CN115901945A - A low-strain quality detection method for square piles - Google Patents

Abstract

The invention relates to the technical field of civil engineering, and relates to a low-strain quality detection method for square piles, which includes: (1) selecting measuring points; (2) installing acceleration sensors; (3) debugging low-strain testing systems; (4) stimulating (5) low-strain test signal processing and inspection; (6) low-strain test signal analysis and defect identification, if there is no defect reflection peak, it is judged that the pile body is complete, and the low-strain detection is over; if there is a defect reflection peak , then it is judged that there may be defects in the pile body, and the next step is entered; (7) Obtain the type and position of the pile body defect. The invention can preferably detect the low-strain quality of square piles.

Description

A low-strain quality detection method for square piles

technical field

The invention relates to the technical field of civil construction engineering, in particular to a method for detecting the low-strain quality of square piles.

Background technique

Pile foundations are widely used in various infrastructure constructions such as municipalities, highways, railways, and ports because of their superior engineering performance such as being able to pass through weak strata, having small post-construction settlement, and high bearing capacity. Due to the stable strength of the material, easy control of the shape, and easy acquisition of raw materials, most of the pile foundations in the current projects are made of concrete pouring and curing. However, various pile body defects are prone to appear in the process of concrete pouring and vibrating maintenance, which will affect the service performance, and the pile foundation needs to be inspected before use. The commonly used methods are static load test method and low strain dynamic test method. The static load test method is a method to directly determine the static ultimate bearing capacity of the pile foundation by observing the settlement of the pile top under a certain static load. However, this method is expensive, the detection process is cumbersome and time-consuming, and the detection result is at the cost of pile foundation settlement damage, so it is only used for sampling a small number of piles (plus sampling detection data), and cannot conduct a comprehensive inspection of the piles of the entire project. evaluate.

The low-strain dynamic measurement method is a method to detect the integrity of the pile body by applying the principle of stress wave reflection. The detection instrument mainly includes side hammer, speed sensor and signal translator. The detection process is: install the speed sensor on the top of the pile, and vertically tap the center of the pile head with a measuring hammer. The excited stress wave propagates down to the bottom of the pile and then reflects back to the top of the pile. The signal is received by the speed sensor and the signal of the complete pile Two distinct peaks can be observed, and the time difference between the peaks can reflect the pile length. Defective pile foundations (such as pile bottoms, broken piles, severe segregation, necking, necking, etc.) will transmit and reflect when the downwardly propagating stress wave encounters a section with obvious wave impedance differences in the pile body. An additional peak appears between the incident and reflected peaks, allowing the location and extent of the defect to be determined. All kinds of low-strain detection instruments widely used in the industry are mostly based on one-dimensional wave theory and the assumption of one-dimensional linear elastic pile body. However, there are some problems in the actual use of this method. First of all, in order to apply effective pulse excitation and ensure sufficient testing space, the area at the end of the measuring hammer should not be too large, the applied force is a local load, and the signal strength and peak arrival time of different receiving points on the pile top section are different , which obviously does not conform to the one-dimensional rod assumption; secondly, the one-dimensional rod assumption also ignores the influence of the cross-sectional shape. In fact, due to the complex wave propagation at the pile head position, there are not only vertical longitudinal waves, but also shear shear waves and Rayleigh waves. These waves reach the side boundary of the pile and return. There is a big difference in the longitudinal wave, which will cause high-frequency interference after being received by the sensor.

The invention patent (patent number: CN201210345037.9, patent name: ) provides a quality detection method for large-diameter pipe piles. The multi-point measurement averaging method proposed in this patent can be effectively applied to the quality detection of circular pipe piles. However, due to the fundamental difference in the characteristics of the interference signals caused by elastic waves propagating in different paths in square piles and circular pipe piles, this method directly When applied to low-strain detection of square piles, high-frequency interference and three-dimensional effects of square sections cannot be eliminated, and the test results are not good.

The use of large-diameter square piles in engineering is not uncommon: taking anti-slide piles as an example, the cross-sectional size of anti-slide piles generally exceeds 1m, which is a typical large-diameter pile foundation (the pile foundation specification stipulates that a large-diameter pile is greater than 600mm). In this case, the detection often has serious three-dimensional effects and high-frequency interference, resulting in misjudgment of detection results. There are certain differences in the vibration signals along the diagonal and along the right-angled sides of square-section piles, but there is no relevant detection technology based on square-shaped characteristics in the industry. Furthermore, when the actual detection points are often constrained by the site conditions, it is difficult to arrange the sensors in the optimal vibration area, or to apply force on the pile core. It is necessary to explore a method that is not easily affected by interference signals and can adapt to complex site conditions Detection method.

Contents of the invention

The content of the present invention is to provide a square pile low-strain quality inspection method, which can overcome some or some defects in the prior art.

A kind of square pile low-strain quality detection method according to the present invention, it comprises the following steps:

(1) Select the measuring point: Take a pair of supplementary points A and A' on the diagonal of the top of the square pile, take a point B beyond half the length of the pile side in the direction of the right angle, and use A, A' and B as test points ;

(2) Acceleration sensors are installed: an acceleration sensor is arranged at A, A' and B respectively;

(3) Low-strain test system debugging: connect each acceleration sensor to a multi-channel low-strain measurement acquisition instrument, and perform instrument debugging, sensor calibration and performance testing;

(4) Vibration excitation and sampling: Turn on the low-strain dynamic measurement acquisition instrument, apply the excitation force with the center point of the square pile top as the excitation point, and the excited stress wave propagates outward on the pile top, involving three time stages:

1. The stress wave propagating in all directions remains as a spherical surface before reaching the right-angle boundary, and both A and B can capture the signal at this stage;

, The stress wave along the right-angled square reaches the boundary and then returns, the reflected wave is superimposed on the incident wave, and an interference wave is formed at A;

, A' After receiving the signal, the stress wave in the diagonal direction continues to propagate outward to reach the corner point and is reflected back. During the return process, it is superimposed with the wave reflected from the right-angled side direction, forming a composite high-frequency interference in the diagonal direction. Received by the acceleration sensors at A' and A in turn;

The acceleration response data measured by each sensor is sent to the low-strain dynamic measurement acquisition instrument, and the acceleration time-history curve is integrated through the built-in software of the low-strain dynamic measurement acquisition instrument to obtain three velocity time-domain response curves;

(5) Low-strain test signal processing and inspection: analyze and process the obtained three speed response curves, first superimpose the responses at A and A', and use the characteristics of the 180-degree phase difference of the interference waves at the two positions to convert the high-frequency The interference wave is eliminated to obtain the test curve. This process is called diagonal supplementary average; compare the processed response with the speed peak at B for test error comparison and inspection;

(6) Low-strain test signal analysis and defect identification: Observe the smoothness of the curve between the incident wave and the reflected wave on the test curve. If there is no defect reflection peak, it is judged that the pile is complete and the low-strain test is over; If the curve between the reflected waves is not smooth and there is a defective reflection peak, it is judged that there may be a defect in the pile body, and the next step is entered;

(7) Repeat steps (1) to (6) once to obtain another set of test curves. If there is no significant difference between the two sets of test curves and both show that there are defects in the pile body, take the average of the speeds obtained from the two sets of test curves , to get the type and location of the pile defect.

As preferably, in step (1), A and A' satisfy:

OA+OA'=R

Wherein, point O is the central point, and R is half of the diagonal length of the square pile;

B satisfies:

OB>a/2

a is half the side length of the square pile.

As a preference, in step (5), the test error comparison test is: if the difference in the peak value of the incident wave is too large, it shows that there is a large operational error in the test process, and it needs to be re-tested; Other on-site conditions make it difficult to carry out measurements, and multiple groups of signals after diagonal compensation and averaging can be selected for mutual inspection.

The advantages of the present invention are:

(1) The high-frequency interference caused by the square boundary is small. Utilize the anti-phase characteristics of the interference wave of paired supplementary measuring points whose sum of the distance from the diagonal to the pile center is R (half the length of the diagonal), superimpose the paired signals to eliminate the high-frequency interference originating from the square boundary ;

(2) The test results are verifiable. Select the measuring point in the traditional best measuring area (0.5-0.8a) in the direction of the right-angled side as the auxiliary measuring point, use the incident wave peak value and arrival time of the auxiliary measuring point signal as the reference signal, and check the signal after the average compensation, if If the averaged signal incidence peak exceeds 5% of the peak value of the traditional method, the test is considered to have failed, and a new test point is selected, which is equivalent to setting a "error red line", which ensures signal fidelity while eliminating high-frequency interference .

(3) The test location is flexible. During the test, the supplementary position on any diagonal line can be tested and signal translated, and the available detection area is no longer restricted by the optimal measurement area position, which makes the test process more flexible and minimizes the limitation of on-site conditions.

Description of drawings

Fig. 1 is the flow chart of a kind of square pile low strain quality detection method in the embodiment;

Fig. 2 is a schematic diagram of low strain detection operation and stress wave propagation near the pile top in the embodiment;

Fig. 3 (a) is the schematic diagram of measuring point standard layout in the embodiment;

Fig. 3 (b) is a schematic diagram of the first method for adjusting the diagonal supplement point under the bad site environment in the embodiment;

Fig. 3 (c) is the schematic diagram of the second method for adjusting the diagonal supplement point under the bad site environment in the embodiment;

Fig. 4 is the schematic diagram of the original velocity signal of the measuring point of the different distances from the pile center in the embodiment;

Fig. 5 is the schematic diagram of the original velocity signal of the measuring point of different distances from the pile center in the diagonal side in the embodiment;

Fig. 6 is a schematic diagram of the speed signal and its effect after diagonal compensation and averaging in the embodiment.

Detailed ways

In order to further understand the content of the present invention, the present invention will be described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the examples are only for explaining the present invention and not for limiting it.

Example

As shown in Fig. 1 and Fig. 2, the present embodiment provides a kind of square pile low-strain quality detection method, and it comprises the following steps:

(1) Select the measuring point: as shown in Figure 3(a), take a pair of supplementary points A and A' on the diagonal of the top of the square pile, and take a point B beyond half the length of the pile side in the direction of the right-angled side. A, A' and B are used as test points;

A and A' satisfy:

OA+OA'=R

Wherein, point O is the central point, and R is half of the diagonal length of the square pile;

B satisfies:

OB>a/2

a is half the side length of the square pile.

If the sensor cannot be arranged in the manner shown in Figure 3(a) due to unrestricted site conditions, the speed sensor can be arranged in the manner shown in Figure 3(b) or Figure 3(c) according to the symmetry of the square section; The method shown in Figure 3 cannot apply force at the pile core, so the measuring point can be determined by exchanging the position of the sensor and the hammer according to the reciprocity theorem of the elastic system.

(2) Install acceleration sensors: Arrange one acceleration sensor at A, A' and B respectively; the arrangement of acceleration sensors should be pasted with gypsum, and the next step can be carried out after the base layer is solidified.

(3) Low-strain test system debugging: connect each acceleration sensor to a multi-channel low-strain measurement acquisition instrument, and perform instrument debugging, sensor calibration and performance testing;

(4) Vibration excitation and sampling: Turn on the low-strain dynamic measurement acquisition instrument, apply the excitation force with the center point of the square pile top as the excitation point, and the excited stress wave propagates outward on the pile top, involving three time stages:

1. The stress wave propagating in all directions remains as a spherical surface before reaching the right-angle boundary, and both A and B can capture the signal at this stage;

, The stress wave along the right-angled square reaches the boundary and then returns, the reflected wave is superimposed on the incident wave, and an interference wave is formed at A;

, A' After receiving the signal, the stress wave in the diagonal direction continues to propagate outward to reach the corner point and is reflected back. During the return process, it is superimposed with the wave reflected from the right-angled side direction, forming a composite high-frequency interference in the diagonal direction. Received by the acceleration sensors at A' and A in turn;

In this way, the signal received by A includes the incident wave from the hammering point, the reflected wave from the right-angled side, and the reflected wave from the corner point; while A' receives the incident wave from the hammering point, and the reflected wave from the corner point Reflected wave; B receives the incident wave and the reflected wave from the right-angled side.

The acceleration response data measured by each sensor is sent to the low-strain dynamic measurement acquisition instrument, and the acceleration time-history curve is integrated through the built-in software of the low-strain dynamic measurement acquisition instrument to obtain three velocity time-domain response curves; Figure 4 and Figure 5 are respectively The speed response curves at different positions along the right-angled sides and diagonals can observe obvious inertial rebound and high-frequency interference.

(5) Low-strain test signal processing and inspection: analyze and process the obtained three speed response curves, first superimpose the responses at A and A', and use the characteristics of the 180-degree phase difference of the interference waves at the two positions to convert the high-frequency The interference wave is eliminated to obtain the test curve. This process is called diagonal supplementary average, as shown in Figure 6; compare the processed response with the speed peak value at B for test error comparison inspection: if the difference between the incident wave peak value is too large , indicating that there is a large operational error in the test process, and it needs to be retested; if the best measurement area at B is difficult to measure due to steel bar layout, concrete pouring or other site conditions, you can choose multiple groups of diagonal supplementary averaged signals Check each other.

(6) Low-strain test signal analysis and defect identification: Observe the smoothness of the curve between the incident wave and the reflected wave on the test curve. If there is no obvious defect reflection peak, it is judged that the pile is complete and the low-strain test is over; The curve between the reflected wave and the reflected wave is not smooth, and if there is a defective reflection peak, it is judged that there may be a defect in the pile body, and the next step is entered;

(7) Repeat steps (1) to (6) once to obtain another set of test curves. If there is no significant difference between the two sets of test curves and both show that there are defects in the pile body, take the average of the speeds obtained from the two sets of test curves , to get the type and location of the pile defect.

The above schematically describes the present invention and its implementation, which is not restrictive, and what is shown in the drawings is only one of the implementations of the present invention, and the actual structure is not limited thereto. Therefore, if a person of ordinary skill in the art is inspired by it, without departing from the inventive concept of the present invention, without creatively designing a structural mode and embodiment similar to the technical solution, it shall all belong to the protection scope of the present invention .

Claims (3)

1. a square pile low-strain quality detection method, is characterized in that: comprise the following steps: (1) Select the measuring point: Take a pair of supplementary points A and A' on the diagonal of the top of the square pile, take a point B beyond half the length of the pile side in the direction of the right angle, and use A, A' and B as test points ; (2) Acceleration sensors are installed: an acceleration sensor is arranged at A, A' and B respectively; (3) Low-strain test system debugging: connect each acceleration sensor to a multi-channel low-strain measurement acquisition instrument, and perform instrument debugging, sensor calibration and performance testing; (4) Vibration excitation and sampling: Turn on the low-strain dynamic measurement acquisition instrument, apply the excitation force with the center point of the square pile top as the excitation point, and the excited stress wave propagates outward on the pile top, involving three time stages: 1. The stress wave propagating in all directions remains as a spherical surface before reaching the right-angle boundary, and both A and B can capture the signal at this stage; , The stress wave along the right-angled square reaches the boundary and then returns, the reflected wave is superimposed on the incident wave, and an interference wave is formed at A; , A' After receiving the signal, the stress wave in the diagonal direction continues to propagate outward to reach the corner point and is reflected back. During the return process, it is superimposed with the wave reflected from the right-angled side direction, forming a composite high-frequency interference in the diagonal direction. Received by the acceleration sensors at A' and A in turn; The acceleration response data measured by each sensor is sent to the low-strain dynamic measurement acquisition instrument, and the acceleration time-history curve is integrated through the built-in software of the low-strain dynamic measurement acquisition instrument to obtain three velocity time-domain response curves; (5) Low-strain test signal processing and inspection: analyze and process the obtained three speed response curves, first superimpose the responses at A and A', and use the characteristics of the 180-degree phase difference of the interference waves at the two positions to convert the high-frequency The interference wave is eliminated to obtain the test curve. This process is called diagonal supplementary average; compare the processed response with the speed peak at B for test error comparison and inspection; (6) Low-strain test signal analysis and defect identification: Observe the smoothness of the curve between the incident wave and the reflected wave on the test curve. If there is no defect reflection peak, it is judged that the pile is complete and the low-strain test is over; If the curve between the reflected waves is not smooth and there is a defective reflection peak, it is judged that there may be a defect in the pile body, and the next step is entered; (7) Repeat steps (1) to (6) once to obtain another set of test curves. If there is no significant difference between the two sets of test curves and both show that there are defects in the pile body, take the average of the speeds obtained from the two sets of test curves , to get the type and location of the pile defect. 2. a kind of square pile low strain quality detection method according to claim 1, is characterized in that: in step (1), A and A ' satisfy: OA+OA'=R Wherein, point O is the central point, and R is half of the diagonal length of the square pile; B satisfies: OB>a/2 a is half the side length of the square pile. 3. a kind of square pile low-strain quality detection method according to claim 2 is characterized in that: in step (5), test error comparative inspection is: if incident wave peak difference is too large, shows that there is larger operation in the test process If the best measurement area at B is difficult to measure due to steel bar layout, concrete pouring or other site conditions, you can choose multiple sets of diagonal supplementary averaged signals for mutual inspection.

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