Centrifuge model and method for a concrete energy pile group pile-cap foundation

Abstract

The present application relates to a kind of concrete energy pile group pile-pile cap foundation centrifuge test model, comprising: scale concrete energy pile, T-shaped connecting piece, screw, pile cap, gasket and nut;Wherein, scale concrete energy pile is connected with the lower end surface of pile cap by T-shaped connecting piece, gasket is set on the upper end surface of pile cap and corresponds with scale concrete energy pile;Screw passes through gasket and is fixed by nut.The beneficial effects of the present application are: the present application embeds T-shaped connecting piece in energy pile, simultaneously uses gasket and other components to connect energy pile and pile cap, limits the relative movement between energy pile and pile cap, realizes the effect of rigid connection of energy pile and pile cap, guarantees the integrity and stability of group pile-pile cap structure under supergravity high g value test environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete energy pile, more particularly, it relates to a concrete energy pile group pile-cap foundation centrifuge test model and method. BACKGROUND

[0002] At present, the technology of utilizing underground shallow geothermal resources is mainly the ground source heat pump technology, but this project occupies a large underground space. The energy pile technology is a new technology combining traditional ground source heat pump technology with pile foundation, which can effectively extract geothermal resources and simultaneously play a double role of bearing load and controlling settlement, and is an important breakthrough point for realizing overall green transformation in the building field and promoting high-quality development of the energy system.

[0003] At present, many energy pile projects in China have entered the stage of large-scale development, such as the Shanghai Expo Axis project and the Nanjing Langshi Pedestrian Street project. Large-scale development has posed unprecedented challenges to the design and safe service of energy pile foundation structures. The safe service of pile foundation structures often has characteristics such as long duration, large scale, and composite load.

[0004] The supergravity physical simulation method has the characteristics of time and scale reduction, and can reproduce the stress conditions of the prototype with a model of 1 / N times the original size under N times the gravity acceleration, accurately reproduce the relevant behavior of the soil at the same position as the prototype, and has outstanding advantages in solving such problems. In recent years, the supergravity physical simulation method has been successfully applied to the study of the stress mechanism and deformation characteristics of energy piles under long-term thermal coupling, however, in actual engineering, energy piles often appear in the form of pile groups. Due to the interaction between piles, soil and caps, the thermodynamic performance of energy pile groups under pile group effect is significantly different from that of single piles. In order to more effectively guide engineering practice, it is necessary to further quantify the heat exchange and load transfer rules between pile groups and surrounding soil, and the key technical difficulty in achieving this research goal is the development of a scaled-down pile group model.

[0005] In order to solve this problem, relevant scholars have developed several scaled-down energy pile group models suitable for normal gravity environment, for example, patent CN109556658A discloses an energy pile group model without a cap structure at the top of the pile, and patent CN113834842A discloses an energy pile group-cap model that realizes temperature change by inserting heating or cooling rods. However, the related models are designed based on normal gravity test environment. Considering the high speed and closed test environment of supergravity physical simulation, the related models and test methods cannot be directly applied to supergravity model tests, therefore, it is urgent to develop a scaled-down energy pile group-cap foundation model suitable for supergravity environment. SUMMARY

[0006] The invention aims to overcome the deficiencies in the prior art and provides a concrete energy pile group pile-cap foundation centrifuge test model and method.

[0007] In a first aspect, a concrete energy pile group pile-cap foundation centrifuge test model is provided, comprising:

[0008] a scaled concrete energy pile, a T-shaped connecting piece, a screw, a pile cap, a gasket and a nut;

[0009] The scaled concrete energy pile is connected to the lower end surface of the pile cap through the T-shaped connecting piece, the gasket is arranged on the upper end surface of the pile cap and corresponds to the scaled concrete energy pile, and the screw passes through the gasket and is fixed through the nut.

[0010] Preferably, a steel wire cage and a silica gel tube are embedded in the scaled concrete energy pile, the steel wire cage is composed of longitudinal reinforcement and hoop rings, the longitudinal reinforcement is arranged in two rows, the hoop rings pass through the longitudinal reinforcement, and the spacing between adjacent hoop rings is equal.

[0011] Preferably, the T-shaped connecting piece comprises upper and lower parts, the upper part of the T-shaped connecting piece is a cuboid, and the lower part of the T-shaped connecting piece is a cylinder; the upper part of the T-shaped connecting piece is provided with small holes for longitudinal reinforcement to pass through and a circular hole for a silica gel tube to pass through; a threaded hole is provided in the center of the T-shaped connecting piece, and the threaded hole penetrates the upper and lower parts of the T-shaped connecting piece.

[0012] Preferably, a through hole is provided on the pile cap, the through hole is composed of a square hole at the lower part and a circular hole at the upper part; the upper part of the T-shaped connecting piece is embedded in the square hole, and the exposed silica gel tube and screw pass through the circular hole.

[0013] Preferably, the scaled concrete energy pile is made of scaled concrete, and the scaled concrete is mixed with gypsum, silica sand, water and copper powder.

[0014] In a second aspect, a preparation method of the scaled concrete energy pile according to any one of the first aspect is provided, comprising:

[0015] S1, taking a screw and passing it through a prefabricated T-shaped connecting piece and a mold top plate from bottom to top, with the screw extending out of the mold top plate;

[0016] S2, taking a hoop ring and passing it through longitudinal reinforcement, arranging the hoop rings at equal intervals, and fixing them with quick-drying glue to obtain a steel wire cage;

[0017] S3, arranging the steel wire cage in a symmetrically split mold, with one end of the steel wire cage sequentially passing through the T-shaped connecting piece and the mold top plate, the other end passing through the mold bottom plate, and the two ends being tightened with iron wires;

[0018] S4, two silica gel tubes are taken in parallel and fixed in the steel reinforcement cage; the water inlet of the silica gel tube passes through the T-shaped connector and the round hole on the mold top plate in turn, and the water outlet of the silica gel tube passes through the opposite round hole; the silica gel tube is a U-shaped silica gel tube;

[0019] S5, a scaled concrete mixture is prepared, water, gypsum and silica sand are mixed in a certain proportion, and copper powder is mixed in the mixture;

[0020] S6, the mixture is injected into the mold, and air curing is carried out at room temperature;

[0021] S7, the mold is removed, and a scaled concrete energy pile is obtained.

[0022] As preferred, in S2, epoxy resin is used to coat the silica sand on the surface of the hoop ring and the longitudinal steel bar.

[0023] As preferred, in S4, the silica gel tube is arranged in a double-U shape, a W shape or a spiral shape.

[0024] In a third aspect, a preparation method of the concrete energy pile group pile-cap foundation centrifuge test model according to any one of the first aspect is provided, comprising:

[0025] S1, the scaled concrete energy piles are arranged in a certain way and hung at a set position in the model box to form a scaled concrete energy pile group;

[0026] S2, sand is dropped around the scaled concrete energy pile group until the top of the pile;

[0027] S3, the pile cap is placed on the top of the scaled concrete energy pile, the T-shaped connector at the top of the pile is embedded into the square hole of the pile cap, and the silica gel tube and the screw pass through the circular hole of the pile cap;

[0028] S4, the gasket covers the circular hole of the pile cap, the screw passes through the center circular hole of the gasket, and the silica gel tube passes through the circular holes around the gasket;

[0029] S5, the nut is placed on the gasket through the screw, and the pile cap and the scaled concrete energy pile group are rigidly connected.

[0030] As preferred, in S2, the sand dropping height and the steel pipe opening size are determined according to the target value of the relative density, and the sand is dropped into the model box along a U-shaped path according to the calibrated sand dropping height and the steel pipe opening size.

[0031] In a fourth aspect, a performance test method of the concrete energy pile group pile-cap foundation centrifuge test model according to any one of the first aspect is provided, comprising:

[0032] S1, arranging thermocouples along the pile body on one side of the scaled concrete energy pile, arranging strain gauges on the other side at the same depth, and covering the sensor surface with glue;

[0033] S2, placing the prepared model on the centrifuge basket with a crane, connecting the sensors to the data acquisition instrument, and then connecting the data acquisition instrument to the computer;

[0034] S3, selecting all or certain pile foundations, connecting the silica gel tube to the heating and refrigeration system of the centrifuge, turning on the heating and refrigeration system during the centrifuge process, applying temperature cyclic load to the pile-cap model of the energy pile group, and reading and recording the strain and temperature change of the pile foundation during the experiment.

[0035] The beneficial effects of the present application are:

[0036] 1. The concrete energy pile group-cap model provided by the present application can effectively simulate the bearing strength (such as bending stiffness and bearing capacity) and nonlinear mechanical properties of reinforced concrete piles, and can also better reproduce the thermal properties (such as thermal expansion coefficient and thermal conductivity) of reinforced concrete energy pile structures.

[0037] 2. The concrete energy pile group-cap model provided by the present application limits the relative movement (such as rotation and translation) between the energy pile and the cap by embedding T-shaped connectors in the energy pile and connecting the energy pile and the cap with gaskets, achieving the effect of rigid connection between the energy pile and the cap, and ensuring the integrity and stability of the pile-cap structure under the high-g value test environment.

[0038] 3. The concrete energy pile group-cap model provided by the present application protects the heat exchange pipe by providing holes on the T-shaped connector, gasket and cap, effectively avoiding the risk of heat exchange pipe rupture under high-g value test environment, and ensuring the continuity of temperature load application during the test process.

[0039] 4. The heat exchange pipe of the scaled concrete energy pile group-cap model provided by the present application can be directly connected to the heating and refrigeration system of the centrifuge, which is easy to realize under the supergravity centrifugal test environment and easy to operate. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a schematic diagram of a scaled concrete energy pile group-cap foundation model;

[0041] Figure 2 is a schematic diagram of a scaled concrete energy pile;

[0042] Figure 3 is a top view of a scaled concrete energy pile;

[0043] Figure 4 is a schematic view of a T-shaped connector;

[0044] Figure 5 is a top view of a T-shaped connector;

[0045] Figure 6 is a side view of a T-shaped connector;

[0046] Figure 7 is a schematic view of a pile cap;

[0047] Figure 8 is a top view of a pile cap;

[0048] Figure 9 is a side view of a pile cap;

[0049] Figure 10 is a schematic view of a spacer;

[0050] Figure 11 is a top view of a spacer;

[0051] Figure 12 is a side view of a spacer;

[0052] Figure 13 is a bending moment-curvature relationship diagram of a scaled concrete energy pile;

[0053] Figure 14 is a diagram of the relationship between thermal axial strain and temperature change of a scaled concrete energy pile;

[0054] Figure 15 is a layout diagram of a scaled concrete energy pile group-pile cap foundation centrifugal test model;

[0055] Figure 16 is a top view of a layout diagram of a scaled concrete energy pile group-pile cap foundation centrifugal test model;

[0056] BRIEF DESCRIPTION OF DRAWINGS: 1, scaled concrete energy pile; 2, T-shaped connector; 3, screw; 4, pile cap; 5, spacer; 6, nut; 7, steel wire cage; 8, silica gel tube; 9, scaled concrete; 10, longitudinal steel bar; 11, hoop ring; 12, K-type thermocouple; 13, strain gauge; 14, thermal insulation layer. DETAILED DESCRIPTION

[0057] The application will be further described below in conjunction with examples. The following examples are only used to help understand the application. It should be pointed out that for ordinary people in the technical field, several modifications can be made to the application without departing from the principles of the application, and these improvements and modifications also fall within the protection scope of the claims of the application.

[0058] Example 1:

[0059] A centrifuge test model for concrete energy pile group pile-cap foundation, such as Figure 1 As shown, it includes:

[0060] Scaled concrete energy pile 1, T-shaped connector 2, screw 3, pile cap 4, washer 5 and nut 6.

[0061] The scaled concrete energy pile 1 is connected to the lower end face of the foundation 4 via a T-shaped connector 2. The gasket 5 is set on the upper end face of the foundation 4 and corresponds to the scaled concrete energy pile 1. The screw 3 passes through the gasket 5 and is fixed by the nut 6.

[0062] This application does not limit the number of scaled concrete energy piles 1 connected to the foundation 4. For example, this application designs and manufactures scaled concrete energy piles based on the law of size similarity (model: prototype = 1:N; N = 35). Taking a 2x2 energy pile group-foundation as an example, the pile group consists of 4 scaled concrete piles with a square cross-section of 18mm side length and a pile length of 300mm. The center distance between adjacent piles is 54mm. The top of the energy pile is connected to a foundation with an outer dimension of 125mm x 125mm x 25mm.

[0063] like Figure 2 and Figure 3 As shown, the scaled-down concrete energy pile is a precast pile, with a wire cage 7 and silicone tubes 8 embedded inside, followed by the pouring of scaled-down concrete 9. The wire cage 7 consists of longitudinal reinforcing bars 10 and stirrup rings 11. The longitudinal reinforcing bars 10 are arranged in double rows, and the stirrup rings 11 pass through the longitudinal reinforcing bars 10, with equal spacing between adjacent stirrup rings 11. To ensure effective connection between the wire cage and the filler, epoxy resin can be used to coat the surface of the wire cage 7 with silica sand. In addition, this application uses silicone tubes 8 instead of heat exchange tubes in traditional energy piles. The silicone tubes 8 are arranged in a double U-shape, W-shape, or spiral shape and fixed inside the wire cage 7. The inlet and outlet of the silicone tubes 8 extend out of the scaled-down concrete energy pile 1 and are connected to an external heating and cooling system. The scaled-down concrete 9 is mixed with gypsum, silica sand, water, and copper powder. Compared to existing concrete, this application adds copper powder to improve its thermal performance. Furthermore, the top of the scaled-down concrete energy pile 1 is connected to a T-shaped connector 2.

[0064] like Figure 4 , Figure 5 and Figure 6As shown, the T-shaped connector 2 consists of two parts, upper and lower. The upper part of the T-shaped connector 2 is a cuboid with a length of 18mm, a width of 18mm, and a height of 5mm, and is connected to the foundation 4. The lower part of the T-shaped connector 2 is a cylinder with a diameter of 6mm and a height of 4mm, and is connected to the top of the scaled concrete energy pile 1. Small holes with a diameter of 1mm are drilled at the four corners of the upper part of the T-shaped connector 2 for the longitudinal reinforcing bars 10 to pass through. A circular hole with a diameter of 3mm is drilled between two adjacent small holes for the silicone tube 8 to pass through. A threaded hole with a diameter of 4mm is drilled in the center of the T-shaped connector 2, and the threaded hole passes through both the upper and lower parts of the T-shaped connector 2.

[0065] Screw 3 passes through T-shaped connector 2 from bottom to top and protrudes from T-shaped connector 2.

[0066] like Figure 7 , Figure 8 and Figure 9 As shown, the pile cap 4 has through holes arranged in a specific pattern, with the center-to-center distance between adjacent through holes being three times the pile diameter. Each through hole consists of a lower square hole and an upper round hole. The square hole measures 18mm x 18mm x 5mm, and the round hole has a diameter of 10mm and a height of 20mm. The upper part of the T-shaped connector 2 is embedded in the square hole, and the exposed silicone tube 8 and screw 3 pass through the round hole. Furthermore, the pile cap material can be aluminum, and the pile cap is rectangular.

[0067] like Figure 10 , Figure 11 and Figure 12 As shown, the gasket 5 has four 3mm diameter holes in the cardinal directions (north, south, east, and west), through which the silicone tube 8 passes. A central 4mm diameter hole is also made in the center of the gasket 5, through which the screw 3 passes and is secured with a nut 6. Furthermore, the gasket covers the circular hole in the foundation. The gasket can be made of aluminum, with a square cross-section of 20mm on each side and a thickness of 2mm.

[0068] Example 2:

[0069] The scaled-down concrete energy pile used in Embodiment 1 of this application is a precast pile, and its preparation method is as follows:

[0070] S1. Take screw 3 and pass it from bottom to top through the prefabricated T-shaped connector 2 and the mold top plate. Screw 3 extends out of the mold top plate. This screw 3 can be an M4 screw.

[0071] S2. Take the stirrup ring 11 and pass it through the longitudinal steel bar 10. Arrange the stirrup rings 11 at equal intervals and fix them with quick-drying glue to obtain the wire cage 7.

[0072] Specifically, the longitudinal steel bars 10 include 4 stainless steel wires with a diameter of 1 mm, and the stirrup rings 11 include 10 stainless steel wires with a diameter of 0.63 mm. Both the longitudinal steel bars and the stirrup rings are made of 316 stainless steel wires, with a yield strength of 380 MPa and 460 MPa respectively, and a thermal expansion coefficient of 18.5 με / ℃. In order to ensure effective connection between the stainless steel wires and the mortar, the surface of the stainless steel wires is coated with silica sand using epoxy resin. The stirrup rings are taken through the longitudinal steel bars, with a spacing of 30 mm between adjacent stirrup rings, and are fixed with quick-drying glue.

[0073] S3, the steel wire cage 7 is arranged in the symmetrically split mold, one end of the steel wire cage 7 sequentially passes through the T-shaped connecting piece 2 and the mold top plate, the other end passes through the mold bottom plate, and the two ends are tightened with iron wires.

[0074] S4, two U-shaped silica gel pipes are taken in parallel and fixed in the steel bar cage; the water inlet of the U-shaped silica gel pipe sequentially passes through the T-shaped connecting piece 2 and the round hole on the mold top plate, and the water outlet of the U-shaped silica gel pipe passes through the opposite round hole.

[0075] The present application uses a silica gel pipe with an inner diameter of 1.5 mm and an outer diameter of 3 mm to replace the heat exchange pipe in the traditional energy pile, and the tensile strength of the silica gel pipe is 10 MPa, and the thermal expansion coefficient is between 70 and 110 με / ℃.

[0076] S5, prepare a scaled concrete mixture, mix water, gypsum and silica sand in a certain proportion, and simultaneously mix copper powder in the mixture.

[0077] In S5, the proportion of water, gypsum and silica sand can be 0.9:1:1, and the volume content of copper powder can be 6%.

[0078] S6, the mixture is injected into the mold and air-cured at (20-23℃) for 28 days.

[0079] S7, remove the mold to obtain the scaled concrete energy pile 1.

[0080] After preparing the scaled concrete energy pile 1, the thermodynamic performance of the scaled concrete energy pile 1 can also be tested. For example, strain gauges and thermocouples are installed on the surface of the scaled concrete energy pile, and are connected to a data acquisition device. According to the experimental plan, mechanical / temperature load is applied to the scaled concrete energy pile, and the strain and temperature change of the pile foundation are read and recorded during the experiment.

[0081] The method for testing the thermodynamic performance of the scaled concrete energy pile is further described below:

[0082] The flexural performance of scaled concrete energy piles under temperature load is tested by temperature-controlled four-point bending test. The scaled concrete energy piles are placed horizontally in the bending test fixture to form a simply supported beam. There are two symmetric loading points above the specimen, and the distance between the loading points is 70 mm. The distance between the two lower support points of the specimen and the proximal loading point is equal, both being 70 mm. Strain gauges and thermocouples are arranged on the lower surface of the middle section of the measured scaled concrete energy pile to measure the maximum strain and temperature on the surface of the scaled concrete energy pile, respectively. During the test, the temperature of the water flow at the inlet and outlet of the scaled concrete energy pile is controlled by a cold and hot circulating water machine. Two specimens are heated / cooled, respectively. When the thermal equilibrium is reached, the surface temperature of the pile is 5℃ and 50℃, respectively. Another scaled concrete energy pile is used to simulate the normal temperature condition by controlling its surface temperature at 20℃. Then, mechanical load is applied to the scaled concrete energy pile, and the load size is recorded. When the pile appears obvious cracks, followed by large deformation, and the strain exceeds 0.00048, the loading is ended. After the test, the curvature and bending moment are obtained based on the theoretical relationship between the maximum strain and the cross-sectional length and the theoretical relationship between the external load and the span, respectively.

[0083] Figure 13 The bending moment-curvature relationship of the scaled concrete energy pile is described. As shown in Figure 13 , when the scaled concrete energy pile appears obvious cracks, the bending moment drops suddenly, and then exhibits ductile failure characteristics. The scaled concrete energy pile can simulate the nonlinear properties of the prototype reinforced concrete energy pile. In addition, by carrying out numerical simulation, the maximum bending moment (325 kNm) of the prototype reinforced concrete energy pile is analyzed. The average bending moment measured by the test is 336 kNm, which is close to the numerical simulation result. The scaled concrete energy pile can simulate the bearing strength of the reinforced concrete pile.

[0084] Furthermore, this embodiment uses a free expansion test as an example to determine the linear thermal expansion coefficient of a scaled-down concrete energy pile. Strain gauges are placed at 105, 170, and 235 mm along the length of the pile on the surface of the scaled-down concrete energy pile (denoted as pile A), and thermocouples are placed at the same depth to measure the axial strain and surface temperature of the pile, respectively. One strain gauge is installed along the main axis of strain (i.e., the axial direction), and another strain gauge is installed perpendicular to it, with the two strain gauges connected in a half-bridge configuration. The scaled-down concrete energy pile is supported by two smooth stainless steel rollers, allowing the pile to expand and contract freely during heating and cooling. Taking the cooling stage as an example, the inlet and outlet water flow temperatures of the energy pile are controlled by a hot and cold circulating water machine to ensure that the surface temperature of the pile foundation varies between the ambient temperature of 22°C and 5°C. Each temperature cycle includes two stages: cooling and warming, and a total of four temperature cycles are performed, each cycle taking 40-50 minutes. To compensate for pile foundation deformation caused by changes in ambient temperature, a parallel experiment was conducted. Another scaled-down concrete energy pile (denoted as pile B) was selected, and strain gauges were arranged at the same positions. The pile was placed next to the scaled-down concrete energy pile being tested, and its strain under ambient temperature was monitored. The strain measured in the parallel experiment of pile B was subtracted from the strain of the scaled-down concrete energy pile being tested.

[0085] Figure 14 Describe the relationship between thermally induced axial strain and pile surface temperature changes. For example... Figure 14 As shown, along the pile depth direction, the axial strain of the scaled-down concrete energy pile exhibits a linear relationship with the change in pile surface temperature, and this change is reversible, indicating that the scaled-down concrete energy pile possesses thermoelastic behavior. By calculating the gradient of the linear curve, the coefficient of thermal expansion of the scaled-down concrete energy pile is 8.9 ± 1.4 με / ℃, which falls within the linear thermal expansion range of concrete (8.5-10 με / ℃), thus replicating the thermal properties (such as the coefficient of thermal expansion) of the reinforced concrete energy pile structure.

[0086] Example 3:

[0087] A method for preparing a centrifuge test model of a concrete energy pile group-pile cap foundation includes:

[0088] S1. The scaled concrete energy piles 1 are arranged in a 2x2 pattern and suspended in the model box at the set position to form a scaled concrete energy pile group.

[0089] S2. Sand is poured around the scaled-down concrete energy pile group, up to the top of the piles.

[0090] The sand removal process includes: determining the sand removal height and the size of the steel pipe opening based on the target value of a relative density of 70%; then, according to the specified sand removal height and the size of the steel pipe opening, using a U-shaped path to remove sand into the model box, with a drop height of 300mm.

[0091] S3, the bearing platform 4 is placed on the top of the scaled concrete energy pile 1, the T-shaped connector 2 on the top of the pile is embedded into the square hole of the bearing platform 4, and the silica gel tube 8 and the screw 3 pass through the circular hole of the bearing platform.

[0092] S4, the gasket 5 covers the circular hole of the bearing platform, the screw 3 passes through the central circular hole of the gasket 5, and the silica gel tube passes through the circular hole around the gasket 5.

[0093] S5, the nut 6 is placed on the gasket 5 through the screw 3, and the bearing platform 4 and the scaled concrete energy pile group form a rigid connection.

[0094] The performance test method of the above-mentioned centrifuge test model of the concrete energy pile group pile-bear platform foundation, as shown in Figure 15 and Figure 16 , comprises the following steps.

[0095] S1, k-type thermocouples 12 are arranged at intervals of 60mm along the pile body on one side of the pile, and strain gauges 13 are arranged at the same depth and equal intervals on the other side, and the surface of the sensor is covered with glue.

[0096] S2, the model prepared in example 3 is placed on the centrifuge basket by using a crane, the sensor is connected to a data acquisition instrument, and the data acquisition instrument is connected to a computer.

[0097] S3, all or certain pile foundations (such as corner pile foundations) are selected, and the silica gel tube thereof is connected to the heating and refrigeration system of the centrifuge; during the rotation process, the heating and refrigeration system is started, temperature cycle load is applied to the energy pile group pile-bear platform model, that is, 45℃ hot water is passed through the pile body, 20℃ normal temperature water is passed through after stabilization, the next cycle is applied after re-stabilization, and a total of 3 temperature cycles are applied. During the experiment, the strain and temperature change law of the scaled concrete energy pile and the pile foundation not connected to the heating and refrigeration system are read and recorded respectively.

Claims

1. A centrifuge model of a concrete energy pile group pile-cap foundation, characterized in that, include: Scaled concrete energy pile (1), T-shaped connector (2), screw (3), pile cap (4), washer (5) and nut (6); The scaled concrete energy pile (1) is connected to the lower end face of the foundation (4) via the T-shaped connector (2). The gasket (5) is placed on the upper end face of the foundation (4) and corresponds to the scaled concrete energy pile (1). The screw (3) passes through the gasket (5) and is fixed by the nut (6). The scaled concrete energy pile (1) is internally equipped with a wire cage (7) and a silicone tube (8). The wire cage (7) is composed of longitudinal steel bars (10) and stirrup rings (11). The longitudinal steel bars (10) are arranged in two rows, and the stirrup rings (11) pass through the longitudinal steel bars (10). The spacing between adjacent stirrup rings (11) is equal. The T-shaped connector (2) comprises two parts, an upper part and a lower part. The upper part of the T-shaped connector (2) is a cuboid, and the lower part of the T-shaped connector (2) is a cylinder. The upper part of the T-shaped connector (2) is provided with a small hole for the longitudinal steel bar (10) to pass through and a round hole for the silicone tube (8) to pass through. The center of the T-shaped connector (2) is provided with a threaded hole, which passes through both the upper and lower parts of the T-shaped connector (2). The support (4) is provided with a through hole, which consists of a square hole at the bottom and a round hole at the top. The upper part of the T-shaped connector (2) is embedded in the square hole, and the exposed silicone tube (8) and screw (3) pass through the round hole.

2. The concrete energy pile group pile-cap foundation centrifuge test model according to claim 1, characterized in that, The scaled concrete energy pile (1) is made of scaled concrete (9), which is mixed with gypsum, silica sand, water and copper powder.

3. A method of producing a scaled concrete energy pile according to any one of claims 1 to 2, characterized in that, include: S1. Take the screw (3) and pass it from bottom to top through the prefabricated T-shaped connector (2) and the mold top plate. The screw (3) extends out of the mold top plate. S2. Take the stirrup ring (11) and pass it through the longitudinal steel bar (10). Arrange the stirrup rings (11) at equal intervals and fix them with quick-drying glue to obtain the wire cage (7). S3. Arrange the wire cage (7) in the symmetrically shaped mold. One end of the wire cage (7) passes through the T-shaped connector (2) and the top plate of the mold in sequence, and the other end passes through the bottom plate of the mold. Tighten the wires at both ends. S4. Take two silicone tubes (8) and connect them in parallel, and fix them in the wire cage (7); the inlet of the silicone tube (8) passes through the T-shaped connector (2) and the round hole on the top plate of the mold in sequence, and the outlet of the silicone tube (8) passes through the opposite round hole. S5. Prepare scaled concrete mixture by mixing water, gypsum and silica sand in a certain proportion, and adding copper powder to the mixture. S6. Pour the mixture into the mold and cure it in air at room temperature; S7. Remove the mold to obtain a scaled-down concrete energy pile (1).

4. The method of claim 3, wherein the scaled concrete energy pile is prepared by, In S2, epoxy resin is used to coat the surface of the stirrup ring (11) and the longitudinal steel bar (10) with silica sand.

5. The method of claim 3, wherein the scaled concrete energy pile is prepared by, In S4, the silicone tube (8) is arranged in a double U-shape, W-shape or spiral shape.

6. A method of preparing a centrifuge test model of a concrete energy pile group pile-raft foundation according to any one of claims 1 to 2, characterized in that, include: S1. Scaled concrete energy piles (1) are arranged in a certain way and suspended in the model box at a set position to form a scaled concrete energy pile group. S2, drop sand around the scaled concrete energy pile group, drop sand to the top of the pile; S3, take the bearing platform (4) and place it on the top of the scaled concrete energy pile (1), the T-shaped connector (2) on the top of the pile is embedded into the square hole of the bearing platform (4), the silica gel tube (8) and the screw (3) pass through the circular hole of the bearing platform; S4, the gasket (5) covers the circular hole of the bearing platform, the screw (3) passes through the center circular hole of the gasket (5), and the silica gel tube passes through the circular hole around the gasket (5); S5, the nut (6) passes through the screw (3) and is placed on the gasket (5), and the bearing platform (4) and the scaled concrete energy pile group form a rigid connection.

7. The method of claim 6, wherein the method further comprises: providing a plurality of concrete energy piles; and coupling the plurality of concrete energy piles to the concrete pile cap.

8. The method of claim 7, wherein the method further comprises: providing a plurality of concrete energy piles; and coupling the plurality of concrete energy piles to the concrete pile cap. In S2, the sand dropping height and the steel pipe opening size are determined according to the target value of the relative density, and then sand is dropped into the model box along the U-shaped path according to the calibrated sand dropping height and the steel pipe opening size.

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