CN115901945A - Square pile low-strain quality detection method - Google Patents
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Abstract
The invention relates to the technical field of civil and architectural engineering, in particular to a low-strain quality detection method for a square pile, which comprises the following steps: (1) selecting a measuring point; (2) installing an acceleration sensor; (3) debugging a low-strain test system; (4) exciting vibration and sampling; (5) processing and checking a low-strain test signal; (6) Analyzing a low-strain test signal and identifying defects, if no reflection peak exists, judging that the pile body is complete, and finishing low-strain detection; if the reflection peak has a defect, judging that the pile body possibly has the defect, and entering the next step; and (7) obtaining the type and position of the pile body defect. The invention can better detect the low-strain quality of the square pile.
Description
Technical Field
The invention relates to the technical field of civil and architectural engineering, in particular to a low-strain quality detection method for a square pile.
Background
The pile foundation can penetrate through weak stratum, has low post-construction settlement and high bearing capacity and other excellent engineering performances, and is widely applied to construction of various infrastructures, such as municipal administration, highways, railways, ports and the like. Due to the reasons of stable material strength, easy control of shape and easy acquisition of raw materials, the pile foundations in most of the prior projects are all made of concrete by pouring and curing. However, various defects of the pile body are easy to occur in the concrete pouring and vibrating maintenance process to influence the service performance, and the pile foundation detection is required before the concrete pouring and vibrating maintenance process is used. The common methods are static load test method and low strain dynamic test method. The static load test method is a method for directly determining the static limit bearing capacity of a pile foundation by observing the pile top settlement condition of the pile foundation under a certain static load. However, the method is high in cost, complex and time-consuming in detection process, and the detection result is at the cost of pile foundation settlement damage, so that the method is only used for sampling detection of a few individual piles (adding sampling detection data), and the piles of the whole project cannot be comprehensively evaluated.
The low strain dynamic measurement method is a method for detecting the integrity of a pile body by applying the principle of stress wave reflection. The detection instrument mainly comprises a side hammer, a speed sensor and a signal translator. The detection process is as follows: the speed sensor is arranged on the pile top, the measuring hammer is used for vertically knocking the center of the pile head, the excited stress wave is downwards transmitted to the pile bottom and then reflected back to the pile top, the signal is received by the speed sensor, two obvious wave crests can be observed from the signal of the complete pile, and the time difference between the peak values can reflect the length of the pile body. If the stress wave propagating downwards encounters a section with obvious wave impedance difference in a pile body, transmission and reflection occur on a defective pile foundation (such as a pile bottom, a broken pile, serious segregation, necking, neck expansion and the like), an extra peak value can be generated between an incident wave crest and a reflection wave crest, and accordingly, the defect position and the defect degree can be judged. Various low-strain detection instruments widely applied in the industry are mainly based on a one-dimensional fluctuation theory as a mechanical basis and are based on the assumption of a one-dimensional linear elastic pile body, but the method has some problems in practical use. Firstly, in order to apply effective pulse excitation and ensure enough test space, the area of the end part of the measuring hammer cannot be too large, the applied force is a local load, the signal intensity and the peak value arrival time of different receiving points on the cross section of the pile top are different, and the assumption of a one-dimensional rod is obviously not met; second, the one-dimensional rod assumption also ignores the influence of the cross-sectional shape. In fact, because the wave propagation conditions at the pile head position are complex, not only vertical longitudinal waves but also shear transverse waves and rayleigh waves exist, the waves arrive at the side boundary of the pile and return, the main branch frequency is greatly different from the expected captured longitudinal waves, and high-frequency interference is caused after the main branch frequency is received by the sensor.
The invention patent (patent number: CN201210345037.9, patent name:) provides a quality detection method for a large-diameter tubular pile. The multipoint measurement averaging method provided by the patent can be effectively applied to quality detection of the circular tubular pile, however, interference signal characteristics caused when elastic waves are transmitted in different paths in the square pile and the circular tubular pile are fundamentally different, the method cannot eliminate high-frequency interference and a three-dimensional effect of a square section when the method is directly applied to low-strain detection of the square pile, and the testing effect is poor.
The use of large diameter square piles in engineering is not uncommon: taking the slide-resistant pile as an example, the section size of the slide-resistant pile generally exceeds 1m, and the slide-resistant pile is a typical large-diameter pile foundation (the specification of the pile foundation is larger than 600mm, namely the large-diameter pile), and detection under the condition often has the common influence of serious three-dimensional effect and high-frequency interference, so that the misjudgment of a detection result is caused. Vibration signals in the square section pile along the diagonal and along the right-angle side have certain difference, but no related detection technology based on the square characteristic exists in the industry. Moreover, when the point distribution is actually detected, the actual point distribution is often limited by field conditions, the sensor is difficult to be arranged in the optimal vibration area, or the force is difficult to be applied to the pile core, and a detection method which is not easily influenced by interference signals and can adapt to complex field conditions needs to be explored.
Disclosure of Invention
It is an object of the present invention to provide a method of low strain quality inspection of square piles which overcomes some or all of the disadvantages of the prior art.
The invention discloses a low-strain quality detection method for a square pile, which comprises the following steps of:
(1) Selecting a measuring point: taking a pair of complementary points A and A 'on a diagonal line of the pile top of the square pile, taking a point B beyond half of the side length of the pile in the direction of a right-angle side, and taking the points A, A' and B as test points;
(2) Installing an acceleration sensor: arranging an acceleration sensor at each of A, A' and B;
(3) Debugging a low-strain test system: connecting each acceleration sensor to a multi-channel low-strain dynamic test acquisition instrument, and performing instrument debugging, sensor calibration and performance test;
(4) Exciting and sampling: opening the low strain dynamic measurement acquisition instrument to apply exciting force by taking the center point of the pile top of the square pile as an exciting point, and outwards spreading the excited stress wave at the pile top, relating to three time stages:
the wave front of the stress wave propagating along each direction is kept to be a spherical surface before reaching the right-angle boundary, and both A and B can capture signals at the stage;
the stress wave square along the right-angle side returns after reaching the boundary, and the reflected wave and the incident wave are superposed to form interference wave at the position A;
after the signal is received by the A ', the stress wave in the diagonal direction continuously spreads outwards to reach the angular point and is reflected back, and is superposed with the wave reflected from the direction of the right-angle side in the return process, so that composite high-frequency interference is formed in the diagonal direction and is sequentially received by the acceleration sensors at the A' and the A;
acceleration response data obtained by measurement of each sensor is transmitted to a low-strain dynamic measurement acquisition instrument, and the acceleration time-course curve is integrated through built-in software of the low-strain dynamic measurement acquisition instrument to obtain 3 speed time-domain response curves;
(5) Low strain test signal processing and inspection: analyzing and processing the obtained 3 speed response curves, superposing the responses at the positions A and A', eliminating high-frequency interference waves by utilizing the characteristic that the phase difference of the interference waves at the two positions is 180 degrees to obtain a test curve, wherein the process is called diagonal complement bit averaging; comparing the processed response with the speed peak value at the position B to carry out test error comparison and inspection;
(6) Low strain test signal analysis and defect identification: observing the curve smoothness between the incident wave and the reflected wave on the test curve, if no reflection peak exists, judging that the pile body is complete, and finishing the low-strain detection; if the curve between the incident wave and the reflected wave is not smooth and a defective reflection peak exists, judging that the pile body possibly has a defect, and entering the next step;
(7) And (3) repeating the steps (1) to (6) once to obtain another 1 group of test curves, and if the 2 groups of test curves have no obvious difference and all show that the pile body has defects, averaging the speeds obtained by the 2 groups of test curves to obtain the type and the position of the defects of the pile body.
Preferably, in step (1), a and a' satisfy:
OA+OA’＝R
wherein, the point O is a central point, and the point R is half of the length of the diagonal line of the square pile;
b satisfies the following conditions:
OB>a/2
and a is half of the side length of the square pile.
Preferably, in step (5), the test error comparison test is as follows: if the difference of the incident wave peak values is too large, the fact that a large operation error exists in the testing process is shown, and the testing needs to be conducted again; if the optimal measurement area at the position B is difficult to measure due to arrangement of reinforcing steel bars, concrete pouring or other field condition constraints, a plurality of groups of signals with the compensated and averaged diagonal positions can be selected for mutual inspection.
The invention has the advantages that:
(1) The square boundary causes little high frequency interference. The characteristic of the opposite phase of the interference waves of the pair of complementary position measuring points that the sum of the distances from the diagonal to the pile center is R (half of the length of the diagonal) is utilized to superpose the pair of signals and eliminate the high-frequency interference from the square boundary;
(2) The test results are verifiable. Selecting a measuring point as an auxiliary measuring point in a traditional optimal measuring area (0.5-0.8 a) in the direction of a right-angle edge, taking an incident wave peak value and arrival time of a signal of the auxiliary measuring point as a reference signal, detecting the signal after bit compensation averaging, if the incident peak of the averaged signal exceeds 5 percent of the peak value of the traditional method, considering that the test fails, reselecting the point for testing, namely setting an error red line, and ensuring signal fidelity while eliminating high-frequency interference.
(3) The test position is flexible. In the test, the complementary position on any diagonal line can be tested and translated, and the available detection area is not limited by the position of the best detection area, so that the test process is more flexible, and the limitation of field conditions is reduced to the maximum extent.
Drawings
FIG. 1 is a flow chart of a low strain quality testing method for square piles according to an embodiment;
FIG. 2 is a schematic diagram of the low strain detection operation and the propagation of stress waves near the pile top in an embodiment;
FIG. 3 (a) is a schematic view showing a standard arrangement of measuring points in the embodiment;
FIG. 3 (b) is a schematic diagram illustrating a first method for adjusting the diagonal complement points under a poor field environment in an embodiment;
FIG. 3 (c) is a diagram illustrating a second method for adjusting a diagonal compensation point under a poor field environment in an embodiment;
FIG. 4 is a schematic diagram of original velocity signals of measuring points at different distances from a pile center on a right-angle side in the embodiment;
FIG. 5 is a diagram illustrating original velocity signals of measuring points at different distances from a center of a pile;
FIG. 6 is a diagram illustrating velocity signals and effects after averaging diagonal complement bits in an embodiment.
Detailed Description
For a further understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings and examples. It is to be understood that the examples are illustrative of the invention and not limiting.
Examples
As shown in fig. 1 and fig. 2, the present embodiment provides a method for detecting low-strain quality of a square pile, which includes the following steps:
(1) Selecting a measuring point: as shown in fig. 3 (a), a pair of complementary points a and a 'is taken from the diagonal of the pile top of the square pile, a point B is taken from the right-angle side direction except for half of the pile side length, and a, a' and B are taken as test points;
a and A' satisfy:
OA+OA’＝R
wherein, the point O is a central point, and R is half of the length of the diagonal line of the square pile;
b satisfies the following conditions:
OB>a/2
a is half of the side length of the square pile.
If field conditions are not limiting, such that the sensors cannot be arranged as in FIG. 3 (a), the speed sensors can be arranged as in FIG. 3 (b) or FIG. 3 (c) based on the symmetry of the square cross-section; if the site environment is limited so that force cannot be applied to the pile core in the manner of fig. 3, the measuring point can be determined for the positions of the force sensor and the force hammer according to the mutual equality principle of the elastic system.
(2) Installing an acceleration sensor: arranging an acceleration sensor at each of A, A' and B; the acceleration sensor is preferably arranged by pasting with plaster, and the next step can be carried out after the surface of the base layer is solidified.
(3) Debugging a low-strain test system: connecting each acceleration sensor to a multi-channel low-strain dynamic test acquisition instrument, and performing instrument debugging, sensor calibration and performance test;
(4) Exciting and sampling: opening the low strain dynamic measurement acquisition instrument to apply exciting force by taking the center point of the pile top of the square pile as an exciting point, and outwards spreading the excited stress wave at the pile top, relating to three time stages:
the wave front of the stress wave propagating along each direction is kept to be a spherical surface before reaching the right-angle boundary, and both A and B can capture signals at the stage;
the stress wave square along the right-angle side returns after reaching the boundary, and the reflected wave and the incident wave are superposed to form interference wave at the position A;
after the signal is received by the A ', the stress wave in the diagonal direction continuously spreads outwards to reach the angular point and is reflected back, and is superposed with the wave reflected back from the direction of the right-angle side in the return process, so that composite high-frequency interference is formed in the diagonal direction and is sequentially received by the acceleration sensors at the A' and the A;
thus, the signal received by A comprises an incident wave from a hammering point, a reflected wave from a right-angle side and a reflected wave from an angular point; a' receives an incident wave from the hammering point and a reflected wave from the angular point; b, receiving the incident wave and the reflected wave at the right-angle side.
Acceleration response data obtained by measurement of each sensor is transmitted to a low-strain dynamic measurement acquisition instrument, and the acceleration time-course curve is integrated through built-in software of the low-strain dynamic measurement acquisition instrument to obtain 3 speed time-domain response curves; fig. 4 and 5 are velocity response curves at different positions along the legs and diagonal, respectively, and significant inertial bounce and high frequency interference are observed.
(5) Low strain test signal processing and inspection: analyzing and processing the obtained 3 speed response curves, superposing the responses at the positions A and A', eliminating high-frequency interference waves by utilizing the characteristic that the phase difference of the interference waves at the two positions is 180 degrees to obtain a test curve, wherein the process is called diagonal compensation averaging and is shown in figure 6; comparing the processed response with the speed peak value at B to carry out test error comparison test: if the difference of the incident wave peak values is too large, the fact that a large operation error exists in the testing process is shown, and the testing needs to be conducted again; if the optimal measurement area at the position B is difficult to measure due to arrangement of reinforcing steel bars, concrete pouring or other field condition constraints, a plurality of groups of signals with the compensated and averaged diagonal positions can be selected for mutual inspection.
(6) Low strain test signal analysis and defect identification: observing the curve smoothness between the incident wave and the reflected wave on the test curve, if no obvious defect reflection peak exists, judging that the pile body is complete, and finishing the low-strain detection; if the curve between the incident wave and the reflected wave is not smooth and has a defective reflection peak, judging that the pile body possibly has a defect, and entering the next step;
(7) And (3) repeating the steps (1) to (6) once to obtain another 1 group of test curves, and if the 2 groups of test curves have no obvious difference and all show that the pile body has defects, averaging the speeds obtained by the 2 groups of test curves to obtain the type and the position of the defects of the pile body.
The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.
Claims (3)
1. A low-strain quality detection method for a square pile is characterized by comprising the following steps: the method comprises the following steps:
(1) Selecting a measuring point: taking a pair of complementary points A and A 'on a diagonal line of the pile top of the square pile, taking a point B beyond half of the side length of the pile in the direction of a right-angle side, and taking the points A, A' and B as test points;
(2) Installing an acceleration sensor: arranging an acceleration sensor at each of A, A' and B;
(3) Debugging a low-strain test system: connecting each acceleration sensor to a multi-channel low-strain dynamic test acquisition instrument, and performing instrument debugging, sensor calibration and performance test;
(4) Exciting and sampling: opening the low strain dynamic measurement acquisition instrument to apply exciting force by taking the center point of the pile top of the square pile as an exciting point, and outwards spreading the excited stress wave at the pile top, relating to three time stages:
the wavefront of the stress wave propagating along each direction is kept to be spherical before reaching the right-angle boundary, and both A and B can capture signals at the stage;
the square stress wave along the right-angle side returns after reaching the boundary, and the reflected wave and the incident wave are superposed to form interference wave at the position A;
after the signal is received by the A ', the stress wave in the diagonal direction continuously spreads outwards to reach the angular point and is reflected back, and is superposed with the wave reflected back from the direction of the right-angle side in the return process, so that composite high-frequency interference is formed in the diagonal direction and is sequentially received by the acceleration sensors at the A' and the A;
acceleration response data obtained by measurement of each sensor is transmitted to a low-strain dynamic measurement acquisition instrument, and the acceleration time-course curve is integrated through built-in software of the low-strain dynamic measurement acquisition instrument to obtain 3 speed time-domain response curves;
(5) Low strain test signal processing and inspection: analyzing and processing the obtained 3 speed response curves, superposing the responses at the positions A and A', eliminating high-frequency interference waves by utilizing the characteristic that the phase difference of the interference waves at the two positions is 180 degrees to obtain a test curve, wherein the process is called diagonal complement average; comparing the processed response with the speed peak value at the position B to carry out test error comparison and inspection;
(6) Low strain test signal analysis and defect identification: observing the curve smoothness between the incident wave and the reflected wave on the test curve, if no reflection peak exists, judging that the pile body is complete, and finishing the low-strain detection; if the curve between the incident wave and the reflected wave is not smooth and has a defective reflection peak, judging that the pile body possibly has a defect, and entering the next step;
(7) And (5) repeating the steps (1) - (6) once to obtain another 1 group of test curves, and if the 2 groups of test curves have no obvious difference and all show that the pile body has defects, averaging the speeds obtained by the 2 groups of test curves to obtain the type and the position of the pile body defects.
2. The low-strain quality detection method for the square pile according to claim 1, characterized by comprising the following steps of: in the step (1), A and A' satisfy:
OA+OA’＝R
wherein, the point O is a central point, and R is half of the length of the diagonal line of the square pile;
b satisfies the following conditions:
OB>a/2
and a is half of the side length of the square pile.
3. The square pile low-strain quality detection method according to claim 2, characterized by comprising the following steps: in the step (5), the test error comparison test comprises the following steps: if the difference of the incident wave peak values is too large, the fact that a large operation error exists in the testing process is shown, and the testing needs to be conducted again; if the optimal measurement area at the position B is difficult to measure due to arrangement of reinforcing steel bars, concrete pouring or other field condition constraints, a plurality of groups of signals with the compensated and averaged diagonal positions can be selected for mutual inspection.
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| CN113376261A (en) * | 2021-07-16 | 2021-09-10 | 武汉中岩科技股份有限公司 | Method for correcting stress wave travel time of low-strain detection of foundation pile |
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- 2022-11-18 CN CN202211449881.6A patent/CN115901945B/en active Active
Patent Citations (7)
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| CN102877490A (en) * | 2012-09-18 | 2013-01-16 | 河海大学 | Method for detecting quality of large-diameter tubular pile at low strain |
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