Low-cycle reciprocating multi-cycle pile foundation uplift static load detection method

Abstract

The application provides a low-cycle reciprocating multi-cycle pile foundation anti-pulling static load detection method, which comprises the following steps: S1, loading and unloading the pile foundation by using N% test load as a low load; S2, repeatedly performing step S1 multiple times; S3, dividing N%-M% test load into multiple periodic loads with an increment of Q%, and sequentially loading and unloading the pile foundation according to each periodic load as the maximum load in order from small to large; and S4, loading the pile foundation step by step until the load reaches 100% test load, and then unloading the pile foundation step by step until the load is 0. The application has the beneficial effect that a multi-cycle loading synergistic stress model is established by using the low-cycle reciprocating principle to perform deformation analysis, a static force test is performed multiple times, the pile foundation component is repeatedly loaded and unloaded in the positive and negative directions, the stress-strain state of the structure under the low-cycle reciprocating stress is explored, and the range and relationship of the elastic-plastic deformation of the pile foundation can be found according to the stress and displacement curves.

Description

Technical Field

[0001] This invention relates to the field of pile foundation pull-out testing technology, and in particular to a method for static load testing of pull-out of low-cycle reciprocating multi-cycle pile foundations. Background Technology

[0002] Traditional unidirectional vertical tensile static load tests, which provide a basis for design, use conventional steel beams to anchor the pile head reinforcement and apply upward force. The top displacement index is used to evaluate whether the tensile bearing capacity of the pile foundation meets the requirements.

[0003] like Figure 1 As shown, the traditional method for testing pull-out resistance involves maintaining the load after each load level is applied, and measuring the vertical displacement of the pile top at the 5th, 15th, 30th, 45th, and 60th minutes, and then measuring every 30 minutes thereafter. The relative stability standard for the settlement of the test pile is: the settlement of the pile top does not exceed 0.1 mm per hour, and this occurs twice consecutively (starting from the 30th minute after the application of the graded load, calculated based on three consecutive vertical displacement observations every 30 minutes over 1.5 hours). When the rate of change of the vertical displacement of the pile top reaches the relative stability standard, the next load level is applied.

[0004] Traditional static load tests for pile foundations involve continuously applying and maintaining a load while observing settlement and displacement. This approach cannot simulate the actual stress conditions under low-cycle reciprocating tensile forces. Unlike the traditional working conditions of pile foundations, high-speed moving equipment undergoes periodic reciprocating motion on a track. The stress on the pile foundation at the bottom of the track is affected by the operating state of the equipment. When the pile foundation is subjected to repeated loading and unloading forces, it cannot be accurately detected by traditional unidirectional vertical tensile static load tests. This makes it impossible to simulate the tensile bearing capacity of the pile foundation under actual operating conditions, thus making it impossible to determine the specific range of elastic-plastic deformation of the pile foundation. Summary of the Invention

[0005] In view of this, in order to solve the problem of bearing capacity testing of pile foundations under low-cycle reciprocating uplift or compressive loads, embodiments of the present invention provide a method for static load testing of low-cycle reciprocating multi-cycle pile foundations.

[0006] An embodiment of the present invention provides a method for detecting the static pull-out load of low-cycle reciprocating multi-cycle pile foundations, comprising the following steps:

[0007] S1. Loading and unloading the pile foundation with N% test load as low load: Gradually increase the load on the pile foundation until the load reaches the periodic load, and then gradually unload the load on the pile foundation until the load is 0. Measure the vertical displacement of the pile foundation after each loading and unloading, where N is a positive number.

[0008] S2, Repeat step S1 multiple times;

[0009] S3. Divide the N%-M% test load into multiple periodic loads with an increment of Q%, where M and Q are both positive numbers. Load and unload the pile foundation in ascending order, with each periodic load as the maximum load: gradually increase the load on the pile foundation until the load reaches the periodic load, and then gradually unload the load on the pile foundation until the load is 0. Measure the vertical displacement of the pile foundation after each loading and unloading.

[0010] S4. After the pile foundation has completed the loading and unloading of M% of the test load, the pile foundation is gradually loaded until the load reaches 100% of the test load. Then the pile foundation is gradually unloaded until the load is 0. The vertical displacement of the pile foundation is measured after each loading and unloading.

[0011] Furthermore, in step S1, N = 10, and 10% of the test load is taken as the low load.

[0012] Furthermore, in step S1, when loading and unloading the pile foundation at each stage, the load for each loading and unloading stage is 5% of the test load.

[0013] Furthermore, in step S1, the time interval between each loading and unloading stage of the pile foundation is 5 minutes.

[0014] Furthermore, in step S3, M = 50, Q = 10, and the increment between adjacent periodic loads is 10%.

[0015] Furthermore, in step S3, when loading and unloading the pile foundation at each stage, the load for each stage of loading and unloading is 5% of the test load.

[0016] Furthermore, in step S3, the time interval between each loading and unloading stage of the pile foundation is 10 minutes.

[0017] Furthermore, in step S4, when the pile foundation is gradually loaded to 20% of the test load, the test load is increased by 5% for each level; when the test load is loaded from 20% to 100%, the test load is increased by 10% for each level.

[0018] Furthermore, in step S4, when applying the test load to the pile foundation in stages, the vertical displacement of the pile foundation is measured at the 5th, 15th, 30th, 45th and 60th minutes after each load is applied, and then the vertical displacement of the pile foundation is measured every 30 minutes thereafter.

[0019] Furthermore, in step S4, when applying loads to the pile foundation in stages, the next level of load is applied only when the pile foundation displacement rate reaches a relatively stable standard.

[0020] The beneficial effects of the technical solutions provided by the embodiments of the present invention are as follows:

[0021] This invention discloses a low-cycle reciprocating multi-cycle pile foundation tensile static load testing method, applied to the bearing capacity testing of pile foundations subjected to low-cycle reciprocating tensile and compressive loads. It employs the low-cycle reciprocating principle to establish a "multi-cycle loading" collaborative stress model for deformation analysis. Multiple reciprocating static tests are applied to the pile foundation components, subjecting them to repeated loading and unloading processes in both positive and negative directions. The static method is used to determine the effect of vibration on the pile foundation components, exploring the stress-strain state of the structure under "low-cycle reciprocating" stress characteristics. The range and relationship of the pile foundation's elastoplastic deformation can be determined based on the stress and displacement curves. Attached Figure Description

[0022] Figure 1 This is a time-load curve of the traditional pull-out resistance testing method in the background technology;

[0023] Figure 2 This is a flowchart of a method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundations according to the present invention;

[0024] Figure 3 This is a time-load curve of a low-cycle reciprocating multi-cycle pile foundation static load testing method according to the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings. The following description presents a preferred embodiment of the various possible embodiments of the present invention, intended to provide a basic understanding of the invention, but not intended to identify key or decisive elements of the invention or to limit the scope of protection sought.

[0026] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0027] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0028] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures. Also, it should be understood that, for ease of description, the dimensions of the various parts shown in the figures are not drawn to actual scale.

[0029] It should be further noted that, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] Please refer to Figure 2 and 3 The present invention provides a method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundation, including the following steps S1-S4.

[0031] S1. Loading and unloading the pile foundation with N% test load as low load: Gradually increase the load on the pile foundation until the load reaches the periodic load, and then gradually unload the load on the pile foundation until the load is 0. Measure the vertical displacement of the pile foundation after each loading and unloading, where N is a positive number.

[0032] Generally, N=10, and 10% of the test load is taken as the low load. When loading and unloading the pile foundation in stages, the load for each stage of loading and unloading is 5% of the test load, and the time interval between each stage of loading and unloading is 5 minutes.

[0033] In this embodiment, the loading and unloading of the pile foundation using 10% of the test load as the low load is as follows: the load is increased to 5% of the test load at the 5th minute, the load is increased to 10% of the test load at the 10th minute, the load is unloaded to 5% of the test load at the 15th minute, and the load is reduced to 0 at the 20th minute, thus completing one cycle of low load loading and unloading. During this period, the vertical displacement of the pile foundation is measured every 5 minutes after loading and unloading.

[0034] S2. Repeat step S1 multiple times. The number of repetitions can be determined according to the actual testing needs. For example, in this embodiment, the above steps are repeated 8 times to complete 9 cycles of pile foundation load loading and unloading.

[0035] S3. Divide the N%-M% test load into multiple periodic loads with an increment of Q%, where M and Q are both positive numbers. Load and unload the pile foundation in ascending order, with each periodic load as the maximum load: gradually increase the load on the pile foundation until the load reaches the periodic load, and then gradually unload the load on the pile foundation until the load is 0. Measure the vertical displacement of the pile foundation after each loading and unloading.

[0036] Generally, M=50, Q=10, and the increment between adjacent periodic loads is 10%. When loading and unloading the pile foundation in stages, the load for each stage of loading and unloading is 5% of the test load, and the time interval between each stage of loading and unloading is 10 minutes.

[0037] In this embodiment, the loading and unloading of test loads of 20%, 30%, 40%, and 50% are performed sequentially from small to large. Specifically:

[0038] The 10th cycle of pile foundation load loading and unloading: A load is added every 10 minutes, and then gradually unloaded after reaching the required value for this cycle. The initial load is 10%, i.e., 10% at the 10th minute, 15% at the 20th minute, 20% at the 30th minute, 15% at the 40th minute, 10% at the 50th minute, and 0% at the 60th minute. The vertical displacement of the pile foundation is measured every 10 minutes during this period.

[0039] The 11th cycle of pile foundation load loading and unloading: Following the 10th cycle of pile foundation load loading and unloading method, the load is applied in stages, with the maximum load increased to 30%, and then gradually unloaded to 0.

[0040] The 12th cycle of pile foundation load loading and unloading: Following the 10th cycle of pile foundation load loading and unloading method, the load is applied in stages, with the maximum load increased to 40%, and then gradually unloaded to 0.

[0041] The 13th cycle of pile foundation load loading and unloading: Following the 10th cycle of pile foundation load loading and unloading method, the load is applied in stages, with the maximum load increased to 50%, and then gradually unloaded to 0.

[0042] S4. After the pile foundation has completed the loading and unloading of M% of the test load, the pile foundation is gradually loaded until the load reaches 100% of the test load. Then the pile foundation is gradually unloaded until the load is 0. The vertical displacement of the pile foundation is measured after each loading and unloading.

[0043] Specifically, when the pile foundation is gradually loaded to 20% of the test load, the test load is increased by 5% for each level; when the test load is loaded from 20% to 100%, the test load is increased by 10% for each level.

[0044] When applying test loads to the pile foundation in stages, the vertical displacement of the pile foundation should be measured at 5, 15, 30, 45, and 60 minutes after each load level is applied, and then every 30 minutes thereafter. The next load level should only be applied when the pile foundation displacement rate reaches a relatively stable standard. The relative stability standard for pile foundation settlement is: the vertical displacement of the pile foundation (pile top settlement) should not exceed 0.1 mm per hour, and this should occur twice consecutively (calculated starting from the 30th minute after the application of the graded load, based on three consecutive 30-minute settlement observations over 1.5 hours).

[0045] During unloading, each load level is maintained for 1 hour. The vertical displacement (settlement at the pile top) of the pile foundation is measured at the 15th, 30th, and 60th minutes, after which the first load level can be unloaded. After unloading to zero, the residual displacement at the pile top is measured for 3 hours, with measurements taken at the 15th and 30th minutes, and then every 30 minutes thereafter.

[0046] like Figure 2 As shown, the present invention discloses a method for static load testing of low-cycle reciprocating pile foundations. This method employs the low-cycle reciprocating principle to establish a collaborative stress model of "multi-cycle loading" for deformation analysis. Multiple reciprocating static tests are applied to the pile foundation components, causing them to repeatedly undergo loading and unloading in both directions. The static method is used to determine the effect of vibration on the pile foundation components, exploring the stress-strain state of the structure under "low-cycle reciprocating" stress characteristics. The range and relationship of the elastoplastic deformation of the pile foundation can be determined based on the stress and displacement curves.

[0047] In this document, the directional terms such as front, back, top, and bottom are defined based on the position of the components in the accompanying drawings and their relative positions to each other, solely for the purpose of clarity and convenience in expressing the technical solution. It should be understood that these are relative concepts and can vary depending on different methods of use and placement; the use of these directional terms should not limit the scope of protection claimed in this application.

[0048] Where there is no conflict, the embodiments and features described above can be combined with each other. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundations, characterized in that, Includes the following steps: S1. Using N% test load as a low load, load and unload the pile foundation: gradually increase the load on the pile foundation until the load reaches the periodic load, and then gradually unload the load on the pile foundation until the load is 0. Measure the vertical displacement of the pile foundation after each loading and unloading, where N is a positive number. S2, Repeat step S1 multiple times; S3. Divide the N%-M% test load into multiple periodic loads with an increment of Q%, where M and Q are both positive numbers. Load and unload the pile foundation in ascending order, with each periodic load as the maximum load: gradually increase the load on the pile foundation until the load reaches the periodic load, and then gradually unload the load on the pile foundation until the load is 0. Measure the vertical displacement of the pile foundation after each loading and unloading. S4. After the pile foundation has completed the loading and unloading of M% test load, the pile foundation is gradually loaded until the load reaches 100% test load, and then the pile foundation is gradually unloaded until the load is 0. The vertical displacement of the pile foundation is measured after each loading and unloading. In step S4, when the pile foundation is gradually loaded to 20% of the test load, the test load is increased by 5% for each level; when the test load is loaded from 20% to 100%, the test load is increased by 10% for each level. In step S4, when the test load is applied to the pile foundation in stages, the vertical displacement of the pile foundation is measured at the 5th, 15th, 30th, 45th and 60th minutes after each load is applied, and then the vertical displacement of the pile foundation is measured every 30 minutes thereafter. In step S4, when the pile foundation is gradually loaded, the next level of load is applied only when the pile foundation displacement rate reaches a relatively stable standard.

2. The method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundations as described in claim 1, characterized in that: In step S1, N=10, and 10% of the test load is taken as the low load.

3. The method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundations as described in claim 2, characterized in that: In step S1, when loading and unloading the pile foundation at each stage, the load for each loading and unloading stage is 5% of the test load.

4. The method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundations as described in claim 3, characterized in that: In step S1, the time interval between each loading and unloading stage of the pile foundation is 5 minutes.

5. The method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundations as described in claim 2, characterized in that: In step S3, M=50, Q=10, and the increment between adjacent periodic loads is 10%.

6. The method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundations as described in claim 5, characterized in that: In step S3, when loading and unloading the pile foundation at each stage, the load for each loading and unloading stage is 5% of the test load.

7. The method for detecting static pull-out load of low-cycle reciprocating multi-cycle pile foundations as described in claim 5, characterized in that: In step S3, the time interval between each loading and unloading stage of the pile foundation is 10 minutes.

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