Method for testing dynamic stress of bridge or wharf pile body by using water pressure in pile side water

Abstract

The invention belongs to the technical field of pile foundation detection, and particularly relates to a method for testing dynamic stress of a bridge or wharf pile body by using water pressure in pile side water, which comprises the following steps of: arranging a hydrophone on the pile side; the hydrophone is put into water; a vertical instantaneous excitation load is applied to the pile top; the instantaneous excitation load causes water pressure change around the pile while enabling the pile body to vibrate, and the hydrophone receives a pressure intensity response result of the water pressure; and obtaining a pile body dynamic stress change value according to the pressure response curve. According to the method, the testing process is simple, a sensor does not need to be installed independently, only the hydrophone needs to be arranged at a certain depth in water, and the problems of engineering time, manpower and economic cost are solved; and the dynamic stress of the pile body is directly reflected on the basis of a pressure curve measured by the hydrophone, so that most of hypotheses and empirical parameter values are reduced, and the test result is more accurate.

Description

Technical Field

[0001] The invention belongs to the technical field of pile foundation detection, and in particular relates to a method for testing the dynamic stress of a bridge or dock pile body by utilizing underwater water pressure at the pile side. Background Art

[0002] Pile foundations are the most commonly used foundation type in various infrastructure projects, including construction, transportation (highways, railway bridges), water conservancy, and municipal engineering. They offer advantages such as high bearing capacity and minimal post-construction settlement. Testing the bearing capacity of pile foundations is crucial for ensuring the quality of pile foundation projects. The quality of testing, methods, and conclusions directly impact the safe and functional operation of the building. Static load tests and dynamic tests are commonly used in engineering projects.

[0003] Static load test is a traditional method for testing bearing capacity and is also the most reliable testing method. It is a very mature testing method, but it often requires a large reaction device, resulting in high testing costs and long cycles. It may even be impossible to implement under some conditions (such as in deep waters and pile foundations used in docks).

[0004] High-strain testing evaluates and calculates the bearing capacity of piles by analyzing the effect of soil resistance on measured force and velocity signals. Therefore, both force and velocity signals must be measured during testing, and the measured data significantly influence the results of high-strain testing. However, in actual applications, inferring pile stress based on strain presents the following problems: ① Existing sensors have difficulty accurately measuring the dynamic strain of the pile; ② The dynamic stress of the pile is not only related to the dynamic strain of the pile, but also requires the knowledge of the pile's Young's modulus. However, existing pile Young's modulus values are mostly based on empirical values. Therefore, indirectly calculating pile stress through strain also has significant errors, posing a significant challenge to the future promotion and application of high-strain methods. Therefore, a method for testing the dynamic stress of bridge or pier piles using underwater hydrostatic pressure on the side of the pile is urgently needed to address this issue. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for testing the dynamic stress of a bridge or pier pile body by utilizing the water pressure in the water at the pile side, so as to solve the above-mentioned problem.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The method of testing the dynamic stress of a bridge or pier pile using underwater water pressure on the pile side includes:

[0008] Set up hydrophones on the pile side;

[0009] Lower the hydrophone into the water;

[0010] Applying vertical instantaneous excitation load to the pile top will generate dynamic stress in the pile body;

[0011] The instantaneous excitation load causes the pile body to vibrate and simultaneously induces a change in water pressure around the pile, and the hydrophone obtains a pressure response value of the water pressure;

[0012] Substituting the pressure response value into the pile body dynamic stress value-pressure response value corresponding curve to obtain the pile body dynamic stress value.

[0013] Optionally, the distance between the hydrophone and the water surface is h, where h>2D, where D is the outer diameter of the pile body;

[0014] The horizontal distance between the hydrophone and the pile body is Δx.

[0015] Optionally, a gravity portion is connected below the hydrophone to prevent the hydrophone from shaking.

[0016] Optionally, the gravity part is a weight block, which is fixed to the bottom of the hydrophone through a connecting rope. The bottom end of the suspension rope is tied to the top of the hydrophone, and the top end of the suspension rope is fixed to the bottom of the bridge body or the bottom of the pier floor. The suspension rope is set vertically.

[0017] Optionally, two hydrophones are provided, and the two hydrophones are symmetrically arranged on both sides of the pile body.

[0018] Optional,

[0019] The method for obtaining the pile body dynamic stress value-pressure response value corresponding curve comprises the following steps:

[0020] An indoor pile is established as an indoor test model, with the bottom of the indoor pile located below the water surface;

[0021] Applying the instantaneous excitation load of a set value to the top of the indoor pile to vibrate the indoor pile body and generate dynamic stress;

[0022] The vibration of the indoor pile body causes changes in water pressure around the pile;

[0023] Obtaining the dynamic stress value of the pile body of the indoor pile and the pressure response value of the water pressure change generated by the indoor pile underwater;

[0024] The value of the transient excitation load is changed, and the above steps are repeated to obtain several pile body dynamic stress values and several pressure response values under indoor pile conditions, and a corresponding curve of the pile body dynamic stress value-pressure response value is plotted.

[0025] Optionally, the method for obtaining the dynamic stress value of the pile body of the indoor pile comprises the following steps:

[0026] A strain gauge is arranged on the pile side of the indoor pile, and the strain gauge is used to obtain the dynamic stress change value of the pile body;

[0027] The method for obtaining the pressure response value of the water pressure change generated by the indoor pile underwater includes the following steps:

[0028] The hydrophone is arranged on one side of the indoor pile and is located below the water surface.

[0029] Optionally, the method for obtaining the pile body dynamic stress value-pressure response value corresponding curve includes the following steps:

[0030] The theoretical value of dynamic stress of pile body is obtained according to the axisymmetric vibration control equation of pile body;

[0031] The data of the pile-water force is obtained based on the pile body dynamic stress theory;

[0032] Obtaining a theoretical value of water pressure response based on the data of the force exerted by the pile on water;

[0033] The pile body dynamic stress value-pressure response value corresponding curve is obtained by plotting the theoretical value of the pile body dynamic stress and the theoretical value of the pressure response.

[0034] Optionally, the axisymmetric vibration control equation of the pile body is:

[0035]

[0036] Where λ p , G p is the Lame constant of the pile material; ρ p is the density of the pile material; U p (r, z, ω) is the displacement function of the pile body particle in the Laplace domain; s=β+iω is a complex variable; the axisymmetric vibration control equation of the pile body is solved by Laplace transformation to obtain the dynamic stress data of the pile body.

[0037] Optionally, the method for obtaining the theoretical value of the pressure response includes the following steps:

[0038] Substitute the theoretical value of the pile body dynamic stress into

[0039]

[0040] Solve and obtain the data of the pile's force on water, and substitute the data of the pile's force on water into

[0041]

[0042] Solve and obtain the theoretical value of the pressure response, where φ f is the fluid displacement potential function; η=(-s 2 ) 1 / 2 ρf is the density of the fluid in the tube; v c Considering the shear wave velocity v of the pipe wall medium ps and the longitudinal wave velocity v of the fluid in the tube w The tube wave velocity.

[0043] Compared with the prior art, the present invention has the following advantages and technical effects:

[0044] During use, hydrophones are placed on the side of the pile and a vertical instantaneous excitation load is applied to the pile top. Under the vertical excitation conditions at the pile top, stress waves propagate along the pile body, simultaneously stimulating new waves in the surrounding area. These new waves on the pile side generate water pressure changes. The pressure value of this water pressure change is obtained through the hydrophone, and the dynamic stress change in the pile body can be obtained from the pressure response curve. This method simplifies the testing process and does not require the installation of separate sensors. Simply placing hydrophones at a certain depth in the water can help reduce engineering time, manpower, and economic costs. Furthermore, the pressure curve measured by the hydrophones directly reflects the dynamic stress of the pile body, eliminating most assumptions and empirical parameter values, resulting in more accurate test results. Furthermore, due to limitations, traditional methods can only place sensors close to the pile top. This leads to significant errors in estimating the pile bearing capacity through high-strain testing due to the stress concentration at the pile top. This method allows simultaneous placement of sensors at multiple depths along the pile side, improving the accuracy of high-strain test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive work.

[0046] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] Reference Figure 1The present invention discloses a method for testing the dynamic stress of a bridge or dock pile body by using water pressure in water on the pile side, comprising:

[0050] Set up hydrophones on the pile side;

[0051] Lower the hydrophone into the water;

[0052] Applying vertical instantaneous excitation load to the pile top will generate dynamic stress in the pile body;

[0053] The transient excitation load causes the pile to vibrate and simultaneously induces changes in the water pressure around the pile. The hydrophone obtains the pressure response value of the water pressure.

[0054] Substitute the pressure response value into the pile body dynamic stress value-pressure response value corresponding curve to obtain the pile body dynamic stress value.

[0055] During use, hydrophones are placed on the side of the pile and a vertical instantaneous excitation load is applied to the pile top. Under the vertical excitation conditions at the pile top, stress waves propagate along the pile body, simultaneously stimulating new waves in the surrounding area. These new waves on the pile side generate water pressure changes. The pressure value of this water pressure change is obtained through the hydrophone, and the dynamic stress change in the pile body can be obtained from the pressure response curve. This method simplifies the testing process and does not require the installation of separate sensors. Simply placing hydrophones at a certain depth in the water can help reduce engineering time, manpower, and economic costs. Furthermore, the pressure curve measured by the hydrophones directly reflects the dynamic stress of the pile body, eliminating most assumptions and empirical parameter values, resulting in more accurate test results. Furthermore, due to limitations, traditional methods can only place sensors close to the pile top. This leads to significant errors in estimating the pile bearing capacity through high-strain testing due to the stress concentration at the pile top. This method allows simultaneous placement of sensors at multiple depths along the pile side, improving the accuracy of high-strain test results.

[0056] As an optional embodiment, the distance between the hydrophone and the water surface is h, where h>2D, where D is the outer diameter of the pile body;

[0057] The horizontal distance between the hydrophone and the pile is Δx.

[0058] As an optional implementation, a gravity portion is connected below the hydrophone to prevent the hydrophone from shaking.

[0059] As an optional embodiment, the gravity part is a weight block, which is fixed to the bottom of the hydrophone through a connecting rope. The bottom end of the suspension rope is tied to the top of the hydrophone, and the top end of the suspension rope is fixed to the bottom of the bridge body or the bottom of the pier floor. The suspension rope is set vertically.

[0060] As an optional implementation, two hydrophones are provided, and the two hydrophones are symmetrically arranged on both sides of the pile body.

[0061] (1) Lower the hydrophone into the water to a certain depth h.

[0062] To minimize the impact of eccentricity on the measured signal, hydrophones are typically placed symmetrically on both sides of the pile. In this method, to avoid interference with the test due to factors such as wind and waves, the hydrophones can be placed at a deeper position (h>2D, where D is the outer diameter of the pile), and weights can be placed below the hydrophones to prevent test failures caused by hydrophone misalignment. Furthermore, to prevent underwater signal attenuation, which can lead to unclear test signals, the distance Δx between the hydrophones and the pile side should not be too far, and the value of Δx should tend to be zero.

[0063] (2) Apply vertical instantaneous excitation F to the top of the pile.

[0064] This part is the same as the traditional high strain method, that is, a heavy hammer is used to apply a high energy impact force to the top of the pile. The impact force will cause a certain permanent displacement between the pile and the soil during the process of propagating along the pile body. During this process, the stress wave will also propagate into the water beside the pile, triggering the water pressure response of the pile side. The response is received by the hydrophone and finally plotted as shown below. Figure 1 The pressure response curve on the right.

[0065] (3) Estimate the change of dynamic stress in the pile body based on the measured pressure response curve.

[0066] There are currently two ideas on how to obtain the corresponding relationship between the pressure curve measured by the hydrophone and the dynamic stress of the pile body.

[0067] First, based on indoor model tests, considering the size effect of the model, a known instantaneous load is applied to the pile top in the indoor test, and strain gauges are arranged on the side of the pile to test the dynamic stress of the pile body (compared with field tests, indoor test strain tests are more accurate and can be used as the basis for calculating the pile body stress). At the same time, hydrophones are arranged on the side of the pile. After repeated tests, a calibration curve of the pressure curve measured by the hydrophone and the dynamic stress of the pile body can be obtained to guide field tests.

[0068] The specific method is:

[0069] As an optional implementation,

[0070] The method for obtaining the corresponding curve of pile body dynamic stress value and pressure response value includes the following steps:

[0071] An indoor pile is built as an indoor test model, with the bottom of the indoor pile located below the water surface;

[0072] Apply a set instantaneous excitation load to the top of the indoor pile to make the pile vibrate and generate dynamic stress;

[0073] The vibration of the indoor pile body will cause the water pressure change around the pile;

[0074] Obtain the dynamic stress value of the indoor pile and the pressure response value of the water pressure generated by the indoor pile underwater;

[0075] By changing the value of the transient excitation load and repeating the above steps, several pile body dynamic stress values and several pressure response values under indoor pile conditions are obtained, and the corresponding curve of pile body dynamic stress value-pressure response value is plotted.

[0076] As an optional implementation, the method for obtaining the dynamic stress value of the indoor pile includes the following steps:

[0077] Strain gauges are arranged on the side of the indoor pile to obtain the dynamic stress change value of the pile body;

[0078] The method for obtaining the pressure response value generated by the indoor pile underwater includes the following steps:

[0079] A hydrophone is set on one side of the indoor pile and is located below the water surface.

[0080] Secondly, based on theoretical analysis, the stress of the pile body can be solved by solving the axisymmetric vibration control equation of the pile body and solving it through Laplace transformation. The response of the pile side pressure can be introduced in this process by introducing the Biot fluid displacement potential function and combining it with the boundary conditions of the interaction between the pile body and the water body in the hole. Based on this method, the correspondence between the pressure measured by the hydrophone and the dynamic stress of the pile body can be established to guide field tests.

[0081] As an optional implementation, a method for obtaining a curve corresponding to a pile body dynamic stress value and a pressure response value includes the following steps:

[0082] The theoretical value of dynamic stress of pile body is obtained according to the axisymmetric vibration control equation of pile body;

[0083] The data of pile-to-water force were numerically calculated based on the dynamic stress theory of pile body;

[0084] The theoretical value of water pressure response is obtained based on the data of pile force on water;

[0085] The corresponding curve of pile body dynamic stress value-pressure response value is drawn based on the theoretical value of pile body dynamic stress and the theoretical value of pressure response.

[0086] As an optional implementation, the axisymmetric vibration control equation of the pile body is:

[0087]

[0088] Where λ p , G p is the Lame constant of the pile material; ρ p is the density of the pile material; U pr, z, ω are the displacement functions of the pile body in the Laplace domain; s = β + iω is a complex variable; the dynamic stress data of the pile body are obtained by solving the axisymmetric vibration control equation of the pile body by Laplace transformation.

[0089] As an optional implementation, a method for obtaining a theoretical value of pressure response includes the following steps:

[0090] Substitute the theoretical value of pile body dynamic stress into

[0091]

[0092] Solve and get the pile force data on water. Substitute the pile force data on water into

[0093]

[0094] Solve and obtain the theoretical value of pressure response, where φ f is the fluid displacement potential function; η=-s 21 / 2 ρ f is the density of the fluid in the tube; v c Considering the shear wave velocity v of the pipe wall medium ps and the longitudinal wave velocity v of the fluid in the tube w The tube wave velocity.

[0095] The specific method is:

[0096] The main control equations involved in pile vibration are:

[0097]

[0098] Where λ p , G p is the Lame constant of the pile material; ρ p is the density of the pile material; U p (r, z, ω) is the displacement function of the pile body in the Laplace domain; s = β + iω is a complex variable.

[0099] In order to solve the displacement potential function equation of the fluid in the measuring tube, only the first-order vibration mode of the pile body is taken for calculation. b At the position, the radial stress on the fluid from the inner wall of the pile is:

[0100]

[0101] By introducing the fluid displacement potential function and considering the radial stress input on the inner wall of the pile, the fluid governing equation in the Laplace domain can be written as:

[0102]

[0103] Where, φ f is the fluid displacement potential function; η=(-s 2 ) 1 / 2 ρ f is the density of the fluid in the tube; v c Considering the shear wave velocity v of the pipe wall medium ps and the longitudinal wave velocity v of the fluid in the tube w The tube wave velocity.

[0104] The pressure response values of several water pressure changes measured on site are plotted into a pressure response value curve, which can be used for analysis of high strain test experiments.

[0105] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0106] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for testing the dynamic stress of a bridge or pier pile using water pressure in water on the pile side, characterized in that: include: Set up hydrophones on the pile side; Lower the hydrophone into the water; Applying vertical instantaneous excitation load to the pile top will generate dynamic stress in the pile body; The instantaneous excitation load causes the pile body to vibrate and simultaneously induces a change in water pressure around the pile, and the hydrophone obtains a pressure response value of the water pressure; Substituting the pressure response value into the pile body dynamic stress value-pressure response value corresponding curve to obtain the pile body dynamic stress value.

2. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 1, characterized in that: The distance between the hydrophone and the water surface is h, where h>2D, where D is the outer diameter of the pile body; The horizontal distance between the hydrophone and the pile body is Δx.

3. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 1, characterized in that: A gravity portion is connected below the hydrophone to prevent the hydrophone from shaking.

4. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 3, characterized in that: The gravity part is a weight block, which is fixed to the bottom of the hydrophone through a connecting rope. The bottom end of the suspension rope is tied to the top of the hydrophone, and the top end of the suspension rope is fixed to the bottom of the bridge body or the bottom of the pier floor. The suspension rope is set vertically.

5. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 1, characterized in that: Two hydrophones are provided, and the two hydrophones are symmetrically arranged on both sides of the pile body.

6. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 1, characterized in that: The method for obtaining the pile body dynamic stress value-pressure response value corresponding curve comprises the following steps: An indoor pile is established as an indoor test model, with the bottom of the indoor pile being located below the water surface; Applying the instantaneous excitation load of a set value to the top of the indoor pile to vibrate the indoor pile body and generate dynamic stress; The vibration of the indoor pile body causes changes in water pressure around the pile; Obtaining the dynamic stress value of the pile body of the indoor pile and the pressure response value of the water pressure change generated by the indoor pile underwater; The value of the transient excitation load is changed, and the above steps are repeated to obtain several pile body dynamic stress values and several pressure response values under indoor pile conditions, and a corresponding curve of the pile body dynamic stress value-pressure response value is plotted.

7. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 6, characterized in that: The method for obtaining the dynamic stress value of the pile body of the indoor pile comprises the following steps: A strain gauge is arranged on the pile side of the indoor pile, and the strain gauge is used to obtain the dynamic stress change value of the pile body; The method for obtaining the pressure response value of the water pressure change generated by the indoor pile underwater includes the following steps: The hydrophone is arranged on one side of the indoor pile and is located below the water surface.

8. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 1, characterized in that: The method for obtaining the pile body dynamic stress value-pressure response value corresponding curve comprises the following steps: The theoretical value of dynamic stress of pile body is obtained according to the axisymmetric vibration control equation of pile body; The data of the pile-water force is obtained based on the pile body dynamic stress theory; Obtaining a theoretical value of water pressure response based on the data of the force exerted by the pile on water; The pile body dynamic stress value-pressure response value corresponding curve is obtained by plotting the theoretical value of the pile body dynamic stress and the theoretical value of the pressure response.

9. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 8, characterized in that: The axisymmetric vibration control equation of the pile body is: Where λ p , G p is the Lame constant of the pile material; ρ p is the density of the pile material; U p (r, z, ω) is the displacement function of the pile body particle in the Laplace domain; s=β+iω is a complex variable; the axisymmetric vibration control equation of the pile body is solved by Laplace transformation to obtain the dynamic stress data of the pile body.

10. The method for testing the dynamic stress of a bridge or dock pile using underwater water pressure at the pile side according to claim 8, characterized in that: The method for obtaining the theoretical value of the pressure response comprises the following steps: Substitute the theoretical value of the pile body dynamic stress into Solve and obtain the water force data, substitute the water force data into Solve and obtain the theoretical value of the pressure response, where φ f is the fluid displacement potential function; η=(-s 2 ) 1 / 2 ; ρ f is the density of the fluid in the tube; v c Considering the shear wave velocity v of the pipe wall medium ps and the longitudinal wave velocity v of the fluid in the tube w The tube wave velocity.

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