Method for testing pile length on basis of hole in pile body that does not reach pile toe

Abstract

The present invention relates to the technical field of pile foundation measurement. Disclosed is a method for testing a pile length on the basis of a hole in a pile body that does not reach a pile toe. In the present invention, a hydrophone is used to perform pile length measurement by means of a sonic logging hole passage pre-embedded in a large-diameter pile. The method comprises: using a test hammer to strike the center of a pile top, and using a hydrophone to perform signal collection and generating intra-hole pressure time-depth response graphs generated by a single strike of the test hammer; and splicing the intra-hole pressure time-depth response graphs acquired at various depths to generate fitted curves of a first-arrival wave and a reflected wave, and determining a pile length on the basis of the fitted curves. The method does not require all sonic logging tubes to be intact, and only one intact sonic logging tube is sufficient. In addition, the method can overcome the problem of it being difficult to detect pile toe reflections of deep and long pile foundations in a low-strain reflected wave method, and a pile body stress wave signal propagates in the form of tube waves by means of liquid in a sonic logging tube with relatively low attenuation, thereby enabling clear and intuitive detection of pile toe reflection signals of ultra-long piles.

Description

A method for testing pile length within the pile body but not reaching the bottom hole. Technical Field

[0001] This invention relates to the field of pile foundation testing technology, and in particular to a method for testing the pile length based on the pile body not reaching the bottom hole. Background Technology

[0002] With the advancement of urbanization, large and super-large buildings and structures are increasingly appearing in engineering construction. Under complex geological conditions, pile foundations can effectively transfer the load of the superstructure to the foundation soil. Their reliability and stability are directly related to the safety and service life of the entire project. Therefore, quality inspection of pile foundations is particularly important.

[0003] However, traditional low-strain reflected wave testing methods for pile foundations are limited by their limited excitation energy, making them unsuitable for effectively detecting the integrity of ultra-long pile foundations. Sonic transmission methods used for drilling pile testing often encounter pipe blockage in practical engineering. Furthermore, during construction, sonic logging pipes are easily deformed by concrete pressure, causing tilting or bending, resulting in increased or decreased spacing between pipes. When a sonic logging pipe is blocked, the hydrophone cannot be lowered further, limiting the detection to the pile body above the blockage. In addition, large-diameter pile foundations typically have 3-4 pre-embedded sonic logging pipes depending on the pile radius. Damage to any one of these pipe channels makes sonic transmission testing impossible, wasting the resources of the remaining intact pipes.

[0004] Due to the aforementioned adverse effects, the analysis and judgment of the results of the acoustic transmission method will be directly affected, and it may even be impossible to give the category of pile integrity. Only core drilling or other reliable methods can be used for testing. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing the pile length based on the hole not reaching the bottom of the pile body, so as to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for testing the pile length based on the length of the pile before reaching the bottom hole, comprising the following steps:

[0007] S1. Fill the pre-embedded sonic logging pipe in the pile body with water and lower a hydrophone into the sonic logging pipe;

[0008] S2. Grind the top center of the pile body smooth.

[0009] S3. Use a measuring hammer to strike the flattened position at the top of the pile, use a hydrophone to collect the signal and generate a hole pressure time-depth response map generated by a single hammer strike.

[0010] S4. Raise the hydrophone upwards a certain distance and repeat step S3.

[0011] S5. Repeat the operation in S4 until the hydrophone reaches the top of the pile to complete the measurement.

[0012] S6. The pore pressure time-depth response maps collected at various depths are stitched together to generate fitting curves for the first arrival wave and the reflected wave. The pile length is determined based on the fitting curves.

[0013] Preferably, the diameter of the hydrophone is 5mm to 20mm smaller than the inner diameter of the acoustic tube.

[0014] Preferably, the hammer striking point is located on the center line of the pile body, and the hydrophone is kept stationary during the striking.

[0015] Preferably, the force of the hammer strikes remains consistent each time.

[0016] Preferably, 2 to 4 tapping tests are performed at the same depth in the pile body, and the average value of the test results is taken.

[0017] Preferably, the upward distance of a single hydrophone is 0.5m to 3m.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] 1. The requirements for the quantity and quality of sonic logging tubes are relatively low; only one sonic logging tube inside the pile is needed for testing.

[0020] 2. The testing equipment is simple, requiring only a set of hydrophones and a measuring hammer;

[0021] 3. The test results are easy to analyze. Based on theoretical and actual test results, the depth of the intersection of the peak fitting curves of the incident wave and the reflected wave in the pore pressure depth diagram can be determined as the depth of the pile bottom.

[0022] 4. Less preparation is needed and testing takes less time, so large-scale surveys can be conducted. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 is a simplified diagram of the time-depth response calculation of the inner hole pressure of the acoustic tube according to the present invention.

[0025] Figure 2 is a fitting curve of the pore pressure depth response of the present invention;

[0026] Figure 3 is a fitting curve of the measured pore pressure time-depth response of the present invention; Detailed Implementation

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] As shown in Figures 1 to 3, the present invention provides a method for testing the pile length based on the pile body within the hole not reaching the bottom of the pile, comprising the following steps:

[0029] S1. Fill the pre-embedded sonic logging pipe in the pile body with water, and lower a hydrophone to the bottom of the sonic logging pipe. If there is a blockage, lower it above the blockage position.

[0030] S2. Grind the top center of the pile body smooth.

[0031] S3. Use a measuring hammer to strike the flattened position at the top of the pile, use a hydrophone to collect the signal and generate a hole pressure time-depth response map generated by a single hammer strike.

[0032] S4. Raise the hydrophone upwards a certain distance and repeat step S3.

[0033] S5. Repeat the operation in S4 until the hydrophone reaches the top of the pile to complete the measurement.

[0034] S6. The pore pressure time-depth response maps collected at various depths are stitched together to generate fitting curves for the first arrival wave and the reflected wave. The pile length is determined based on the fitting curves.

[0035] This invention uses a hydrophone to detect pile length by utilizing pre-embedded sonic logging channels within large-diameter piles. This method does not require all sonic logging tubes to be intact; only one is needed. Furthermore, this method overcomes the difficulty of detecting bottom reflections in deep, long piles using the low-strain reflection wave method. The pile stress wave signal propagates as a tube wave through the liquid in the sonic logging tube, resulting in minimal attenuation. Therefore, the bottom reflection signal of ultra-long piles can be detected more clearly and intuitively.

[0036] Further optimization of the scheme involves using a sonic logging tube with an inner diameter of 50mm to 60mm, and a hydrophone with a diameter 5mm to 20mm smaller than the inner diameter of the sonic logging tube.

[0037] To further optimize the scheme and avoid the influence of noise generated by displacement on the judgment, the hammer impact point is located on the center line of the pile body, and the hydrophone is kept stationary during the impact.

[0038] The scheme was further optimized so that the force of each hammer strike remained consistent, and the striking force was related to the pile length; the longer the pile, the greater the striking force.

[0039] To further optimize the plan, 2 to 4 tapping tests were conducted at the same depth in the pile body, and the average value of the test results was taken.

[0040] Further optimization of the scheme resulted in a single hydrophone lifting distance ranging from 0.5m to 3m. The lifting distance is related to the number and spacing of the hydrophones connected in series; lifting distance = number of series × spacing between adjacent hydrophones. For example, with a spacing of 0.5m and 6 series hydrophones, the lifting distance per cycle is 3m. The spacing between adjacent hydrophones is related to the designed pile length. For ultra-long piles, a spacing of 0.5m is generally used. The ultimate goal is to achieve equal spacing for measuring the water pressure response from the bottom to the top of the measuring tube.

[0041] This invention provides a method for testing the pile length within the borehole before reaching the pile bottom. Figures 1 and 2 show a simplified calculation diagram and a fitting curve of the borehole pressure-time-depth response inside the sonic logging tube. The pile body is simplified as an elastic rod, and it is assumed that the fluid inside the logging tube can only move in the vertical direction. The specific calculation formula is as follows:

[0042] (1)

[0043] Equation (1) is the control equation for the vibration of the soil around the pile, where: r is the radial position of the soil mass; s = β + iω is a complex variable, β is a positive real number, i is the imaginary unit, and ω is the frequency in the Laplace domain; βs = s / v s * , where v s * =[(1+iD s )G s / ρ s ] 1 / 2 The shear wave velocity is taken into account for soil hysteretic damping.

[0044] (2)

[0045] Equation (2) is the control equation for the vertical vibration of a large-diameter pile, neglecting radial displacement, where: λ p G p ρ is the Lamé constant of the pile material; s U represents the density of the pile material. p (r,z,ω) is the displacement function of the pile mass point in the Laplace domain; s=β+iω is a complex variable.

[0046] (3)

[0047] Equation (3) is the governing equation for the displacement potential function of the fluid inside the measuring tube, where: φ f Let be the fluid displacement potential function; z be the depth of the fluid particle; η = (−s) 2 ) 1 / 2 ;ρ f v is the density of the fluid in the pipe; c For the tube wave velocity; F p The radial stress exerted on the fluid in the pipe by the inner wall of the pile can be obtained by combining equations (1) and (2) with the boundary conditions; k c The slack factor is the water pressure response coefficient inside the measuring tube.

[0048] Solving the above equation by considering the boundary conditions, the expression for the water pressure response at any depth in the measuring tube is:

[0049] (4)

[0050] In the formula: M, N, P, A, B are undetermined coefficients, which can be solved by combining boundary conditions; v pp ζ represents the longitudinal wave velocity of the pile body; ζ represents the eigenvalue related to the complex variable s, which can be solved by computer.

[0051] The calculated pore pressure-time-depth response fitting curve shows two straight lines with different slopes descending from the top of the sonic logging tube. After trial calculations, the line with the larger slope represents the longitudinal wave velocity of the pile body, while the line with the smaller slope represents the pipe wave velocity within the sonic logging tube. Figure 3 shows the measured pore pressure-time-depth response fitting curve of this invention. By comparing the measured results in Figure 3 with the analytical calculation results in Figure 2 based on field testing, it can be seen that there are two straight lines with different slopes descending from the pile top. The steeper line corresponds to the longitudinal wave velocity of the pile body, while the gentler line corresponds to the pipe wave velocity. Furthermore, there is an upward-propagating water pressure response at the pile bottom depth, with the slope corresponding to the pipe wave velocity. The analytical results and the measured results show good consistency, proving the rationality of this pile length testing method.

[0052] Compared with the low-strain reflection wave method, this method can detect a more obvious pile bottom reflection signal, and the result of determining the pile length is more accurate.

[0053] Compared with the acoustic transmission method, this invention only requires one acoustic logging tube channel to detect pile length; and even if the acoustic logging tube is blocked below the middle, the pile length can still be indirectly determined by the time-depth response curve detected by the hydrophone.

[0054] Compared to the side-hole transmission wave method, this invention is equivalent to using a pre-embedded sonic logging tube within the pile as a borehole prepared in the soil in the side-hole method, significantly reducing the workload. Furthermore, the soil response time-depth map measured by the side-hole method is affected by the stratification of the soil surrounding the pile, while this method utilizes the fluid in the tube as the transmission medium for pile information, resulting in less interference and more readable pore pressure time-depth curves.

[0055] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for testing pile length within the pile body but not reaching the bottom hole, characterized in that, Includes the following steps: S1. Fill the pre-embedded sonic logging pipe in the pile body with water and lower a hydrophone into the sonic logging pipe; S2. Grind the top center of the pile body smooth. S3. Use a measuring hammer to strike the flattened position at the top of the pile, use a hydrophone to collect the signal and generate a hole pressure time-depth response map generated by a single hammer strike. S4. Raise the hydrophone upwards a certain distance and repeat step S3. S5. Repeat the operation in S4 until the hydrophone reaches the top of the pile to complete the measurement. S6. The pore pressure time-depth response maps collected at various depths are stitched together to generate fitting curves for the first arrival wave and the reflected wave. The pile length is determined based on the fitting curves.

2. The method for testing pile length based on the pile body not reaching the bottom hole according to claim 1, characterized in that, The diameter of the hydrophone is 5mm to 20mm smaller than the inner diameter of the acoustic tube.

3. The method for testing pile length based on the pile body not reaching the bottom hole according to claim 1, characterized in that, The hammer striking point is located on the center line of the pile body, and the hydrophone is kept still during the striking.

4. The method for testing pile length based on the pile body not reaching the bottom hole according to claim 3, characterized in that, The force of each strike by the measuring hammer remains consistent.

5. The method for testing pile length based on the pile body not reaching the bottom hole according to claim 4, characterized in that, Perform 2 to 4 tapping tests at the same depth in the pile body, and take the average value of the test results.

6. The method for testing pile length based on the pile body not reaching the bottom hole according to claim 1, characterized in that, The distance the hydrophone can be raised in a single operation is 0.5m to 3m.

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