Centrifugal model test equipment and method for measuring thermal-mechanical coupling of energy pile

Abstract

The invention discloses centrifugal model test equipment and method for measuring thermal-mechanical coupling of an energy pile, and belongs to the cross technical field of geotechnical engineering test technology and geothermal energy development and utilization, the centrifugal model test equipment comprises a centrifugal machine, a model box, a soil body, an energy pile model, a strain gauge, a pore water pressure sensor and a pile top loading device; the model box is arranged in a hanging basket of the centrifugal machine; the soil body is arranged in the model box, the lower end of the energy pile model is embedded in the soil body, and the upper end of the energy pile model is connected with the pile top loading device; the model box comprises a transparent observation surface which is arranged on the side surface of the model box; the energy pile model is of a half-pile structure, and the symmetrical section of the energy pile model is attached to the transparent observation surface of the model box; the strain gauge is arranged on one side, away from the transparent observation surface, of the energy pile model; according to the centrifugal model test equipment and method for measuring thermal-mechanical coupling of the energy pile, the problems that in the prior art, the internal process is invisible, and key performance parameters are missing are solved.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of geotechnical engineering testing technology and geothermal energy development and utilization, and in particular relates to a centrifugal model test device and method for measuring the thermo-mechanical coupling of energy piles. Background Technology

[0002] Energy pile technology is an innovative solution that integrates geothermal heat exchange pipes into building pile foundations, achieving the dual functions of "structural load-bearing" and "geothermal energy harvesting." This technology utilizes a stable temperature field within a depth range of 5–200 meters underground, and completes heat transfer between the building and the ground through the flow of a circulating working fluid in closed pipes. In summer, waste heat from the building's interior is transferred to the cooler underground soil layers via the working fluid; in winter, heat is extracted from the relatively warmer ground layers for building heating, forming a two-way energy utilization model of "heat dissipation in summer and heat extraction in winter."

[0003] Because energy piles are typically large in size, conducting full-scale tests faces numerous challenges due to limitations in testing equipment, space, and cost. Therefore, scaled-down model testing has become a more feasible research approach. However, traditional experimental methods suffer from technical bottlenecks such as the lack of visualization of internal processes and the absence of key performance parameters. Summary of the Invention

[0004] The purpose of this invention is to provide a centrifugal model test device and method for measuring the thermo-mechanical coupling of energy piles, thereby solving the problems of lack of visualization of internal processes and missing key performance parameters in existing technologies.

[0005] To achieve the above objectives, this invention provides a centrifuge model test device for measuring the thermo-mechanical coupling of an energy pile, comprising a centrifuge, a model box, soil, an energy pile model, strain gauges, pore water pressure sensors, and a pile top loading device. The centrifuge includes a basket, and the model box is placed inside the basket. The soil is placed inside the model box, with the lower end of the energy pile model embedded in the soil, and the upper end of the energy pile model connected to the pile top loading device. The model box includes a transparent observation surface, which is located on the side of the model box. The energy pile model is configured as a half-pile structure, and the symmetrical cross-section of the energy pile model is aligned with the transparent observation surface of the model box. Strain gauges are placed on the side of the energy pile model away from the transparent observation surface, and multiple strain gauges are evenly distributed along the height direction of the energy pile. The pore water pressure sensors are evenly distributed along the radial direction of the energy pile, and the pore water pressure sensors are set at the same height as the strain gauges along the height direction of the energy pile model.

[0006] Preferably, it also includes a thermal circulation system; the thermal circulation system includes a first circulation loop and a second circulation loop; the first circulation loop is connected to the model box, and the second circulation loop is connected to the energy pile model; The first circulation loop includes a constant temperature circulating liquid buried pipeline, a flow meter, and a first constant temperature and constant flow control pump; the flow meter is installed on the constant temperature circulating liquid buried pipeline; one end of the constant temperature circulating liquid buried pipeline is connected to the first constant temperature and constant flow control pump, and the other end is connected to the energy pile model. The first constant temperature and constant flow control pump is provided with a third water inlet at one end and a third water outlet at the other end; a first temperature sensor is provided at one end of the third water inlet and the other end is connected to the internal structure of the first constant temperature and constant flow control pump; a second temperature sensor is provided at one end of the third water outlet and the other end is connected to the internal structure of the first constant temperature and constant flow control pump. The second circulation loop includes a constant temperature circulating liquid pipeline and a second constant temperature and constant flow control pump; one end of the constant temperature circulating liquid pipeline is connected to the second constant temperature and constant flow control pump, and the other end is connected to the model box. The second constant temperature and constant flow control pump is equipped with a fourth water inlet at one end and a fourth water outlet at the other end; one end of the fourth water inlet is connected to the internal structure of the second constant temperature and constant flow control pump; one end of the fourth water outlet is connected to the internal structure of the second constant temperature and constant flow control pump.

[0007] Preferably, the energy pile model includes a heat exchange pipeline, a first inlet, and a first outlet; the middle part of the heat exchange pipeline is embedded inside the energy pile model, and both ends of the heat exchange pipeline are set on the side wall of the energy pile, one end is set as the first inlet, and the other end is set as the first outlet; the first outlet is connected to the third inlet through a constant temperature circulating liquid embedded pipeline, and the first inlet is connected to the third outlet through a constant temperature circulating liquid embedded pipeline. The model box includes a temperature control plate, which is set on the bottom surface inside the model box. Soil is set above the temperature control plate. A second water inlet and a second water outlet are set on the upper surface of the temperature control plate. The second water outlet is connected to a fourth water inlet through a temperature-controlled circulating liquid pipeline.

[0008] Preferably, the internal structure of the first thermostatic and constant flow control pump is the same as that of the second thermostatic and constant flow control pump, both including a first three-way thermostatic bath, a first one-way valve, a second one-way valve, a first temperature pump head, a second temperature pump head, and a second three-way thermostatic bath; the third / fourth inlet is connected to the inlet of the first three-way thermostatic bath, and the two outlets of the first three-way thermostatic bath are respectively connected to one end of the first one-way valve and the second one-way valve; the other end of the first one-way valve is connected to one inlet of the second three-way thermostatic bath through the first temperature pump head, and the other end of the second one-way valve is connected to the other inlet of the second three-way thermostatic bath through the second temperature pump head; the outlet of the second three-way thermostatic bath is connected to the third / fourth outlet.

[0009] Preferably, the pile top loading device includes a reaction frame, a lead screw, a servo motor, a force sensor, a laser displacement sensor, an extension plate, and a sleeve clamp; the lead screw passes through the reaction frame and is connected to one end of the force sensor, and the other end of the force sensor is connected to the sleeve clamp through the extension plate; the servo motor is mounted on the reaction frame, and one end of the servo motor is sleeved on the lead screw; a laser displacement sensor is provided at one end of the reaction frame.

[0010] Preferably, it also includes a synchronous optical monitoring system and a digital image acquisition device; the synchronous optical monitoring system includes a high-speed infrared thermal imager, which is set outside the transparent observation surface, with the optical axis of the high-speed infrared thermal imager facing the transparent observation surface; the digital image acquisition device is set above the high-speed infrared thermal imager.

[0011] This invention also provides a method for measuring the thermo-mechanical coupling of energy piles using a centrifugal model test device, comprising the following steps: S1. Model preparation: Soil is filled into the model box, and an energy pile model with strain gauges and a pore water pressure sensor are installed at the same time, so that the symmetrical cross section of the energy pile model fits the transparent observation surface. S2, Consolidation: Start the centrifuge to consolidate the soil in the model under the target hypergravity conditions; S3, Thermo-Mechanical Coupling Simulation and Synchronous Optical Monitoring: Under hypergravity conditions, the pile top loading device and thermal circulation system are activated to apply mechanical and thermal loads to the energy pile model; the high-speed infrared thermal imager and digital image acquisition device are activated to acquire and record the two-dimensional temperature spatiotemporal evolution data and the two-dimensional displacement / strain field spatiotemporal evolution data of the energy pile model and the soil. S4. Heat transfer efficiency analysis: The heat transfer efficiency of the energy pile model is calculated using data from the first temperature sensor, the second temperature sensor, and the flow meter. The spatiotemporal evolution data of the two-dimensional temperature field are correlated with the heat transfer efficiency to study the influence of the soil temperature field distribution on the heat transfer performance of the energy pile.

[0012] Preferably, in S1, a lubricating medium layer is coated between the transparent observation surface and the soil, and between the transparent observation surface and the energy pile model, to reduce the boundary friction effect.

[0013] Preferably, in S3, the temperature of the water inlet of the energy pile model is controlled by the first circulation loop to simulate the actual operating conditions of the energy pile; the temperature of the constant temperature control plate at the bottom of the model box is controlled by the second circulation loop to form a stable vertical temperature gradient in the soil.

[0014] Preferably, in S4, the expression for calculating the heat exchange efficiency is: ; In the formula, This refers to the heat exchange power. Specific heat capacity of the circulating fluid; The density of the circulating fluid; This represents the volumetric flow rate of the circulating fluid. The outlet temperature; This refers to the inlet water temperature.

[0015] Therefore, the centrifugal model test equipment and method for measuring the thermo-mechanical coupling of energy piles described above have the following beneficial effects: (1) A revolutionary observation from “black box” to “white box” has been realized: For the first time under real stress conditions, the three core processes of heat transfer, soil particle movement and heat exchange efficiency of energy pile are visualized and quantified simultaneously, providing an unprecedented experimental perspective for understanding the thermo-mechanical coupling mechanism; (2) A direct correlation between heat transfer efficiency and multi-physics field was established: Through synchronous monitoring, a quantitative relationship between "soil temperature field evolution" and "energy pile heat transfer efficiency" can be directly established, clarifying the heat transfer performance variation law of energy pile under different thermo-mechanical conditions, and providing accurate data support for optimization design; (3) Overcoming the technical challenge of balancing stress similarity and process observation: This invention integrates the stress realism of supergravity centrifugation simulation, the non-contact advantage of optical full-field measurement, and the accurate evaluation of heat transfer performance, thus solving the technical contradiction that has long plagued this field and forming a complete, rigorous, and powerful experimental research platform.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a cross-sectional view of a centrifugal model test device for measuring the thermo-mechanical coupling of energy piles according to the present invention; Figure 2 This is a top view of a centrifugal model test device for measuring the thermo-mechanical coupling of an energy pile according to the present invention; Figure 3 This is a schematic diagram of the energy pile model according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the first constant temperature and constant flow control pump according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the pile top loading device according to an embodiment of the present invention.

[0018] Figure Labels 1. Model box; 101. Thermostatic control plate; 102. Second water inlet; 103. Second water outlet; 2. Soil; 3. Energy pile model; 301. Heat exchange pipeline; 302. First water inlet; 303. First water outlet; 4. Strain gauge; 5. Pore water pressure sensor; 6. Pile top loading device; 601. Reaction frame; 602. Lead screw; 603. Force sensor; 604. Extension plate; 605. Sleeve clamp; 606. Laser displacement sensor; 607. Servo motor; 7. First thermostatic and constant flow control pump; 701. 702. Temperature sensor; 703. Second temperature sensor; 704. Third water inlet; 705. Third water outlet; 706. First three-way constant temperature bath; 707. First one-way valve; 708. Second one-way valve; 709. First temperature pump head; 710. Second temperature pump head; 711. Second three-way constant temperature bath; 8. Second constant temperature and constant flow control pump; 801. Fourth water inlet; 802. Fourth water outlet; 9. Constant temperature circulating liquid buried pipeline; 10. Constant temperature circulating liquid pipeline; 11. High-speed infrared thermal imager; 12. Digital image acquisition device. Detailed Implementation

[0019] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0020] Please see Figure 1-5A centrifuge model test device for measuring the thermo-mechanical coupling of an energy pile includes a centrifuge, a model box 1, soil 2, an energy pile model 3, strain gauges 4, pressure sensors 603, a pile top loading device 6, a thermal circulation system, a synchronous optical monitoring system, and a digital image acquisition device 12. The centrifuge includes a basket, and the model box 1 is placed inside the basket. The soil 2 is placed inside the model box 1, and the lower end of the energy pile model 3 is embedded in the soil 2. The upper end of the energy pile model 3 is connected to the pile top loading device 6. The model box 1 includes a transparent observation surface, which is located on the side of the model box 1. The energy pile model 3 is configured as a half-pile structure, and the symmetrical cross-section of the energy pile model 3 is aligned with the transparent observation surface of the model box 1. The measuring surface is in contact with the surface; strain gauges 4 are set on the side of the energy pile model 3 away from the transparent observation surface, and multiple strain gauges 4 are evenly arranged along the height direction of the energy pile; pressure sensors 603 are evenly distributed along the radial direction of the energy pile, and the pressure sensors 603 are set at the same height as the strain gauges 4 along the height direction of the energy pile model 3; the thermal circulation system includes a first circulation loop and a second circulation loop; the first circulation loop is connected to the model box 1, and the second circulation loop is connected to the energy pile model 3; the synchronous optical monitoring system includes an infrared thermal imager, which is set outside the transparent observation surface, and the optical axis of the infrared thermal imager is directly facing the transparent observation surface; the digital image acquisition device 12 is set above the infrared thermal imager.

[0021] The first circulation loop includes a constant temperature circulating liquid embedded pipe 9, a flow meter, and a first constant temperature and constant flow control pump 7; the flow meter is installed on the constant temperature circulating liquid embedded pipe 9; one end of the constant temperature circulating liquid embedded pipe 9 is connected to the first constant temperature and constant flow control pump 7, and the other end is connected to the energy pile model 3; one end of the first constant temperature and constant flow control pump 7 is provided with a third inlet 703, and the other end is provided with a third outlet 704; one end of the third inlet 703 is provided with a first temperature sensor 701, and the other end is connected to the internal structure of the first constant temperature and constant flow control pump 7; one end of the third outlet 704 is provided with a second temperature sensor 701. The temperature sensor 702 is connected at one end to the internal structure of the first constant temperature and constant flow control pump 7; the second circulation loop includes a constant temperature circulating liquid pipeline 10 and a second constant temperature and constant flow control pump 8; one end of the constant temperature circulating liquid pipeline 10 is connected to the second constant temperature and constant flow control pump 8, and the other end is connected to the model box 1; one end of the second constant temperature and constant flow control pump 8 is provided with a fourth water inlet 801, and the other end is provided with a fourth water outlet 802; one end of the fourth water inlet 801 is connected to the internal structure of the second constant temperature and constant flow control pump 8; one end of the fourth water outlet 802 is connected to the internal structure of the second constant temperature and constant flow control pump 8.

[0022] The internal structure of the first thermostatic and constant flow control pump 7 is the same as that of the second thermostatic and constant flow control pump 8, both including a first three-way thermostatic bath 705, a first one-way valve 706, a second one-way valve 707, a first temperature pump head 708, a second temperature pump head 709, and a second three-way thermostatic bath 710; the third / fourth inlet 703 / 801 is connected to the inlet of the first three-way thermostatic bath 705, and the two outlets of the first three-way thermostatic bath 705 are respectively connected to one end of the first one-way valve 706 and the second one-way valve 707; the other end of the first one-way valve 706 is connected to one inlet of the second three-way thermostatic bath 710 through the first temperature pump head 708, and the other end of the second one-way valve 707 is connected to the other inlet of the second three-way thermostatic bath 710 through the second temperature pump head 709; the outlet of the second three-way thermostatic bath 710 is connected to the third / fourth outlet 703 / 801.

[0023] The internal structure of the first thermostatic and constant flow control pump 7 is the same as that of the second thermostatic and constant flow control pump 8. Both are connected to one end of the first three-way thermostatic tank 705 via the third / fourth inlet 801. The other end of the first three-way thermostatic tank 705 is connected to one end of the first one-way valve 706 and the second one-way valve 707 in sequence. The other end of the first one-way valve 706 is connected to one end of the second three-way thermostatic tank 710 via the first temperature pump head 708. The other end of the second one-way valve 707 is connected to one end of the second three-way thermostatic tank 710 via the second temperature pump head 709. The other end of the second three-way thermostatic tank 710 is connected to the third / fourth outlet 802.

[0024] The energy pile model 3 includes a heat exchange pipe 301, a first inlet 302, and a first outlet 303. The middle part of the heat exchange pipe 301 is embedded inside the energy pile model 3, and the two ends of the heat exchange pipe 301 are set on the side wall of the energy pile. One end is set as the first inlet 302, and the other end is set as the first outlet 303. The first outlet 303 is connected to the third inlet 703 through the constant temperature circulating liquid buried pipe line 9, and the first inlet 302 is connected to the third outlet 704 through the constant temperature circulating liquid buried pipe line 9. The model box 1 includes a constant temperature control plate 101, which is set on the bottom surface inside the model box 1. Soil 2 is set above the constant temperature control plate 101. A second water inlet 102 and a second water outlet 103 are set on the upper surface of the constant temperature control plate 101. The second water outlet 103 is connected to a fourth water inlet 801 through a constant temperature circulating liquid pipeline 10, and the second water inlet 102 is connected to the fourth water outlet 802 through a constant temperature circulating liquid pipeline 10.

[0025] The pile top loading device 6 includes a reaction frame 601, a lead screw 602, a servo motor 607, a force sensor 603, a laser displacement sensor 606, an extension plate 604, and a sleeve clamp 605. The lead screw 602 passes through the reaction frame 601 and is connected to one end of the force sensor 603. The other end of the force sensor 603 is connected to the sleeve clamp 605 through the extension plate 604. The servo motor 607 is mounted on the reaction frame 601, and one end of the servo motor 607 is sleeved on the lead screw 602. The laser displacement sensor 606 is provided at one end of the reaction frame 601.

[0026] A method for measuring the thermo-mechanical coupling of an energy pile using a centrifugal model test device includes the following steps: S1. Preparation Model: Prepare a dedicated model box 1: Model box 1 is made of titanium alloy. The front of model box 1 is a piece of high-strength aviation glass with a thickness of not less than 100mm, forming the core transparent observation surface. The transparent observation surface undergoes rigorous cleaning: using a non-woven cloth soaked in analytical grade anhydrous ethanol, the inner wall of the glass is wiped until it is smooth and free of any oil, fingerprints, or dust residue. To establish ideal low-friction boundary conditions, a layer of petroleum jelly lubricant with a thickness of approximately 0.5-1.0mm is evenly applied to the clean inner wall of the glass using a scraper. The petroleum jelly layer should be continuous and free of air bubbles. Its core function is to form a near-slip-free lubricating interface between the aviation glass and the subsequently filled soil 2 and the semi-pile model, thereby effectively eliminating the constraint effect of the model box 1 boundary on the deformation and heat transfer of the soil 2, ensuring that the test results truly reflect the prototype's response in an infinite domain.

[0027] Precision fabrication and installation of energy pile model 3: Based on the principles of geometric and material similarity, energy pile model 3 is precisely fabricated at a predetermined scale (e.g., 1:30). This model is a semi-cylinder obtained by cutting a cylinder along its central axis; its planar cross-section serves as the core observation surface. The model is constructed using micro-concrete material with thermodynamic properties similar to the prototype concrete, with a maximum aggregate size of no more than 2mm. Internally embedded are miniature U-shaped copper heat exchange tubes with an outer diameter of 3mm and a wall thickness of 0.5mm, serving as heat exchange pipes 301. The first inlet 302 and the first outlet 303 of the heat exchange pipes 301 are precisely machined and pre-installed at the top of the model, with the joints sealed with epoxy resin to prevent leakage.

[0028] Completed, with smooth cross-section. The energy pile model 3 was precisely positioned and installed by tightly fitting its planar cross-section against the inner wall of the aviation glass coated with Vaseline. A laser plumb line was used for calibration to ensure that the vertical deviation of the pile axis was less than 1 / 1000, and that the pile tip maintained the designed distance from the bottom of the model box 1. This carefully constructed "half-pile-glass" interface is the core observation window for achieving high-precision visualization throughout the entire process.

[0029] Soil Body 2 Layered Filling and Sensor Network Deployment: Inside model box 1, remolded soil is filled around the installed energy pile model 3 using a layered compaction method to form Soil Body 2. The thickness of each layer is controlled at 50mm, and the density uniformity of Soil Body 2 is ensured to be consistent with the prototype by controlling the compaction energy. During the filling process, a monitoring instrument network is precisely deployed at key mechanical and thermal locations: Temperature-compensated foil strain gauges 4 are attached at different heights of the pile (pile top, pile middle, and pile end), and the axial and bending strain of the pile is measured using a full-bridge connection method. In the soil body 2 around the pile, pressure sensors 603 are embedded along the radial and depth directions (corresponding to the elevation of strain gauges 4). The sensor diaphragms are in close contact with the soil body 2 to monitor the dissipation of excess pore water pressure and changes in effective stress during the thermo-mechanical coupling process. All sensor wires extend through the edge of model box 1 to prevent interference with the energy pile and Soil Body 2.

[0030] Precise integration of loading and thermal circulation systems: A servo motor 607 drives the loading device at the top of the energy pile model 3. The device's high-strength sleeve clamp 605 securely holds the pile head with pre-tightened bolts and features a dedicated pipeline clearance groove to ensure uninterrupted connection and sealing of the heat exchange pipelines at the pile top. The servo motor 607 provides constant displacement with an accuracy of ±0.01mm or constant load with an accuracy of ±1N via a precision ball screw 602. High-precision force sensors 603 (accuracy 0.1%FS) and laser displacement sensors 606 (resolution...) are also included. These are used for real-time monitoring of pile top load and displacement. The first inlet 302 and the first outlet 303 of the energy pile model 3 are connected to the corresponding interfaces of the first constant temperature and constant flow control pump 7 (temperature control accuracy ±0.1℃, flow accuracy ±1%FS) through the constant temperature circulating liquid buried pipe line 9 to form the first circulation loop (energy pile thermal circulation). The constant temperature circulating liquid buried pipe line 9 adopts a flexible heat-insulated pipeline.

[0031] The second inlet 102 and the second outlet 103 of the aluminum alloy thermostatic control plate 101, which is located at the bottom of the soil 2, are connected to another thermostatic circulation tank through a thermostatic circulation fluid pipeline 10 to form a second circulation loop (surface temperature gradient simulation). The surface of the thermostatic control plate 101 is anodized and blackened to enhance heat absorption efficiency.

[0032] The coordinated deployment of multiple optical monitoring systems involves a high-speed infrared thermal imager 11 (sampling frequency 100Hz, thermal sensitivity 0.03℃) and a digital image acquisition device 12, securely mounted on a vibration-isolated platform with three-dimensional adjustment capabilities, precisely aligned with the aviation glass observation surface of the model box 1. The digital image acquisition device 12 can be configured with dual high-speed CMOS cameras (resolution 2048×2048, sampling frequency 200Hz). Before the experiment, a white matte primer is sprayed onto the pile profile and the surface of the adjacent soil 2. Then, a high-contrast black and white speckle pattern with a speckle diameter of 0.5-2mm is created using stochastic speckle technology for high-precision image correlation analysis by the DIC system. The high-speed infrared thermal imager 11 and the DIC camera achieve microsecond-level synchronization via a hardware trigger signal, which is crucial for achieving spatiotemporal matching of multi-physics data.

[0033] S2, consolidation; After completing all equipment connections and debugging, start the centrifuge. Refer to Table 1 for the main parameters of the centrifuge. Accelerate smoothly to the target g value (e.g., 30g) at an acceleration rate not exceeding 5g / s. Under this hypergravity environment, model soil 2 begins to consolidate rapidly. By monitoring the data from pore water pressure sensor 5 in real time, when the pore water pressure at each measuring point dissipates to more than 95% and the rate of change per hour is less than 5%, the primary consolidation of soil 2 is considered complete. At this point, the effective stress field in the model is equivalent to the prototype stress field.

[0034] Table 1. Main parameters of the centrifuge

[0035] S3, thermo-mechanical coupling simulation and synchronous optical monitoring; Precise establishment of the temperature gradient field: Keep the centrifuge running and start the second thermal circulation loop connected to the thermostatic control plate 101. Set the temperature of the thermostatic control plate 101 to the deep stratum temperature to be simulated (e.g., 15°C). At the same time, control the air temperature in the environmental chamber at the top of the model box 1 to simulate the shallow surface temperature (e.g., 35°C). Continuously run the system for at least 2 hours, monitoring with thermocouples buried in the soil 2, until the temperature field stabilizes, establishing a stable vertical temperature gradient field (approximately 1-2°C / 10cm) in the soil 2 that corresponds to the actual stratum.

[0036] Precise application of mechanical load: The pile top loading device 6 is activated, causing the servo motor 607 to apply a load to the top of the energy pile model 3 at a constant displacement rate of 0.01 mm / min. Data is collected in real time by the force sensor 603 and the laser displacement sensor 606, and a load-displacement curve is plotted until the load reaches the design value (e.g., 1.5 times the prototype working load) and then remains constant to simulate the long-term load of the superstructure.

[0037] Multi-system synchronous monitoring of the thermo-mechanical coupling process: On the basis of stable mechanical load, the core coupling effect test is initiated. The first thermal circulation loop connected to the energy pile model 3 is started, and the temperature of the first constant temperature and constant flow control pump 7 is set to the simulated working condition (such as summer heat exhaust working condition, inlet water temperature 40℃), and the flow rate is controlled at a representative flow rate (e.g. 0.5m / s).

[0038] At the same time, all data acquisition systems are triggered and run synchronously through the main control computer.

[0039] The high-speed infrared thermal imager 11 begins continuous imaging. It dynamically captures and records a complete physical process at a frequency of 10Hz: how heat is released from the embedded pipes inside the energy pile and conducted to the surrounding soil 2 through the pile's concrete material. The monitoring software generates a spatiotemporal evolution sequence of the temperature field, clearly showing the dynamic images of the entire process: the pile's temperature rises, heat diffuses into the soil 2 in the form of "thermal waves," and the radius of thermal influence gradually expands over time. These images allow for the direct quantification of key heat transfer parameters such as temperature gradient and thermal diffusion rate.

[0040] The DIC dual high-speed cameras simultaneously begin continuous recording. At a frequency of 20Hz, it will precisely measure and present the displacement and movement of soil particles 2 driven by the thermal expansion of the pile through three-dimensional reconstruction of the speckle field. The analysis software will generate continuous three-dimensional displacement and strain contour maps, allowing researchers to directly observe how the soil 2 around the pile is compressed, how the displacement field develops outward from the pile-soil interface, and whether localized shear slip zones exist.

[0041] The first temperature sensor 701 and the second temperature sensor 702 can be PT100 temperature sensors. The heat exchange efficiency monitoring system, consisting of the first temperature sensor 701, the second temperature sensor 702, and the flow meter, works synchronously, recording the inlet and outlet temperatures and flow rates of the circulating liquid at a frequency of 1Hz, providing a basis for subsequent heat exchange power calculations.

[0042] Data from all contact sensors (strain gauge 4, pore water pressure sensor 5, force sensor 603, etc.) are synchronously recorded by a high-speed data acquisition system at a frequency of 100Hz, providing quantitative, local physical parameters that are mutually verified and supplemented with the optical full-field measurement results.

[0043] S4. Heat exchange efficiency analysis; The thermal cycling was continued for at least 24 hours (the model time is equivalent to about 3 months for the prototype) until the infrared and DIC data display system reached a new quasi-steady state, or obvious signs of soil failure were observed. Subsequently, the thermal cycling system and the pile top loading device 6 were stopped sequentially, and the centrifuge speed was gradually reduced to a stop at a deceleration rate not exceeding 5g / s.

[0044] After the experiment, the collected multi-source data were fused and analyzed. The core of this analysis lies in the spatiotemporal alignment and correlation analysis of the temperature field spatiotemporal sequence recorded by the infrared thermal imager, the displacement / strain field spatiotemporal sequence recorded by the DIC system, and the power time-series data calculated by the heat transfer efficiency monitoring system. Through the developed data fusion platform, a quantitative causal relationship can be directly established between "where and when the temperature rises," "where and how deformation occurs," and "how the heat transfer efficiency changes," profoundly revealing the influence mechanism of the energy pile's thermo-mechanical coupling effect on its structural response and heat transfer performance.

[0045] The key parameters involved in the experiment include: Temperature measurement: The infrared thermal imager is calibrated on-site using a blackbody furnace, with an absolute accuracy of ±0.5℃ and a relative accuracy of ±0.1℃; the PT100 temperature sensor has an accuracy of ±0.1℃.

[0046] Displacement Measurement: The DIC system is calibrated using a precision displacement stage, achieving an in-plane displacement measurement accuracy better than 0.01 pixels (approximately). ); Laser displacement sensor 606 accuracy ±0.1%FS.

[0047] Strain measurement: Strain gauge 4 is calibrated using an equal-strength beam, ensuring measurement accuracy. .

[0048] Therefore, this invention employs the aforementioned centrifugal model test equipment and method for measuring the thermo-mechanical coupling of energy piles, achieving a revolutionary shift from "black box" to "white box" observation: For the first time under real stress conditions, it simultaneously visualizes and quantifies the three core processes of heat transfer, soil particle movement, and heat exchange efficiency of energy piles, providing an unprecedented experimental perspective for understanding the thermo-mechanical coupling mechanism; It establishes a direct correlation between heat exchange efficiency and multi-physics fields: Through synchronous monitoring, it can directly establish a quantitative relationship between "soil temperature field evolution" and "energy pile heat exchange efficiency," clarifying the changing law of heat exchange performance of energy piles under different thermo-mechanical conditions, and providing accurate data support for optimized design; It overcomes the technical challenge of balancing stress similarity and process observation: This invention integrates the stress realism of centrifugal simulation, the non-contact advantages of optical full-field measurement, and the accurate evaluation of heat exchange performance, resolving a long-standing technical contradiction in this field and forming a complete, rigorous, and powerful experimental research platform.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A centrifugal model test device for measuring the thermo-mechanical coupling of energy piles, characterized in that: The system includes a centrifuge, a model box, soil, an energy pile model, strain gauges, pore water pressure sensors, and a pile top loading device. The centrifuge includes a basket, and the model box is placed inside the basket. The soil is placed inside the model box, with the lower end of the energy pile model embedded in the soil and the upper end of the energy pile model connected to the pile top loading device. The model box includes a transparent observation surface, which is located on the side of the model box. The energy pile model is configured as a half-pile structure, with its symmetrical cross-section fitting flush with the transparent observation surface of the model box. Strain gauges are placed on the side of the energy pile model away from the transparent observation surface, with multiple strain gauges evenly distributed along the height of the energy pile. The pore water pressure sensors are evenly distributed along the radial direction of the energy pile, and are set at the same height as the strain gauges along the height of the energy pile model.

2. The centrifugal model test device for measuring the thermo-mechanical coupling of energy piles according to claim 1, characterized in that: It also includes a thermal circulation system; the thermal circulation system includes a first circulation loop and a second circulation loop; the first circulation loop is connected to the model box, and the second circulation loop is connected to the energy pile model. The first circulation loop includes a constant temperature circulating liquid buried pipeline, a flow meter, and a first constant temperature and constant flow control pump; the flow meter is installed on the constant temperature circulating liquid buried pipeline; one end of the constant temperature circulating liquid buried pipeline is connected to the first constant temperature and constant flow control pump, and the other end is connected to the energy pile model. The first constant temperature and constant flow control pump is provided with a third water inlet at one end and a third water outlet at the other end; a first temperature sensor is provided at one end of the third water inlet and the other end is connected to the internal structure of the first constant temperature and constant flow control pump; a second temperature sensor is provided at one end of the third water outlet and the other end is connected to the internal structure of the first constant temperature and constant flow control pump. The second circulation loop includes a constant temperature circulating liquid pipeline and a second constant temperature constant flow control pump. One end of the constant temperature circulating fluid pipeline is connected to the second constant temperature and constant flow control pump, and the other end is connected to the model box; The second constant temperature and constant flow control pump is equipped with a fourth water inlet at one end and a fourth water outlet at the other end; one end of the fourth water inlet is connected to the internal structure of the second constant temperature and constant flow control pump; one end of the fourth water outlet is connected to the internal structure of the second constant temperature and constant flow control pump.

3. The centrifugal model test device for measuring the thermo-mechanical coupling of energy piles according to claim 2, characterized in that: The energy pile model includes a heat exchange pipeline, a first inlet, and a first outlet. The middle part of the heat exchange pipeline is embedded inside the energy pile model, and both ends of the heat exchange pipeline are set on the side wall of the energy pile. One end is set as the first inlet, and the other end is set as the first outlet. The first outlet is connected to the third inlet through a constant temperature circulating liquid embedded pipeline, and the first inlet is connected to the third outlet through a constant temperature circulating liquid embedded pipeline. The model box includes a temperature control plate, which is set on the bottom surface inside the model box. Soil is set above the temperature control plate. A second water inlet and a second water outlet are set on the upper surface of the temperature control plate. The second water outlet is connected to a fourth water inlet through a temperature-controlled circulating liquid pipeline.

4. The centrifugal model test device for measuring the thermo-mechanical coupling of energy piles according to claim 3, characterized in that: The internal structure of the first thermostatic and constant flow control pump is the same as that of the second thermostatic and constant flow control pump, both including a first three-way thermostatic bath, a first one-way valve, a second one-way valve, a first temperature pump head, a second temperature pump head, and a second three-way thermostatic bath; the third / fourth inlet is connected to the inlet of the first three-way thermostatic bath, and the two outlets of the first three-way thermostatic bath are respectively connected to one end of the first one-way valve and the second one-way valve; the other end of the first one-way valve is connected to one inlet of the second three-way thermostatic bath through the first temperature pump head, and the other end of the second one-way valve is connected to the other inlet of the second three-way thermostatic bath through the second temperature pump head; the outlet of the second three-way thermostatic bath is connected to the third / fourth outlet.

5. The centrifugal model test device for measuring the thermo-mechanical coupling of energy piles according to claim 4, characterized in that: The pile top loading device includes a reaction frame, a lead screw, a servo motor, a force sensor, a laser displacement sensor, an extension plate, and a sleeve clamp. The lead screw passes through the reaction frame and is connected to one end of the force sensor, while the other end of the force sensor is connected to the sleeve clamp through the extension plate. The servo motor is mounted on the reaction frame, with one end of the servo motor sleeved on the lead screw. A laser displacement sensor is installed at one end of the reaction frame.

6. The centrifugal model test device for measuring the thermo-mechanical coupling of energy piles according to claim 5, characterized in that: It also includes a synchronous optical monitoring system and a digital image acquisition device; the synchronous optical monitoring system includes a high-speed infrared thermal imager, which is set outside the transparent observation surface, with the optical axis of the high-speed infrared thermal imager facing the transparent observation surface; the digital image acquisition device is set above the high-speed infrared thermal imager.

7. A method for measuring the thermo-mechanical coupling of an energy pile using a centrifugal model test device as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Model preparation: Soil is filled into the model box, and an energy pile model with strain gauges and a pore water pressure sensor are installed at the same time, so that the symmetrical cross section of the energy pile model fits the transparent observation surface. S2, Consolidation: Start the centrifuge to consolidate the soil in the model under the target hypergravity conditions; S3, Thermo-Mechanical Coupling Simulation and Synchronous Optical Monitoring: Under hypergravity conditions, the pile top loading device and thermal circulation system are activated to apply mechanical and thermal loads to the energy pile model. Start the high-speed infrared thermal imager and digital image acquisition device to acquire and record the two-dimensional temperature spatiotemporal evolution data and the two-dimensional displacement / strain field spatiotemporal evolution data of the energy pile model and soil. S4. Heat transfer efficiency analysis: The heat transfer efficiency of the energy pile model is calculated using data from the first temperature sensor, the second temperature sensor, and the flow meter. The spatiotemporal evolution data of the two-dimensional temperature field are correlated with the heat transfer efficiency to study the influence of the soil temperature field distribution on the heat transfer performance of the energy pile.

8. The method for measuring the thermo-mechanical coupling of an energy pile using a centrifugal model test device according to claim 7, characterized in that: In S1, a lubricating medium layer is applied between the transparent observation surface and the soil, and between the transparent observation surface and the energy pile model, to reduce the boundary friction effect.

9. The method for measuring the thermo-mechanical coupling of an energy pile using a centrifugal model test device according to claim 8, characterized in that: In S3, the temperature of the water inlet of the energy pile model is controlled by the first circulation loop to simulate the actual operating conditions of the energy pile; the temperature of the constant temperature control plate at the bottom of the model box is controlled by the second circulation loop to form a stable vertical temperature gradient in the soil.

10. The method for measuring the thermo-mechanical coupling of an energy pile using a centrifugal model test device according to claim 9, characterized in that: In S4, the formula for calculating the heat transfer efficiency is: ； In the formula, This refers to the heat exchange power. Specific heat capacity of the circulating fluid; The density of the circulating fluid; This represents the volumetric flow rate of the circulating fluid. The outlet temperature; This refers to the inlet water temperature.

Images