flow rate of upstream deeply buried pipe energy piles will aggravate thermal disturbance. This phenomenon is slightly retarded if seepage velocity is increased. Additionally, when the circulating-medium flow rate of the deeply buried pipe energy pile group under seepage is within the optimal range, slightly reducing the circulating-medium flow rate of the upstream deeply buried pipe energy piles can reduce thermal disturbance to the downstream piles without affecting the overall heat-exchange efficiency.

A simple load transfer method for energy pile groups

Various analysis methods have been developed to simulate the performance of energy pile groups subjected to thermal and mechanical loads. Although they considered the interactions between piles in the group, the ‘sheltering-reinforcing’ effect was usually ignored during the analysis, or the methods were not experimentally validated. Therefore, to address this gap, we propose an experimentally validated load transfer model that considers the ‘sheltering-reinforcing’ effect for the thermomechanical analysis of energy pile groups. The proposed method modeled two well-documented full-scale field tests and two finite-element simulation cases. The comparison results showed that the proposed method could capture several essential aspects of the energy pile group, including thermally induced strain, stress, displacement, and group effects. Furthermore, a parametric analysis was performed to evaluate the effects of relevant parameters on the thermomechanical behavior of the energy pile group.

Influence of a rigid cap on thermo-mechanical behavior of nonsymmetrical thermally loaded energy pile group in clay

This paper presents the results of a series of cyclic nonsymmetrical thermally loaded model-scale tests conducted on floating pile groups, with and without a rigid cap in saturated clay. The energy pile in each group was subjected to 10 two-way (heating–cooling) thermal cycles with an amplitude of 15 °C to investigate the potential effects of a rigid cap on the thermomechanical behavior of energy pile groups. It was found that the rigid cap restrained the expansion/contraction of the energy pile in response to temperature change and reduced its irreversible settlement, resulting in a lower differential settlement between the energy and nonenergy piles. Consequently, a lower tilting was observed in the pile group with a rigid cap. In addition, the thermally induced axial load was significantly increased (especially in cooling mode) due to the restriction of a rigid cap. The thermomechanical load transfer profile of the energy pile was also affected by it, resulting in the downward transmission of shaft resistance.

Zoning operation of energy piles to alleviate the soil thermal imbalance of ground source heat pump systems

• Zoning operation of energy piles is investigated to alleviate soil thermal imbalance. • Dense heat injection into the central piles can relieve the cold accumulation. • Heat extraction from the outer layer piles can relieve the cold accumulation. • A reasonable strategy is proposed to achieve good system efficiency and reliability. Energy piles have attracted increasing interest for application in ground source heat pumps, because it is environment-friendly, energy-efficient, and without additional drilling cost. However, when there is a large difference between the heating and cooling loads, the system will suffer from a soil thermal imbalance which may further decline the system performance and even cause a system failure. A hybrid ground source heat pump system that integrates auxiliary equipment can solve the problem, however, it needs additional investment and a complicated control strategy. In this paper, the zoning operation of energy piles can effectively improve the temperature recovery ability of soil in the energy pile group and thus alleviate the soil thermal imbalance. Specifically, a heating-dominated residential building in Beijing is selected for a case study, with 144 energy piles arranged in a 12 × 12 layout. An analytical model of the spiral-coil energy pile group with seepage will be adopted, which can consider the groundwater flow, the geometry of spiral coils, and the thermal interaction among different energy piles, achieving high calculation accuracy and fast calculation speed. Based on this analytical energy pile model, a system model will be built to investigate the system performance influenced by different zoning operation strategies. Results show that intensive heat injection into the center of the pile group (Strategy 2 and Strategy 3) or heat extraction from the outer layer of the pile group (Strategy 4) can relieve the cold accumulation. Strategy 2 can relieve the outlet temperature decline from 5.54 °C to 4.46 °C and improve the heating COP from 3.297 to 3.423 compared to the conventional full operation strategy. Although the annual heat pump COP of Strategy 2 is a little lower than that of conventional full operation strategy, Strategy 2 has the shortest unmet heating or cooling time. Therefore, the proposed zoning operation strategy can achieve good system efficiency and excellent system reliability compared to the conventional strategy.

Laboratory investigations on the thermo-mechanical behaviour of an energy pile group operated in heat release mode

Compared to the single energy pile, the thermo-mechanical behavior of pile group become more complicated due to mutual influences of different piles. A model test device of pile group with 2 × 2 layout was built to study the thermo-mechanical characteristics of pile group with different number of energy piles, inlet temperatures and connection forms of buried pipes. The results show that compared to single energy pile, the energy pile group mode will lead to the decrease of heat exchange performance and the increase of pile tip soil pressure and pile head displacement. But, the side friction and axial force of pile will decrease as a result of pile group effect. Meanwhile, increasing the inlet temperature can enhance heat exchange characteristics of pile group, but it will also result in the increase of the soil temperature, pile head displacement, pile tip soil pressure, pile shaft axial force and pile side friction. Additionally, reducing the number of energy piles in pile group can improve the heat exchange rate per unit pile depth, but the total heat transfer amount of energy pile group will decrease. With the increase of the number of energy pile in pile group, the temperature change and pile head displacement of the pile increase, but the pile side friction and pile body axial force decrease. Under current experimental conditions, the pile head displacement and pile body axial force in parallel connection mode are larger than those in series connection modes, and the pile body excess temperature is the smallest in parallel mode of four energy piles and the largest in series mode of four energy piles. For the series connection mode, the heat exchange performance, pile body excess temperature, pile head displacement and pile body axial force gradually decrease along the series direction due to the decrease of temperature change.

Influence of pile head restraint on the performance of floating elevated energy pile groups in soft clay

Thermal elongation of energy piles (EPs) depends on the end restraints to displacement. The EP head is restrained by a working load and non-energy piles (NEPs) within an energy pile group, depending on the cap rigidity. The existence of both EPs and NEPs in non-symmetrical thermally loaded energy pile groups imposes different restraints on EP heads, resulting in different pile elongations. This would induce load redistribution between the piles, thereby influencing the serviceability of energy pile groups in soft soil. In this paper, a 3-D numerical parametric study was conducted after back-analysing a centrifuge test on a floating elevated energy pile group subjected to cyclic non-symmetrical thermal loading in soft clay. Effects of the number of EPs and NEPs in a 2 × 2 group, the flexural stiffness of the cap, and the factor of safety (FS; i.e., working load level) were studied. The non-symmetrical thermally loaded pile group with 3EPs and a rigid cap subjected to the lowest FS showed the maximum settlement due to the largest thermomechanical loading distributed between the piles through the rigid cap. In contrast, a flexible cap over the 2EPs group induced the maximum tilting due to a closer distance between EPs and NEPs in a side tilting. The axial load reduction was significant mainly in the 1EP group during cooling and at a higher FS, resulting in tension along the EP, which should be considered in the design.

An elasto-plastic numerical analysis of THM responses of floating energy pile foundations subjected to asymmetrical thermal cycles

Although end-bearing energy pile foundations subjected to symmetrical thermal cycles have been extensively studied in the laboratory and in the field, the mechanisms underlying the thermo-hydro-mechanical (THM) interactions in floating energy pile groups and rafts, especially when subjected to asymmetrical thermal loads, are not well understood. In this study, an advanced thermo-mechanical bounding surface model was implemented in finite-element (FE) code to investigate the THM interactions of a two-by-two floating energy pile group and pile raft, focusing on asymmetrical thermal cycles. Computed results are compared with published centrifuge model test results in soft clay. It is revealed that the irreversible volumetric contraction of the soil adjacent to the energy piles accumulates with each thermal cycle, resulting in a decrease in the horizontal stress and hence shaft resistance of the floating piles. During thermal cycles, the stress states of the soil around the energy pile shaft and the soil beneath the pile toe approach the critical state line along different paths. The induced temperature in the soil adjacent to the non-energy pile (NEP) is 5°C lower than that in the soil at the energy pile EP1, which is flanked by the other two energy piles EP2 and EP3. Consequently, the induced excess pore pressure in the soil at the NEP is approximately 20% smaller than that in the soil at EP1. The irreversible volumetric soil contraction at the NEP is about half that at EP1, resulting in approximately 45% less toe settlement. The thermally induced ratcheting settlements of the head and toe of the NEP are less than those of the energy piles, resulting in unacceptable ratcheting tilting of the floating energy pile group. However, the excessive tilting can be reduced by the use of a pile raft.