Pit slot model test model pile deformation and mechanical property test system and method

Abstract

The invention discloses a pit slot model test model pile deformation and mechanical property test system and method, and belongs to the technical field of geotechnical engineering physical model tests and pile foundation tests. The method comprises the steps that before a model pile is poured, an inclination measuring guide pipe is axially embedded in a pile body; during installation, a flexible inclinometer is inserted, and measuring points are arranged along the pile length; actually measuring the rigidity of the model pile in a four-point bending or three-point bending mode; collecting continuous displacement data of the pile body through horizontal loading; and based on a p-y curve theory and a numerical difference inversion algorithm, the internal force of the pile body and the resistance distribution of soil around the pile are inversed through displacement data. The system comprises a pre-embedded sensing assembly, a data acquisition assembly and a data processing device. The full-pile-length continuous deformation monitoring of the model pile is realized, the defects of incomplete traditional point type measurement and strong hypothesis of internal force inversion dependence are overcome, the test precision and reliability are remarkably improved, and the method is particularly suitable for refined research of a pile-soil interaction mechanism in an indoor pit slot model test.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering physical model testing and pile foundation testing technology, specifically to a pit model test system and method for testing the deformation and mechanical properties of model piles. Background Technology

[0002] In geotechnical engineering, particularly in slope protection, foundation pit engineering, and geological disaster prevention, anti-slide piles are a widely used structural form. To deeply study the interaction mechanism between anti-slide piles and the surrounding soil and rock, and to optimize design parameters, indoor physical model tests (such as pit model tests) are often used for simulation studies. These tests, by simulating actual geological conditions and engineering structures under controlled conditions, can intuitively and economically reveal the stress and deformation laws of the pile-soil system.

[0003] In model tests, accurately and precisely obtaining the deformation and internal force distribution of the model pile is crucial for evaluating its performance and verifying the theoretical model. Currently, testing techniques for model piles mainly have the following limitations: (1) Insufficient accuracy and completeness of deformation testing: Traditional pile deformation testing often uses methods such as attaching discrete strain gauges to the pile surface or arranging a small number of displacement gauges. These methods can only obtain strain or displacement information at a limited number of measuring points, making it difficult to continuously and completely depict the deformation curve of the entire pile, especially failing to accurately capture the abrupt deformation characteristics near potential slip surfaces. For small-sized model piles, the space for sensor placement is limited, further increasing the difficulty of testing.

[0004] (2) Internal force inversion methods rely on strong assumptions and have limited accuracy: Existing technologies often rely on strain data from discrete measuring points to directly derive the bending moment and shear force of the pile body through material mechanics formulas (such as the relationship between bending moment and curvature). This method is heavily dependent on the density and location of the measuring points, and when the measuring points are sparse, a large number of assumptions need to be made about the distribution of internal forces between the measuring points, resulting in large errors in the inversion results. It is difficult to accurately reflect the true distribution of internal forces along the pile body, especially the distribution of shear force and soil resistance.

[0005] (3) Lack of systematic testing schemes for pit model tests: Pit model tests are characterized by small model size, clear boundary conditions, and the need for precise capture of pile-soil interaction processes. However, existing testing technologies mostly directly adopt methods from field monitoring or larger-scale model tests, lacking a systematic solution that integrates high-precision deformation monitoring and reliable internal force inversion for small-sized model piles within pits. For example, how to achieve non-destructive pre-embedding and high survival rate of deformation sensors within small-section model piles, and how to use limited but more continuous deformation data to accurately invert the entire set of internal forces and resistances are urgent problems to be solved.

[0006] In summary, current technologies lack an integrated testing technology and system that can be applied to pit model tests, achieve continuous deformation monitoring along the entire length of the model pile, and accurately invert the internal forces of the pile and the resistance of the surrounding soil based on the monitoring data. This limits the depth and reliability of model tests in revealing the complex interaction mechanism between the pile and the soil. Summary of the Invention

[0007] To address the problems existing in the background technology, the present invention provides a test system and method for testing the deformation and mechanical properties of model piles in pit and trench model tests. The core of this invention is to combine internal pre-embedded continuous deformation monitoring with mechanical inversion analysis based on displacement data to form a complete testing and evaluation system.

[0008] I. Testing Methods The present invention provides a method for testing the deformation and mechanical properties of a pit-type pile in a test, which mainly includes the following steps: (1) Sensor pre-embedding and model preparation: Before pouring the concrete of the model pile, one or more flexible inclinometer guide pipes are pre-tied and fixed to the pile body steel reinforcement skeleton to ensure that the guide pipes are arranged in a continuous manner along the pile body axis, especially through the pre-set potential slip surface area. Then, concrete is poured and cured to form a complete model pile with inclinometer guide pipes pre-embedded inside.

[0009] (2) Pile installation and sensor arrangement: Install the solidified model pile in the test model (such as slope or foundation pit soil). Insert the flexible inclinometer into the pre-embedded inclinometer guide tube and arrange the measuring points along the pile length at a set interval (such as 20-50cm, preferably 30cm).

[0010] (3) Pile bending stiffness (EI) test: Before formal horizontal loading, basic mechanical performance tests can be performed on the model pile. Place it on a simply supported / continuous support and apply vertical load using a four-point bending or three-point bending method. At the same time, use a dial gauge placed at the bottom of the pile and a flexible inclinometer inside the guide pipe to measure the deflection and deformation curves respectively. The actual bending stiffness EI of the pile body is obtained by calculation, and the dial gauge data is used to verify the flexible inclinometer data to ensure the reliability of subsequent deformation test data.

[0011] (4) Continuous deformation data acquisition: Graded horizontal loads are applied to the test model (simulating soil movement) and / or model pile (direct jacking). Under each load level, horizontal displacement data at each measuring point along the entire length of the pile is continuously and automatically acquired using a flexible inclinometer to obtain a complete pile displacement curve.

[0012] (3) Mechanical property inversion analysis: Based on the collected high-precision, full-field continuous displacement data, the following process is used to invert the internal forces of the pile and the soil resistance: a. Modeling: Based on the Py curve theory, using the "m" method or "k" method, etc., elastic foundation beam models are used to establish the governing differential equations for the free segment of the pile above the slip surface and the anchored segment below the slip surface.

[0013] b. Discrete solution: The central difference method is used to discretize the governing equations into a system of linear algebraic equations about the displacements of each node.

[0014] c. Iterative inversion: Using measured displacement data as known conditions and fitting targets, an iterative algorithm (such as continuously adjusting the foundation reaction coefficient m or k) is used to achieve the best fit between the numerically calculated displacement curve and the measured curve.

[0015] d. Output results: When the calculation meets the convergence criteria, based on the finally determined model parameters, the distribution of bending moment, shear force, rotation angle and soil resistance at each depth of the pile is output synchronously.

[0016] II. Testing System Corresponding to the above method, the present invention also provides a test system for the deformation and mechanical properties of a pit-type test pile, the system mainly comprising: Embedded sensing subsystem: including a flexible inclinometer guide tube embedded inside the model pile, which serves as a channel for deformation transmission and sensor protection.

[0017] Data acquisition subsystem: Includes a flexible inclinometer and its data acquisition unit, used to realize the automatic and real-time acquisition and storage of continuous deformation data of the pile body.

[0018] Data processing and inversion analysis subsystem: This is a computing device (such as a computer) containing a processor and memory, which stores a computer program that performs the aforementioned mechanical property inversion analysis steps. This program can read the collected displacement data, run iterative inversion algorithms, and visualize the distribution charts of pile deformation, internal forces, and soil resistance.

[0019] III. Programs and Storage Media The present invention also relates to a computer program product and a computer-readable storage medium. When the instructions in the program product or the program on the storage medium are executed by a processor, the "mechanical property inversion analysis" step in the above-mentioned test method can be implemented, that is, the inversion calculation from continuous displacement data to a complete set of mechanical property parameters can be completed.

[0020] Compared with the prior art, the present invention has the following significant advantages: 1. The bending stiffness of the model pile was measured to clarify the basic mechanical parameters of the model pile. The inclinometer data was checked during the test to ensure the accuracy of the test.

[0021] 2. By pre-embedding the flexible inclinometer guide tube inside the pile body and using a flexible inclinometer for measurement, high-density displacement data of the model pile from the top to the bottom of the pile can be obtained non-destructively and continuously, completely depicting the deformation curve and accurately locating the deformation change zone (such as the slip surface position), thus solving the problems of discontinuity and missing information in point measurement.

[0022] 3. Using a highly complete continuous displacement field as input for inversion analysis greatly reduces prior assumptions about the distribution of internal forces in the pile. Combined with rigorous elastic foundation beam theory and iterative fitting algorithms, the inverted bending moment, shear force, and soil resistance distributions are closer to the actual mechanical state, significantly improving the accuracy and reliability of the inversion results.

[0023] 4. This invention integrates sensor pre-embedding technology, data acquisition hardware, and inversion algorithm software to form a standardized and streamlined testing system specifically designed for pit model testing. This system is highly operable, effectively protects the sensors during the pouring process, and has a high survival rate, making it particularly suitable for small-scale, high-precision indoor model testing.

[0024] 5. This invention can simultaneously output deformation, internal force and soil resistance data, providing researchers with an unprecedented, mutually corroborating complete dataset, which greatly facilitates the analysis of in-depth scientific issues such as load transfer mechanism, slip surface development process and pile failure mode, and has important scientific research and engineering guidance value. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the installation of the flexible inclinometer in an embodiment of the present invention.

[0026] Figure 2 This is the load-deflection curve of the C1 model pile in the four-point bending test in this embodiment of the invention.

[0027] Figure 3 This is the load-deflection curve of the C2 model pile in the four-point bending test in this embodiment of the invention.

[0028] Figure 4 This is the load-deflection curve of the C3 model pile in the four-point bending test in this embodiment of the invention.

[0029] Figure 5 This is the load-deflection curve of the C4 model pile in the four-point bending test in this embodiment of the invention.

[0030] Figure 6 This is the load-deflection curve of the C5 model pile in the four-point bending test in this embodiment of the invention.

[0031] Figure 7 This is the load-deflection curve of the C6 model pile in the four-point bending test in this embodiment of the invention.

[0032] Figure 8 The curve of flexural deformation of the C1 model pile in the embodiment of the present invention is obtained by a flexible inclinometer during a four-point bending test (3 loading-unloading cycles).

[0033] Figure 9 The curve of flexural deformation of the C2 model pile in the embodiment of the present invention is measured by a flexible inclinometer in a four-point bending test (two loading-unloading cycles).

[0034] Figure 10 The curve of flexural deformation of the C3 model pile in the embodiment of the present invention is obtained by a flexible inclinometer during a four-point bending test (3 loading-unloading cycles).

[0035] Figure 11 The curve of flexural deformation of C4 model pile in the embodiment of the present invention is obtained by a flexible inclinometer during a four-point bending test (two loading-unloading cycles).

[0036] Figure 12 The curve of flexural deformation of the C5 model pile in the embodiment of the present invention is measured by a flexible inclinometer in a four-point bending test (two loading-unloading cycles).

[0037] Figure 13 The curve of flexural deformation of C6 model pile in the embodiment of the present invention is obtained by flexible inclinometer in four-point bending test (2 loading-unloading).

[0038] Figure 14 This is a plan view of the test components for a single-row model pile pushing test according to an embodiment of the present invention.

[0039] Figure 15 This is the pile deformation distribution curve of model C1 pile in the horizontal pile pushing test in the embodiment of the present invention.

[0040] Figure 16 This is the pile deformation distribution curve of model C2 pile in the horizontal pile pushing test in the embodiment of the present invention.

[0041] Figure 17 This is the pile deformation distribution curve of the C3 model pile in the horizontal pile pushing test in the embodiment of the present invention.

[0042] Figure 18 This is the pile deformation distribution curve of the C4 model pile in the horizontal pile pushing test in the embodiment of the present invention.

[0043] Figure 19 This is the pile deformation distribution curve of the C5 model pile in the horizontal pile pushing test in the embodiment of the present invention.

[0044] Figure 20 This is the pile deformation distribution curve of the C6 model pile in the horizontal pile pushing test in the embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0046] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0047] This embodiment details a specific implementation process of the test method of the present invention, combined with... Figures 1 to 20 Please provide an explanation.

[0048] Step 1: Sensor pre-embedding and model pile preparation.

[0049] According to the experimental design, determine the dimensions of the model pile (e.g., outer diameter D=400 mm, inner diameter d=70 mm), reinforcement (e.g., reinforcement ratio 1%), and the pre-embedded location of the inclinometer guide pipes. When tying the steel reinforcement cage of the model pile, securely tie one or more flexible inclinometer guide pipes (usually round pipes made of PVC or high-density polyethylene) along the pile axis inside the cage using binding wire. Ensure the guide pipes are straight and continuous, especially in areas that need to cross pre-set potential slip surfaces. Subsequently, erect the formwork and pour model pile concrete (e.g., micro-concrete). During pouring, take care to avoid displacement or blockage of the guide pipes. After pouring, perform standard curing (e.g., 28 days) to form a complete model pile with pre-embedded inclinometer guide pipes inside. Finally, install a flexible inclinometer for testing; the specific installation is as follows... Figure 1 As shown in the figure. In this model test, flexible inclinometers were installed in pile holes C-1, C-2, C-3, C-4, C-5, and C-6 to measure the deformation of the pile body, and the internal force distribution of the pile body was calculated using the Py curve theory. The length of each segment of the flexible inclinometer was set to 30cm.

[0050] Step 2: Pile bending stiffness (EI) test and data calibration.

[0051] This step aims to accurately obtain the basic mechanical parameters of the model pile and verify the testing accuracy of the flexible inclinometer.

[0052] Twenty-eight days after the model pile was poured, its bending stiffness (EI) was tested using a four-point bending test. The specific experimental procedure is as follows: (1) Geometric data and calculation parameters The model pile has an outer diameter of 400mm and an inner diameter of 70mm. Its cross-sectional geometric properties are: moment of inertia I = 0.001255458m. 4 ; (2) Load data ① The total weight of the pile = (6.35 + 5.3 + 5.3 + 0.77) × 57 = 1010.04 kg = 1.01 t = 10.10 kN; Self-weight: q = 2.02 kN / m.

[0053] ② External load: 150×150×550 concrete blocks are used as counterweights. 25 blocks are suspended from the model piles at a distance of L / 4 from both ends. The weight of a single counterweight is 24kg (0.24kN). Therefore, the load on each side is 6kN, and the total load is 12kN (1.2t).

[0054] ③ Calculation of deflection and bending stiffness (EI) I. Maximum deflection at mid-span of a simply supported beam under uniformly distributed load: (1) In the formula: —Maximum deflection at mid-span of the model pile (unit: m); q—Self-weight of the model pile (unit: kN / m); E—Elastic modulus of the model pile (unit: kPa); I—Elastic moment of inertia of the model pile (unit: m) 4 ); EI—Bending stiffness of model piles (unit: kN.m) 2 ); l — Length of the model pile (unit: m).

[0055] Therefore, the bending stiffness (EI) is: (2) II. Maximum deflection at mid-span of a simply supported beam under two concentrated loads F at mid-span L / 4: (3) In the formula: w max —Maximum deflection at mid-span of the model pile (unit: m); F—Concentrated load (unit: kN) acting on the model pile at L / 4. E—Elastic modulus of the model pile (unit: kPa); I—Elastic moment of inertia of the model pile (unit: m) 4 ); EI—Bending stiffness of model piles (unit: kN.m) 2 ); l — Length of the model pile (unit: m).

[0056] thus: (4) III. After the deflections of both are superimposed: (5) thus, (6) (3) Calculation of expected deflection Based on existing experimental data, the elastic modulus of micro-concrete is E = 5977.8 MPa = 5977800 kPa. When self-weight is acting:

[0057] After applying a concentrated load:

[0058] (4) Calculation of equivalent stiffness Equivalent stiffness after applying concentrated load: (7) The stiffness of the model pile was measured using a flexible inclinometer and a dial gauge. The flexible inclinometer was arranged along the entire length of the pile, and three dial gauges were arranged in the middle section of the load for measurement.

[0059] After the stiffness tests of the model piles were completed, a detailed analysis was conducted on the test data of the six model piles. The stiffness tests mainly focused on the deflection measured by a dial gauge, and the data from the flexible inclinometer was also calibrated. The dial gauge test data is as follows: Figure 2-7 As shown. Figure 2-7 The figure shows the load-deflection curves of the model piles in a four-point bending test. It can be seen from the figure that under a small external load, the pile deflection exhibits a linear variation. The loading and unloading curves basically coincide. The model piles C1 to C6 show the largest deflection deformation, with pile C5 showing the largest at 2.187 mm, and the average value being 1.83 mm.

[0060] From the above analysis, the maximum deflection at mid-span of a simply supported beam under two concentrated loads F at mid-span L / 4 is: (8) thus: (9) The pile stiffness EI of piles C1~C6 is EI = 13131.4 kN•m 2 .

[0061] The data curves of the flexible inclinometer are as follows: Figures 8-13 As shown in the figure, the pile deflection curve measured by the flexible inclinometer in the four-point bending test of the model pile is consistent with the bending moment deformation under the four-point bending test of a simply supported beam under a small external load. This fully demonstrates that pure bending deformation occurs in the middle section of the pile under the four-point bending test conditions. Further comparison of the deflection values ​​measured by the dial gauge and the flexible inclinometer shows a maximum difference of 0.13 mm, which fully demonstrates that the flexible inclinometer test data has high accuracy and can be used to test the pile deformation in the test, obtaining accurate pile deformation results.

[0062] Step 3: Results of pile deformation test In the single-row circular pile pushing test, the model piles had an outer diameter of 400 mm, an inner diameter of 70 mm, a length of 5 m, and a pile spacing of 0.9 m. A total of 6 model piles were installed, positioned in the middle of the slope model. To further investigate the influence of anchorage depth on the mechanical properties of the piles, three anchorage depths were set: C-1 and C-2 had an anchorage depth of 2.25 m, C-3 and C-4 had an anchorage depth of 2.05 m, and C-5 and C-6 had an anchorage depth of 1.75 m. The model piles were prefabricated and then installed. After the sliding mass was filled, an electric Luoyang shovel was used to drill holes. After drilling, the model piles were installed and filled with cement-fly ash grout in the same proportion as the model piles.

[0063] like Figure 14 As shown, in the single-row circular pile pushing test, a flexible inclinometer was used to measure the displacement changes of the pile body. The flexible inclinometer was arranged along the entire length of the pile body, with a spacing of 30 cm between adjacent measuring points, and the data acquisition frequency was set to 1 time / s. The test was conducted using a step-by-step loading method, starting with the fourth level of loading and gradually increasing to the corresponding load, and then gradually unloading to 0. The test was repeated once under the same load level. Under each load level, the holding time of the loading system adopted a dual-control standard, that is, after observing for 20 minutes under each load level and after the monitoring data from the earth pressure gauge, flexible inclinometer, total station, or 3D laser scanning stabilized for 5 minutes, the next level of loading was carried out. During loading, the loading rate of the pusher plate gradually decreased from top to bottom to ensure that the displacement of the upper, middle, and lower pusher plates showed a decreasing state. The pusher plates were labeled CH1, CH2, and CH3 from top to bottom, and the specific loading regime is shown in the table below.

[0064] Table 1 Loading regime for single-row circular pile pushing test

[0065]

[0066]

[0067] After the test, the pile deformation curves under various load levels were extracted, such as... Figure 15-20 As shown.

[0068] Figures 15-20 The displacement curves for piles C1 to C6 are shown in the figure. It can be seen that the overall pile displacement tends to be smooth, gradually decreasing from the pile top downwards. Deformation is more pronounced above the slip surface, with a more prominent distribution pattern, while deformation is smaller below the slip surface, exhibiting an overall "Y"-shaped distribution. As the external load increases, the pile deformation gradually increases, then gradually decreases during unloading. Finally, after unloading, a small amount of residual deformation remains. Comparing the displacement curves of each pile reveals that the pile displacements under various load levels are larger for piles C5 and C6. This is because the anchorage depth of piles C5 and C6 is shallower, resulting in greater overall deformation and thus larger displacements after the pile is subjected to load. The pile displacements for piles C1, C2, C3, and C4 show little change.

[0069] Step 4: Calculation of internal forces in the pile body This step is the core algorithm of the present invention, which transforms the continuous displacement field into an internal force field.

[0070] Calculated using the "m" method, assuming the pile stiffness is EI and the calculated pile width is B. p The length of the pile is l The length of the free segment is h 1 The length of the anchorage section is h 2 The depth of any point is z The corresponding deflection is y ( z The thrust load acting at that location is p ( z The static equilibrium equations for the pile body are established as follows: Sliding body part (0≤ z ≤ h 1 ) (10) EI—Bending stiffness of model piles (unit: kN.m) 2 ); y—Deformation at any point depth z on the model pile (unit: m); z—Depth of any point on the model pile (unit: m); —The deformation at any point in the model pile at depth z and the fourth derivative of depth z; m1—Proportional coefficient of the subgrade coefficient of the soil in front of the model pile above the slip surface as a function of depth (unit: kN / m) 4 ); Bp —Equivalent calculated width of the model pile body, taken according to the standard (unit: m); p ( z — The thrust load (unit: kN) borne at any point at depth z on the model pile. h1—Length above the sliding surface of the model pile (unit: m); l—Total length of the model pile (unit: m) Slide section ( h 1 ≤ z ≤ l ) (11) EI—Bending stiffness of model piles (unit: kN.m) 2 ); y—Deformation at any point depth z on the model pile (unit: m); z—Depth of any point on the model pile (unit: m); m2—Proportional coefficient of subgrade coefficient of the soil in front of the model pile below the slip surface as a function of depth (unit: kN / m) 4 ); B p —Equivalent calculated width of the model pile body, taken according to the standard (unit: m); p ( z — The thrust load (unit: kN) borne at any point at depth z on the model pile. The boundary conditions for the above equilibrium equations are as follows: Calculated using the "k" method, assuming the pile stiffness is EI and the calculated pile width is B. p The length of the pile is l The length of the free segment is h 1 The length of the anchorage section is h 2 The depth of any point is z The corresponding deflection is y ( z The thrust load acting at that location is p ( z The static equilibrium equations for the pile body are established as follows: Sliding body part (0≤ z ≤ h 1 ) (12) Slide section ( h 1 ≤ z ≤l ) (13) In the formula, K2—Soil subgrade coefficient in front of the model pile below the slip surface (unit: kN / m) 3 ); The boundary conditions for the above equilibrium equations are as follows: When the pile top Z=0, the pile bending moment M=0 and the shear force Q=0, that is... (14) In the formula: —The second derivative of the deformation y at any point in the model pile at depth z with respect to depth z.

[0071] (15) In the formula: —The third derivative of the deformation y at any point in the model pile at depth z with respect to depth z.

[0072] At the boundary between the sliding body and the sliding bed, when Z=h1, Displacement continuity condition: (16) In the formula: h1—Length of the model pile body at the slip surface (unit: m); —Deformation at the lower part of the slip surface of the model pile (unit: m); —Deformation at the slightly upper part of the slip surface of the model pile (unit: m).

[0073] Continuity condition for corners: (17) In the formula: h1—Length of the model pile body at the slip surface (unit: m); y—Deformation at any point depth z on the model pile (unit: m); z—Depth of any point on the model pile (unit: m); —The first derivative of the deformation y and depth z at a slightly lower position of the model pile; —The first derivative of the deformation y and depth z at a position slightly above the pile body of the model.

[0074] Moment continuity condition: (18) In the formula: —The second derivative of the deformation y and depth z at a slightly lower position of the model pile; —The second derivative of the deformation y and depth z at a position slightly above the pile body of the model.

[0075] Shear equilibrium condition: (19) In the formula: —The third derivative of the deformation y and depth z at a slightly lower position of the model pile; —The third derivative of the deformation y and depth z at a position slightly above the pile body of the model; —External load (kN) on the model pile body at the slip surface.

[0076] At the bottom of the pile, Z= l hour, (20) (twenty one) —The first-order differential of the pile deformation y at any point on the pile body with respect to the depth z.

[0077] Equations (10) to (13) are fourth-order differential equations, which are solved using numerical analysis. The specific idea is to divide the pile body into several nodes and use difference approximation to replace the differential to transform the continuous fourth-order differential equations into a discrete algebraic equation system. The specific implementation is as follows: divide the pile body into grid nodes along the pile length direction (z-axis), and divide the pile length into n+1 segments, thereby forming n+2 nodes; among them, the nodes above the ground line are -1, -2, ..., -n, etc., and the nodes below the ground line are 1, 2, 3, ..., n, n+1, n+2, etc.

[0078] The central difference formulas for the first, second, third, and fourth derivatives are: (twenty two) In the formula:

[0079] Therefore, the equilibrium differential equations of equations (10) to (13) are transformed into: (twenty three) In the formula:

[0080] For each node (2≤i≤n-1), the equation is established as follows: (twenty four) In the formula:

[0081] This can lead to a system of linear equations. (25) In the formula:

[0082] When i=0, M=0, Q=0, therefore we get (26) (27) In the formula: y -1 —Displacement of the pile body at the virtual node "-1"; y -2 —Displacement of the pile body at the virtual node "-2"; y1—Displacement of the pile at node “1”; y2 — Displacement of the pile at node “2”.

[0083] When i = n + 1, M n+1 =0, Q n+1 =0, therefore we get (28) (29) In the formula: —Displacement of the pile at node “n-1”; —Displacement of the pile at node “n”; —Displacement of the pile at virtual node “n+2”; When 0 < i < n+1 (30) From equations (24) to (30), the displacement of any point on the pile can be obtained. When solving the equations, we should first assume that m(Z) is the displacement of each point. i Then calculate the horizontal displacement y at each point. i , calculate the y i The displacement is fitted to the measured displacement, and the horizontal force pi at each point is calculated based on the pile deformation curve. Then, the corresponding m (Z) can be calculated from pi and yi. i The value of m (Z) or the value of k, and the assumed value of m (Z) i The values ​​of m(Z) or k are compared, and an iterative method is used to solve the problem until the values ​​of m(Z) are found in the previous two iterations. iThe value of ) or k is close to the given value. The final value of m (Z) is obtained from the deflection at each point, the pile bending stiffness (EI), and the final value of m (Z). i By substituting the k-value into the central difference formulas of the first, second, third, and fourth derivatives, the rotation angle, bending moment, shear force, and soil resistance at any point on the pile can be further calculated.

[0084] According to the theory of mechanics of materials, the bending moment M at any section z of the model pile body is... z Shear force Q z Pile perimeter load q z The following relationship exists: (31) In the formula:

[0085] Using the central difference formula, we can obtain: (32) In the formula:

[0086] (33) In the formula:

[0087] By substituting the deflection at each point, the measured bending stiffness (EI) of the pile body, and the final m(Zi) or k value into the central difference formulas of the first, second, third, and fourth derivatives, the rotation angle Φ and bending moment M of the model pile body at any point can be further calculated. z Shear force Q z Pile perimeter load q z .

[0088] The advantages of this invention are: through the integrated process of pre-embedding, continuous monitoring and high-precision inversion, it not only obtains a continuous deformation field that is difficult to achieve with traditional methods, but also inverts the distribution of internal forces and soil resistance with high reliability, providing an unprecedented complete data chain for pile-soil interaction research.

[0089] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for testing the deformation and mechanical properties of a model pile in a pit-and-groove model test, characterized in that, Includes the following steps: (1) Preparation steps: Before casting the model pile, a duct measuring inclination pipe is pre-embedded along the axial direction inside the pile body; (2) Installation steps: Install the solidified model pile in the test model, insert the flexible inclinometer into the inclinometer guide tube, and set multiple measuring points along the length of the pile; (3) Stiffness test of model pile: The model pile equipped with the flexible inclinometer is placed in a simply supported or continuously supported state, and a vertical load is applied by four-point bending or three-point bending. The deflection of the pile body is measured by a dial gauge placed at the bottom of the pile body, and the bending deformation of the pile body is measured by the flexible inclinometer. The bending stiffness EI of the model pile is calculated according to the relationship between load and deflection, and the deformation data measured by the flexible inclinometer is calibrated by the deflection data measured by the dial gauge. (4) Loading test steps: Apply a horizontal load to the test model and / or the model pile, and use the flexible inclinometer to collect the horizontal displacement data of the model pile at each loading stage; (5) Inversion analysis steps: Based on the horizontal displacement data of the pile body, the Py curve theory is used and the numerical difference inversion algorithm is used to calculate the internal force distribution of the model pile body and the soil resistance distribution around the pile.

2. The method for testing the deformation and mechanical properties of a pit-type pile in a test according to claim 1, characterized in that, The inversion analysis steps specifically include: Based on the theory of elastic foundation beams, a set of static equilibrium differential equations is established to describe the stress and deformation of the model pile in the free section above the sliding surface and the anchored section below the sliding surface. The differential equations are discretized into a system of linear algebraic equations concerning the discrete nodal displacements of the pile body using the central difference method. Using the measured horizontal displacement data of the pile body as input, the foundation reaction coefficient is adjusted through iterative calculation so that the calculated displacement obtained by the algebraic equations is matched with the measured displacement, thereby solving for the internal force of the pile body and the soil resistance around the pile.

3. The method for testing the deformation and mechanical properties of a pit-type pile in a test according to claim 2, characterized in that, The theory of elastic foundation beams is the m-method or the k-method.

4. The method for testing the deformation and mechanical properties of a pit-type pile in a test according to claim 1, characterized in that, The flexible inclinometer has measuring points arranged at equal intervals of 20cm to 50cm along the length of the pile.

5. The method for testing the deformation and mechanical properties of a pit-type pile in a test according to claim 4, characterized in that, The spacing is 30cm.

6. The method for testing the deformation and mechanical properties of a pit-type pile in a test according to claim 1, characterized in that, The inclinometer guide tube is a flexible tube, which is tied and fixed to the steel reinforcement skeleton of the pile body before the model pile is poured.

7. A system for testing the deformation and mechanical properties of a pit-type pile in a test, characterized in that, For implementing the test method according to any one of claims 1 to 6, comprising: The embedded sensing components include at least one inclinometer guide pipe embedded in the model pile; The data acquisition component includes a flexible inclinometer that can be inserted into the inclinometer guide tube for acquiring horizontal displacement data of the pile body. The data processing device is configured to perform the inversion analysis step, receive displacement data transmitted by the data acquisition component, and output the calculation results of the pile internal force distribution and the soil resistance around the pile.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the inversion analysis step in the test method as described in claim 1.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the inversion analysis step in the test method as described in claim 1.

Images