CN109469114B - Low-strain existing foundation pile integrity detection method capable of eliminating upper structure influence - Google Patents
Low-strain existing foundation pile integrity detection method capable of eliminating upper structure influence Download PDFInfo
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D33/00—Testing foundations or foundation structures
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
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Abstract
The invention provides a method for detecting the integrity of an existing foundation pile with low strain, which can eliminate the influence of an upper structure. The method utilizes the fact that the upper structure can be considered to be approximately fixedly connected with the pile top under the condition that the upper structure meets a certain condition, the influence of the upper structure is approximately a secondary excitation effect which has a certain time delay and is opposite to the initial excitation, analysis and calculation are carried out according to a stress wave theory, and secondary excitation formed by the upper structure is completely eliminated. The method has the advantages of simple principle, simplicity in operation, one or two sensors in installation number, simplicity in acquisition equipment, accurate and reliable result and strong engineering application and popularization prospects compared with other low-strain testing methods.
Description
Technical Field
The invention relates to the field of engineering detection, in particular to a method for detecting the integrity of an existing foundation pile.
Background
The existing foundation pile integrity detection has important significance for the safety and quality identification of the existing building, and when the quality of the foundation pile needs to be known, the foundation pile integrity (defect) detection needs to be carried out. Since the existing foundation piles are partially or completely buried under the foundation, the detection thereof is affected by the superstructure and the foundation, and the defect detection of the foundation piles is difficult.
The most common method adopted by the existing foundation pile integrity detection is a low-strain method, the pile top is excited by a small hammer or a force rod, a speed or acceleration sensor is used for actually measuring the speed or an admittance curve of a pile body, the rod fluctuation theory is used for identifying and analyzing the defects of the pile body, the low-strain detection method is simple to operate, the result is reliable, the method is recommended to be a standard method for detecting the integrity of the pile body by building and traffic industry standards, and the method is generally applied in the industry.
However, the low strain method is used for detecting the existing foundation pile, and the analysis of the signal has great difficulty due to the influence of the upper structure, and is mainly reflected in that: 1) the influence of the upper structure on the excitation is that the conventional low-strain excitation pulse is a bell-shaped pulse, the reflection rule of the conventional low-strain excitation pulse on the defect is simple and known, and under the influence of the upper structure, the excitation is no longer the bell-shaped pulse on the pile body no matter the excitation is carried out on the upper structure of the pile body or the pile top, the phase amplitude and the like of the pulse are possibly greatly changed, so that the corresponding defect reflection is more complicated and changeable and is difficult to identify; 2) the superstructure and defects cause a distinction in reflection. When no upper structure exists, reflection is generated only when the generalized impedance of the pile body changes, and downward reflection is generated in the upper structure of the foundation pile, so that the reflection of the upper structure and the reflection of defects are superposed together and are difficult to distinguish.
At present, some exploration and research are also carried out in the aspect of domestic, and the patent aspect mainly comprises a method for detecting the integrity of a high bearing platform pile under the existing building by a universal frequency response function method (patent publication No. CN 103774700A). The method is aimed at a high bearing platform pile under the existing building, the method utilizes the high bearing platform pile to expose the ground surface, adopts 2 strain sensors and 2 acceleration sensors symmetrically arranged on the side of the pile to measure the strain and speed response of a pile body, separates an upper traveling wave and a lower traveling wave by using a frequency response function, and finally judges the defects and the pile length of the pile according to the separated upper traveling wave.
The method for detecting the integrity of the high bearing platform pile under the existing building by using the universal frequency response function method partially solves the problems encountered by the existing foundation pile detection and has certain positive significance, but the influence of the upper structure on the excitation is not completely eliminated, the influence of the upper structure on the excitation still exists, and the defect reflection is still difficult to identify. When detecting simultaneously, need 2 power and 2 speedtransmitter of symmetry installation. The installation quantity of the sensors is large, the equipment is complex, the requirement on a data acquisition system is high, and the field operation is complex and time-consuming.
China is a large foundation construction country, foundation piles are widely used, the quality of the foundation piles needs to be known for various reasons after an engineering structure is built, the existing foundation pile detection method using a low-strain method is not ideal in effect, defective signals are difficult to distinguish, equipment is complex, field operation is complex and time-consuming, and a new method is urgently needed to be invented.
Disclosure of Invention
In order to solve the problems in the background art, the invention provides the existing foundation pile integrity detection method capable of eliminating the influence of the upper structure.
In order to achieve the purpose, the invention adopts the following technical scheme:
1. a method of low strain testing existing pile integrity with superstructure mitigation, comprising the steps of:
1) treating foundation piles;
2) equipment installation: installing an excitation block on the foundation pile, and installing a speed sensor at the lower part of the excitation block;
3) exciting the excitation block to obtain proper pulse;
4) acquiring data of a speed sensor, and obtaining a speed wave curve with the influence of an upper structure eliminated by the acquired data in a data processing mode;
5) and determining the position of the existing pile with the defects according to the speed wave curve obtained in the step 4).
Preferably, the speed sensor is one or two mounted up and down.
When the speed sensor is one, the data processing mode is as follows:
obtaining V 'according to the formula V ═ V' + V ═ V '(t) -V' (t-2L 1/Wc);
v is a speed wave curve collected by a speed sensor, V ' is a speed wave formed by a downward pulse tau ' formed by excitation, V ' is a speed wave curve after the influence of the superstructure is eliminated, and V ' is a speed wave formed by a downward pulse tau ' formed by the reflection of an upward pulse formed by excitation by the superstructure; the amplitude of the pulse tau 'is different from that of the pulse tau', L1 is the distance from the excitation block to the pile top, and Wc is the pile body wave speed.
When the number of the speed sensors is two, the data processing mode is as follows: the up-going and down-going waves are separated by two sensors, the up-going velocity wave V ≠ ≠ according to the elastic rod stress wave theory,
obtaining V '@ according to a formula V ═ V' @ + V '@ V @ V' (t) @ -V '(t-2L 1/Wc) @ c where V' @ is an upward velocity wave caused by a downward pulse τ 'formed by excitation, V' @ is a velocity wave curve in which an influence on a superstructure is removed, and V '@ is an upward velocity wave caused by a downward pulse τ' formed by reflection of an upward pulse formed by excitation by the superstructure; the amplitude of the pulse tau 'is different from that of the pulse tau', L1 is the distance from the excitation block to the pile top, and Wc is the pile body wave speed.
Specifically, the foundation pile treatment refers to excavation of the top of the foundation pile: for the foundation piles with the foundation piles completely or partially buried under the foundation, soil around the foundation piles needs to be excavated, and the upper parts of the foundation piles are suspended about 1.5-2.5 m.
Specifically, the vibration excitation block is arranged on the side face of the foundation pile 1-4 times of the pile diameter below the pile top, and the sensor is arranged at the position of about one time of the pile diameter below the vibration excitation block.
Specifically, when the length-pile diameter ratio of a bearing platform or a bearing plate connected with the foundation pile is more than 2, torsional waves are adopted for excitation, and an included angle of 90 degrees is formed between an excitation block and a sensor; when the ratio of the thickness of the bearing platform or the bearing platform connected with the foundation pile to the diameter of the pile is more than 3 and the ratio of the thickness to the excitation wavelength is more than 2, longitudinal waves are adopted for excitation.
Specifically, in step 5), low-pass filtering is required to be performed on the velocity wave.
Specifically, the sampling frequency of the speed sensor is not lower than 100 KHz.
The speed sensor can be replaced by an acceleration sensor, and when the acceleration sensor is adopted, the speed data is obtained by integrating the acquired acceleration data.
The invention has the beneficial effects that: the method can completely eliminate secondary excitation formed by the upper structure, has a simple principle and simple operation, and has the advantages of one or two sensors, simple acquisition equipment, accurate and reliable result and stronger engineering application and popularization prospects compared with other low-strain testing methods.
Drawings
The invention will be further explained with reference to the drawings
FIG. 1 is a schematic view of an installation structure of an apparatus used in the method of the present invention;
FIG. 2 is a schematic diagram of a velocity wave propagation characteristic of a foundation pile according to the method of the present invention;
FIG. 3 is a velocity waveform diagram collected by two velocity sensors in embodiment 1;
FIG. 4 is a velocity waveform of velocity 1 of FIG. 3 after the superstructure effects have been removed;
fig. 5 is a velocity upgoing wave diagram with the superstructure effect removed in example 1.
Detailed Description
The invention will be further described with reference to the following description and embodiments in conjunction with the accompanying drawings:
the invention provides a method for detecting the integrity of an existing foundation pile with low strain, which can eliminate the influence of an upper structure, and fig. 1 shows a schematic view of an equipment installation structure adopted by the method, wherein: piece 1, first sensor 2, second sensor 3, foundation pile 4, basis 5, superstructure 6, binary channels data acquisition appearance 7 vibrate, piece 1 installs 1 ~ 4 times pile diameter position below 4 pile tops of foundation pile, first sensor 2 is installed in 1 lower part of piece that vibrates about a time pile diameter distance department, when needs separation uplink and downlink wave, install a second sensor 3 again in first sensor 2's below, piece 1 vibrates, first sensor 2 and second sensor 3 accessible mechanical fixation or sticky mode fixes the side at foundation pile 4. The first sensor 2 and the second sensor 3 are speed sensors or acceleration sensors, and when the acceleration sensors are adopted, data acquired by the acceleration sensors need to be subjected to integration processing to obtain speed data.
The method comprises the following steps:
1) firstly, excavating the top of a foundation pile 4: for the foundation piles which are completely or partially buried under the foundation, soil around the foundation piles needs to be excavated, so that the upper parts of the foundation piles are suspended about 1.5-2.5 m.
2) Then installing an excitation block 1 on the side surface of the foundation pile at a position 1-4 times the pile diameter below the pile top; then, one or two speed or acceleration sensors (when the up-down traveling wave separation is needed) are arranged along the vibration measuring direction at the distance which is about one time of the pile diameter at the lower part of the vibration excitation block 1;
3) then, a vibration exciting hammer is adopted to carry out vibration excitation on the vibration exciting block 1 for multiple times to obtain required pulses;
4) collecting data of a speed sensor, wherein the sampling frequency is not lower than 100kHz, and obtaining a speed wave curve without influence of an upper structure by the collected data in a data processing mode;
for an existing foundation pile with a superstructure, due to the fact that during pile body excitation, velocity pulses formed by excitation propagate simultaneously upwards and downwards along the pile body, forming pulses τ 'which propagate downwards and pulses τ' ″ which propagate upwards, reflect from the superstructure and go downwards, as shown in fig. 2, the pulses τ 'and τ' ″ form double excitations on the pile body below the excitation mass 1, and due to the pulses τ 'being formed by reflection from the superstructure, there is a phase delay of 2L1/Wc with the pulse wave τ', L1 is the distance of the excitation mass 1 from the pile top, and Wc is the pile body wave speed. According to one-dimensional rod stress wave theory, if two pulses τ 'and τ' ″ are similar in behavior and proportional in amplitude, then the reflections caused by these two pulses are also proportional, and the velocity wave V 'formed by pulse τ' and the velocity wave V 'formed by pulse τ'. are correspondingly proportional. When the upper structure satisfies the condition: when the length-diameter ratio of the bearing platform or the plate connected with the foundation pile is more than 2; or the length to pile diameter ratio of the bearing platform or plate connected with the foundation pile is more than 3, and the thickness to excitation wavelength ratio is more than 3, the superstructure can be considered to be approximately fixed on the pile top, and the tau' are opposite in direction and have a difference of two times in amplitude, so that:
τ＇＇＝－τ＇ (1)
V＇＇＝－V＇ (2)
when the two excitations act together, according to the principle of superposition of elastic waves,
v ═ V ' + V ' (' 3) wherein V is the velocity wave curve collected by the velocity sensor; taking into account that τ 'is phase delayed by 2L1/Wc compared to τ', there is
V＝V＇+V＇＇＝V＇(t)-V＇(t-2L1/Wc) (4)
V is measured by a sensor, and V' can be obtained by the formula (4), namely, the speed curve after the influence of the upper structure is eliminated.
When the length-pile diameter ratio of a bearing platform or a bearing plate connected with the foundation pile is more than 2, adopting torsional waves to perform excitation, and when adopting torsional waves to perform excitation, forming an included angle of 90 degrees between an excitation block and a sensor; when the length-pile diameter ratio of a bearing platform or a bearing plate connected with the foundation pile is more than 3 and the thickness-excitation wavelength ratio is more than 3, exciting by adopting longitudinal waves;
when two sensors are installed, the up and down traveling waves can be separated. And solving to obtain upper and lower traveling waves V ↓andV ↓accordingto an elastic rod stress wave theory.
The method also comprises the following steps:
V↑＝V＇↑+V＇＇↑＝V＇(t)↑-V＇(t-2L1/Wc)↑ (5)
v' ≠ i, i.e., a velocity profile in which the influence of the upper structure is eliminated, is obtained from the above equation (5).
6) Determining the position of the defect and the pile length: the obtained V 'or V' ≠ is low-pass filtered, and the defect position is determined according to the velocity wave V 'or V' ℃ @.
The following provides a specific example
Example 1
The thickness of the upper part of an existing foundation pile is 1m, the diameter of the foundation pile is 0.5m, the length of the pile is 10m, an excitation block is arranged 1m below the pile top, the receiving positions of speed sensors are 1.5m and 2.0m below the pile top respectively, after the excitation block is excited, the data of the two speed sensors are collected, a waveform diagram as shown in figure 3 is obtained, the speed 1 is a waveform collected by the upper speed sensor, and the speed 2 is a waveform collected by the lower speed sensor.
Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.
Claims (7)
1. A method of low strain testing existing pile integrity with superstructure mitigation, comprising the steps of:
1) treating foundation piles;
2) equipment installation: installing an excitation block on the foundation pile, and installing a speed sensor at the lower part of the excitation block;
3) exciting the excitation block to obtain proper pulse;
4) acquiring data of a speed sensor, and obtaining a speed wave curve with the influence of an upper structure eliminated by the acquired data in a data processing mode;
5) determining the position of the existing pile with defects according to the velocity wave curve obtained in the step 4);
the speed sensors are one or two arranged up and down;
when the speed sensor is one, the data processing mode is as follows:
obtaining V 'according to the formula V ═ V' + V ═ V '(t) -V' (t-2L 1/Wc);
v is a speed wave curve collected by a speed sensor, V ' is a speed wave formed by a downward pulse tau ' formed by excitation, V ' is a speed wave curve after the influence of the superstructure is eliminated, and V ' is a speed wave formed by a downward pulse tau ' formed by the reflection of an upward pulse formed by excitation by the superstructure; the difference between the amplitudes of the pulse tau 'and the pulse tau' ″, L1 is the distance from the excitation block to the pile top, and Wc is the pile body wave speed;
when the number of the speed sensors is two, the data processing mode is as follows: the up-going and down-going waves are separated by two sensors, the up-going velocity wave V ≠ ≠ according to the elastic rod stress wave theory,
obtaining V '@ according to a formula V ═ V' @ + V '@ V @ V' (t) @ -V '(t-2L 1/Wc) @ c where V' @ is an upward velocity wave caused by a downward pulse τ 'formed by excitation, V' @ is a velocity wave curve in which an influence on a superstructure is removed, and V '@ is an upward velocity wave caused by a downward pulse τ' formed by reflection of an upward pulse formed by excitation by the superstructure; the amplitude of the pulse tau 'is different from that of the pulse tau', L1 is the distance from the excitation block to the pile top, and Wc is the pile body wave speed.
2. The method for detecting the integrity of the existing foundation pile with low strain capable of eliminating the influence of the superstructure according to claim 1, wherein the foundation pile processing is excavation of the top of the foundation pile: for the foundation piles with the foundation piles completely or partially buried under the foundation, soil around the foundation piles needs to be excavated, and the upper parts of the foundation piles are suspended about 1.5-2.5 m.
3. The method for detecting the integrity of the existing foundation pile with low strain and capable of eliminating the influence of the superstructure according to claim 1, wherein the vibration excitation block is installed on the side surface of the foundation pile 1-4 times the pile diameter below the pile top, and the sensor is installed at the position 1 time the distance of the pile diameter below the vibration excitation block.
4. The method for detecting the integrity of an existing foundation pile with low strain capable of eliminating the influence of the superstructure as claimed in claim 1, wherein when the length of the bearing platform or the plate connected with the foundation pile is more than 2 to the diameter of the pile, the vibration is excited by using torsional waves, and the vibration exciting block and the sensor form an included angle of 90 degrees; when the ratio of the thickness of the bearing platform or the bearing platform connected with the foundation pile to the diameter of the pile is more than 3 and the ratio of the thickness to the excitation wavelength is more than 2, longitudinal waves are adopted for excitation.
5. A method of low strain pre-existing pile integrity testing with superstructure mitigation according to claim 1, wherein in step 5) low pass filtering of the velocity wave is required.
6. A method of low strain testing of existing pile integrity with elimination of superstructure effects as claimed in claim 1, wherein the sampling frequency of the speed sensor is not less than 100 KHz.
7. A method of low strain testing of existing pile integrity with elimination of superstructure effects as claimed in claim 1 wherein the velocity sensors are replaced by acceleration sensors and when acceleration sensors are used the velocity data is obtained by integrating the acceleration data collected.
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| CN112211236B (en) * | 2020-11-15 | 2022-07-26 | 山东贝特建筑项目管理咨询有限公司 | Engineering pile body defect detection method |
| CN112663689B (en) * | 2020-12-16 | 2022-02-11 | 浙江大学 | Multi-measuring-point low-strain detection method for high-bearing-platform pile foundation |
| CN115404920B (en) * | 2022-08-05 | 2024-03-12 | 广东交科检测有限公司 | Foundation pile detection method and system |
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