Device and method for testing the pile-soil friction coefficient of steel spiral piles

Abstract

The application provides a kind of steel spiral pile and determination method of pile-soil friction coefficient testing device.The testing device includes steel spiral pile, limiting support, rotation limiter, force equipment, pressure gauge, ammeter, scale, camera and data acquisition analyzer.Data collected by pressure gauge, ammeter and camera can be gathered by data acquisition analyzer, and the testing process is analyzed and controlled in real time, and the real force-displacement (F-U) curve of steel spiral pile in the whole loading process is given.The determination method can convert the friction coefficient of each part of steel spiral pile and soil into the friction coefficient of whole pile and soil, and based on the comparison method of test and numerical simulation, the real and accurate pile-soil friction coefficient can be obtained.The problem that pile-soil friction coefficient cannot be accurately measured in the current spiral pile design and construction is solved.The determination method of the application is simple, fast and practical, and the determination data is comprehensive, real and accurate.

Description

Technical Field

[0001] This invention belongs to the field of building construction technology, and in particular relates to a pile-soil friction coefficient testing device and method for steel helical piles. Background Technology

[0002] Steel helical piles, also known as ground screws, are pipe piles with helical blades wound around the surface of a hot-forged metal tube. They are screwed into the ground by specialized ground screw tightening equipment, replacing the original concrete foundation, with the top connected to the load. As an underground foundation, ground screws have advantages such as convenient construction, short construction period, minimal impact from the construction environment, no damage to the local environment, and easy relocation and recycling.

[0003] Steel helical piles are generally assembled from three parts: a steel pipe, a helical surface, and a bottom pile tip. After the helical pile is driven into the predetermined position in the stratum using helical pressing or vertical driving methods, pile bearing capacity (compression, tension, etc.) tests need to be carried out to verify the pile foundation's bearing performance. The pile-soil friction coefficient is often a key construction parameter that hinders design and construction. Conventional pile-soil friction coefficient testing methods cannot accurately detect and obtain the coefficient due to the following problems:

[0004] 1. The construction process of helical piles will squeeze and disturb the surrounding soil. After construction, there will be a certain gap between the pile and the soil, and the pile-soil contact surface will not be completely in contact. This will bring more difficulties to the determination of important construction parameters (pile-soil friction coefficient) during pile bearing capacity testing.

[0005] 2. During the contact between the steel pipe, helical surface, and bottom pile tip of the helical pile and the soil, the interaction between each part and the soil is inconsistent. For example, the side wall of the steel pipe is approximately perpendicular to the soil, the side wall of the pile tip is inclined to the soil, the outer surface of the helical surface is approximately perpendicular to the soil, and the upper and lower surfaces of the helical surface are in a combined tension and compression contact with the soil.

[0006] 3. During the compression or tension stage, the interaction between the various parts of the helical pile and the surrounding soil includes complex and dynamic relationships such as vertical friction, inclined friction, tensile load, and ballast load.

[0007] Traditional laboratory material testing methods for determining the pile-soil friction coefficient can only obtain friction values ​​for a single working condition, such as the vertical friction coefficient between the steel pipe sidewall and the soil, or the inclined friction coefficient between the pile tip sidewall and the soil. The helical pile structure is complex, and the bearing capacity test studies the interaction between the helical pile as a whole and the soil. A single working condition cannot be used to guide the relationship coefficient between the helical pile as a whole and the soil, and cannot be directly used for the design and construction of helical pile structures. Summary of the Invention

[0008] The purpose of this invention is to provide a testing device and method for the pile-soil friction coefficient of steel helical piles, so as to solve the problem that the pile-soil friction coefficient cannot be accurately measured in the current design and construction of helical piles.

[0009] The present invention is implemented as follows: a testing device for the coefficient of friction between a steel helical pile and soil includes a steel helical pile, a limiting bracket, a rotation limiter, a force application device, a pressure gauge, an ammeter, a scale, a camera, and a data acquisition and analysis instrument.

[0010] The steel spiral pile is used to drive into the soil;

[0011] The limiting bracket is used to ensure that the steel helical pile is always perpendicular to the ground surface, and the top end of the steel helical pile is rotatably inserted into the limiting bracket.

[0012] The rotation limiter is used to prevent the steel helical pile from rotating after loading. The rotation limiter is fixed on the limit bracket and located at the top of the steel helical pile.

[0013] The force-applying device is an electrically powered device used to apply pressure or tension to the top of the steel helical pile;

[0014] The pressure gauge is used to measure the pressure or tension borne by the top of the steel helical pile in real time;

[0015] The ammeter is used to measure the current flowing into the force-applying device in real time.

[0016] The ruler is fixed horizontally at the top of the steel helical pile and is positioned above the soil.

[0017] The camera is used to monitor the vertical position change of the ruler relative to the ground surface in real time;

[0018] The ammeter is connected to the force-applying device via a cable. The pressure gauge, ammeter, and camera are all connected to the data acquisition and analysis instrument via cable or wireless communication to transmit signals. The data acquisition and analysis instrument is used to collect the data collected by the pressure gauge, ammeter, and camera, and to analyze and control the test process in real time, providing the true force-displacement (FU) curve of the steel helical pile throughout the loading process.

[0019] Furthermore, the rotary limiter includes a hollow sleeve, which is vertically fixed on the limiting bracket; the steel helical pile is vertically inserted into the hollow sleeve.

[0020] Furthermore, the limiting bracket includes several right-angled triangular support plates, with one right-angled end of each right-angled triangular support plate close to the steel helical pile, and the top of the right-angled end of each right-angled triangular support plate being fixedly connected to the outer periphery of the hollow sleeve.

[0021] Furthermore, the pile body material of the steel helical pile should preferably be ordinary steel or low alloy steel pipe, the wall thickness of the steel pipe should not be less than 4mm, and the galvanized layer of the pile body should not be less than 80μm.

[0022] To achieve the above-mentioned objectives, the present invention also provides a method for determining the pile-soil friction coefficient of a steel helical pile using the aforementioned testing device, the method comprising the following steps:

[0023] S10. The test is carried out using the test device, and the current intensity A of the force application device, the top pressure / tension force F of the steel helical pile and the displacement U of the steel helical pile are collected respectively. The test process is controlled in real time by the data acquisition and analysis instrument, and the true force-displacement (FU) curve of the steel helical pile during the entire loading process is given.

[0024] S20. Based on the preliminary engineering design of the steel helical pile, the design parameters, stratum parameters and pile body parameters are preliminarily determined, a numerical simulation analysis model is established, and a finite element simulation model trial calculation is carried out. Based on the maximum settlement value, the preliminary estimated pile-soil friction coefficient μ0 of the simulated steel helical pile can be obtained, and the simulated force-displacement (FU) curve of the simulated steel helical pile is obtained.

[0025] S30. Based on the engineering design requirements and calculation accuracy, determine the allowable error range / value Δ for curve fitting. Perform mathematical fitting and comparative analysis between the actual force-displacement (FU) curve and the simulated force-displacement (FU) curve. When the error between the two is greater than the allowable error range / value Δ, return to the simulation analysis, adjust the initial value μ0 to μ1 using the interpolation method, recalculate the model to obtain the second simulated force-displacement (FU) curve, and continue to conduct error comparison. Repeat this process until a value μ smaller than the error requirement is obtained. The obtained μ value is the pile-soil friction coefficient of the steel helical pile. The obtained pile-soil friction coefficient can provide a scientific reference for the design and construction of steel helical piles.

[0026] Compared with the prior art, the beneficial effects of this invention are as follows:

[0027] This invention proposes a pile-soil friction coefficient testing device and a method for determining the pile-soil friction coefficient using this device. This method converts the friction coefficients of individual components of a steel helical pile with the soil into the overall pile-soil friction coefficient. Based on experimental testing and numerical simulation comparison, the true and accurate pile-soil friction coefficient can be obtained. This solves the current problem of inaccurate pile-soil friction coefficient measurement in the design and construction of helical piles. The testing method of this invention is simple, fast, highly practical, and provides comprehensive, accurate, and reliable data. Attached Figure Description

[0028] Figure 1This is a schematic diagram of the structure of a pile-soil friction coefficient testing device for steel helical piles provided in an embodiment of the present invention;

[0029] Figure 2 This is a flowchart of a method for determining the pile-soil friction coefficient of a steel helical pile, provided in an embodiment of the present invention.

[0030] Explanation of reference numerals in the attached diagram:

[0031] 1-Steel spiral pile, 2-Limit bracket, 3-Rotation limiter, 4-Force application equipment, 5-Pressure gauge, 6-Ammeter, 7-Scale, 8-Camera, 9-Data acquisition and analysis instrument, 10-Soil, 11-Ground surface. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "front," "rear," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention; the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "joined" 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 direct connection or an indirect connection through an intermediate medium, or they can refer to the internal communication 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.

[0034] Please refer to Figure 1 This embodiment shows a test device for the coefficient of friction between a steel helical pile and soil, including a steel helical pile 1, a limiting bracket 2, a rotation limiter 3, a force application device 4, a pressure gauge 5, an ammeter 6, a scale 7, a camera 8, and a data acquisition and analysis instrument 9.

[0035] The steel spiral pile 1 is used to drive into the soil 10. The pile body material of the steel spiral pile 1 should preferably be ordinary steel or low alloy steel pipe, the wall thickness of the steel pipe of the pile body should not be less than 4mm, and the zinc coating of the pile body should not be less than 80μm.

[0036] The limiting bracket 2 is used to ensure that the steel helical pile 1 is always perpendicular to the ground surface 11, and the top end of the steel helical pile 1 is rotatably inserted into the limiting bracket 2. The rotating limiter 3 is used to prevent the steel helical pile 1 from rotating after loading. The rotating limiter 3 is fixed on the limiting bracket 2 and located at the top of the steel helical pile 1.

[0037] The force-applying device 4 is an electrically powered device used to apply pressure or tension to the top of the steel helical pile 1;

[0038] Pressure gauge 5 is used to measure the pressure or tension borne by the top of the steel helical pile 1 in real time;

[0039] Ammeter 6 is used to measure the current flowing into the force-applying device 4 in real time;

[0040] The ruler 7 is fixed horizontally at the top of the steel helical pile 1 and is located above the soil 10;

[0041] Camera 8 is used to monitor the vertical position change of scale 7 relative to ground surface 11 in real time;

[0042] The ammeter 6 is connected to the force application device 4 via a cable. The pressure gauge 5, ammeter 6, and camera 8 all transmit signals to the data acquisition and analysis instrument 9 via cable or wireless communication. For example, a wireless transmitting module can be added to the ammeter 6, and a wireless receiving module can be added to the data acquisition and analysis instrument 9. The wireless transmitting module transmits the signal from the ammeter 6 to the wireless receiving module of the data acquisition and analysis instrument 9, and the wireless receiving module then transmits the signal to the data acquisition and analysis instrument 9. The data acquisition and analysis instrument 9 is used to collect the data collected by the pressure gauge 5, ammeter 6, and camera 8, and analyze and control the test process in real time, providing the true force-displacement (FU) curve of the steel helical pile 1 throughout the loading process.

[0043] Specifically, the rotary limiter 3 includes a hollow sleeve, which is vertically fixed on the limit bracket 2; the steel helical pile 1 is vertically inserted into the hollow sleeve.

[0044] Specifically, the limiting bracket 2 includes several right-angled triangular support plates, with one right-angled end of each right-angled triangular support plate close to the steel spiral pile 1, and the top of the right-angled end of the right-angled triangular support plate being fixedly connected to the outer periphery of the hollow sleeve.

[0045] Based on the aforementioned testing device, this embodiment also provides a method for determining the pile-soil friction coefficient of the steel helical pile 1. Please refer to [link / reference]. Figure 2 The method includes the following steps:

[0046] S10. The test is carried out using a testing device. The current intensity A of the force application device 4, the top pressure / tension force F of the steel helical pile 1 and the displacement U of the steel helical pile 1 are collected respectively. The test process is controlled in real time by the data acquisition and analysis instrument 9, and the true force-displacement (FU) curve of the steel helical pile 1 during the entire loading process is given.

[0047] S20. Based on the preliminary engineering design of the steel helical pile 1, the design parameters, stratum parameters and pile body parameters are preliminarily determined, a numerical simulation analysis model is established, and a finite element simulation model trial calculation is carried out. Based on the maximum settlement value, the preliminary estimated pile-soil friction coefficient μ0 of the simulated steel helical pile can be obtained, and the simulated force-displacement (FU) curve of the simulated steel helical pile is obtained.

[0048] S30. Based on the engineering design requirements and calculation accuracy, determine the allowable error range / value Δ for curve fitting. Perform mathematical fitting and comparative analysis between the actual force-displacement (FU) curve and the simulated force-displacement (FU) curve. When the error between the two is greater than the allowable error range / value Δ, return to the simulation analysis. Use interpolation to adjust the initial value μ0 to μ1, recalculate the model to obtain the second simulated force-displacement (FU) curve, and continue to compare the errors. Repeat this process until a value μ smaller than the error requirement is obtained. The obtained μ value is the actual pile-soil friction coefficient of the steel helical pile 1. The obtained pile-soil friction coefficient can provide a scientific reference for the design and construction of the steel helical pile 1.

[0049] The testing apparatus and method described in this embodiment are applicable to the determination of pile-soil friction coefficients in various strata, including fill, silt, cohesive soil, sand, loose to medium-dense gravelly soil, completely weathered rock, and strongly weathered soft rock. They can be applied to geotechnical and underground engineering, trenchless pile construction, foundation reinforcement, and prefabricated building foundations.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the pile-soil friction coefficient of a steel screw pile using a testing device; characterized in that, The test device comprises a steel spiral pile, a limiting support, a rotation limiter, a force applying device, a pressure gauge, an ammeter, a ruler, a camera and a data acquisition and analysis instrument. The steel spiral pile is used to screw into the soil. The limiting support is used to make the steel spiral pile always perpendicular to the ground surface, and the top end of the steel spiral pile is rotatably arranged in the limiting support. The rotation limiter is used to prevent the steel spiral pile from rotating after being loaded, and is fixed on the limiting support and located at the top of the steel spiral pile. The force applying device is a power device powered by electricity, which is used to apply pressure or tension to the top of the steel spiral pile. The pressure gauge is used to measure the pressure or tension borne by the top of the steel spiral pile in real time. The ammeter is used to measure the current flowing into the force applying device in real time. The ruler is horizontally fixed at the top position of the steel spiral pile and located above the soil. The camera is used to monitor the vertical position change of the ruler relative to the ground surface in real time. The ammeter is connected with the force applying device through a cable, and the pressure gauge, ammeter and camera realize signal transmission through a cable or wireless communication mode, the data acquisition and analysis instrument is used to collect the data collected by the pressure gauge, ammeter and camera, and analyze and control the test process in real time, and give the real force-displacement (F-U) curve of the steel spiral pile in the whole loading process. The method comprises the following steps: S10. The test device is used to carry out the test, the monitoring current intensity A of the force applying device, the top pressure / tension F of the steel spiral pile and the displacement U of the steel spiral pile are collected respectively, the data acquisition and analysis instrument is used to control the test process in real time, and the real force-displacement (F-U) curve of the steel spiral pile in the whole loading process is given. S20. According to the preliminary design of the steel spiral pile, the design parameters, stratum parameters and pile body parameters are preliminarily determined, a numerical simulation analysis model is established, a finite element simulation model is tried, and the maximum settlement value is obtained. The preliminary estimated pile-soil friction coefficient μ0 of the simulation steel spiral pile is obtained, and the simulation force-displacement (F-U) curve of the simulation steel spiral pile is obtained. S30. According to the engineering design requirements and calculation accuracy, the error range / value ∆ allowed for curve fitting is formulated, the real force-displacement (F-U) curve is compared and analyzed with the simulation force-displacement (F-U) curve by mathematical method, when the error between the two curves is greater than the allowed error range / value ∆, return to the simulation analysis, adjust the initial value μ0 to μ1 by interpolation method, recalculate the model to obtain the second simulation force-displacement (F-U) curve, continue to carry out error comparison, and cycle repeatedly until the μ value less than the error requirement is obtained. The μ value obtained is the pile-soil friction coefficient of the steel spiral pile, and the pile-soil friction coefficient obtained can provide scientific reference for the design and construction of the steel spiral pile.

2. The method of claim 1, wherein, The rotation limiter comprises a hollow sleeve, which is vertically fixed on the limiting support, and the steel spiral pile is vertically inserted into the hollow sleeve.

3. The method of claim 2, wherein, The limiting support comprises several right-angled triangle support plates, and a right-angled end of each of the right-angled triangle support plates is close to the steel spiral pile, and a top of the right-angled end of the right-angled triangle support plate is fixedly connected with an outer periphery of the hollow sleeve.

4. The method of claim 1, wherein, The pile body material of the steel spiral pile is preferably ordinary steel or low-alloy steel pipe, the wall thickness of the pile body steel pipe is not less than 4 mm, and the galvanizing layer of the pile body is not less than 80 μm.

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