通能岩土工程有限公司 桩基低应变动测报告
Figure 10 piles in the measured waveform curve 2.6 piles in the wave curve
On the pile, if there is no dross or scum pile less, piles and
Bedrock good contact, then pile the reflected signal is not obvious, but after index discharge
Technical processing and large, and sometimes can see the reflection of a reverse signal. If pile
The end of scum more, sometimes you can see the phase with the reflected wave appears, the floating
Residue on the absorption of a strong wave, and sometimes it is difficult to see the reflected signal (Figure 10). 3 Data Analysis
Dynamic test and static test the biggest difference is that the dynamic test includes multiple frequency components of the dynamic signal recording problems. In the analysis of pile integrity, usually using only time-domain waveforms by time domain analysis of the curve to determine the pile the integrity of the body, without using the measured spectrum curve, which is actually a waste of half of the resources. In fact, the spectral analysis is to study the problem of dynamic test system the primary means of frequency response. study the spectrum of the waveform curve, you can better guidance on-site testing and to supporting the integrity of the pile. Figure 11 shows a pile of a site, from the time domain curve can be seen in 1. 7 ms at a small
reflection may be flawed here, but its spectral curve can be seen, almost equal distance between the resonance peak, the pile should be a complete pile.
Figure 12 shows the root of the same site of another reduced diameter pile, its spectral curve see that the resonance peak spacing is not equal. At the same
31 / 35
通能岩土工程有限公司 桩基低应变动测报告
time, the choice of sensor installation method, the use of spectral analysis the installation of their resonant frequency, and then select the highest resonant frequency method of installation is necessary, because it will give full extension system Measurement of
Test range. We all know better than hammer nylon hammer test is good, when the force rod test piles grow the best, although the time domain vibration effect can be compared
Good or bad, but the interpretation and understanding of good and bad is often based on the analysis of the spectrum concept of frequency of use.
Spectral curve of Figure 11 complete pile
32 / 35
通能岩土工程有限公司 桩基低应变动测报告
Figure 12 necking pile spectrum curve
In many cases, due to the presence of interfering components, if not for the time domain filtering is difficult to analyze, then become an important means of filtering, but sometimes, the filter easily lead to waveform distortion as well as impact analysis to determine; contrast , in the frequency domain, all frequency components at a glance, as long as the test system used a careful analysis is very easy to correct the interference components. time-domain signal is poor compliance or interference too serious, the use of frequency domain analysis and comparison of the signals in common (resonance peak), the analysis of these resonance peaks corresponding to the defect, and then turn in the time domain to verify that this is a very good way, and sometimes difficult to find the time domain reflection pile, but can be found in the frequency domain , the time domain is difficult to detect shallow defects, the frequency domain is also
easier to find. Of course, frequency domain analysis Time domain analysis can be an essential complement to its own frequency domain analysis because there are still many shortcomings, difficult to determine the nature of such
defects, defect location and for the calculation of large deviation caused by the same defects difficult to identify other adjacent resonance peaks. These effects of the frequency domain analysis
The effect is not widely used frequency domain analysis the main reason for it. However, frequency domain analysis of time-domain analysis is an effective complement, and this is no doubt [5]. Note 4 Detection
4.1 vibration problems
Detection in the pile, and stirred the pulse of high-quality key to quality is to improve the detection, analysis and years of practical experience has shown
33 / 35
通能岩土工程有限公司 桩基低应变动测报告
that vibration technology is the detection of reflected wave method an
important part of integrity. In testing, the commonly used instantaneous state excitation, the simplest way is by hand or boomerang hammer excitation, the mechanism based on the collision theory. When the pile of concrete piles longer or poor continuity, the use of iron or wood is difficult to identify
hand-hammer excitation pile reflected signal, the reason is iron or wooden hammers high frequency excitation signal, the propagation of the pile
decreases rapidly at this time can be composed of different materials with different quality of the force rod easier to obtain pile excitation reflected signal. In testing should pay attention to and improve the frequency of excitation pulse, can improve the resolution, but easy to attenuation of high frequency waves are not readily available on the long pile pile reflection, so only use a low frequency pulse to obtain pile reflection, and then high-frequency waves to detect the lack of top of pile
Depression. View of the record from the measured waveform [4], the vibrating frequency of the pulse is about 300 ~ 1 500 Hz or so. Different pile length and pile type, the excitation
Not the same frequency, usually about 60 m or 30 m pile friction around piles, the pulse wave frequency at about 300 ~ 500 Hz; 10 ~ 20m of piling, the pulse wave frequency of 500 ~ 1000 Hz or so; less than 10 m of piling, the pulse wave frequency can be as high as 1 000 ~ 1 500 Hz. exciting to note when the other problem is that excitation energy should be moderate, not the energy the better. For hard formation, the energy spread of pulse wave in the pile more, the required excitation energy should be slightly larger. In addition, when altogether exciting, agile, not sloppily, preferably by experienced people
dedicated excitation, so basically the same each time the excitation waveform is conducive to comparative analysis. 4.2 sensor and the choice of binder
Detection sensor is a pile of \sensitivity and dynamic range of the measured waveform is very large.
Reflection Method have special requirements on the sensor, the sensor is near the excitation point, excitation signal is either a strong distortion of the receiver down, while tens of meters long put spread after to receive the reflected wave and converted into electrical signals, so the scope and range of the sensor's dynamic range should be wide enough, and have high sensitivity. in the strong excitation, the remaining vibration is shorter, which require it to have good damping properties. Under normal circumstances, we can use multiple sensors with different characteristics measuring several sets of curves, by comparing to further improve accuracy of analysis. In the case of sensor
performance is better, you must choose a good binder, so that the sensor and get a good coupling pile. At present there are commonly used in adhesive plaster, plasticine, snake skin cream, butter, etc. In addition, some inspectors also use chewing gum as a binder after. In the binder, gypsum powder, the coupling of high frequency bonding, then the coupling of several lower
34 / 35
通能岩土工程有限公司 桩基低应变动测报告
frequency. It should be noted that, when the pile head relatively wet, the use of rubber cement and gypsum as a binder snakeskin effect of the bond is not very good at this time is best to use gypsum powder. 4.3 Treatment of pile head
Piles tend to have a layer of floating pulp pile head, especially the artificial drilled pile, pile head is generally lower than the ground, by precipitation after the pile, the pile will appear thick layer of floating the upper part of pulp, which makes When excited by energy in the hammer is not enough focus,
divergence faster, lower-frequency excitation pulse wave, impact test results, and therefore must be floating pulp testing destroyed, while maintaining the pile head formation. In addition, precast piles penetration damage that may arise during the pile head, pile in when they can get rid of floating pulp have broken pile head, which would rapidly decay elastic wave energy, and in severe irregular pulse so excited, seriously affect the test results, even
miscarriage of justice caused by the phenomenon. Therefore, we should pay attention to when testing pile head condition. 4.4 Auxiliary data collection
Pile testing should note that during the secondary data collection, secondary data to analyze the pile with the defect type. The supporting information, including geotechnical engineering geological investigation report, Pile hole technology, equipment and technology into a pile and pile construction records. Based on these auxiliary data, which can analyze the possible defects, and even the site of defects occur. For example, artificial drilled pile, impossible necking, while the scum pile may be the main defects of these piles ; for the vibration of pile, the pile should be noted that the upper part of the defects, such piles prone to the phenomenon of necking or broken pile. in soft ground and hard ground on the interface of the possible formation of the reflected
wave and so on. If the sensor is close to the bar installation, the steel will affect the detection of the waveform. these are detected during the pile must pay attention to.
35 / 35