A method of testing the length of a pile based on the absence of a hole in the pile shaft to the pile base

Abstract

The application discloses a method for testing pile length based on a hole in a pile body not reaching a pile bottom, relates to the technical field of pile foundation detection, and uses a hydrophone to test the pile length by means of a sound measuring hole channel pre-buried in a large-diameter pile, uses a weight to knock at the middle of the top of the pile, collects signals by using the hydrophone, and generates a hole pressure versus time-depth response graph generated by one weight knock; the hole pressure versus time-depth response graphs collected at all depths are spliced to generate a fitting curve of the first arrival wave and the reflected wave, and the pile length is determined according to the fitting curve. The method does not need all the sound measuring tubes to be intact, and only one intact sound measuring tube is needed. Meanwhile, the method can overcome the problem that the low strain reflected wave method is difficult to detect the pile bottom reflection of a deep and long pile foundation, the stress wave signals of the pile body are propagated in the form of tube waves through the liquid in the sound measuring tube, the attenuation is small, and therefore the pile bottom reflection signals of the super-long pile can be clearly and intuitively detected.

Description

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 of S4 until the hydrophone reaches the top of the pile body position, and the measurement is completed;

[0012] S6, splice the pore pressure time-depth response graph collected at each depth to generate the fitting curve of the first arrival wave and the reflected wave, and determine the pile length according to the fitting curve.

[0013] Preferably, the diameter of the hydrophone is 5-20mm smaller than the inner diameter of the sounding pipe.

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

[0015] Preferably, the force of each hammering of the measuring hammer is kept consistent.

[0016] Preferably, 2-4 times of hammering detection is performed at the same depth of the pile body, and the average value of the detection results is taken.

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

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

[0019] 1. The number and quality of the sounding pipe are required to be low, and only one sounding pipe in the pile can be used for testing;

[0020] 2. The testing equipment is simple, and only one set of hydrophone and one measuring hammer are needed;

[0021] 3. The testing results are easy to analyze, and through theory and actual testing results, the intersection depth of the wave peak fitting curve of the incident wave and the reflected wave in the pore pressure time-depth graph is the depth of the pile bottom;

[0022] 4. The preparation is less and the testing time is short, so that large-area survey can be carried out. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0024] Figure 1 The present application is a sounding pipe inner pore pressure time-depth response calculation diagram;

[0025] Figure 2 The present application is a pore pressure time-depth response fitting curve diagram;

[0026] Figure 3A measured borehole pressure versus depth response fitting curve graph is obtained for the present application; DETAILED DESCRIPTION

[0027] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The described embodiments are only a part of the embodiments of the present application, not all the embodiments. All other embodiments obtained by a person of ordinary skill in the art without creative labor belong to the scope of protection of the present application. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0028] As shown in the Figures 1 to 3 The present application provides a method for testing pile length based on a hole in a pile body without reaching the pile bottom, comprising the following steps:

[0029] S1, filling water into a sounding pipe pre-buried in the pile body, and lowering a hydrophone to the bottom of the sounding pipe, if there is a blocked pipe, then lowering to the position above the blocked pipe;

[0030] S2, grinding the top center of the pile body;

[0031] S3, using a weight to knock at the grinding position of the pile top, collecting signals using the hydrophone and generating a borehole pressure versus depth response graph generated by the first weight knock;

[0032] S4, lifting the hydrophone upward by a certain distance and repeating the operation of step S3;

[0033] S5, repeating the operation of S4 until the hydrophone reaches the top position of the pile body, and completing the measurement;

[0034] S6, splicing the borehole pressure versus depth response graphs collected at each depth to generate a fitting curve of the first wave and the reflected wave, and determining the pile length according to the fitting curve.

[0035] The present application uses a hydrophone to detect the pile length through the sounding hole channel pre-buried in the large-diameter pile. The method does not require all sounding pipes to be intact, only one intact pipe is required. At the same time, the method can overcome the problem that the low-strain reflected wave method is difficult to detect the bottom reflection of deep and long pile foundation. The stress wave signal of the pile body propagates in the form of pipe wave through the liquid in the sounding pipe, with small attenuation, so that the bottom reflection signal of the super-long pile can be detected more clearly and intuitively.

[0036] Further optimization scheme, the inner diameter of the sounding pipe is 50mm-60mm, and the diameter of the hydrophone is less than 5mm-20mm of the inner diameter of the sounding pipe.

[0037] Further optimization scheme, in order to avoid the influence of the displacement generated by the received clutter on the judgment, the weight knocking point is located on the center line of the pile body, and the hydrophone is kept stationary during knocking.

[0038] Further optimization scheme, the force of the hammer remains consistent each time it strikes, and the striking force is related to the length of the pile, the longer the pile, the greater the striking force.

[0039] Further optimization scheme, 2-4 times of knocking detection is carried out at the same depth of the pile body, and the average value of the detection results is taken.

[0040] Further optimization scheme, the distance of single hydrophone upward lifting is 0.5m-3m.

[0041] The method for testing the length of the pile based on the hole in the pile body not reaching the bottom of the pile provided by the application, Figure 1 And 2 The sound measuring tube hole pressure time-depth response calculation diagram and hole pressure time-depth response fitting curve diagram are shown. The pile body is simplified as an elastic rod, and it is assumed that the fluid in the measuring tube can only move in the vertical direction.

[0042]

[0043] Formula (1) is a vibration control equation of the soil body around the pile, wherein r is the radial position of the soil body point; s=beta+iomega is a complex variable, beta is a positive real number, i is an imaginary unit, and omega is the frequency in the Laplace domain; beta s=s / v s * , wherein v s * =[(1+iD s )G s / p s ] 1 / 2 is the shear wave velocity considering the hysteresis damping of the soil body.

[0044]

[0045] Formula (2) is a vertical vibration control equation of the pile body of a large-diameter pile ignoring radial displacement, wherein lambda p , G p is the Lame constant of the pile body material; p s is the density of the pile body material; U p (r,z,omega) is the displacement function of the pile body point in the Laplace domain; s=beta+iomega is a complex variable.

[0046]

[0047] Formula (3) is a fluid displacement potential function control equation in a measuring tube, wherein: φ f is a fluid displacement potential function; z is a depth of a fluid particle; η = (-s 2 ) 1 / 2 ; ρ f is a fluid density in the tube; v c is a tube wave wave speed; F p is a radial stress of the fluid in the tube from an inner sidewall of the pile, which can be solved in combination with boundary conditions, and formula (1) and formula (2) are solved in combination; k c is a water pressure response concentration coefficient in the measuring tube.

[0048] The above formula is solved in combination with boundary conditions, and the expression of the water pressure response at any depth in the measuring tube is as follows:

[0049]

[0050] In the formula, M, N, P, A and B are undetermined coefficients, which can be solved in combination with boundary conditions; v pp is a pile longitudinal wave wave speed; and ζ is a characteristic root related to a complex variable s, which can be solved by a computer.

[0051] It can be seen from a fitting curve graph of the calculated pore pressure time-depth response that there are two fitting straight lines with different slopes from the top of the acoustic measuring tube downwards. Through trial calculation, the straight line with a larger slope is the pile longitudinal wave wave speed, and the straight line with a smaller slope is the tube wave wave speed in the acoustic measuring tube. Figure 3 The fitting curve graph of the measured pore pressure time-depth response of the present application, by comparing Figure 3 the measured results with Figure 2 analytical calculation results, it can be seen that there are two straight lines with different slopes from the top of the pile downwards, the straight line with a relatively steep slope corresponds to the pile longitudinal wave wave speed, and the straight line with a relatively slow slope corresponds to the tube wave wave speed. In addition, there is a water pressure response propagating upwards at the depth of the pile bottom, and the slope corresponds to the tube wave wave speed. The analytical results are in good consistency with the measured results, which proves the rationality of the pile length testing method.

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

[0053] Compared with the acoustic wave transmission method, the present application only needs one acoustic measuring tube channel to detect the pile length; and even if the acoustic measuring tube is blocked below the middle part, the pile length can still be indirectly judged through the time-depth response curve detected by the hydrophone.

[0054] Compared with the side-hole transmission wave method, the method is equivalent to using the pre-buried sounding pipe in the pile as the drilled hole prepared in the soil in the side-hole method, and greatly reduces the workload. In addition, the time-depth graph of the soil response measured by the side-hole method will be disturbed by the layering of the soil around the pile, while the method uses the fluid in the pipe as the propagation medium of the pile information, and the disturbance is smaller, and the time-depth curve of the hole pressure is more readable.

[0055] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

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. The diameter of the hydrophone is 5mm to 20mm smaller than the inner diameter of the acoustic tube, and the distance the hydrophone is lifted upwards in a single operation is 0.5m to 3m.

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 hammer striking point is located on the center line of the pile body, and the hydrophone is kept still during the striking.

3. The method for testing pile length based on the pile body not reaching the bottom hole according to claim 2, characterized in that, The force of each strike by the measuring hammer remains consistent.

4. The method for testing pile length based on the pile body not reaching the bottom hole according to claim 3, 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.

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