A pile foundation integrity detection method based on thermal response

Abstract

The application provides a pile foundation integrity detection method based on thermal response and belongs to the field of pile foundation detection. The detection method comprises detection preparation, parameter setting, detection of M positions, data analysis and processing. Specifically, a sensor is placed in N embedded temperature measuring tubes, then detection of multiple positions is carried out along the axial direction according to the setting, and a time-temperature curve of each temperature measuring tube at each position is generated. The obtained time-temperature curve is analyzed and processed to obtain a final abnormal curve, and the corresponding temperature measuring tube serial number and position serial number confirm the position of the pile foundation defect. The application utilizes the difference between the thermal conductivity coefficients of the pile body material and the pile body defect position, compares the thermal conduction efficiency of the detected pile foundation at different positions with the standard thermal conduction efficiency of the test pile to determine the defect position of the detected pile foundation, has high accuracy, is simple and intuitive, does not cause damage to the pile foundation, and belongs to nondestructive testing.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of pile foundation detection, in particular to a pile foundation integrity detection method based on thermal response. BACKGROUND

[0002] Large-diameter pile foundation is one of the most common foundation forms, and most of the large-diameter piles below the ground surface are constructed by cast-in-place process. During the construction process, defects such as broken pile, neck expansion, neck shrinkage, segregation, mud inclusion, sedimentation, and cavity are easily caused by environmental or human factors, which greatly affects the stress performance of the pile foundation. Currently, the commonly used methods for detecting underground pile foundation include acoustic wave transmission method, static load test method, coring method, and low strain method.

[0003] The acoustic wave transmission method is to emit acoustic waves into the pile foundation by artificial means, and to judge the internal defects of the pile foundation and their positions by the propagation speed and amplitude of the received acoustic waves. However, the acoustic waves are easily reflected and refracted when encountering different medium interfaces (such as the coarse aggregate-cement and cement-steel interfaces existing in large quantities in the reinforced concrete pile) during transmission, which affects the detection results. For example, the automatic detection system and method for multi-pipeline ultrasonic nondestructive testing and three-dimensional modeling and positioning of bad points, which was authorized on December 13, 2022, in China, cyclically emits and receives acoustic wave signals by multiple ultrasonic probes, and comprehensively determines the defect position and shape of the pile foundation according to the multiple cycle results. However, this method still cannot solve the problem of difficulty in extracting effective acoustic wave signals caused by the reflection or refraction of acoustic waves in the pile foundation due to different medium interfaces during transmission.

[0004] The static load test method needs to apply a load on the top of the pile foundation, and judges the quality of the pile according to whether the deformation of the pile foundation under the experimental load meets the requirements. For example, the detection device for pile foundation, which was authorized on October 29, 2021, in China, applies a counterforce on the pile top by a gantry to detect the quality of the pile foundation. This method has a large experimental device size, is difficult to install, and cannot provide the defect position of the pile foundation when the pile foundation detection is unqualified.

[0005] The coring method judges the quality of the pile foundation by drilling and coring in the pile. The drilling in the pile foundation easily damages the internal structure of the pile foundation, which has a negative impact on the quality of the pile foundation that is difficult to repair.

[0006] The low strain method generates stress waves by exciting the pile top, and produces reflected waves when encountering the pile bottom or discontinuous interface. A single velocity sensor is used to receive the reflected wave signals, and the characteristics of the reflected waves are analyzed to judge the integrity of the pile foundation. This method needs to install equipment on the top of the pile foundation, and is not suitable for pile foundations with upper structures. SUMMARY

[0007] In order to overcome the prior art deficiencies, the present application proposes a pile foundation integrity detection method based on thermal response, which utilizes the difference in thermal conductivity coefficients of pile body material and pile body defect position to accurately measure the pile foundation defect position.

[0008] The purpose of the present application is achieved by providing a pile foundation integrity detection method based on thermal response, which pre-buries a set of detection components in the pile foundation during pouring, the detection components including one heat source pipe, N identical temperature measuring pipes and N+1 plugs; the heat source pipe is pre-buried at the axis of the pile foundation along the axial direction of the pile foundation, the N temperature measuring pipes are pre-buried in the pile foundation in parallel with the heat source pipe and in a uniform distribution manner, and the plugs are pre-buried at the bottom position of the heat source pipe and each temperature measuring pipe, which is flush with the bottom of the pile foundation; the top of the heat source pipe and the N temperature measuring pipes are flush with the top of the pile foundation, and the top of the pile foundation is slightly higher than the ground surface;

[0009] The detection method includes the following steps:

[0010] Step 1, detection preparation

[0011] The detection preparation includes the preparation of the detection device, which includes one heat source, N+1 temperature sensors, one heating control cabinet and one temperature collector;

[0012] During detection, the heat source and one temperature sensor are placed in the heat source pipe, and the other N temperature sensors are placed in the N temperature measuring pipes; the heating control cabinet is connected to the heat source through wires to supply heat to the heat source at a constant power; the collector is connected to the N+1 temperature sensors through data lines to continuously record the temperature data of each temperature sensor and automatically generate the required time-temperature curve;

[0013] Step 2, parameter setting

[0014] Set to detect M positions along the axial direction of the pile foundation, and mark any one detection position as position W m , m is the position number, m = 1, 2,..., M; in the detection of position W m , the vertical distance from the heat source and the N+1 temperature sensors to the top surface of the pile foundation is m×h; in the detection of position W M , the heat source and the N+1 temperature sensors are located at the bottom of the pile foundation, and the vertical distance from the bottom to the top surface of the pile foundation is M×h;

[0015] Set to detect P rounds for each of the M positions, and set the heating duration of each round of detection to be the same and to be the duration t;

[0016] The detection starts from position W1 and is performed in the order of position number m;

[0017] Step 3, detection of position W1

[0018] A heat source head and a temperature sensor are placed in the heat source tube, and N temperature sensors are placed in N temperature measuring tubes respectively, and the vertical distance between the heat source head and the N+1 temperature sensors and the top surface of the pile foundation is h during the entire detection of position W1;

[0019] Step 3.1, first round of detection

[0020] The heating control cabinet is opened, and the heat source head is heated at a constant power, and the collector synchronously records the time and temperature data of the N+1 temperature sensors during the heating process;

[0021] After reaching the heating time t, the heating control cabinet is closed, and ventilation is performed in the heat source tube until the temperature of the N+1 temperature sensors returns to the value before heating, and the collector synchronously records the time and temperature data of the N+1 temperature sensors during the cooling process;

[0022] After cooling, for each temperature sensor in the temperature measuring tube, the collector outputs a time-temperature curve, i.e. N time-temperature curves are obtained in the first round of detection of position W1, and the starting point of the time-temperature curve coincides with the origin of a plane coordinate system, and the vertical axis of the coordinate system is temperature and the horizontal axis is time;

[0023] Step 3.2, P rounds of step 3.1 are repeated to obtain P×N time-temperature curves of position W1, i.e. for each temperature sensor in the temperature measuring tube, P time-temperature curves are obtained through detection;

[0024] Each temperature sensor in the temperature measuring tube is referred to as an effective sensor, and P curves corresponding to each effective sensor obtained in the detection of position W1 are referred to as a curve family, i.e. N curve families of N effective sensors are obtained through step 3.2;

[0025] Step 3.3, error analysis and discrete fitting are performed on the N curve families respectively to obtain a fitted time-temperature curve of each effective sensor at position W1;

[0026] That is, through error analysis and discrete fitting, N fitted time-temperature curves of N effective sensors are obtained in the detection of position W1;

[0027] Step 4, detection of position W m

[0028] The heat source head and the N+1 temperature sensors are moved downward by h each time in the order of m=1, 2,..., M, and when reaching position W​m Then, perform a detection and processing step according to steps 3.1-3.3 to obtain a location W. m N fitted time-temperature curves;

[0029] After all M positions are completed, a total of M×N fitted time-temperature curves are obtained. Any one of these curves is denoted as the fitted curve Q. mn Where n is the number of the temperature measuring tube, denoted as the temperature measuring tube serial number, n = 1, 2, ..., N;

[0030] The combination of the location number m and the temperature measuring tube number n defines the location of each detection point on the pile foundation;

[0031] Step 5, Data Analysis and Processing

[0032] Step 5.1, combine the M×N fitted curves Q obtained in step 4. mn The temperature measuring tubes are divided into Z groups according to their radial positions, and any group in the Z groups is denoted as the z-th group, where z is the group number, z = 1, 2, ..., Z;

[0033] Step 5.2, for each fitted curve Q in the z-th group mn Each fitted curve is compared with the standard time-temperature curve range corresponding to a group z, and the fitted curves Q that do not completely fall within the standard time-temperature curve range are identified. mn This is recorded as the final anomaly curve;

[0034] Step 5.3: Following the method in Step 5.2, evaluate each curve in group Z to obtain M×N fitted curves Q. mn All final anomaly curves:

[0035] The location of the detection point is determined by the position number m corresponding to the final abnormal curve and the temperature measuring tube number n, and it is identified as the location of the pile foundation defect.

[0036] Preferably, the heat source pipe and temperature measuring pipe are cleaned before the location W1 is detected to ensure that there are no impurities.

[0037] Preferably, the process of performing error analysis and discrete fitting on the N families of curves in step 3.3 to obtain a fitted time-temperature curve for each effective sensor at position W1 is as follows:

[0038] First, fit the data points of the P time-temperature curves in each family of curves obtained in step 3.2 to obtain a fitted heating temperature-time curve for the error to be removed. Then, compare the P time-temperature curves in each family of curves with the fitted heating temperature-time curve for the error to be removed in that family of curves, and identify the time-temperature curves whose curve correlation coefficient is less than the preset standard value R of curve correlation coefficient as error curves.

[0039] Then, extract the data points of each heating temperature-time curve from the remaining time-temperature curve family after removing the error curves in each curve family, and perform curve fitting on all the extracted data points to obtain the fitted time-temperature curve.

[0040] Preferably, the process for determining the range of the standard time-temperature curve is as follows:

[0041] Steps 3-4 are repeated K times using the test pile to obtain K×M×N standard fitted time-temperature curves. This family of standard curves is called the original family of standard curves.

[0042] The original standard curve family is divided into Z groups according to the radial position of the temperature measuring tube, and any one of the curve families is denoted as the standard curve family corresponding to the z-th group. The range enclosed by the upper and lower envelopes of the standard curve family corresponding to the z-th group is denoted as the standard time-temperature curve range corresponding to the z-th group.

[0043] The test pile is a defect-free pile foundation made with reference to the information of the pile foundation, which includes the material of the pile foundation, the length and diameter of the pile foundation, and the material, size and spatial location information of the heat source pipe and the temperature measuring pipe.

[0044] Preferably, the pile foundation is a circular cast-in-place reinforced concrete pile with a diameter of not less than 1.5m.

[0045] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0046] (1) This invention utilizes the difference in thermal conductivity coefficient between the pile material and the location of pile defects to determine the location of defects in the pile foundation by comparing the thermal conductivity efficiency at different locations of the tested pile foundation with the standard thermal conductivity efficiency of the test pile, which is highly accurate.

[0047] (2) The size of the pile foundation defect can be evaluated based on the test results. The axial dimension of the defect along the pile foundation can be determined based on the location of the continuous pile foundation defect along the pile foundation in the test results. The radial dimension of the defect along the pile foundation can be determined based on the location of the pile foundation defect that appears continuously at a similar horizontal position in the temperature measuring tubes arranged along the radial direction of the pile foundation.

[0048] (3) This detection method mainly uses thermal response to detect pile foundation defects. It is a non-destructive testing method and will not have a negative impact on the pile body.

[0049] (4) This testing method can directly determine whether there is a defect in the tested pile foundation at this location by comparing the temperature-time curve, which is simple and intuitive. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the operation of the detection component and detection device in Embodiment 1 of the present invention;

[0051] Figure 2 This is a diagram showing the layout of the temperature measuring tube in Embodiment 1 of the present invention;

[0052] Figure 3 This is a diagram showing the layout of the temperature measuring tube in Embodiment 2 of the present invention;

[0053] Figure 4 This is a schematic diagram of the abnormal curve and the fitted time-temperature curve in Example 1 of this embodiment;

[0054] Figure 5 This is a schematic diagram illustrating the determination of the standard time-temperature curve range in Example 1.

[0055] Figure 6 This is a schematic diagram of the operation of the detection component and detection device in Embodiment 2 of the present invention.

[0056] In the diagram, 1. Heat source pipe; 2. Temperature measuring pipe; 3. Short pipe; 4. Pile foundation; 5. Heating control cabinet; 6. Data acquisition unit; 7. Temperature sensor; 8. Heat source head; 9. Plug; 10. Data cable; 11. Wire; 12. Thin wire; 13. Reinforcing cage. Detailed Implementation

[0057] The present invention will now be described in further detail with reference to the accompanying drawings.

[0058] Example 1.

[0059] Figure 1 This is a schematic diagram of the operation of the detection component and detection device in Embodiment 1 of the present invention. Figure 1 As can be seen, the present invention provides a method for detecting the integrity of pile foundations based on thermal response. A set of detection components is pre-embedded in the pile foundation 4 during the pouring process. The detection components include a heat source pipe 1, N identical temperature measuring pipes 2, and N+1 plugs 9. The heat source pipe 1 is pre-embedded at the center of the pile foundation 4 along the axial direction of the pile foundation 4. The N temperature measuring pipes 2 are pre-embedded in the pile foundation 4 in a parallel and evenly distributed manner with the heat source pipe 1. The plugs 9 are pre-embedded at the bottom of the heat source pipe 1 and each temperature measuring pipe 2, and this position is flush with the bottom of the pile foundation 4. The tops of the heat source pipe 1 and the N temperature measuring pipes 2 are flush with the top of the pile foundation 4, and the top of the pile foundation 4 is slightly higher than the ground surface.

[0060] In this embodiment, both the heat source tube 1 and the temperature measuring tube 2 are made of metal.

[0061] In this embodiment, the pile foundation 4 is a circular cast-in-place reinforced concrete pile with a diameter of not less than 1.5m. Additionally, by... Figure 1 It can be seen that the top of pile foundation 4 has no closed structure, that is, heat source pipe 1 and temperature measuring pipe 2 are both hollow straight pipes, and the tops of pile foundation 4, heat source pipe 1 and temperature measuring pipe 2 are directly connected to the atmosphere.

[0062] The detection method includes the following steps:

[0063] Step 1, Test Preparation

[0064] The testing preparation includes the preparation of the testing device, which includes a heat source 8, N+1 temperature sensors 7, a heating control cabinet 5, and a temperature acquisition device 6.

[0065] During testing, the heat source 8 and one temperature sensor 7 are placed in the heat source pipe 1, and the other N temperature sensors 7 are placed in N temperature measuring tubes 2 respectively. The heating control cabinet 5 is connected to the heat source 8 through the wire 10 to supply heat to the heat source 8 with constant power. The data acquisition unit 6 is connected to N+1 temperature sensors 7 through the data line to continuously record the temperature data of each temperature sensor 7 and automatically generate the required time-temperature curve.

[0066] Step 2, Parameter Setting

[0067] Set up M detection points along the axis of pile foundation 4, and denote any one of these detection points as position W. m , m is the location number, m = 1, 2, ..., M; where, in the detection at location W1, the vertical distance from the heat source 8 and the N+1 temperature sensors 7 to the top surface of the pile foundation 4 is h; location W m During the detection, the vertical distance between the heat source 8 and the N+1 temperature sensors 7 and the top surface of the pile foundation 4 was m×h; at position W M During the detection, the heat source 8 and N+1 temperature sensors 7 are located at the bottom of the pile foundation 4, and the vertical distance between the bottom and the top surface of the pile foundation 4 is M×h.

[0068] It is set that P rounds of detection are performed for each of the M positions, and the heating time for each round of detection is set to be the same, which is denoted as the duration t;

[0069] The detection is set to start from position W1 and proceed in the order of position number m.

[0070] In this embodiment, N+1 temperature sensors 7 and heat sources 8 are respectively tied to the lower ends of N+2 graduated thin wires 12. That is, the temperature sensors 7 and heat sources 8 are placed in designated positions in the heating tube 1 and the temperature measuring tube 2 by means of suspension. Then, the upper ends of the thin wires 12 are fixed to a stable structure to keep the height of the temperature sensors 7 and heat sources 8 from the top constant during detection at each position.

[0071] Step 3, Detection of position W1

[0072] A heat source 8 and a temperature sensor 7 are placed inside the heat source pipe 1. Simultaneously, N temperature sensors 7 are placed inside N temperature measuring pipes 2 respectively, and are maintained in the detection of the entire position W1. The vertical distance between the heat source 8 and the N+1 temperature sensors 7 and the top surface of the pile foundation 4 is h.

[0073] Step 3.1, First Round of Testing

[0074] Open the heating control cabinet 5 and heat the heat source 8 with constant power. The data acquisition device 6 simultaneously records the time and temperature data of N+1 temperature sensors 7 during the heating process.

[0075] After the heating time t is reached, the heating control cabinet 5 is turned off and ventilation is introduced into the heat source pipe 1 until the temperature of N+1 temperature sensors 7 returns to the value before heating. The data acquisition device 6 synchronously records the time and temperature data of N+1 temperature sensors 7 during the cooling process.

[0076] After cooling, for each temperature sensor 7 in the temperature measuring tube 2, the data acquisition unit 6 outputs a time-temperature curve. That is, the first round of detection at position W1 yields a total of N time-temperature curves. The starting point of the time-temperature curve coincides with the origin of a planar coordinate system, where the vertical axis represents temperature and the horizontal axis represents time.

[0077] In this embodiment, before the location W1 is detected, the heat source pipe 1 and the temperature measuring pipe 2 are cleaned to ensure that there are no impurities.

[0078] Step 3.2, repeat step 3.1 for P wheels to obtain P×N time-temperature curves for position W1, that is, for each temperature sensor 7 in the temperature measuring tube 2, P time-temperature curves are obtained by detection;

[0079] Each temperature sensor 7 inside the temperature measuring tube 2 is called an effective sensor, and the P curves corresponding to each effective sensor detected at position W1 are recorded as a family of curves. That is, N families of curves for N effective sensors are obtained through step 3.2.

[0080] Step 3.3: Perform error analysis and discrete fitting on the N families of curves respectively to obtain a fitted time-temperature curve for each effective sensor at position W1;

[0081] That is, through error analysis and discrete fitting, N fitting time-temperature curves of N effective sensors were obtained in the detection of position W1.

[0082] In this embodiment, the process of performing error analysis and discrete fitting on N families of curves to obtain a fitted time-temperature curve for each effective sensor at position W1 is as follows:

[0083] First, fit the data points of the P time-temperature curves in each family of curves obtained in step 3.2 to obtain a fitted heating temperature-time curve for the error to be removed. Then, compare the P time-temperature curves in each family of curves with the fitted heating temperature-time curve for the error to be removed in that family of curves, and identify the time-temperature curves whose curve correlation coefficient is less than the preset standard value R of curve correlation coefficient as error curves.

[0084] Then, extract the data points of each heating temperature-time curve from the remaining time-temperature curve family after removing the error curves in each curve family, and perform curve fitting on all the extracted data points to obtain the fitted time-temperature curve.

[0085] For details on the error curve and the state of the fitting time-temperature curve, please refer to... Figure 4 .

[0086] Step 4, Position W m Detection

[0087] Following the sequence m = 1, 2, ..., M, the heat source 8 and N+1 temperature sensors 7 are moved downwards by h each time, until they reach position W. m Then, perform a detection and processing step according to steps 3.1-3.3 to obtain a location W. m N fitted time-temperature curves;

[0088] After all M positions are completed, a total of M×N fitted time-temperature curves are obtained. Any one of these curves is denoted as the fitted curve Q. mn Where n is the number of temperature measuring tube 2, denoted as temperature measuring tube serial number, n = 1, 2, ..., N.

[0089] The combination of the location number m and the temperature measuring tube number n defines the location of each detection point on pile foundation 4.

[0090] Step 5, Data Analysis and Processing

[0091] Step 5.1, combine the M×N fitted curves Q obtained in step 4. mn The temperature measuring tube 2 is divided into Z groups according to its radial position, and any group in the Z groups is denoted as the z-th group, where z is the group number, z = 1, 2, ..., Z;

[0092] Step 5.2, for each fitted curve Q in the z-th group mn Each fitted curve is compared with the standard time-temperature curve range corresponding to a group z, and the fitted curves Q that do not completely fall within the standard time-temperature curve range are identified. mn Recorded as the final anomaly curve;

[0093] Step 5.3: Following the method in Step 5.2, evaluate each curve in group Z to obtain M×N fitted curves Q. mn All final anomaly curves:

[0094] The location of the detection point is determined by the position number m corresponding to the final abnormal curve and the temperature measuring tube number n, and it is identified as the location of the pile foundation defect.

[0095] Figure 5 A schematic diagram illustrating the determination of the standard time-temperature curve range in this embodiment is provided. Figure 5 As can be seen, in this embodiment, the process for determining the range of the standard time-temperature curve is as follows:

[0096] Steps 3-4 are repeated K times using the test pile to obtain K×M×N standard fitted time-temperature curves. This family of standard curves is called the original family of standard curves.

[0097] The original standard curve family is divided into Z groups according to the radial position of the temperature measuring tube 2, and any one of the curve families is denoted as the standard curve family corresponding to the z-th group. The range enclosed by the upper and lower envelopes of the standard curve family corresponding to the z-th group is denoted as the standard time-temperature curve range corresponding to the z-th group.

[0098] The test pile is a defect-free pile foundation made with reference to the information of pile foundation 4. The information of pile foundation 4 includes the material of pile foundation 4, the length and diameter of pile foundation 4, and the material, size and spatial location information of heat source pipe 1 and temperature measuring pipe 2.

[0099] Figure 2 The arrangement of the temperature measuring tubes 2 in Example 1 is shown in the figure. As can be seen from the figure, in this example, there are 12 temperature measuring tubes 2, divided into two groups, i.e., Z=2.

[0100] First, the six temperature measuring tubes 2 of the first group are evenly distributed on the steel cage 13 at the edge of the pile foundation 2. Then, on any cross section of the pile foundation 4, starting from the position of the six temperature measuring tubes 2, six rays are drawn towards the axis of the pile foundation 4, and one temperature measuring tube 2 is arranged on each ray at equal intervals D.

[0101] In actual construction, D = 0.3-0.5m.

[0102] Example 2.

[0103] Figure 3 and Figure 6 This is a schematic diagram of the operation of the detection component and detection device in Embodiment 2 of the present invention.

[0104] Depend on Figure 3 As can be seen, in this embodiment, there are 18 temperature measuring tubes 2, divided into three groups, i.e., Z=3. First, the 6 temperature measuring tubes 2 of the first group are evenly distributed on the steel cage 13 at the edge of the pile foundation 2. Then, on any cross-section of the pile foundation 4, taking the position of the 6 temperature measuring tubes 2 as the starting point, 6 rays are drawn towards the axis of the pile foundation 4. Two reference points are set on each ray at equal intervals D. In the cross-section, with the center of the cross-section as the base point, two temperature measuring tubes 2 are placed at positions 20° and 40° clockwise from the two reference points on each ray, respectively.

[0105] Depend on Figure 6 As can be seen, the top of the pile foundation 4 has an upper structure. The detection component also includes N+1 short pipes 3. One end of each of the N+1 short pipes 3 is connected to the top of the heat source pipe 1 and the temperature measuring pipe 2, respectively. The other end passes through the side wall of the pile foundation 4 and is connected to the atmosphere. The position of the short pipes 3 is above the ground surface and below the top surface of the pile foundation 4.

Claims

1. A method for detecting the integrity of pile foundations based on thermal response, characterized in that, The pile foundation (4) is pre-embedded with a set of detection components during the pouring process. The detection components include a heat source pipe (1), N identical temperature measuring pipes (2) and N+1 plugs (9). The heat source pipe (1) is pre-embedded at the center of the pile foundation (4) along the axial direction of the pile foundation (4). The N temperature measuring pipes (2) are parallel to the heat source pipe (1) and pre-embedded in the pile foundation (4) in a uniform distribution. The plugs (9) are pre-embedded at the bottom of the heat source pipe (1) and each temperature measuring pipe (2), and this position is flush with the bottom of the pile foundation (4). The tops of the heat source pipe (1) and the N temperature measuring pipes (2) are flush with the top of the pile foundation (4). The top of the pile foundation (4) is slightly higher than the ground surface. The detection method includes the following steps: Step 1, Test Preparation The testing preparation includes the preparation of the testing device, which includes a heat source (8), N+1 temperature sensors (7), a heating control cabinet (5), and a temperature acquisition device (6). During testing, the heat source (8) and a temperature sensor (7) are placed in the heat source tube (1), and the other N temperature sensors (7) are placed in N temperature measuring tubes (2). The heating control cabinet (5) is connected to the heat source (8) through wires (10) to supply heat to the heat source (8) at a constant power. The data acquisition device (6) is connected to N+1 temperature sensors (7) through data lines to continuously record the temperature data of each temperature sensor (7) and automatically generate the required time-temperature curve. Step 2, Parameter Setting Set up M detection points along the axis of the pile foundation (4), and denote any one of these detection points as position W. m m is the position number, m=1,2,...,M; where, in the detection at position W1, the vertical distance from the heat source (8) and N+1 temperature sensors (7) to the top surface of the pile foundation (4) is h; position W m In the detection, the vertical distance between the heat source (8) and the N+1 temperature sensors (7) and the top surface of the pile foundation (4) is m×h; at position W M In the detection, the heat source (8) and N+1 temperature sensors (7) are located at the bottom of the pile foundation (4), and the vertical distance between the bottom and the top surface of the pile foundation (4) is M×h. It is set that P rounds of detection are performed for each of the M positions, and the heating time for each round of detection is set to be the same, which is denoted as the duration t; The detection is set to start from position W1 and proceed in the order of position number m; Step 3, Detection of position W1 A heat source head (8) and a temperature sensor (7) are placed inside the heat source pipe (1). Simultaneously, N temperature sensors (7) are placed in N temperature measuring pipes (2) respectively. During the detection of the entire position W1, the vertical distance between the heat source head (8) and the N+1 temperature sensors (7) and the top surface of the pile foundation (4) is h. Step 3.1, First Round of Testing Open the heating control cabinet (5) and heat the heat source (8) with constant power. The data acquisition device (6) synchronously records the time and temperature data of N+1 temperature sensors (7) during the heating process. After the heating time t is reached, the heating control cabinet (5) is closed and ventilation is introduced into the heat source pipe (1) until the temperature of N+1 temperature sensors (7) is restored to the value before heating. The collector (6) synchronously records the time and temperature data of N+1 temperature sensors (7) during the cooling process. After cooling, for each temperature sensor (7) in the temperature measuring tube (2), the collector (6) outputs a time-temperature curve. That is, the first round of detection at position W1 yields a total of N time-temperature curves. The starting point of the time-temperature curve coincides with the origin of a plane coordinate system. The vertical axis of the coordinate system is temperature, and the horizontal axis is time. Step 3.2, repeat step 3.1 for P wheels to obtain P×N time-temperature curves at position W1, that is, for each temperature sensor (7) in the temperature measuring tube (2), P time-temperature curves are obtained by detection; The temperature sensor (7) inside each temperature measuring tube (2) is called an effective sensor, and the P curves corresponding to each effective sensor detected at position W1 are recorded as a family of curves, that is, the N families of curves of N effective sensors are obtained through step 3.

2. Step 3.3: Perform error analysis and discrete fitting on the N families of curves respectively to obtain a fitted time-temperature curve for each effective sensor at position W1; That is, after error analysis and discrete fitting, N fitting time-temperature curves of N effective sensors were obtained in the detection of position W1. Step 4, Position W m Detection Following the order m=1,2,...,M, the heat source (8) and N+1 temperature sensors (7) are moved downwards by h each time, until they reach position W. m Then, perform a detection and processing step according to steps 3.1-3.3 to obtain a location W. m N fitted time-temperature curves; After all M positions are completed, a total of M×N fitted time-temperature curves are obtained. Any one of these curves is denoted as the fitted curve Q. mn Where n is the number of the temperature measuring tube (2), denoted as the temperature measuring tube serial number, n=1,2,...,N; The combination of the location number m and the temperature measuring tube number n defines the location of each detection point on the pile foundation (4); Step 5, Data Analysis and Processing Step 5.1, combine the M×N fitted curves Q obtained in step 4. mn The temperature measuring tube (2) is divided into Z groups according to its radial position, and any group in the Z group is denoted as the z-th group, where z is the group number, z=1,2,...,Z; Step 5.2, for each fitted curve Q in the z-th group mn Each fitted curve is compared with the standard time-temperature curve range corresponding to a group z, and the fitted curves Q that do not completely fall within the standard time-temperature curve range are identified. mn This is recorded as the final anomaly curve; Step 5.3: Following the method in Step 5.2, evaluate each curve in group Z to obtain M×N fitted curves Q. mn All final anomaly curves: The location of the detection point is determined by the position number m corresponding to the final abnormal curve and the temperature measuring tube number n, and it is identified as the location of the pile foundation defect.

2. The pile foundation integrity detection method based on thermal response according to claim 1, characterized in that, Before the location W1 is detected, the heat source pipe (1) and the temperature measuring pipe (2) are cleaned to ensure that there are no impurities.

3. The method for detecting pile foundation integrity based on thermal response according to claim 1, characterized in that, The process of performing error analysis and discrete fitting on the N family of curves in step 3.3 to obtain a fitted time-temperature curve for each effective sensor at position W1 is as follows: First, fit the data points of the P time-temperature curves in each family of curves obtained in step 3.2 to obtain a fitted heating temperature-time curve for the error to be removed. Then, compare the P time-temperature curves in each family of curves with the fitted heating temperature-time curve for the error to be removed in that family of curves, and identify the time-temperature curves whose curve correlation coefficient is less than the preset standard value R of curve correlation coefficient as error curves. Then, extract the data points of each heating temperature-time curve from the remaining time-temperature curve family after removing the error curves in each curve family, and perform curve fitting on all the extracted data points to obtain the fitted time-temperature curve.

4. The pile foundation integrity detection method based on thermal response according to claim 1, characterized in that, The process for determining the range of the standard time-temperature curve is as follows: Steps 3 and 4 are repeated K times using the test pile to obtain K×M×N standard fitted time-temperature curves. These K×M×N standard fitted time-temperature curves are called the original standard curve family. The original standard curve family is divided into Z groups according to the radial position of the temperature measuring tube (2), and any one of the curve families is recorded as the standard curve family corresponding to the z-th group. The range enclosed by the upper envelope and lower envelope of the standard curve family corresponding to the z-th group is recorded as the standard time-temperature curve range corresponding to the z-th group. The test pile is a defect-free pile foundation made with reference to the information of the pile foundation (4). The information of the pile foundation (4) includes the material of the pile foundation (4), the length and diameter of the pile foundation (4), and the material, size and spatial location information of the heat source pipe (1) and the temperature measuring pipe (2).

5. The method for detecting pile foundation integrity based on thermal response according to claim 1, characterized in that, The pile foundation (4) is a circular cast-in-place reinforced concrete pile with a diameter of not less than 1.5m.

Images