CN103774700B - Method for detecting integrity of high flat bed pile under existing building through overtone response function method - Google Patents

Abstract

The invention discloses a method for detecting the integrity of high cap piles under existing buildings and structures by means of a pan frequency response function method. The present invention comprises the following steps: step 1. collection of data; step 2. analyzing the collected data by the pan frequency response function method; step 3. judging the length and integrity of the foundation pile of the high cap pile; The top surface of the upper cap is excited to obtain the velocity signal and force signal at a certain position on the pile body, and the pan frequency response function of this position is calculated by using the pan frequency response function method to analyze the integrity of the pile body. When the top surface of the foundation pile cap is excited, for a certain position of the foundation pile, a downgoing wave is generated first, and then an upgoing wave is formed by reflection at the bottom of the pile (defect). The change of the upgoing wave relative to the downgoing wave is only related to the position For the following pile-soil correlation, the Fourier transform of the upgoing wave is divided by the Fourier transform of the downgoing wave to obtain a pan frequency response function. Using this pan frequency response function to evaluate the integrity of the pile below the position can eliminate the superstructure Influence.

Description

Method for testing the integrity of high-capped piles under existing buildings using the pan-frequency response function method

technical field

The invention relates to a technology for detecting the integrity of high cap piles under existing buildings, in particular to a method for detecting the integrity of high cap piles under existing buildings using a pan frequency response function method.

Background technique

High cap pile foundation is a common foundation form in bridges, docks and other projects. In recent years, natural disasters have occurred frequently in various countries around the world. After each large-scale disaster such as destructive earthquakes, landslides, and tsunamis, many bridges, The wharf will be damaged and damaged in different degrees, and these damages and damages will not only occur in the structure of the bridge and the upper part of the wharf, but also in the foundation part of the lower part. On the other hand, because some of the pile foundations of high-cap pile foundations such as bridges and wharf piles are exposed on the ground, they are easily damaged and damaged by man-made accidents, such as collisions with vehicles and ships, and explosion impacts. After the occurrence of these natural disasters or man-made accidents, it is necessary to test and evaluate its safety, and most of the pile body of the high-cap pile foundation is located underground (underwater), which is concealed and complicated. Compared with the superstructure, its detection and evaluation In terms of evaluation, it has higher difficulty and technical requirements.

The routine detection methods of foundation pile quality include single pile static load test, low strain reflection wave method, acoustic wave transmission method, and drilling coring method. When using conventional detection methods, the pile top is usually required to be a free end. Pile, the conventional method is difficult to operate. In addition, for the side hole transmitted wave method for the detection of existing building foundation piles, holes need to be drilled near the pile side and each pile needs to detect dozens or even hundreds of measuring points, the detection efficiency is relatively low, and the cost Higher, not suitable for large-scale quality surveys, especially for docks and bridge piles on the water, the actual operation is difficult, and for longer piles, the inclination of the borehole will lead to unreliable test results.

Therefore, a method that can effectively eliminate the influence of the superstructure on the test results without damaging the superstructure and the pile body, and transform the foundation piles under the complex structural system into the single pile test mode for detection and analysis is used for post-disaster Accurate and objective assessment of the foundation safety performance of bridges, docks and other structures has great practical significance.

Contents of the invention

The purpose of the present invention is to provide a method for detecting the integrity of high cap piles under existing buildings and structures by means of a pan-frequency response function method. That is, the method of detecting the length and integrity of foundation piles without damaging foundation piles and superstructures.

The technical solution adopted by the present invention to solve its technical problems is as follows:

Step 1. Data collection;

Step 2. Analyze the collected data by the pan frequency response function method;

Step 3. Judging the pile length and integrity of the high cap pile foundation.

The data collection described in step 1 is specifically as follows:

1-1. Install two sets of sensors symmetrically at a certain position of the pile body under test;

Each group of sensors includes an acceleration sensor and a strain sensor, and the two groups of sensors are connected to the dynamic data acquisition and analyzer through wires; and the acceleration sensor in one group is used as a sampling trigger;

The installation direction of the two groups of sensors is consistent with the axial direction of the tested foundation pile; the installation position is the position of the detection surface, and the distance between the detection surface and the bottom surface of the cap is greater than 1.5m;

1-2. Use the vibrating hammer to vibrate vertically on the top surface of the corresponding cap directly above the foundation pile under test, the sampling trigger is triggered, and then two sets of sensors collect data signals and transmit the signals to dynamic data acquisition and analysis The instrument performs synchronous display and storage; the acceleration sensor collects the acceleration signal at the position of the detection surface of the pile body, and the strain sensor collects the strain signal at the position of the detection surface of the pile body;

If the degree of agreement between the acceleration signal and the strain signal collected by the two groups of sensors in steps 1-2 is quite different, adjust the excitation position and repeat the collection; if the waveform is abnormal and the sampling quality cannot be judged, then collect and store it multiple times; The excitation position of the excitation hammer is the position of the top surface of the cap corresponding to the center of the section of the foundation pile under test.

The data collected by analyzing the collected data through the pan frequency response function method described in step 2 is as follows:

2-1. Convert the collected acceleration signal and strain signal into velocity signal (v) and force signal (p);

2-2. Obtain the pan frequency response function of the detection surface position;

Combining the velocity signal v and force signal p obtained in step 2-1 with the mechanical impedance z of the section of the pile body at the position of the detection surface, the pan frequency response function is obtained as follows:

Among them, DFT means discrete Fourier transform;

2-3. Calculate the upgoing wave curve obtained by simulating the half-sine pulse downgoing wave input at the top of the pile section below the detection surface;

Upgoing wave curve = IDFT [Overall Frequency Response Function × FT (simulated half-sine pulse downgoing wave)]

Among them, IDFT stands for Inverse Discrete Fourier Transform, and FT stands for Fourier Transform.

Judging the length and integrity of the high cap pile foundation piles described in step 3, the details are as follows:

3-1. Calculate the pile length below the detection surface of the high cap pile:

Calculate the pile length H below the detection surface of the high cap pile according to the pile bottom reflection signal of the upward wave curve:

H=t×c/2

Among them, t represents the moment when the reflection signal at the bottom of the pile appears; c represents the propagation velocity of the one-dimensional longitudinal stress wave of the pile body;

3-2. Judging whether the pile body below the detection surface of the high cap pile is complete:

If the upward wave curve has other reflection signals before the pile bottom reflection appears, it means that there is a defect in the pile below the detection surface, and the defect position L is calculated:

L=t _d ×c/2

Among them, t _d represents the moment when the defect reflection signal appears;

If there is no other reflection signal on the upgoing wave curve before the reflection at the bottom of the pile, it means that the pile below the detection surface is complete.

The beneficial effects of the present invention are:

(1) This method can completely eliminate the influence of the superstructure on the integrity detection of the pile body without destroying the superstructure and the pile body, so that the pile to be tested can be "isolated" from the complex structure, and the single pile after isolation The problem is easy to analyze and evaluate with reference to the traditional single-pile one-dimensional vibration problem, which greatly reduces the difficulty of the problem and improves the reliability of the test results;

(2) No complicated construction such as drilling is required, the operation is simple and convenient, the economic cost is low, and at the same time, it will not cause damage to the foundation piles in service, and can be popularized and adopted in projects that require a large number of general surveys;

(3) Part of the pile body of high cap piles (such as bridges and wharf piles) is exposed above the ground (water surface), which is especially suitable for testing and analysis by this method. For low cap pile foundations under other existing structures, if they pass Excavating around the pile body to expose a part of the side of the pile body can also be tested and evaluated by the above method.

Description of drawings

Fig. 1 is a schematic diagram of the detection structure of the present invention;

Fig. 2 is the installation schematic diagram of two groups of sensors in the present invention;

In the figure, the vibrating hammer 1, the bearing platform 2, the wire 3, the dynamic data acquisition and analyzer 4, the foundation pile under test 5, the strain sensor 6, the detection surface 7, the acceleration sensor 8, the foundation soil 9, and the adjacent foundation pile 10 .

Detailed ways

The method of the present invention will be further described below in conjunction with accompanying drawing of description:

As shown in Figure 1 and Figure 2, the method of detecting the integrity of high cap piles under existing structures by the pan frequency response function method includes the following steps:

Step 1. Data collection;

Step 2. Analyze the collected data by the pan frequency response function method;

Step 3. Judging the pile length and integrity of the high cap pile foundation.

The data collection described in step 1 is specifically as follows:

1-1. Install two groups of sensors symmetrically at a certain position of the pile body of the foundation pile 5 under test;

Each group of sensors includes an acceleration sensor 8 and a strain sensor 6, and the two groups of sensors are connected to the dynamic data acquisition and analyzer 4 by wire 3; and the acceleration sensor in one group is used as a sampling trigger;

The installation direction of the two groups of sensors is consistent with the axial direction of the tested foundation pile 5; the installation position is the position of the detection surface 7, and the distance between the detection surface 7 and the bottom surface of the cap 2 is greater than 1.5m.

1-2. Use the vibrating hammer 1 to vibrate vertically on the top surface of the corresponding cap directly above the foundation pile 5 under test, the sampling trigger is triggered, and then two sets of sensors collect data signals and transmit the signals to the dynamic data acquisition and the analyzer 4 for synchronous display and storage; wherein the acceleration sensor collects the acceleration signal at the position of the detection surface of the pile body, and the strain sensor collects the strain signal at the position of the detection surface of the pile body.

If the degree of agreement between the acceleration signal and the strain signal collected by the two groups of sensors in steps 1-2 is quite different, adjust the excitation position and repeat the collection; if the waveform is abnormal and the sampling quality cannot be judged, then collect and store it multiple times;

The data collected by analyzing the collected data through the pan frequency response function method described in step 2 is as follows:

2-1. Convert the collected acceleration signal and strain signal into velocity signal (v) and force signal (p);

2-2. Obtain the pan frequency response function of the detection surface position;

Combining the velocity signal (v) and force signal (p) obtained in step 2-1 with the mechanical impedance (z) of the section of the pile body at the position of the detection surface, the pan frequency response function is obtained as follows:

Among them, DFT means discrete Fourier transform;

2-3. Calculate the upgoing wave curve obtained by simulating the half-sine pulse downgoing wave input at the top of the pile section below the detection surface;

Upgoing wave curve = IDFT [Overall Frequency Response Function × FT (simulated half-sine pulse downgoing wave)]

Among them, IDFT stands for Inverse Discrete Fourier Transform, and FT stands for Fourier Transform.

Judging the length and integrity of the high cap pile foundation piles described in step 3, the details are as follows:

3-1. Calculate the pile length below the detection surface of the high cap pile:

Calculate the pile length H below the detection surface of the high cap pile according to the pile bottom reflection signal of the upward wave curve:

H=t×c/2

Among them, t represents the moment when the reflection signal at the bottom of the pile appears; c represents the propagation velocity of the one-dimensional longitudinal stress wave of the pile body;

3-2. Judging whether the pile body below the detection surface of the high cap pile is complete:

If the upward wave curve has other reflection signals before the pile bottom reflection appears, it means that there is a defect in the pile below the detection surface, and the defect position L is calculated:

L=t _d ×c/2

Among them, t _d represents the moment when the defect reflection signal appears;

If there is no other reflection signal on the upgoing wave curve before the reflection at the bottom of the pile, it means that the pile below the detection surface is complete.

The working principle of the present invention is as follows:

Under the condition of one-dimensional vibration (fluctuation), the fluctuation of any section of the pile body can be decomposed into two parts, the upward and downward waves. A section on the upper part of the foundation pile under test (according to the location of the sensor installed) is taken as the detection surface, and the position of the initial excitation source is located above the detection surface. When the vibration is not excited, the pile body is in a static state. After the vibration is excited, relative to the detection surface, a downgoing wave should be generated first. When the downgoing wave encounters the impedance change interface of the pile body or the pile tip and the foundation soil during the downward propagation process When it acts, it will reflect and form an upward wave. The downgoing wave is the result of the joint action of the exciting force, the upper structure (including the cap, the buildings on the cap, and adjacent foundation piles), the pile body above and below the detection surface, and the foundation soil, while the upgoing wave is the result of the downgoing wave reaching below the detection surface. Therefore, the change of the upgoing wave measured at the detection surface relative to the downgoing wave only reflects the effect of the pile body and foundation soil below the detection surface, that is, the relationship between this change is only related to the The length of the pile, the integrity of the pile body and the condition of the soil around the pile are related. Therefore, similar to the traditional frequency response function, the Fourier transform of the upward velocity wave (or force wave) at the detection surface can be divided by the Fourier transform of the downward velocity wave (or force wave) to define the general velocity (force ) frequency response function (abbreviated as pan frequency response function), the pan frequency response function uniquely reflects the integrity of the pile below the detection surface and the condition of the soil layer and has nothing to do with the pile body and structure above the detection surface, so it can be The integrity of the pile body below the detection surface is detected and evaluated by using the pan frequency response function, and the influence of the superstructure and the pile body can be completely eliminated. The above-mentioned up-going wave and down-going wave can be calculated from the measured velocity response and cross-sectional force wave response at the detection surface. After the over-the-top frequency response function at the detection surface is obtained, a half-sine pulse downgoing wave can be virtually input on the top of the pile section below the detection surface through numerical analysis method, and the corresponding upgoing wave curve can be obtained. Through this upgoing wave curve, intuitive and accurate Determine the nature and location of pile defects.

Claims (1)

1. general frequency response function method detects the method for Vertical spots integrality under existing construction of structures, it is characterized in that comprising the steps:

The collection of step 1. data;

The data that step 2. is collected by the analysis of general frequency response function method;

Step 3. judges the long and integrality of Vertical spots foundation pile stake;

The collection of the data described in step 1 is specific as follows:

1-1. installs two sensors symmetrically at the pile body certain position of tested foundation pile;

Often organize sensor and comprise an acceleration transducer and a strain transducer, by wire, two sensors is connected to Dynamic Data Acquiring and analyzer; And the acceleration transducer wherein in a group is as sample trigger;

The installation direction of described two sensors is axially consistent with tested foundation pile; Installation site is the position of detection faces, and the distance of detection faces distance cushion cap bottom surface is greater than 1.5m;

The vertical exciting of cushion cap end face that 1-2. exciting hammer is corresponding directly over tested foundation pile, sample trigger is triggered, then two sensors image data signal, and signal transmission is carried out simultaneous display and storage to Dynamic Data Acquiring and analyzer; Wherein acceleration transducer gathers the acceleration signal of pile body detection faces position, and strain transducer gathers the strain signal of pile body detection faces position;

If the degree of agreement of the acceleration signal that step 1-2 two sensors collects and strain signal differs greatly, then adjust Position of Vibrating repeated acquisition; If waveform occurs that abnormal causing cannot differentiate sampling quality quality, then multi collect storing; The Position of Vibrating of described exciting hammer is the cushion cap top side location that tested foundation pile kernel of section is corresponding;

The data collected by the analysis of general frequency response function method described in step 2, specific as follows:

The acceleration signal of collection and strain signal are converted to rate signal v and force signal p by 2-1.;

2-2. obtains the general frequency response function of detection faces position;

The rate signal v obtained by step 2-1 and force signal p, in conjunction with pile body cross section, detection faces position mechanical impedance z, obtains general frequency response function as follows:

Wherein, DFT represents discrete Fourier transform;

2-3. calculates the upgoing wave curve obtained after the following pile cutoff of detection faces withstands on the input of simulation half-sine pulse down going wave;

Upgoing wave curve=IDFT [general frequency response function × FT (simulation half-sine pulse down going wave)]

Wherein, IDFT represents inverse discrete Fourier transform, and FT represents Fourier transformation;

Long and the integrality of judgement Vertical spots foundation pile stake described in step 3, specific as follows:

It is long that 3-1. calculates the stake of below Vertical spots detection faces:

Below the Vertical spots detection faces long H of stake is calculated according to upgoing wave curve pile bottom reflection signal:

H＝t×c/2

Wherein, t represents the moment that pile bottom reflection signal occurs; C represents pile body one dimension longitudinal stress velocity of wave propagation;

3-2. judge that whether the following pile body of Vertical spots detection faces is complete:

If upgoing wave curve had other reflected signals before pile bottom reflection occurs, then the following pile body existing defects of detection faces is described, and calculates defective locations L:

L＝t _d×c/2

Wherein, t _drepresent the moment that defect reflection signal occurs;

If upgoing wave curve did not occur other reflected signals before pile bottom reflection occurs, then illustrate that the following pile body of detection faces is complete.