Centrifugal test pile bearing characteristic test method and device with multi-working condition synchronous loading

Abstract

The application relates to the technical field of geotechnical engineering testing, in particular to a centrifugal test pile bearing property test method and device for multi-working-condition synchronous loading. The method comprises the following steps: under each load loading level in the step-by-step switching mode, corresponding pile top loads are synchronously applied to each test pile by gravity loads generated by each loading component in a centrifugal field. During the synchronous loading process, monitoring data of each test pile is collected. According to fluctuation characteristics of the monitoring data of each test pile in the synchronous loading process, a comprehensive deviation value of each test pile is determined. Abnormality of the test pile is determined according to the comprehensive deviation value, when it is determined that the test pile is abnormal, the synchronous loading of the current load loading level is paused, a loading posture of the loading component corresponding to the abnormal test pile is adjusted, and after the adjustment is completed, the synchronous loading of the current load loading level is restored. Therefore, the accuracy of a pile foundation bearing property test result is improved.

Description

Technical Field

[0001] This application relates to the field of geotechnical engineering testing technology, specifically to a test method and apparatus for the bearing characteristics of centrifugal test piles under simultaneous loading under multiple working conditions. Background Technology

[0002] In geotechnical engineering, piles are widely used in onshore buildings, offshore wind turbines, and fixed offshore platforms due to their high bearing capacity and wide applicability. In reclaimed areas and soft soil areas, soil consolidation settlement can easily induce negative skin friction on the pile sides, affecting the bearing capacity of the pile foundation. Therefore, research on the bearing characteristics of pile foundations and the pile-soil interaction mechanism is particularly important.

[0003] Centrifuge testing technology for geotechnical piles simulates the stress state of pile foundations by restoring the stress level of the prototype in a centrifugal force field, making it an effective means of studying the bearing characteristics of pile foundations. Current centrifuge tests primarily employ servo loading systems for pile top loading, using servo motors or hydraulic actuators to independently control individual model piles. Furthermore, schemes have been developed that apply the same load to multiple model piles using rigid loading plates, and schemes that use multi-channel servo actuators to control the loading of each individual pile separately. However, these servo-based loading methods are complex, have low long-term operational stability in a centrifugal environment, and are difficult to obtain pile foundation response data under multiple load conditions simultaneously in a single test. Multiple independent tests are required for comparison under various load conditions, and differences in soil preparation and consolidation processes between different batches of tests affect data comparability.

[0004] Therefore, how to achieve synchronous and stable loading of multiple model piles under different load conditions in a single centrifugal test, so as to eliminate the influence of environmental differences between different batches of tests, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the technical problem of improving the accuracy of pile foundation bearing capacity test results, the purpose of this application is to provide a method and apparatus for testing the bearing capacity of centrifugal piles under multi-condition synchronous loading. The specific technical solution adopted is as follows: Firstly, a method for testing the bearing characteristics of centrifugal test piles under multi-condition synchronous loading is provided. This method includes: determining the target mass of the loading component corresponding to each test pile based on the target centrifugal acceleration and the prototype load; synchronously applying the corresponding pile top load to each test pile under progressively switching load levels through the gravity load generated by each loading component in the centrifugal force field; collecting monitoring data from each test pile during synchronous loading and arranging the collected data in chronological order to form a collection sequence for each test pile under each monitoring data type; determining the comprehensive deviation value of each test pile based on the fluctuation characteristics of the monitoring data during synchronous loading; determining anomalies in the test piles based on the comprehensive deviation value; pausing synchronous loading at the current load level when an abnormal test pile is identified, adjusting the loading posture of the loading component corresponding to the abnormal test pile, and resuming synchronous loading at the current load level after adjustment.

[0006] One possible approach is to determine the target mass of the loaded component corresponding to each test pile, including: determining the centrifugal acceleration multiple based on the ratio of the target centrifugal acceleration to the gravitational acceleration; and obtaining the prototype load corresponding to each test pile.

[0007] The target mass of each loaded component is determined based on the conversion relationship between prototype load, centrifugal acceleration multiple, and gravitational acceleration.

[0008] As one possible approach, each loading component is placed inside a corresponding guide sleeve. The bottom of the loading component is a flat surface, and the top of the test pile is provided with a spherical contact surface. The bottom flat surface of the loading component and the spherical contact surface form a spherical-flat contact, so that the gravity load of the loading component is transmitted along the axial direction of the test pile.

[0009] One possible approach is to determine the comprehensive deviation value of each test pile, including: for each monitoring data type, calculating the variance of the monitoring data for each test pile in the acquisition sequence, and using the variance as a quantification of the data dispersion of the test pile under the corresponding monitoring data type; for each monitoring data type, determining the relative deviation of the current test pile relative to the other test piles under the corresponding monitoring data type based on the difference between the variance of the current test pile and the variances of the other test piles; and processing the relative deviation of the same test pile under each monitoring data type using a preset data fusion algorithm, and determining the comprehensive deviation value of each test pile based on the processing results.

[0010] One possible approach is to determine anomalies in the test piles based on a comprehensive deviation value. This includes: determining the degree of load deviation of the current test pile based on the difference between the pile top load at the current monitoring time and a preset load value. If the load deviation exceeds a first preset threshold, or the comprehensive deviation value exceeds a second preset threshold, the current test pile is deemed to be abnormal. The first preset threshold is determined based on the maximum value of the load deviation during prior normal synchronous loading, and the second preset threshold is determined based on the average comprehensive deviation value of each test pile during prior normal synchronous loading.

[0011] One possible approach is to adjust the loading posture of the loading member corresponding to the abnormal test pile, including: adjusting the alignment of the loading member relative to the axis of the corresponding test pile, so that the vertical axis of the loading member coincides with the vertical axis of the test pile. After the axis alignment is adjusted, the vertical movement freedom of the loading member within the corresponding guide sleeve is adjusted to remove any movement resistance during vertical movement. After the movement resistance is removed, the free vertical movement of the loading member within the guide sleeve is restored, completing the adjustment of the loading posture.

[0012] As one possible implementation, the method further includes: obtaining the settlement increment of each test pile at the current monitoring time relative to the previous monitoring time under the current load level; determining the judgment coefficient of each test pile based on the proportion of the comprehensive deviation value of each test pile to the sum of the comprehensive deviation values ​​of all test piles; determining the equivalent settlement of the entire synchronous loading based on the settlement increment of each test pile and the corresponding judgment coefficient of each test pile; when the equivalent settlement is less than a preset settlement threshold, determining that the current load level has reached a stable state, switching to the next load level, and continuing synchronous loading.

[0013] As one possible approach, the method further includes: during the switching of different load levels, constructing a load-displacement curve for each test pile based on the pile top load and corresponding pile top displacement. When the displacement increment of the load-displacement curve of the test pile continuously increases without convergence trend during a consecutive preset number of load levels, it is determined that the test pile has reached the ultimate bearing capacity state, the current loading state of the test pile that has reached the ultimate bearing capacity state is locked, and the increase of the load on the test pile is terminated.

[0014] As one possible approach, the monitoring data also includes the axial strain of each test pile and the pore water pressure of the surrounding soil. The axial strain of the pile is collected using strain gauges placed at equal intervals along the axial direction of the test pile. The pore water pressure of the surrounding soil is collected using pore water pressure gauges placed in the soil layer around the pile.

[0015] Secondly, a multi-condition synchronous loading centrifugal test pile bearing characteristic testing device is provided, comprising: The loading device includes multiple loading components and corresponding guide sleeves. Each loading component has a different mass and is respectively set inside the corresponding guide sleeve. It is used to apply the corresponding load level of the pile top load to each test pile under the action of centrifugal force.

[0016] The mounting device is fixed to the top of the centrifuge model box to fix the loading device above the centrifuge model box and to make the loading direction of the loading component consistent with the centrifugal acceleration direction.

[0017] The model pile device includes a test pile and a spherical contact surface set on the top of the test pile. The test pile is used to bear and transfer the load at the top of the pile to simulate the stress and deformation characteristics of the prototype pile foundation. The spherical contact surface is used to contact the bottom plane of the loading member to realize the transfer of load along the axial direction of the test pile.

[0018] Centrifuge model box is used to fill the test soil and fix the position of each test pile, providing a closed test space for pile foundation bearing and loading tests.

[0019] The monitoring system is used to collect real-time monitoring data of each test pile during synchronous loading at progressively changing load levels. The collected data is arranged chronologically to form a collection sequence. Based on the fluctuation characteristics of the monitoring data in the collection sequence, the system determines the comprehensive deviation value of each test pile and uses this comprehensive deviation value to determine anomalies. It is also used to trigger a pause in synchronous loading at the current load level when an abnormal test pile is detected, and to trigger a resumption of synchronous loading at the current load level after the loading attitude adjustment is completed.

[0020] This application has the following beneficial effects: By employing gravity loading to simultaneously apply different loads to multiple model piles in the same centrifuge test, the comparability of data due to differences in soil preparation and consolidation states in multiple independent tests is eliminated. A closed-loop control mechanism is formed by determining the comprehensive deviation value based on the fluctuation characteristics of the monitoring data and identifying anomalies. When an anomaly is detected, loading is paused, the attitude is adjusted, and loading is resumed, ensuring the synchronicity and stability of the entire multi-condition synchronous loading process. This also avoids the problems of low stability of the servo system in a centrifugal environment and the complexity of multi-channel coordination control. In this way, accurate and comparable pile foundation bearing capacity data under multiple conditions can be efficiently obtained in a single centrifuge test, thereby improving the accuracy of pile foundation bearing capacity test results. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating a method for testing the bearing characteristics of a centrifugal test pile under simultaneous loading under multiple working conditions, provided in one embodiment of this application. Figure 2This is a schematic diagram of a centrifugal test pile bearing characteristic test device under multi-condition synchronous loading provided in one embodiment of this application; Figure 3 This is an overall schematic diagram of a gravity loading structure provided in one embodiment of this application; Figure 4 This is an overall front view of a gravity-loaded structure provided in one embodiment of this application; Figure 5 This is a schematic diagram of the overall installation of a centrifuge model box according to one embodiment of this application; Figure 6 This is a cross-sectional schematic diagram of a loading device provided in one embodiment of this application; Figure 7 This is a partial enlarged view of a loading device provided in one embodiment of this application; Figure 8 This is a cross-sectional schematic diagram of a gravity loading structure provided in one embodiment of this application; Figure 9 This is a schematic diagram of a model pile device provided in one embodiment of this application. Detailed Implementation

[0022] The following description, in conjunction with the accompanying drawings, details the specific scheme of the centrifugal test pile bearing characteristic test method under multi-condition synchronous loading provided in this application.

[0023] Please see Figure 1 It shows a flowchart of a method for testing the bearing characteristics of centrifugal test piles under multi-condition synchronous loading according to an embodiment of this application, as follows: Figure 1 As shown, the method includes the following steps: S11-S15.

[0024] S11. Determine the target mass of the loading component corresponding to each test pile based on the target centrifugal acceleration and the prototype load.

[0025] In this embodiment, the target centrifugal acceleration refers to the preset centrifugal acceleration value achieved during centrifuge operation. It is determined comprehensively based on the prototype scale, soil stress level, actual model box space constraints, and centrifuge rated capacity, and is used to ensure that the stress field of the model in the centrifugal force field satisfies a similarity relationship with the stress field of the prototype project. The prototype load refers to the vertical load value borne by the actual engineering pile foundation under design conditions, which can be obtained from the engineering survey report or pile foundation structural design drawings. The loading component is a physical element used to generate gravity loads; its mass determines the magnitude of the gravity load generated under a given centrifugal acceleration. The target mass refers to the mass required for the loading component to generate a gravity load equal to the pile top load required to be applied to the test pile under the target centrifugal acceleration.

[0026] In centrifuge model tests, physical quantities at the model scale and those at the prototype scale must follow a similarity conversion relationship to ensure that the test results accurately reflect the actual stress and deformation behavior of the prototype. Due to the high cost and long testing cycle of each centrifuge run, multiple load conditions must be applied simultaneously in a single test. Different load conditions correspond to different pile top load values, which in turn correspond to loading components of different masses. Therefore, before performing simultaneous loading, it is necessary to calculate the target mass of the loading component corresponding to each test pile based on the target centrifugal acceleration and the prototype load. This ensures that after the centrifugal acceleration stabilizes, the gravity load generated by each loading component is accurately equal to the pile top load required for each test pile.

[0027] One possible approach to determining the target mass of the loaded component corresponding to each test pile includes: determining the centrifugal acceleration factor based on the ratio of the target centrifugal acceleration to gravitational acceleration; obtaining the prototype load corresponding to each test pile; and determining the target mass of each loaded component based on the conversion relationship between the prototype load, the centrifugal acceleration factor, and gravitational acceleration.

[0028] Specifically, the aforementioned centrifugal acceleration multiple refers to the ratio of the centrifugal acceleration generated during centrifuge operation to the standard gravitational acceleration, used to convert physical quantities at the model scale to the prototype scale. The centrifugal acceleration multiple is determined by dividing the target centrifugal acceleration by the standard gravitational acceleration; the resulting ratio is used as the centrifugal acceleration multiple. The prototype load refers to the vertical load value borne by the actual engineering pile foundation corresponding to each test pile under design conditions, obtained through engineering survey reports or pile foundation structural design drawings. The conversion relationship refers to the mathematical correlation between the prototype load, the centrifugal acceleration multiple, and the standard gravitational acceleration. Based on this conversion relationship, the mass required for the loaded component to generate the corresponding pile top load under the target centrifugal acceleration can be calculated.

[0029] In centrifugal tests with simultaneous loading under multiple conditions, each test pile requires a different pile top load, which is provided by the gravity load generated by the loading member in the centrifugal force field. Under a given centrifugal acceleration multiple, the gravity load generated by the loading member is proportional to its mass. Therefore, to achieve different pile top loads for each test pile, a loading member with a corresponding target mass needs to be configured for each test pile. The centrifugal similarity principle establishes the conversion rules between physical quantities at the model scale and the prototype scale. Based on this centrifugal similarity principle, the target mass of each loading member can be calculated through the conversion relationship between the prototype load, the centrifugal acceleration multiple, and the standard gravity acceleration. The target mass is determined by the following formula: in, The target mass of the loaded component is expressed in kilograms; P is the prototype load corresponding to the test pile, expressed in Newtons. This is a multiple of the centrifugal acceleration, dimensionless; The acceleration due to gravity is expressed in meters per second squared. Based on the above calculations, multiple sets of loading components with different masses were manufactured. The outer diameter of the loading component is smaller than the inner diameter of the guide sleeve, and a clearance is provided between the outer diameter of the loading component and the inner diameter of the guide sleeve. This clearance ensures that the loading component can move freely axially within the guide sleeve without jamming.

[0030] S12. Under each load level that is switched step by step, the corresponding pile top load is applied to each test pile synchronously through the gravity load generated by each loading component in the centrifugal force field.

[0031] The aforementioned load loading levels refer to each level value in a progressively increasing sequence of pile top load values ​​set for simulating pile foundation load performance testing. In this embodiment, an equal load grading method is adopted, with each load increment set at one-eighth to one-tenth of the ultimate load, and each load holding time not less than thirty minutes. The centrifugal force field refers to the centrifugal acceleration environment generated within the centrifugal model chamber during centrifuge operation. The loaded component is subjected to centrifugal force in this environment, resulting in a gravity load. The gravity load refers to the vertical force generated by the loaded component under centrifugal force in the centrifugal force field, the magnitude of which is equal to the product of the mass of the loaded component and the centrifugal acceleration at its location. The pile top load refers to the vertical force applied to the top of the test pile through the loaded component, used to simulate the superstructure load borne by the prototype pile foundation in actual engineering.

[0032] In centrifugal simulation tests, the loaded components are subjected to standard gravity only in a non-centrifugal state. The resulting gravity load is much smaller than the pile top load value required at the target centrifugal acceleration. Therefore, the loaded components can only generate a gravity load corresponding to the target mass in the centrifugal force field after the centrifuge reaches the target centrifugal acceleration. Simultaneously, to achieve synchronous acquisition of multi-condition data in a single test, all loaded components need to be subjected to force simultaneously in the same centrifugal acceleration field, thus synchronously applying their respective pile top loads to each test pile. Furthermore, testing the bearing capacity characteristics of pile foundations typically requires obtaining the load-displacement relationship curve, which is obtained through a step-by-step loading method. Therefore, the pile top load needs to be set to multiple load levels that switch sequentially, maintaining a constant load at each load level until the pile condition stabilizes before switching to the next load level.

[0033] Specifically, each loading component is housed within its corresponding guide sleeve. During the soil preparation stage, test soil is layered and filled into the centrifuge model box, controlling the soil density and moisture content within the range specified in the test design. The test soil undergoes vacuum saturation and pre-consolidation treatment to achieve a uniform saturation state, stable pore water pressure distribution, and elimination of residual stress generated during sample preparation. The bearing plate is fixed to the top of the centrifuge model box, and the guide sleeve is bolted to the designated position on the bearing plate, aligning the axis of the guide sleeve with the axis of the test pile. Ball bearings are inserted into the ball bearing channel on the inner wall of the guide sleeve, and the loading component corresponding to the target mass is placed into the guide sleeve, slowly lowered until the bottom of the loading component lightly touches the spherical contact surface at the top of the test pile. Loading modules for multiple test piles are installed simultaneously, ensuring that the bottom of each loading component maintains contact with the spherical contact surface at the top of the corresponding test pile. The test system, consisting of the loading device, model pile device, and centrifuge model box, is placed in the centrifuge basket. The centrifuge is started and accelerated in stages to the target centrifugal acceleration. The acceleration is increased step by step in increments of 10% of the centrifuge's rated acceleration. After each acceleration is completed, the centrifuge is kept running at a constant speed for 1 to 2 minutes. After the centrifuge's operating status stabilizes, the next acceleration stage is entered until the target centrifugal acceleration is reached. The centrifuge is kept running stably at the target centrifugal acceleration by the centrifuge's closed-loop servo control system.

[0034] In addition, before synchronous loading begins, centrifugal consolidation of the soil is required to ensure the stability of the initial test state. Therefore, after the centrifuge accelerates to the target centrifugal acceleration, the monitoring system collects real-time data on soil pore water pressure and pile strain. Under centrifugal force, the soil gradually consolidates, the pore water pressure gradually dissipates, and the pile strain gradually stabilizes. When the pore water pressure changes by less than 1 kPa for one consecutive hour, the soil is considered to have completed consolidation and entered the initial stable loading state. At this point, synchronous loading at the current load level begins.

[0035] S13. During the synchronous loading process, the monitoring data of each test pile is collected, and the collected monitoring data is arranged in chronological order to form the collection sequence of each test pile under each monitoring data type.

[0036] The aforementioned synchronous loading process refers to the period during which each test pile simultaneously bears its corresponding gravity load level in the same centrifugal acceleration field and generates a pile top response. Monitoring data refers to the physical quantity data characterizing the stress and deformation state of the test piles, collected in real time by the monitoring system during the synchronous loading process. The monitoring data includes at least the pile top load and pile top displacement for each test pile. The acquisition sequence refers to time-series data formed by arranging the monitoring data collected at various monitoring times in chronological order for the same test pile and under the same monitoring data type. Each data element in the acquisition sequence corresponds to a monitoring data value at a specific monitoring time.

[0037] During synchronous loading, monitoring data such as pile top load and pile top displacement of each test pile change over time. These changes reflect the stress response and deformation development process of the test pile under gravity load. However, data from a single monitoring moment only reflects the instantaneous state at that moment and cannot reveal the trend and fluctuation characteristics of the test pile's state over time. To quantitatively assess the state stability of each test pile during loading and the degree of deviation from the state of other test piles, it is necessary to acquire the monitoring data changes of each test pile at multiple consecutive monitoring moments. The acquisition sequence organizes the discrete monitoring moment data into a continuous time series in chronological order.

[0038] Specifically, during the synchronous loading process, the monitoring system collects the pile top load and pile top displacement values ​​of each test pile in real time according to a preset sampling frequency. The preset sampling period is determined based on the sampling capacity of the monitoring system, for example, it can be 0.1 seconds. For each test pile, the monitoring system arranges the collected pile top load values ​​in chronological order of monitoring time, forming a collection sequence for that test pile under the pile top load monitoring data type; it also arranges the collected pile top displacement values ​​in chronological order of monitoring time, forming a collection sequence for that test pile under the pile top displacement monitoring data type. The first data element in each collection sequence corresponds to the collected value at the first monitoring time after the start of the synchronous loading process, and the last data element corresponds to the collected value at the current monitoring time. The time interval between two adjacent data elements is equal to the preset sampling period. In this way, each test pile forms its own collection sequence under each monitoring data type.

[0039] In some embodiments, the monitoring data also include the axial strain of each test pile and the pore water pressure of the surrounding soil. The axial strain of the pile is collected using strain gauges placed at equal intervals along the axial direction of the test pile. The pore water pressure of the surrounding soil is collected using pore water pressure gauges placed in the surrounding soil layers. Earth pressure cells are also placed at representative soil layers around the pile to collect the radial earth pressure exerted by the surrounding soil on the test pile.

[0040] S14. Based on the fluctuation characteristics of the monitoring data of each test pile during the synchronous loading process, determine the comprehensive deviation value of each test pile.

[0041] The aforementioned fluctuation characteristics refer to the degree of fluctuation in the monitoring data of each test pile over time within the acquisition sequence. This degree of fluctuation is quantified by the statistical dispersion of the monitoring data within the acquisition sequence. The comprehensive deviation value is a comprehensive index used to quantitatively evaluate the consistency and stability of the overall loading state of each test pile relative to all test piles under synchronous loading conditions. The comprehensive deviation value is obtained by comprehensively processing the relative deviations of each test pile under multiple monitoring data types. The larger the comprehensive deviation value, the lower the stability of the state of that test pile compared to other test piles.

[0042] For each type of monitoring data, the variance of the monitoring data for each test pile is calculated based on the acquisition sequence of each test pile. The variance quantifies the degree of fluctuation of the test pile relative to its own mean under this type of monitoring data. Based on this, for the same type of monitoring data, the relative deviation of each test pile under that monitoring data type is determined by comparing the relative magnitude of the variance of each test pile with the variance of other test piles. For each test pile, the relative deviation obtained under each monitoring data type is input into a preset data fusion algorithm for comprehensive processing. The preset data fusion algorithm balances the relative deviation under each monitoring data type to eliminate the excessive influence of local fluctuations in a single monitoring data type on the overall evaluation, and finally outputs the comprehensive deviation value of each test pile.

[0043] S15. Based on the comprehensive deviation value, the test pile is judged to be abnormal. When the test pile is judged to be abnormal, the synchronous loading of the current load level is suspended, the loading posture of the loading component corresponding to the abnormal test pile is adjusted, and the synchronous loading of the current load level is restored after the adjustment is completed.

[0044] The aforementioned anomaly determination refers to the process of judging whether each test pile exhibits an abnormal loading state at the current monitoring moment based on the comprehensive deviation value and the degree of load offset at the pile top. Suspending synchronous loading at the current load level means that when the monitoring system determines the existence of an abnormal test pile, it suspends the loading operation at the current load level to prevent the abnormal state from escalating and avoid overall test failure or data distortion. Loading attitude refers to the spatial position and movement state of the loading component relative to the test pile, including the alignment of the loading component's vertical axis with the test pile's vertical axis and the vertical movement freedom of the loading component within the guide sleeve. Resuming synchronous loading at the current load level means that after the loading attitude adjustment of the abnormal test pile is completed, the monitoring system triggers the control operation to continue synchronous loading at the current load level for all test piles.

[0045] During multi-condition synchronous loading, although the comprehensive deviation value can identify test piles whose state deviates from the overall condition, the causes of deviation include axis alignment deviation, obstructed vertical movement, and local disturbance of the soil around the pile. Different causes require targeted adjustment measures. If the deviation is not identified and adjusted in time, the abnormal state of a single pile will gradually accumulate and intensify with the increase of the loading level, causing the test pile to reach its bearing limit state prematurely, while other test piles continue to be loaded, resulting in a loss of overall synchronization and a lack of comparability between the data of each condition. Therefore, it is necessary to make real-time judgments on each test pile based on the comprehensive deviation value, and to pause synchronous loading when an anomaly is detected, adjust the loading posture, eliminate the deviation factors, and then resume synchronous loading. Real-time judgment based on monitoring data and a closed-loop control mechanism of pause-adjustment-resumption are used to ensure the synchronization and stability of the entire multi-condition synchronous loading process.

[0046] The anomaly determination of test piles based on comprehensive deviation values ​​includes two methods: load deviation degree determination and comprehensive deviation value determination. In load deviation degree determination, the absolute value of the difference between the pile top load value at the current monitoring time and the preset load value is calculated, and then the ratio of this absolute value to the preset load value is calculated. This ratio is recorded as the load deviation degree. When the load deviation degree is greater than a first preset threshold, the current test pile is determined to be abnormal. In comprehensive deviation value determination, when the comprehensive deviation value of the current test pile at the current monitoring time is greater than a second preset threshold, the current test pile is determined to be abnormal. The first preset threshold is determined based on the maximum value of the load deviation degree during the prior normal synchronous loading process, and the second preset threshold is determined based on the average value of the comprehensive deviation values ​​of all test piles during the prior normal synchronous loading process. Meeting either of these two determination methods constitutes an anomaly determination for the current test pile.

[0047] After identifying an abnormal test pile, the monitoring system reports the abnormal test pile information and suspends synchronous loading at the current load level. Adjusting the loading posture of the loading component corresponding to the abnormal test pile involves adjusting the axis alignment and vertical movement freedom. In axis alignment adjustment, the loading component's axis alignment relative to the corresponding test pile is adjusted so that the vertical axis of the loading component coincides with the vertical axis of the test pile. After axis alignment adjustment, the vertical movement freedom of the loading component within the corresponding guide sleeve is adjusted. Any movement resistance during vertical movement is checked and eliminated to ensure the loading component can move freely vertically within the guide sleeve without additional frictional resistance or jamming. After eliminating movement resistance, free vertical movement of the loading component within the guide sleeve is restored. After completing the above loading posture adjustments, synchronous loading at the current load level is resumed. Each test pile continues to bear the corresponding pile top load at the current load level, maintaining a stable state of multi-condition synchronous loading. If the load deviation of the adjusted test pile returns to below the first preset threshold and the overall deviation value returns to below the second preset threshold, then the synchronous loading of subsequent loading levels will continue.

[0048] As one possible approach, the comprehensive deviation values ​​of each test pile are determined, including: S141-S143.

[0049] S141. For each type of monitoring data, calculate the variance of the monitoring data of each test pile in the acquisition sequence, and use the variance as the quantitative value of the data dispersion of the test pile under the corresponding monitoring data type.

[0050] The aforementioned variance refers to a statistic used to measure the degree of dispersion of monitoring data for each test pile relative to its own mean within the acquisition sequence. The quantified value of data dispersion is the numerical result obtained through variance calculation, which characterizes the degree of fluctuation of the monitoring data of the corresponding test pile around its mean under the corresponding monitoring data type.

[0051] For each monitoring data type, the variance of the monitoring data for each test pile is calculated based on the acquisition sequence of each test pile. Each data element in the acquisition sequence is the monitoring data value at the corresponding monitoring time. The arithmetic mean of all data elements in the acquisition sequence under that monitoring data type is used as the mean reference value. The square of the difference between each data element in the acquisition sequence and the mean reference value is calculated. The sum of all squared differences is divided by the total number of data elements in the acquisition sequence minus one. The result is the variance of the monitoring data for that test pile under that monitoring data type. Following this method, variance calculation is performed for each test pile under each monitoring data type. Each test pile corresponds to a variance value under each monitoring data type, which is the quantification of the data dispersion of that test pile under that monitoring data type. The larger the variance value, the more drastic the fluctuation of the monitoring data for that test pile under that monitoring data type.

[0052] S142. For each type of monitoring data, based on the difference between the variance of the current test pile and the variances of the other test piles, determine the relative deviation of the current test pile from the other test piles under the corresponding monitoring data type.

[0053] The aforementioned relative deviation refers to the relative magnitude of the variance of the monitoring data of the current test pile compared to the variances of the monitoring data of all other test piles under the same monitoring data type. It is used to characterize the deviation of the fluctuation degree of the current test pile under the corresponding monitoring data type from the overall level of synchronous loading. The relative deviation degree is a dimensionless quantitative indicator; the larger the value, the more significant the fluctuation deviation of the current test pile under that monitoring data type.

[0054] After calculating the quantified value of the data dispersion of each test pile under each monitoring data type using variance, the variance value of each test pile only reflects the degree of fluctuation of its own monitoring data around its mean, and cannot reflect the relative magnitude of the fluctuation of that test pile compared to other test piles. In the actual multi-pile synchronous loading process, all test piles are under the same centrifugal acceleration field and the same soil environment conditions. The variance of the monitoring data of each test pile should have a consistent trend. Therefore, the average variance of all test piles under the same monitoring data type can accurately represent the normal fluctuation benchmark under this working condition. Therefore, by analyzing the deviation of the current test pile's own variance from the average variance of all test piles, the degree of deviation of the current test pile relative to the other test piles can be intuitively quantified.

[0055] Based on the above logic, the degree of relative deviation is determined by the following formula: in, For the first The test pile and the remaining test piles were in the [number]th test pile. The relative deviation obtained by comparative analysis under different monitoring data types; and The first The first test pile and the first The first test pile during the loading process Variance of monitoring data under different monitoring data types; The total number of test piles subjected to synchronous loading; For all The test pile was in the first The arithmetic mean of the variances of the monitored data types; To adjust the parameter, a value of 0.001 is used to avoid the denominator being zero, which would prevent comparison.

[0056] S143. The relative deviation of the same test pile under various monitoring data types is processed by a preset data fusion algorithm, and the comprehensive deviation value of each test pile is determined based on the processing results.

[0057] The aforementioned preset data fusion algorithm refers to a preset algorithm rule used to comprehensively process the relative deviation of the same test pile under various monitoring data types. This algorithm normalizes the relative deviation under each monitoring data type and calculates the mean. In this embodiment, the preset data fusion algorithm specifically adopts the maximum-minimum normalization algorithm and weighted mean calculation. The normalization result refers to the value obtained after scaling the relative deviation under each monitoring data type to a uniform numerical range. The comprehensive deviation value refers to the comprehensive value obtained after averaging the normalization results of the same test pile under various monitoring data types. This value is used to comprehensively reflect the degree of deviation of the test pile from the overall state of other test piles during synchronous loading.

[0058] For each test pile, the relative deviation of the test pile under each monitoring data type is obtained. First, the maximum-minimum normalization algorithm is used to normalize the relative deviation of the same test pile under each monitoring data type, mapping the relative deviation under different monitoring data types to a unified numerical range of [0,1], so as to eliminate the influence of differences in units or numerical ranges between different monitoring data types on the fusion results. The normalization process is determined by the following relationship: in, For the first The test pile was in the first The relative deviation after normalization for different monitoring data types; and All The test pile was in the first The minimum and maximum values ​​of relative deviation for each type of monitoring data; This is the second adjustment parameter, with a value of 0.0001, used to prevent the denominator from being zero.

[0059] Then, the arithmetic mean of the normalized results for the same test pile under all monitoring data types is calculated, and the resulting average is used as the comprehensive deviation value for that test pile. The comprehensive deviation value is determined by the following formula: in, For the first The overall deviation value of each test pile; To monitor the total number of data types.

[0060] The above-mentioned comprehensive deviation value determined based on the preset data fusion algorithm The value range is [0,1]. This comprehensive deviation value is a comprehensive evaluation of the absolute deviation of the test pile from other test piles across multiple data dimensions. The larger the value, the more significant the difference in the overall state characteristics of the test pile compared to other test piles, and the higher the possibility of an abnormal loading state; the smaller the value, the more consistent the fluctuation pattern of the monitoring data of the test pile is with the overall level of synchronous loading.

[0061] As one possible approach, the test pile is assessed for anomalies by combining the deviation characteristics of the pile top load with the comprehensive deviation value, including: S151-S152.

[0062] S151. Determine the load offset degree of the current test pile based on the difference between the pile top load and the preset load value at the current monitoring time.

[0063] The aforementioned preset load value refers to the theoretical pile top load value corresponding to the current test pile under the current load level. This value is determined based on the target mass of the loaded component and the centrifugal acceleration at the current monitoring time. The difference between the pile top load and the preset load value is the algebraic difference between the actual pile top load value collected at the current monitoring time and the preset load value. The load deviation degree is a normalized value obtained by calculating the ratio of the absolute value of the above difference to the preset load value, used to reflect the deviation of the pile top load of the current test pile from the preset load value at the current monitoring time.

[0064] The comprehensive deviation value reflects the overall state deviation of the test pile relative to the synchronous loading process under various monitoring data types. This comprehensive deviation value is calculated by accumulating data from multiple monitoring times, and its changes are gradual, resulting in a relatively delayed response to sudden changes. However, during multi-condition synchronous loading, some abnormal states may manifest as sudden changes in the pile top load, such as a sudden surge or drop in the pile top load after the loading component is released. These sudden changes can be directly observed in the pile top load data at a single monitoring time. If only the comprehensive deviation value is relied upon for long-term state monitoring, such sudden anomalies may not be captured in time. Therefore, in order to take into account both long-term cumulative deviation and sudden change anomalies, this application adopts a parallel approach of rapid transient identification based on the degree of load offset and progressive cumulative judgment based on the comprehensive deviation value, thereby ensuring the timeliness and comprehensiveness of anomaly state judgment.

[0065] Specifically, at the current monitoring moment, the actual pile top load value of the current test pile is obtained through the monitoring system, the preset load value of the current test pile under the current load level is read, and the absolute value of the difference between the actual pile top load value and the preset load value is calculated. The absolute value is divided by the preset load value, and the resulting ratio is recorded as the load offset degree. The specific normalization method for the load offset degree is determined by the following relationship: in, This represents the degree of load offset of the current test pile; This represents the actual pile top load value of the current test pile at the current monitoring time; This is the preset load value for the current test pile under the current load level.

[0066] The load offset degree can normalize the deviation of the pile top load at the current monitoring time from the preset load value into a dimensionless relative proportion, thereby eliminating the influence of the difference in preset load values ​​between different load loading levels on the offset judgment. Following the above method, the load offset degree is calculated for each test pile at the current monitoring time.

[0067] It is important to note that in multi-condition synchronous loading, the preset load values ​​of each test pile differ significantly. Directly using absolute load values ​​for anomaly comparison would confuse the normal load ranges under different conditions, rendering the criterion ineffective. Therefore, this embodiment does not use the absolute load magnitude as the anomaly assessment standard. Instead, it uses the normalized relative deviation of the real-time load of the test pile relative to its theoretical preset load value as a unified dimensionless measurement scale, ensuring that instantaneous anomalies under each condition can be determined based on the same numerical benchmark.

[0068] S152. When the load deviation is greater than the first preset threshold, or the comprehensive deviation is greater than the second preset threshold, it is determined that there is an abnormality in the current test pile.

[0069] The first preset threshold is determined based on the maximum load deviation during the prior normal synchronous loading process, and the second preset threshold is determined based on the average comprehensive deviation of each test pile during the prior normal synchronous loading process. For example, the first preset threshold can be 0.05, and the second preset threshold can be 0.15, with the specific values ​​determined based on the actual data from the prior normal synchronous loading process. The prior normal synchronous loading process refers to a prior synchronous loading test process that uses the same test equipment and the same test procedure, and has been verified to have no abnormal judgment results. Before the first test, the above-mentioned first and second preset thresholds are obtained by conducting a set of standard loading tests in advance.

[0070] The load offset of the current test pile at the current monitoring time is obtained and compared with a first preset threshold. The comprehensive deviation value of the current test pile at the current monitoring time is obtained and compared with a second preset threshold. If the load offset is greater than the first preset threshold, or the comprehensive deviation value is greater than the second preset threshold, then the current test pile is determined to be abnormal at the current monitoring time. An abnormality determination is triggered if either of these two determination conditions is met.

[0071] The first preset threshold is determined as follows: The load offset of each test pile at each monitoring moment during the prior normal synchronous loading process is obtained, and the maximum value of the load offset is determined. This maximum value is used as the first preset threshold. The first preset threshold is essentially a relative deviation critical value established based on historical normal data. When the currently calculated load offset exceeds this historical maximum critical value, a sudden change anomaly judgment can be triggered.

[0072] The second preset threshold is determined as follows: the comprehensive deviation value of each test pile at each monitoring time during the normal synchronous loading process is obtained, the arithmetic mean of the comprehensive deviation values ​​of all test piles at all monitoring times is calculated, and the average value is used as the second preset threshold.

[0073] As one possible approach, the loading posture of the loading component corresponding to the abnormal test pile is adjusted, including: S153-S155.

[0074] S153. Adjust the alignment of the loading component with respect to the corresponding test pile axis so that the vertical axis of the loading component coincides with the vertical axis of the test pile.

[0075] Obtain the projection positions of the vertical axis of the currently loaded component onto the horizontal plane, and the projection positions of the vertical axis of the test pile onto the horizontal plane. Determine the horizontal offset direction and distance between the two projection positions. Based on the horizontal offset direction and distance, move the loaded component laterally within the horizontal plane until the projection position of the vertical axis of the loaded component onto the horizontal plane coincides with the projection position of the vertical axis of the test pile onto the horizontal plane. At this point, the vertical axes of the loaded component and the test pile are in a state of coincidence. After the axis alignment is adjusted, the contact uniformity between the various areas of the bottom plane of the loaded component and the spherical contact surface at the top of the test pile is restored, and the gravity load generated by the loaded component can be transmitted along the axial direction of the test pile without producing an eccentric component.

[0076] S154. After the axis alignment is adjusted, adjust the vertical movement degree of freedom of the loading component in the corresponding guide sleeve to remove the movement resistance state of the loading component during vertical movement.

[0077] The aforementioned vertical movement degree of freedom refers to the ability of the loading component to move freely in the vertical direction within the guide sleeve. This ability is determined by the gap between the outer wall of the loading component and the inner wall of the guide sleeve, as well as the fit between the balls and the ball channels. The motion-resistance state refers to the physical state in which the loading component, due to additional resistance during vertical movement, cannot slide freely along the axial direction of the guide sleeve. This state results in the gravity load generated by the loading component not being fully transferred to the top of the test pile.

[0078] Specifically, the motion resistance of the loading component during vertical movement is removed, allowing the loading component to regain its ability to move freely vertically within the guide sleeve, and the gravity load generated by the loading component can be fully transferred to the top of the test pile.

[0079] S155. After the motion restriction is lifted, the free vertical movement of the loading component within the guide sleeve is restored, completing the adjustment of the loading posture.

[0080] The aforementioned restoration of free vertical movement refers to the ability of the loaded component to slide vertically within the guide sleeve without additional resistance. Completing the adjustment of the loading posture means that the loaded component reaches the physical state required for normal loading in terms of both axial alignment and vertical movement freedom. This includes the vertical axis of the loaded component coinciding with the vertical axis of the test pile, and the loaded component having unobstructed vertical movement capability within the guide sleeve.

[0081] Specifically, after the motion resistance is removed, it is confirmed visually or using displacement sensors that the loading component can move freely vertically within the guide sleeve without generating additional resistance. Once the free vertical movement of the loading component within the guide sleeve is confirmed, the loading attitude adjustment of the current test pile is complete. After the loading attitude adjustment is completed, synchronous loading at the current load level is resumed. The loading component moves downwards along the guide sleeve axis in the centrifugal force field, and the bottom plane of the loading component re-establishes spherical-plane contact with the spherical contact surface at the top of the test pile. The gravity load generated by the loading component is transferred to the pile body along the axial direction of the test pile. At this point, the adjusted test pile is in the same loading state as other test piles without abnormalities, and all test piles continue to synchronously bear the corresponding pile top load under the current load level.

[0082] As one possible implementation method, the approach also includes: S144-S147.

[0083] S144. Obtain the settlement increment of each test pile at the current monitoring time relative to the previous monitoring time under the current load level.

[0084] The current monitoring time refers to the monitoring time at which the stability determination is currently being performed. The previous monitoring time refers to the monitoring time preceding the current monitoring time. The time interval between the current monitoring time and the previous monitoring time is a preset stability determination period, which is longer than the preset sampling period, for example, it can be 1 minute. The settlement increment refers to the difference between the pile top displacement value of the same test pile at the current monitoring time and the pile top displacement value at the previous monitoring time, used to characterize the change in the vertical displacement of the pile top at the current monitoring time relative to the previous monitoring time.

[0085] Before obtaining the settlement increment, boundary determination is required: if the current monitoring time is the first monitoring time in the synchronous loading process, the settlement increment of the test pile at the current monitoring time is set to zero; if the current monitoring time is not the first monitoring time, the difference between the pile top displacement value at this time and the pile top displacement value at the previous monitoring time is used as the settlement increment of the test pile.

[0086] Specifically, at the current monitoring moment, the monitoring system acquires the pile top displacement value of each test pile at the current monitoring moment, as well as the pile top displacement value of each test pile at the previous monitoring moment. For each test pile, the pile top displacement value at the current monitoring moment is subtracted from the pile top displacement value at the previous monitoring moment, and the difference is recorded as the settlement increment of the test pile at the current monitoring moment relative to the previous monitoring moment. Following this method, the settlement increment is calculated for each test pile to obtain the settlement increment corresponding to each test pile at the current monitoring moment. A positive settlement increment indicates that the test pile has undergone a downward vertical displacement at the current monitoring moment relative to the previous monitoring moment, that is, further settlement has occurred at the pile top.

[0087] S145. Determine the judgment coefficient for each test pile based on the proportion of the comprehensive deviation value of each test pile to the sum of the comprehensive deviation values ​​of all test piles.

[0088] The larger the overall deviation value of the test pile, the lower the reference value of its settlement change for judging the stability under synchronous loading. In order to convert the reference value of each test pile into a coefficient that can be used for weighting, and to make the sum of the coefficients of all test piles equal to 1, it is necessary to normalize the reference value of each test pile.

[0089] The judgment coefficient is determined by the following formula: in, The number up to the current monitoring time Judgment coefficients for stability analysis of test piles under load; and These are the [number]th monitoring points up to the current monitoring time. The first test pile and the first The overall deviation value of each test pile; This represents the total number of test piles subjected to synchronous loading. The larger the comprehensive deviation value of a test pile, the lower the reference value of its settlement change for judging the stability under synchronous loading, and the smaller the corresponding judgment coefficient. To avoid the denominator being zero, when the denominator... When the value is less than a preset minimum threshold (e.g., 0.001), the judgment coefficient for each test pile is set equally. The preset minimum threshold can be determined based on the experimental accuracy requirements.

[0090] S146. Based on the settlement increment of each test pile and the judgment coefficient corresponding to each test pile, determine the equivalent settlement of the entire synchronous loading.

[0091] The equivalent settlement is determined by the following formula: in, To synchronously load the overall equivalent settlement up to the current monitoring time; For the first The settlement increment of each test pile at the current monitoring time relative to the previous monitoring time; The number up to the current monitoring time Judgment coefficient for each test pile.

[0092] Since the sum of the judgment coefficients for all test piles equals 1, the equivalent settlement is essentially a weighted average of the settlement increments of each test pile, and its value ranges between the minimum and maximum settlement increments. The smaller the equivalent settlement, the slower the overall settlement rate of all test piles under the current load level, and the closer the pile-soil system is to a stable equilibrium state.

[0093] S147. When the equivalent settlement is less than the preset settlement threshold, it is determined that the current load level has reached a stable state, and the load level is switched to the next load level and synchronous loading continues.

[0094] The aforementioned preset settlement threshold refers to a pre-set critical value used to determine whether the overall synchronous loading has reached a stable state under the current load level. This critical value is used to measure whether the overall settlement change corresponding to the equivalent settlement has converged to an acceptable range. When the equivalent settlement is less than the preset settlement threshold, it indicates that the overall settlement rate of all test piles under the current load level has decreased to below the preset convergence standard, and the pile-soil system has reached a stable equilibrium state under the current load level.

[0095] Specifically, after calculating the equivalent settlement at the current monitoring time, the equivalent settlement value is compared with a preset settlement threshold. The preset settlement threshold is determined based on the conventional criteria for determining deformation convergence in the centrifugal model test of the pile foundation. In this embodiment, the exemplary value of the preset settlement threshold is 0.01 mm. When the equivalent settlement is less than 0.01 mm, the current load level is determined to have reached a stable state. After determining that a stable state has been reached, the load level is switched to the next load level and synchronous loading continues. Each test pile continues to bear the corresponding pile top load under the next load level. In the above manner, the equivalent settlement is continuously monitored under each load level until the equivalent settlement meets the stability determination condition, at which point the load level is switched to the next load level, and the synchronous loading test of all load levels is completed step by step.

[0096] As one possible implementation method, the approach also includes: S148-S149.

[0097] S148. During the switching process of each load loading level, the load-displacement curve of each test pile is constructed based on the pile top load and the corresponding pile top displacement.

[0098] At each load level, once the equivalent settlement is less than the preset settlement threshold and the current load level is determined to have reached a stable state, the pile top load and pile top displacement values ​​corresponding to that load level are recorded, forming a data point. As the load levels are switched sequentially, the corresponding pile top load and pile top displacement values ​​are recorded for each level, forming multiple data points. Using the pile top load as the ordinate and the pile top displacement as the abscissa, all data points corresponding to all load levels are plotted on a coordinate plane, and adjacent data points are connected sequentially to obtain a complete load-displacement curve. Following this method, a corresponding load-displacement curve is constructed for each test pile. Each data point on the load-displacement curve corresponds to a load level, and the direction of the line connecting adjacent data points reflects the changing trend of the test pile displacement as the load increases.

[0099] Furthermore, the monitoring system constructs axial force distribution curves and skin friction evolution curves using the following methods: With pile depth as the abscissa and cross-sectional axial force as the ordinate, the cross-sectional axial force calculated from strain gauge data at different depths is used as discrete data points. A line fitting is then performed to obtain the axial force distribution curve, which is used to analyze the axial force transmission law of the pile and the proportion of end resistance to side resistance. Similarly, with pile depth as the abscissa and pile side skin friction as the ordinate, the calculated skin friction results at each point, obtained by converting the difference in cross-sectional axial force at adjacent depths, are used as discrete data points. A line fitting is then performed to obtain the skin friction evolution curve, which reveals the process, peak value, and distribution law of pile side skin friction. Based on the comparative analysis of these characteristic curves, the pile foundation stiffness, ultimate bearing capacity, and deformation characteristics under different load levels are revealed, demonstrating the pile foundation bearing mechanism and the interaction law between the pile and soil.

[0100] S149. When the displacement increment of the load-displacement curve of the test pile continues to increase without convergence trend in a series of preset load loading levels, it is determined that the test pile has reached the ultimate bearing capacity state, the current loading state of the test pile that has reached the ultimate bearing capacity state is locked, and the load of the test pile is terminated.

[0101] The "continuous preset quantity" refers to the number of load levels continuously examined during the ultimate bearing capacity determination, which is the pre-set judgment window size. The displacement increment refers to the difference in pile top displacement between two adjacent load levels in a steady state. The convergence trend refers to the decreasing displacement increment between adjacent load levels as the load level increases. The ultimate bearing capacity state refers to the physical state in which the soil around the pile undergoes shear failure, the pile structure approaches yield, or the pile-soil system loses its bearing capacity during load increase. Locking the current loading state means that the centrifuge control system stops the load-raising operation of the loading module containing the test pile, allowing the test pile to continue bearing the current load without unloading or further increasing the load.

[0102] During the gradual switching of load levels, the displacement of the test pile gradually increases with each increase in load. Under normal loading conditions, the displacement increment caused by each load increase should gradually decrease with the increase in load level, that is, the slope of the load-displacement curve gradually becomes flatter, indicating that the pile-soil system is approaching stability. However, when the test pile approaches its bearing limit, the surrounding soil gradually enters a plastic state, and the displacement increment caused by each load increase no longer decreases but continues to increase, that is, the load-displacement curve shows a flat section. If the above trend is not identified and loading is not stopped in time, continuing to increase the load will lead to sudden failure of the test pile, pile fracture, or overall shear failure of the surrounding soil, resulting in damage to the test pile, disturbance of the surrounding soil, and failure of monitoring data. Therefore, during the gradual switching of load levels, it is necessary to determine in real time whether the test pile has reached its bearing limit state based on the trend of displacement increment change of the load-displacement curve, and to stop the load increase of the test pile in time when it reaches the bearing limit state.

[0103] Specifically, after each load level is determined to have reached a stable state and the pile top displacement value is recorded, the displacement increment of that load level relative to the previous load level is calculated. Following this method, the displacement increment between adjacent load levels is continuously calculated during the step-by-step switching process. When, in a consecutive preset number of load levels, the displacement increment of each load level relative to the previous load level is greater than the displacement increment between the previous adjacent load levels, and the increasing trend of the aforementioned displacement increment does not show any signs of decreasing, it is determined that the test pile has reached its bearing limit state. In this embodiment, the preset number is exemplarily three. When the test pile is determined to have reached its bearing limit state, the centrifuge control system locks the current loading state of the test pile, ensuring that the test pile continues to bear the current load at the current load level, and terminates the load lifting operation on the test pile. After locking and terminating the lifting operation, the test pile no longer participates in the switching of load levels, while the remaining test piles that have not reached their bearing limit state continue to undergo synchronous loading at the specified load levels.

[0104] After loading is completed, the loading components are removed in reverse stages according to the loading level, completing the synchronous unloading of multiple test piles under multiple working conditions. The rebound amount of the test piles and the soil pore pressure recovery data are recorded by the monitoring system during unloading to analyze the unloading deformation characteristics of the pile foundation, the elastic recovery capacity of the soil, and the pore pressure dissipation law. After unloading, the centrifuge is controlled by the centrifuge control system to decelerate in stages until it stops completely, avoiding damage to the device and model due to sudden stop.

[0105] In a design, such as Figure 2As shown, a centrifugal test pile bearing characteristics test device with multi-condition synchronous loading is provided, including: loading device 21, installation device 22, model pile device 23, centrifugal model box 401 and monitoring system 25.

[0106] The loading device 21 includes multiple loading components 101 and corresponding guide sleeves 102. Each loading component 101 has a different mass and is respectively disposed inside the corresponding guide sleeve 102. It is used to apply a pile top load of the corresponding load level to each test pile under the action of centrifugal force.

[0107] A moving gap is provided between the outer diameter of each loading member 101 and the inner diameter of the corresponding guide sleeve to ensure that each loading member can move freely along the axial direction within the corresponding guide sleeve. The inner wall of each guide sleeve is provided with a ball channel 104 extending along the axial direction. A ball 103 is provided in the ball channel 104. The ball 103 is tangentially engaged with the outer surface of the loading member 101 to guide and constrain the movement of the loading member 101, limit the lateral displacement of the loading member 101 and reduce the vertical friction, so that each loading member 101 applies the corresponding load level of the pile top load to each test pile under the action of centrifugal force.

[0108] The mounting device 22 is fixed to the top of the centrifuge model box 401 and is used to fix the loading device 21 above the centrifuge model box 401 and make the loading direction of the loading component 101 consistent with the centrifugal acceleration direction.

[0109] The aforementioned installation device 22 includes a bearing plate 201 and fasteners 202. The bearing plate 201 is provided with a through hole for the test pile to pass through, and the guide sleeve 102 is fixed to the bearing plate 201 by the fasteners 202.

[0110] The model pile device 23 includes a test pile 301 and a spherical contact surface 302 disposed on the top of the test pile. The test pile 301 is used to bear and transmit the load at the top of the pile to simulate the stress and deformation characteristics of the prototype pile foundation. The spherical contact surface 302 is used to contact the bottom plane of the loading member to realize the transmission of the load along the axial direction of the test pile.

[0111] Centrifuge model box 401 is used to fill the test soil and fix the position of each test pile, providing a closed test space for pile foundation bearing and loading tests.

[0112] The monitoring system 25 is used to collect monitoring data of each test pile in real time during synchronous loading at various load levels that are switched step by step. The collected monitoring data is arranged in chronological order to form a collection sequence. Based on the fluctuation characteristics of the monitoring data of each test pile in the collection sequence, the comprehensive deviation value of each test pile is determined, and anomaly judgment is made based on the comprehensive deviation value. It is also used to trigger a pause in synchronous loading at the current load level when an abnormal test pile is determined, and to trigger a resumption of synchronous loading at the current load level after the loading attitude adjustment is completed.

[0113] To better understand the technical solution of this application, such as Figure 3 The diagram shows an overall schematic of a gravity loading structure, which includes a loading component 101, a guide sleeve 102, a ball bearing channel 104, a bearing plate 201, a fastener 202, and a test pile 301.

[0114] The loading component 101 is coaxially disposed inside the guide sleeve 102. The flange base of the guide sleeve 102 is fastened to the upper surface of the bearing plate 201 by multiple sets of fasteners 202. The bearing plate 201 is horizontally arranged, with a through hole in its middle for the test pile 301 to pass through vertically. The bottom opening of the guide sleeve 102 corresponds to the through hole of the bearing plate 201, allowing the test pile 301 to dock with the loading mechanism from below.

[0115] In this embodiment, the fastener can be a bolt, and the loading component can be a weight.

[0116] Furthermore, such as Figure 4 The image shows an overall front view of a gravity-loaded structure, illustrating the relative positions of the components within the same vertical plane. Figure 4 The image shows a loading component 101, a guide sleeve 102, a bearing plate 201, a fastener 202, and a test pile 301. Figure 4 The overall assembly state of the gravity loading structure is shown from an external perspective. The loading component 101 is located inside the guide sleeve 102 with its top protruding. The guide sleeve 102 is vertically installed on the bearing plate 201, and the test pile 301 extends downward through the bearing plate 201 vertically. The guide sleeve 102 is fixed to the bearing plate 201 by fasteners 202.

[0117] like Figure 5 The diagram shows an overall installation schematic of a centrifuge model box 401. Figure 5The diagram shows a centrifuge model box 401, a loading component 101, a guide sleeve 102, and a bearing plate 201. The bearing plate 201 serves as the top cover of the centrifuge model box 401 and is fixed to the top opening of the centrifuge model box 401 via a detachable connector. The loading component 101 and the guide sleeve 102 are both located on the outside and above the centrifuge model box 401. Multiple test piles 301 pass through the bearing plate 201 and are inserted into the test soil inside the centrifuge model box 401, thus forming multiple independent loading units.

[0118] like Figure 6 The diagram shows a cross-sectional view of a loading device 21. Figure 6 The image shows the loading member 101, guide sleeve 102, ball bearing 103, and fastener 202, with section lines BB marked. From Figure 6 As can be seen, the loading member 101 is coaxially placed in the center of the inner cavity of the guide sleeve 102; the ball bearings 103 are arranged between the inner wall of the guide sleeve 102 and the outer surface of the loading member 101, and form a rolling fit with the two to limit the movement of the loading member 101 laterally and reduce the vertical movement friction; the fastener 202 is set at the flange structure at the bottom of the guide sleeve 102 for fixing the position of the guide sleeve 102.

[0119] like Figure 7 As shown, a partially enlarged view of a loading device 21 is presented. Figure 7 The diagram shows the loading member 101, guide sleeve 102, ball 103, and ball channel 104, illustrating the microstructure of the sliding fit. The ball channel 104 is recessed into the inner wall of the guide sleeve 102 and opens inward to accommodate the ball 103. The ball 103 is embedded within the ball channel 104, its outer side constrained by the inner wall of the guide sleeve 102, and its inner side tangentially rolling with the outer surface of the loading member 101. This allows the ball 103 to roll within the ball channel 104 while effectively limiting the lateral displacement of the loading member 101, simultaneously converting sliding friction into rolling friction and reducing vertical movement resistance.

[0120] like Figure 8 The diagram shows a cross-sectional view of a gravity-loaded structure, used to visually illustrate the vertical force transmission path and the longitudinal section structure of each component. Specifically, Figure 8 The gravity-loaded structure in the middle is along Figure 6A cross-sectional view of the BB line shows a loading component 101, a guide sleeve 102, balls 103, a ball channel 104, a bearing plate 201, fasteners 202, a test pile 301, and a spherical contact surface 302. The guide sleeve 102 is fixed to the bearing plate 201 by the fasteners 202. The balls 103 fill the space between the outer wall of the loading component 101 and the ball channel 104 on the inner wall of the guide sleeve 102. The bottom of the loading component 101 is a wide, flat structure that directly contacts the spherical contact surface 302 located at the top of the test pile 301; the test pile 301 passes through a through-hole in the bearing plate 201. This structure allows the gravity load of the loading component 101 to be transmitted unidirectionally downwards along the axis of the test pile 301 through the centered contact between the flat bottom and the spherical surface.

[0121] like Figure 9 The diagram shows a schematic representation of a model pile device 23. Figure 9 The diagram shows the test pile 301 of the model pile device 23 and the spherical contact surface 302 disposed on the top of the test pile. The spherical contact surface 302 is integrally disposed at the top of the test pile 301 (the uppermost part of the pile top). The specific construction of the spherical contact surface 302 is as follows: a smoothly transitioning spherical crown outer edge is machined outwardly in the pile top region, and a micro-arc-shaped, gently sloping contact surface is formed at the highest point of the orthographic projection of the outer edge of the crown. This gently sloping contact surface is used to make large-area contact with the broad, flat bottom of the loading member 101 during assembly, achieving axial centering transfer of load and releasing stress concentration.

Claims

1. A method for testing the bearing characteristics of centrifugal test piles under simultaneous loading under multiple working conditions, characterized in that, The method includes: The target mass of the loaded component corresponding to each test pile is determined based on the target centrifugal acceleration and the prototype load. Under each load loading level that is switched step by step, the corresponding pile top load is applied synchronously to each of the test piles by the gravity load generated by each loading component in the centrifugal force field; During the synchronous loading process, monitoring data of each test pile is collected, and the collected monitoring data is arranged in chronological order to form a collection sequence of each test pile under each monitoring data type. Based on the fluctuation characteristics of the monitoring data of each test pile during the synchronous loading process, the comprehensive deviation value of each test pile is determined; The test pile is judged to be abnormal based on the comprehensive deviation value. When the test pile is judged to be abnormal, the synchronous loading of the current load level is suspended, the loading posture of the loading component corresponding to the abnormal test pile is adjusted, and the synchronous loading of the current load level is restored after the adjustment is completed. The determination of the comprehensive deviation value of each test pile includes: for each monitoring data type, calculating the variance of the monitoring data of each test pile in the acquisition sequence, and using the variance as a quantitative value of the data dispersion of the test pile under the corresponding monitoring data type; for each monitoring data type, determining the relative deviation of the current test pile relative to the other test piles under the corresponding monitoring data type based on the difference between the variance of the current test pile and the variances of the other test piles; processing the relative deviation of the same test pile under each monitoring data type using a preset data fusion algorithm, and determining the comprehensive deviation value of each test pile based on the processing result; The step of determining anomalies in the test piles based on the comprehensive deviation value includes: determining the load deviation degree of the current test pile based on the difference between the pile top load at the current monitoring time and a preset load value; determining that the current test pile is abnormal when the load deviation degree is greater than a first preset threshold or the comprehensive deviation value is greater than a second preset threshold; the first preset threshold is determined based on the maximum value of the load deviation degree during the previous normal synchronous loading process, and the second preset threshold is determined based on the average value of the comprehensive deviation values ​​of each test pile during the previous normal synchronous loading process; The monitoring data also includes the axial strain of each test pile and the pore water pressure of the soil around the pile; the axial strain of the pile is collected by strain gauges installed at equal intervals along the axial direction of the test pile; the pore water pressure of the soil around the pile is collected by pore water pressure gauges installed in the soil layer around the pile.

2. The method for testing the bearing characteristics of centrifugal test piles under multi-condition synchronous loading according to claim 1, characterized in that, Determining the target mass of the loaded component corresponding to each test pile includes: The centrifugal acceleration factor is determined based on the ratio of the target centrifugal acceleration to the gravitational acceleration. Obtain the prototype loads corresponding to each of the test piles; The target mass of each loading component is determined based on the conversion relationship between the prototype load, the centrifugal acceleration multiple, and the gravitational acceleration.

3. The method for testing the bearing characteristics of centrifugal test piles under multi-condition synchronous loading according to claim 1, characterized in that, Each loading component is disposed within a corresponding guide sleeve. The bottom of the loading component is a plane, and the top of the test pile is provided with a spherical contact surface. The bottom plane of the loading component and the spherical contact surface form a spherical-plane contact, so that the gravity load of the loading component is transmitted along the axial direction of the test pile.

4. The test method for bearing characteristics of centrifugal test piles under multi-condition synchronous loading according to claim 3, characterized in that, The loading posture of the loading component corresponding to the abnormally adjusted test pile includes: Adjust the alignment of the loading member with respect to the corresponding test pile so that the vertical axis of the loading member coincides with the vertical axis of the test pile; After the axis alignment is adjusted, the vertical movement degree of freedom of the loading component within the corresponding guide sleeve is adjusted to remove the movement resistance that exists during the vertical movement of the loading component; After the motion restriction is lifted, the loading component resumes free vertical movement within the guide sleeve, thus completing the adjustment of the loading posture.

5. The method for testing the bearing characteristics of centrifugal test piles under multi-condition synchronous loading according to claim 1, characterized in that, The method further includes: Obtain the settlement increment of each test pile at the current monitoring time relative to the previous monitoring time under the current load level; The judgment coefficient for each test pile is determined based on the proportion of the comprehensive deviation value of each test pile to the sum of the comprehensive deviation values ​​of all test piles. Based on the settlement increment of each test pile and the judgment coefficient corresponding to each test pile, the equivalent settlement of the entire synchronous loading is determined; When the equivalent settlement is less than the preset settlement threshold, it is determined that the current load level has reached a stable state, and the load level is switched to the next load level and synchronous loading continues.

6. The test method for bearing characteristics of centrifugal test piles under multi-condition synchronous loading according to claim 5, characterized in that, The method further includes: During the switching process of each load loading level, load-displacement curves of each test pile are constructed based on the pile top load and corresponding pile top displacement of each test pile. When the displacement increment of the load-displacement curve of the test pile continues to increase without convergence trend during a series of preset load loading levels, it is determined that the test pile has reached the ultimate bearing capacity state. The current loading state of the test pile that has reached the ultimate bearing capacity state is locked, and the load on the test pile is stopped.

7. A multi-condition synchronous loading centrifugal test pile bearing characteristic testing device, comprising the steps of the multi-condition synchronous loading centrifugal test pile bearing characteristic testing method according to any one of claims 1 to 6, characterized in that, include: The loading device includes multiple loading components and corresponding guide sleeves. Each loading component has a different mass and is respectively disposed inside the corresponding guide sleeve. It is used to apply a pile top load of corresponding load level to each test pile under the action of centrifugal force. The mounting device is fixed to the top of the centrifuge model box and is used to fix the loading device above the centrifuge model box and make the loading direction of the loading component consistent with the centrifugal acceleration direction. The model pile device includes a test pile and a spherical contact surface disposed on the top of the test pile. The test pile is used to bear and transmit the pile top load to simulate the stress and deformation characteristics of the prototype pile foundation. The spherical contact surface is used to contact the bottom plane of the loading member to realize the transmission of load along the axial direction of the test pile. Centrifuge model box, used to fill the test soil and fix the position of each test pile, providing a closed test space for pile foundation bearing and loading tests; The monitoring system is used to collect monitoring data of each test pile in real time during synchronous loading at each load level that is switched step by step. The collected monitoring data is arranged in chronological order to form a collection sequence. The comprehensive deviation value of each test pile is determined based on the fluctuation characteristics of the monitoring data of each test pile in the collection sequence. The system is also used to determine the anomaly of the test pile based on the comprehensive deviation value. The system is also used to trigger a pause in synchronous loading at the current load level when an anomaly is determined to exist in the test pile, and to trigger a resumption of synchronous loading at the current load level after the loading attitude adjustment is completed.

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