CN115901945B - Low-strain quality detection method for square piles - Google Patents
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Abstract
The invention relates to the technical field of civil construction engineering, in particular to a method for detecting low-strain quality of square piles, which comprises the following steps: (1) selecting a measuring point; (2) installing an acceleration sensor; (3) low strain test system debugging; (4) excitation and sampling; (5) low strain test signal processing and inspection; (6) Analyzing the low strain test signal and identifying the defects, if no reflection peak exists, judging that the pile body is complete, and ending the low strain detection; if the reflection peak is defective, judging that the pile body possibly has defects, and entering the next step; and (7) obtaining the type and the 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 construction engineering, in particular to a low-strain quality detection method for square piles.
Background
The pile foundation can pass through weak stratum, has small post-construction settlement, high bearing capacity and other excellent engineering performances, and is widely applied to the construction of various infrastructures such as municipal administration, highways, railways, ports and the like. Because the material strength is stable, the shape is easy to control, and the raw materials are easy to obtain, the pile foundations in most of the current projects are made of concrete through casting and curing. However, various pile body defects are easy to occur in the concrete pouring, vibrating and curing process, so that the service performance is influenced, and pile foundation detection is needed before use. The usual methods are static load test and low strain dynamic measurement. The static load test method is a method for directly determining the static limit bearing capacity of the pile foundation by observing the pile top settlement condition of the pile foundation under a certain static load. However, this method is costly, the detection process is tedious and time-consuming, and the detection result is at the cost of pile foundation settlement damage, so it is only used for sampling and detecting a few individual piles (sampling detection data), and it is not possible to comprehensively evaluate the piles of the whole engineering.
The low strain dynamic measurement method is a method for detecting the integrity of the pile body by applying the stress wave reflection principle. The detecting 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 center of the pile head is vertically knocked by the measuring hammer, the excited stress wave propagates downwards to the pile bottom and then is reflected back to the pile top, the signal is received by the speed sensor, two obvious wave peaks can be observed by the signal of the complete pile, and the time difference between the wave peaks can reflect the length of the pile body. The defect pile foundation (such as pile bottom, broken pile, serious segregation, necking, neck expansion and the like) can generate transmission and reflection if the stress wave propagated downwards encounters a section with obvious wave impedance difference in the pile body, and an additional peak value can appear between an incident peak value and a reflection peak value, so that the defect position and defect degree can be judged. Various low strain detection instruments widely applied in industry are based on one-dimensional fluctuation theory as a mechanical basis and on the premise of one-dimensional linear elastic pile body assumption, however, the method has some problems in practical use. Firstly, in order to apply effective pulse excitation and ensure enough test space, the end area of the measuring hammer cannot be too large, the applied force is a local load, and the signal intensity and the peak arrival time of different receiving points on the pile top section are different, so that the method obviously does not accord with the assumption of a one-dimensional rod; second, a dimension bar assumption also ignores the effect of cross-sectional shape. In fact, since the wave propagation condition of the pile head position is complex, there are not only vertical longitudinal waves, but also shear transverse waves and Rayleigh waves, these waves arrive at the side boundary of the pile and return, the main frequency division rate is greatly different from the longitudinal waves expected to be captured, and high-frequency interference is caused after the waves are received by the sensor.
The invention patent (patent number: CN201210345037.9, patent name: the specification) provides a method for detecting the quality of a large-diameter tubular pile. The multipoint measurement average method provided by the patent can be effectively applied to the quality detection of the round tubular pile, however, because the interference signal characteristics caused by the propagation of elastic waves in different paths in the square pile and the round tubular pile are fundamentally different, the method cannot eliminate high-frequency interference and the three-dimensional effect of the square section when being directly applied to the low-strain detection of the square pile, and the test effect is poor.
The use of large diameter square piles in engineering is not uncommon: taking the anti-slide pile as an example, the cross section size of the anti-slide pile is generally more than 1m, and the anti-slide pile is a typical large-diameter pile foundation (the pile foundation specification prescribes that the pile foundation is more than 600mm or the large-diameter pile), and the detection under the condition often has serious three-dimensional effect and high-frequency interference co-influence, so that the detection result is misjudged. Vibration signals along a diagonal line and a right-angle side in the square section pile have certain difference, but related detection technology based on square shape characteristics is not available in the industry. Moreover, when actual detection is performed, the actual detection is often limited by site conditions, it is difficult to precisely arrange the sensor in an optimal vibration area, or to apply force on the pile center, and it is necessary to explore a detection method which is not easily affected by interference signals and can adapt to complex site conditions.
Disclosure of Invention
The invention provides a low-strain quality detection method for square piles, which can overcome certain or some defects in the prior art.
The invention relates to a low-strain quality detection method for square piles, which comprises the following steps of:
(1) Selecting measuring points: taking a pair of complementary points A and A 'on the diagonal line of the pile top of the square pile, taking a point B outside half of the pile edge length in the right-angle side direction, and taking A, A' and B as test points;
(2) And (3) installing an acceleration sensor: one acceleration sensor is arranged at each of A, A' and B;
(3) Low strain test system debugging: connecting each acceleration sensor to a multichannel low-strain dynamic measurement acquisition instrument, and performing instrument debugging, sensor calibration and performance test;
(4) Excitation and sampling: opening a low-strain dynamic measurement acquisition instrument, applying exciting force by taking the center point of the pile top of the square pile as an exciting point, and spreading excited stress waves outwards at the pile top, wherein the three time phases are as follows:
the wave front of the stress wave propagating along all directions is kept to be spherical before reaching the right-angle boundary, and signals can be captured by A and B at the stage;
the stress wave along the square of the right-angle side returns after reaching the boundary, the reflected wave is overlapped with the incident wave, and an interference wave is formed at the position A;
after the signal is received by the A ', stress waves in the diagonal direction continuously propagate outwards to reach the corner points and are reflected back, the stress waves are overlapped with the waves reflected back from the right-angle side direction in the returning process, composite high-frequency interference is formed in the diagonal direction, and the composite high-frequency interference is sequentially received by the acceleration sensors at the A' and the A;
the 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, firstly superposing the responses at the A and A', and eliminating the high-frequency interference waves by utilizing the characteristic that the phases of the interference waves at the two positions differ by 180 degrees to obtain a test curve, wherein the process is called diagonal bit filling 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 smoothing condition between the incident wave and the reflected wave on the test curve, and judging that the pile body is complete if no reflection peak exists, and ending 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 defects, and entering the next step;
(7) Repeating the steps (1) - (6) once to obtain another 1 group of test curves, and averaging the speeds obtained by the 2 groups of test curves to obtain the defect type and position of the pile body if the 2 groups of test curves have no obvious difference and all the pile body has defects.
Preferably, in step (1), a and a' satisfy:
OA+OA’＝R
wherein the O point is a center point, and R is half of the diagonal length of the square pile;
b satisfies the following conditions:
OB>a/2
a is half of the side length of the square pile.
Preferably, in step (5), the test error comparison test is: if the difference of the incident wave crest values is too large, indicating that a large operation error exists in the test process, and retesting is needed; if the optimal area B is difficult to measure due to the arrangement of the reinforcing steel bars, concrete pouring or other site condition constraints, the signals after the diagonal position compensation averaging can be selected to be mutually inspected.
The invention has the advantages that:
(1) The square boundary causes little high frequency interference. The paired signals are overlapped by utilizing the characteristic that interference waves of paired position compensating measuring points with the sum of distances from the diagonal line to the pile center being R (half of the length of the diagonal line) are opposite in phase, so that high-frequency interference from square boundaries is eliminated;
(2) The test results can be verified. And selecting a measuring point as an auxiliary measuring point in the traditional optimal measuring area (0.5-0.8 a) in the right-angle side direction, checking the signal after the bit compensation averaging by taking the incident wave peak value and the arrival time of the signal of the auxiliary measuring point as reference signals, and if the average signal incident peak value exceeds 5% of the peak value of the traditional method, considering that the test fails, and re-selecting the point for testing, which is equivalent to setting an error red line, thereby ensuring the signal fidelity while eliminating the high-frequency interference.
(3) The test position is flexible. In the test, the supplementary position on any diagonal line can be used for testing and signal translation, and the available detection area is not limited by the position of the optimal detection area, so that the test process is more flexible, and the limitation of field conditions is reduced to the greatest extent.
Drawings
FIG. 1 is a flow chart of a method for detecting low strain quality of square piles according to an embodiment;
FIG. 2 is a schematic diagram of the low strain detection operation and stress wave propagation near the pile top according to an embodiment;
FIG. 3 (a) is a schematic diagram of standard arrangement of measuring points in the embodiment;
FIG. 3 (b) is a schematic diagram of a first diagonal patch point adjustment approach in a poor field environment in an embodiment;
FIG. 3 (c) is a schematic diagram of a second diagonal patch point adjustment approach in a poor field environment in an embodiment;
FIG. 4 is a schematic diagram of original speed signals of measuring points with different distances from the center of the pile on the right-angle side;
FIG. 5 is a schematic diagram of original speed signals of measuring points with different distances from the center of the pile at diagonal sides in the embodiment;
FIG. 6 is a diagram illustrating the velocity signal and the effect after the diagonal bit-filling is averaged in the embodiment.
Detailed Description
For a further understanding of the present invention, the present invention will be described in detail with reference to the drawings and examples. It is to be understood that the examples are illustrative of the present invention and are not intended to be limiting.
Examples
As shown in fig. 1 and 2, the present embodiment provides a method for detecting low strain quality of square piles, which includes the following steps:
(1) Selecting measuring points: as shown in fig. 3 (a), a pair of complementary points a and a 'are taken from the diagonal line of the square pile top, a point B is taken outside half the pile side length in the right-angle direction, and A, A' and B are taken as test points;
a and A' satisfy:
OA+OA’＝R
wherein the O point is a center point, and R is half of the diagonal length of the square pile;
b satisfies the following conditions:
OB>a/2
a is half of the side length of the square pile.
If the field conditions are not limited, so that the sensors cannot be arranged in the manner of fig. 3 (a), the speed sensors may be arranged in the manner of fig. 3 (b) or fig. 3 (c) according to the symmetry of the square section; if the site environment restrictions result in the inability to apply force to the pile core in the manner of fig. 3, the measurement points can be determined for the modulation sensor and the hammer position according to the reciprocal theorem of the elastic system.
(2) And (3) installing an acceleration sensor: one acceleration sensor is arranged at each of A, A' and B; the acceleration sensor is arranged by plaster, and the base layer surface can be subjected to the next step after solidification.
(3) Low strain test system debugging: connecting each acceleration sensor to a multichannel low-strain dynamic measurement acquisition instrument, and performing instrument debugging, sensor calibration and performance test;
(4) Excitation and sampling: opening a low-strain dynamic measurement acquisition instrument, applying exciting force by taking the center point of the pile top of the square pile as an exciting point, and spreading excited stress waves outwards at the pile top, wherein the three time phases are as follows:
the wave front of the stress wave propagating along all directions is kept to be spherical before reaching the right-angle boundary, and signals can be captured by A and B at the stage;
the stress wave along the square of the right-angle side returns after reaching the boundary, the reflected wave is overlapped with the incident wave, and an interference wave is formed at the position A;
after the signal is received by the A ', stress waves in the diagonal direction continuously propagate outwards to reach the corner points and are reflected back, the stress waves are overlapped with the waves reflected back from the right-angle side direction in the returning process, composite high-frequency interference is formed in the diagonal direction, and the composite high-frequency interference is sequentially received by the acceleration sensors at the A' and the A;
thus, the signal received by A contains the incident wave from the hammering point, the reflected wave from the right-angle side, and the reflected wave from the corner point; whereas a' receives an incident wave from the hammer point and a reflected wave from the corner point; b receives the incident wave and the reflected wave of the right-angle side.
The 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 locations along the right-angle side and diagonal, respectively, where significant inertial bounce and high frequency disturbances are observed.
(5) Low strain test signal processing and inspection: analyzing and processing the obtained 3 speed response curves, firstly superposing the responses at the A and A', and eliminating the high-frequency interference waves by utilizing the characteristic that the phases of the interference waves at the two positions differ by 180 degrees to obtain a test curve, wherein the process is called diagonal bit filling average, as shown in fig. 6; comparing the processed response with the speed peak value at the position B for testing error comparison and inspection: if the difference of the incident wave crest values is too large, indicating that a large operation error exists in the test process, and retesting is needed; if the optimal area B is difficult to measure due to the arrangement of the reinforcing steel bars, concrete pouring or other site condition constraints, the signals after the diagonal position compensation averaging can be selected to be mutually inspected.
(6) Low strain test signal analysis and defect identification: observing the curve smoothing condition between the incident wave and the reflected wave on the test curve, and judging that the pile body is complete if no obvious defect reflection peak exists, and ending 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 defects, and entering the next step;
(7) Repeating the steps (1) - (6) once to obtain another 1 group of test curves, and averaging the speeds obtained by the 2 groups of test curves to obtain the defect type and position of the pile body if the 2 groups of test curves have no obvious difference and all the pile body has defects.
The invention and its embodiments have been described above by way of illustration and not limitation, and the invention is illustrated in the accompanying drawings and described in the drawings in which the actual structure is not limited thereto. Therefore, if one of ordinary skill in the art is informed by this disclosure, the structural mode and the embodiments similar to the technical scheme are not creatively designed without departing from the gist of the present invention.
Claims (2)
1. A low strain quality detection method for square piles is characterized in that: the method comprises the following steps:
(1) Selecting measuring points: taking a pair of complementary points A and A 'on the diagonal line of the pile top of the square pile, taking a point B outside half of the pile edge length in the right-angle side direction, and taking A, A' and B as test points;
in step (1), a and a' satisfy:
OA+OA’＝R
wherein the O point is a center point, and R is half of the diagonal length of the square pile;
b satisfies the following conditions:
OB>a/2
a is half of the side length of the square pile;
(2) And (3) installing an acceleration sensor: one acceleration sensor is arranged at each of A, A' and B;
(3) Low strain test system debugging: connecting each acceleration sensor to a multichannel low-strain dynamic measurement acquisition instrument, and performing instrument debugging, sensor calibration and performance test;
(4) Excitation and sampling: opening a low-strain dynamic measurement acquisition instrument, applying exciting force by taking the center point of the pile top of the square pile as an exciting point, and spreading excited stress waves outwards at the pile top, wherein the three time phases are as follows:
I. the wave front of the stress wave propagating along each direction is kept to be spherical before reaching the right angle boundary, and signals can be captured by A and B at the stage;
II. The stress wave along the square of the right-angle side returns after reaching the boundary, the reflected wave is overlapped with the incident wave, and an interference wave is formed at the position A;
after receiving signals, stress waves in the diagonal direction continue to propagate outwards to reach corner points and are reflected back, the stress waves are overlapped with waves reflected back from the right-angle side direction in the returning process, composite high-frequency interference is formed in the diagonal direction, and the composite high-frequency interference is sequentially received by acceleration sensors at the positions A' and A;
the 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, firstly superposing the responses at the A and A', and eliminating the high-frequency interference waves by utilizing the characteristic that the phases of the interference waves at the two positions differ by 180 degrees to obtain a test curve, wherein the process is called diagonal bit filling 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 smoothing condition between the incident wave and the reflected wave on the test curve, and judging that the pile body is complete if no reflection peak exists, and ending 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 defects, and entering the next step;
(7) Repeating the steps (1) - (6) once to obtain another 1 group of test curves, and averaging the speeds obtained by the 2 groups of test curves to obtain the defect type and position of the pile body if the 2 groups of test curves have no obvious difference and all the pile body has defects.
2. The method for detecting the low-strain quality of the square pile according to claim 1, wherein the method comprises the following steps: in the step (5), the test error comparison test is: if the difference of the incident wave crest values is too large, indicating that a large operation error exists in the test process, and retesting is needed; if the optimal area B is difficult to measure due to the arrangement of the reinforcing steel bars, concrete pouring or other site condition constraints, the signals after the diagonal position compensation averaging can be selected to be mutually inspected.
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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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