Field Test and Numerical Simulation on the Long-Term Thermal Response of PHC Energy Pile in Layered Foundation

Zhang, Guozhu; Cao, Ziming; Liu, Yiping; Chen, Jiawei

doi:10.3390/s21113873

Cited by 27 publications

(5 citation statements)

References 38 publications

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“…The geometric size, mesh density, and boundary conditions of the model are shown in Figure 4, in which a ground radius of 10 m and depth of 40 m were adopted to avoid the boundaries influencing the heat transfer. A vertical single U-shaped GHE with a radius of 110 mm and a depth of 30 m is set at the central position [35,36]. The clearance distance from the bottom side to the GHE should be larger than 10m to avoid the influence of bottom boundaries [37].…”

Section: Geometric Size Boundary and Initial Conditionsmentioning

confidence: 99%

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Wu,

Chen,

Liu

et al. 2024

Buildings

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Backfill material used as a heat-transfer medium in boreholes of ground heat exchangers (GHEs) has a great influence on heat-transfer efficiency. Abandoned waste material causing environmental pollution has become a key issue around the world. To make full use of solid waste, backfill material made of waste fly ash in combination with graphite of high thermal conductivity was proposed. First, the thermal properties of cement/fly ash blended with different mass ratio of graphite were tested through laboratory tests. Then, a numerical model was established, in which the accuracy was validated based on a field test. Finally, an investigation of the long-term performance (over a period of 90 days) for four boreholes backfilled with natural sand, cement/fly ash, and cement/fly ash combined with different proportions of graphite was conducted through this numerical model, and the heat-transfer rates under constant inlet temperature in four boreholes decreased from 13.31, 44.97, 45.95, and 46.73 W/m to 14.18, 14.96, 15.66, and 16.19 W/m after the 90-day operation. Considering the influence of groundwater seepage, the horizontal groundwater flow had a positive impact, improving the long-term heat-transfer performance. The heat-transfer rates of four testing boreholes decreased from 44.46, 46.38, 47.22, and 47.68 W/m to 21.18, 21.93, 22.62, and 23.13 W/m. However, long-term groundwater seepage in a vertical direction caused a sharp decrease in the heat-transfer rate, and the values after 90 days were 10.44, 10.62, 10.78, and 10.81 W/m, which were the lowest of all the working conditions. The feasibility of using fly ash blended with graphite as backfill material was further validated through a comprehensive perspective, including indoor laboratory, field testing, and numerical simulation, which has rarely been conducted in previous research.

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Section: Geometric Size Boundary and Initial Conditionsmentioning

confidence: 99%

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Wu,

Chen,

Liu

et al. 2024

Buildings

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“…It is found that the existence of water in soil has a great role in promoting the efficiency of energy piles [9,[12][13][14]. It is also concluded that the pile diameter ratio, pile spacing, the diameter of the heat exchange tube in the pile, the water flow velocity in the pipe, the inlet water temperature, and the properties of the strata around the energy pile will affect the working efficiency of the energy pile [15][16][17][18][19][20]. In terms of the long-term working performance of the energy pile, the thermal cycle of the energy pile will lead to a decrease in the soil moisture content around the pile, resulting in a decrease in the thermal conductivity of the soil around the pile, which will increase the temperature around the energy pile and reduce the heat exchange efficiency of the energy pile [21,22].…”

Section: Introductionmentioning

confidence: 99%

Study on Thermodynamic Properties of Spiral Tube-Encapsulated Phase-Change Material Energy Pile

Liu,

Zhang,

Yang

et al. 2024

Buildings

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Based on the research status of phase-change material (PCM) energy piles, this paper proposes a new type of PCM energy pile-spiral tube-encapsulated PCM energy pile. In order to study the related properties of the energy pile, this study designed and processed the relevant test equipment and built an indoor scale model experimental system. The thermodynamic performance of the spiral tube-encapsulated phase-change energy pile under summer conditions was studied by the test system. Through the indoor scale model test, it is found that compared with the traditional energy pile, the spiral tube-encapsulated PCM energy pile improves the heat exchange capacity of the unit pile body in the early and middle stages of operation, and reduces the surface temperature of the pile body and the heating rate of the surface temperature of the pile body. The upward displacement of the energy pile top is reduced. The heat exchange capacity of the unit pile depth is increased by 6.52 W/m, the maximum pile surface temperature difference is 0.62 °C, and the maximum pile top displacement difference is 0.005 mm. In addition, the total heat transfer of the spiral tube-encapsulated PCM energy pile during the whole operation period is 3.38% higher than that of the traditional energy pile. However, during the whole operation period, the surface stress value of the spiral tube encapsulated PCM energy pile is higher than that of the traditional energy pile. The maximum difference between the two is 9.84 kPa and the maximum difference is 10.8%. The difference between the two is finally stabilized at 1.4 kPa with an increase in time, and the final difference is only 8.8%.

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“…Quantification of soil disturbance, such as displacement field, stress field, and disturbance range during pile driving is crucial for a comprehensive investigation of the disturbance effects of pile formation on the soil. On-site experiments [9][10][11][12], model tests [13][14][15][16], analytical solutions [17][18][19][20], and numerical simulations [21][22][23][24] have been carried out to investigate the effect of pile driving on soil disturbance. However, in terms of on-site experiments, current research is limited to the non-visibility of soil and embedded monitoring [9]; the obtained test results are not the entire displacement field, but rather local discrete points, which also affect the accuracy of the results.…”

Section: Introductionmentioning

confidence: 99%

Study on Disturbance Mechanism of Squeezed and Non-Squeezed Soil Piles on Soft Soil Foundation

et al. 2023

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The construction process of pile foundations can significantly disrupt the soil. Therefore, it is necessary to limit the degree of soil disturbance caused by pile foundation construction to an acceptable level. This paper examines the disturbance effects of pile driving on soft soil foundations, specifically analyzing the squeezing effect of squeezed soil piles and the unloading effect of non-squeezed soil piles. To investigate these effects, two typical squeezed soil piles, a hydrostatic pile, and a bag grouting pile, as well as a typical non-squeezed soil pile (a bored pile) are selected. Specifically, a novel construction method for numerical models, which simulates the mechanical processes of different pile types under standard grids, is proposed. Three crucial indicators—soil displacement field, stress field, and disturbance influence range—are chosen to compare the disturbance effects of three types of piles on the soil. Results indicate that the two types of squeezed soil piles cause significant disturbance to the soil displacement field, especially in the horizontal direction, while causing a relatively slight disturbance to the soil stress field. Among the two of them, the disturbance magnitude and range of the hydrostatic pile are greater than those of the bag grouting pile. For the non-squeezed soil pile, the soil displacement field changes minimally and the stress field remains basically unchanged during the pile driving process of the bored pile. To compare and quantify the disturbance effects of three types of piles on soil, the soil disturbance range in the horizontal direction of each pile is normalized by its radius. Results indicate that the horizontal disturbance values of maximum horizontal stress for all three types of piles are approximately 1/5 of the pile length above the pile tip, with normalized values of 7.6, 5.5, and 3.5, respectively. The maximum horizontal deformation disturbance range in the horizontal direction occurs near the ground surface and has normalized values of 15.2, 7.5, and 1.1 for the three types of piles, respectively. Therefore, the hydrostatic pile has the greatest disturbance effect, followed by the bag grouting pile and the bored pile. However, within the allowable range of disturbance in practical engineering, the optimal piling method can be selected by comprehensively considering factors such as the construction difficulty and economic costs.

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Field Test and Numerical Simulation on the Long-Term Thermal Response of PHC Energy Pile in Layered Foundation

Cited by 27 publications

References 38 publications

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Study on Thermodynamic Properties of Spiral Tube-Encapsulated Phase-Change Material Energy Pile

Study on Disturbance Mechanism of Squeezed and Non-Squeezed Soil Piles on Soft Soil Foundation

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