Real-time measuring device and method for soil rigidity in physical model test

Abstract

The invention discloses a physical model test soil rigidity real-time measurement device and a physical model test soil rigidity real-time measurement method. A soil physical model is installed in the piezoelectric elastic wave velocity test system, a function generator transmits pulse signals to an excitation element and a data acquisition system, the pulse signals are transmitted to a receiving element after passing through the soil physical model, and signals of the receiving element are amplified by a signal amplifier and then transmitted to the data acquisition system. The data acquisition system is used for acquiring a signal passing through the piezoelectric elastic wave velocity test system and a pulse signal directly emitted by the function generator, and inputting the acquired signal into the post-processing analysis system, and the post-processing analysis system analyzes and processes the input signal to obtain the rigidity of the soil physical model. According to the invention, the rapid attenuation and recovery process of the soil body rigidity such as cyclic loading and wave loading after the model is liquefied can be captured, the defect that the traditional piezoelectric elastic wave velocity test system cannot rapidly monitor the soil body rigidity in real time is overcome, and the system has the advantages of high measurement precision, high automation degree and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of physical model test monitoring, and in particular relates to a physical model test soil body stiffness real-time measurement device and method. Background Art

[0002] The stiffness parameters of rock and soil materials, such as small strain shear modulus, Young's modulus, shear wave velocity and compression wave velocity, are important parameters for geotechnical engineering analysis and design, and are widely used in construction site classification, site dynamic response analysis and sand liquefaction identification. Since rock and soil materials are composed of scattered particles, their small strain shear modulus G max , Young's modulus E is related to density, effective stress, strain size, and particle arrangement state. Therefore, the stiffness of rock and soil will change rapidly during consolidation, earthquake liquefaction, and loading. For example, in the Christchurch earthquake in New Zealand, according to the records of the REHS station, it was observed that the small strain shear stiffness of liquefied sites after the earthquake showed an approximately logarithmic recovery over time. If the stiffness change of soil can be actually measured, it will be of great significance to engineering practice and scientific research.

[0003] Physical simulation based on scaled models simplifies actual geotechnical problems while ignoring minor factors, and is an important research method in the geotechnical field. Currently, there are two widely used types of physical model tests: normal gravity physical model tests and super gravity physical model tests. As mentioned above, it is very necessary to monitor the stiffness of the soil when conducting physical model tests. In actual sites, since there will be aftershocks after an earthquake, the coda waves recorded by the strong earthquake station can be used to perform horizontal and vertical spectral ratio HVSR analysis to obtain the development law of the small strain shear stiffness of the site before and after the earthquake over time. However, in actual physical model tests, the vibration table is mostly unidirectional and cannot be excited multiple times in a short period of time. Therefore, the HVSR method is difficult to apply to physical model tests. Another method is to use piezoelectric elements to measure the elastic wave velocity and invert the stiffness of the model based on the principles of elastic mechanics. However, the existing model test elastic wave velocity test system mostly uses an oscilloscope to collect and save the test data, which has two problems: first, although the sampling frequency of the oscilloscope is very high (up to 100MHz), its data saving is usually very slow. It takes 1-2 minutes to save the data once, which eventually leads to a too low data sampling frequency; second, the waveform obtained by the oscilloscope cannot be recorded in real time, and the obtained waveform is mostly judged after manual processing. Manual judgment is not only labor-intensive and subjective, but also depends on the professional experience of people. The above shortcomings are more obvious in the hypergravity model test, because in the hypergravity physical model test, according to the similarity theory, the time similarity coefficient is the square of the centrifuge acceleration g value. The stiffness change of the prototype may take several days or even months, while the hypergravity model test may only take a few minutes. The traditional oscilloscope data collection method obviously has insufficient sampling frequency and cannot capture the stiffness change law of the model in real time. Summary of the invention

[0004] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a real-time measurement device and method for soil stiffness in a physical model test, so as to solve the technical difficulties existing in the model stiffness measurement technology in the existing physical model test.

[0005] The technical solution adopted by the present invention is:

[0006] 1. A real-time measurement device for soil stiffness in physical model tests:

[0007] It includes a signal generating system, a piezoelectric elastic wave velocity testing system, a data acquisition system and a post-processing analysis system; a soil physical model is installed in the piezoelectric elastic wave velocity testing system, a function generator in the signal generating system transmits a pulse signal to the input end of the piezoelectric elastic wave velocity testing system and the data acquisition system, the pulse signal in the piezoelectric elastic wave velocity testing system is transmitted to the data acquisition system from the output end of the piezoelectric elastic wave velocity testing system after passing through the soil physical model, the data acquisition system is used to collect the signal passing through the piezoelectric elastic wave velocity testing system and the pulse signal directly emitted by the function generator, and the collected signal is input into the post-processing analysis system, and the post-processing analysis system is used to analyze and process the input signal to obtain the stiffness of the soil physical model.

[0008] The piezoelectric elastic wave velocity testing system comprises a piezoelectric element excitation element, a piezoelectric element receiving element, a soil physical model and a signal amplifier; the piezoelectric element excitation element and the piezoelectric element receiving element are both buried in the soil physical model, the function generator in the signal generating system transmits a pulse signal to the piezoelectric element excitation element of the piezoelectric elastic wave velocity testing system, the piezoelectric element excitation element generates fluctuations under the excitation of the pulse signal, the fluctuations generated by the piezoelectric element excitation element are propagated to the piezoelectric element receiving element via the soil physical model, the piezoelectric element receiving element generates an electrical signal under the fluctuations and transmits the electrical signal to the signal amplifier, and then the signal amplifier amplifies the electrical signal and transmits it to the data acquisition system.

[0009] The post-processing analysis system is mainly composed of a filtering module, a window division module and a phase difference discrimination module connected in sequence. The data acquisition system inputs the collected signal into the post-processing analysis system, and obtains the signal phase difference after filtering by the filtering module, intercepting by the window division module and the phase difference discrimination module in sequence. Then, the signal phase difference is used to obtain the elastic wave velocity and stiffness of the soil physical model. The signal phase difference is the signal phase difference between the electrical signal generated after the piezoelectric elastic wave velocity test system and the pulse signal directly emitted by the function generator.

[0010] The pulse signal waveform emitted by the function generator is one of a sine wave and a square wave, and the number of pulses emitted by the function generator per unit time is equal to the number of signals collected per unit time.

[0011] The piezoelectric element excitation element and the piezoelectric element receiving element both adopt one of a compression element, a bending element and a torsion shear element, and the compression element, the bending element and the torsion shear element are used to generate compression waves, shear waves and torsion shear waves respectively.

[0012] 2. A real-time measurement method for soil stiffness in a physical model test includes the following steps:

[0013] Step S1, first set up a real-time stiffness measurement device: connect the signal generation system, the piezoelectric elastic wave velocity test system, the data acquisition system and the post-processing analysis system in sequence, and connect the signal generation system and the data acquisition system at the same time, prepare a soil physical model, and bury the piezoelectric element excitation element and the piezoelectric element receiving element at a preset position in the soil physical model, and measure the distance between the piezoelectric element excitation element and the piezoelectric element receiving element at the same time;

[0014] Step S2, then, apply a load to the soil physical model, and start the function generator in the signal generating system at the same time, the function generator transmits a pulse signal to the piezoelectric element excitation unit and the data acquisition system, the piezoelectric element excitation unit generates fluctuations under the excitation of the pulse signal, the fluctuations generated by the piezoelectric element excitation unit are transmitted to the piezoelectric element receiving unit through the soil of the soil physical model, the piezoelectric element receiving unit generates an electrical signal under the fluctuations and transmits the electrical signal to the signal amplifier, and then the signal amplifier amplifies the electrical signal and transmits it to the data acquisition system;

[0015] Step S3: Finally, the data acquisition system inputs the collected signals into the post-processing analysis system, and the post-processing analysis system analyzes and processes the input signals to obtain the real-time stiffness of the soil physical model.

[0016] In step S3, the signals collected by the data acquisition system include the pulse signal directly emitted by the function generator and the electrical signal generated by the pulse signal after passing through the piezoelectric elastic wave velocity testing system. The post-processing analysis system is mainly composed of a filtering module, a window division module and a phase difference discrimination module connected in sequence. The data acquisition system inputs the collected signal into the post-processing analysis system, and the signal phase difference between the initial pulse signal and the electrical signal is obtained after filtering by the filtering module, intercepting by the window division module and by the phase difference discrimination module in sequence. Then, the signal phase difference is used to obtain the elastic wave velocity and stiffness of the soil physical model.

[0017] In step S3, the specific method of obtaining the stiffness of the soil physical model by using the signal phase difference is as follows:

[0018] First, the signal phase difference between the initial pulse signal and the electrical signal is obtained by using the cross-correlation function method or the peak-to-peak method. Then, the propagation time difference t between the wave excited by the piezoelectric element excitation element and the wave received by the piezoelectric element receiving element is obtained according to the signal phase difference. Then, the stiffness G of the soil physical model is obtained according to the following formula:

[0019] G=ρ sat V s 2

[0020]

[0021] Among them, ρsat is the saturated density of the soil physical model; V s is the elastic shear wave velocity; L is the distance between the piezoelectric element excitation element and the piezoelectric element receiving element.

[0022] The real-time measurement system and method for soil stiffness in physical model tests of the present invention can capture the rapid changes in soil stiffness of the model after liquefaction and cyclic loading, overcoming the shortcomings of traditional piezoelectric elastic wave velocity testing systems that cannot quickly monitor soil stiffness, and has the advantages of simple device, high measurement accuracy, and high degree of automation.

[0023] The beneficial effects of the present invention are:

[0024] 1. The high-speed data acquisition system of the present invention replaces the traditional oscilloscope to collect and store data, which can shorten the traditional test time from 1-2min to 1ms, overcoming the problem that the traditional model stiffness or elastic wave velocity measurement system cannot monitor the model stiffness in real time. In addition, the present invention does not require an oscilloscope, simplifies the measurement system, increases the reliability of the system, and reduces the difficulty of test monitoring and the test cost.

[0025] 2. The present invention can adjust the emission frequency of the pulse function generator to freely change the sampling frequency of the data. The sampling frequency of the data can be increased by increasing the frequency of pulse emission. A lower emission frequency can be used for model tests with slow wave velocity changes. For model tests with fast wave velocity changes, such as earthquake loads or wave loads, an ultra-high emission frequency can be used. Compared with traditional methods, the sampling frequency can be increased by 100-1000 times, and traditional measurement methods cannot achieve stiffness measurement of such tests.

[0026] 3. The present invention adopts an automated post-processing data system. The data obtained by the data acquisition system can be directly transferred to the post-processing data system. The post-processing system can automatically determine the filter cut-off frequency and perform filtering through time-frequency conversion technology. The system after filtering automatically imports the window division module, automatically intercepts and divides the window, and finally the phase difference discrimination module uses the cross-correlation function method or the peak-peak method to automatically obtain the signal phase difference between the initial pulse signal and the electrical signal. Compared with the traditional stiffness monitoring system, it is more intelligent and can automatically process massive test data, greatly reducing the workload of data post-processing.

[0027] 4. The present invention can also improve the stiffness measurement accuracy. The phase difference error obtained by the automated post-processing data system is less than 10 microseconds, while the error of manual judgment is usually at the millisecond level. The model stiffness measurement accuracy is improved by 2 orders of magnitude. In addition, the accuracy of manual judgment is very dependent on previous experience, while automated processing is based on precise and objective phase difference judgment techniques such as the cross-correlation function method or the peak-to-peak method, thus avoiding subjective human judgment errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall composition of the system;

[0029] Figure 2 It is the principle of data post-processing process;

[0030] Figure 3 is the original signal collected by the embodiment;

[0031] Figure 4 is a signal of a certain window obtained by data post-processing in the embodiment;

[0032] Figure 5 The signal time difference result obtained by the embodiment;

[0033] Figure 6 The embodiment obtains the soil stiffness change process.

[0034] In the figure: 1. Function generator; 2. Piezoelectric element excitation element; 3. Piezoelectric element receiving element; 4. Soil physical model; 5. Signal amplifier; 6. Data acquisition system; 7. Signal post-processing system. DETAILED DESCRIPTION

[0035] The device of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

[0036] like Figure 1 As shown, the device includes a signal generating system, a piezoelectric elastic wave velocity testing system, a data acquisition system 6 and a post-processing analysis system 7; a soil physical model 4 is installed in the piezoelectric elastic wave velocity testing system, and a function generator 1 in the signal generating system transmits a pulse signal to the input end of the piezoelectric elastic wave velocity testing system and the data acquisition system 6. The pulse signal in the piezoelectric elastic wave velocity testing system is transmitted to the data acquisition system 6 from the output end of the piezoelectric elastic wave velocity testing system after passing through the soil physical model 4. The data acquisition system 6 is used to collect the signal passing through the piezoelectric elastic wave velocity testing system and the pulse signal directly emitted by the function generator 1, and input the collected signal into the post-processing analysis system 7. The post-processing analysis system 7 is used to analyze and process the input signal to obtain the stiffness of the soil physical model 4.

[0037] The piezoelectric elastic wave velocity test system includes a piezoelectric element excitation unit 2, a piezoelectric element receiving unit 3, a soil physical model 4 and a signal amplifier 5; the piezoelectric element excitation unit 2 and the piezoelectric element receiving unit 3 are both buried in the soil physical model 4, and the function generator 1 in the signal generating system transmits a pulse signal to the piezoelectric element excitation unit 2 of the piezoelectric elastic wave velocity test system. The piezoelectric element excitation unit 2 generates fluctuations under the excitation of the pulse signal, and the fluctuations generated by the piezoelectric element excitation unit 2 are propagated to the piezoelectric element receiving unit 3 through the soil physical model 4. The piezoelectric element receiving unit 3 generates an electrical signal under the fluctuations and transmits the electrical signal to the signal amplifier 5, and then the signal amplifier 5 amplifies the electrical signal and transmits it to the data acquisition system 6.

[0038] like Figure 2 As shown, the post-processing analysis system 7 is mainly composed of a filtering module, a window division module and a phase difference discrimination module connected in sequence. The data acquisition system 6 inputs the collected signal into the post-processing analysis system 7, and obtains the signal phase difference after filtering by the filtering module, intercepting by the window division module and the phase difference discrimination module in sequence. Then, the elastic wave velocity and stiffness of the soil physical model 4 are obtained by combining the signal phase difference with the model stiffness inversion principle. The signal phase difference is the signal phase difference between the electrical signal generated after the piezoelectric elastic wave velocity test system and the pulse signal directly emitted by the function generator 1. The above two signals are collected by the data acquisition system 6.

[0039] The waveform of the pulse signal emitted by the function generator 1 is one of a sine wave and a square wave. The number of pulses emitted by the function generator 1 per unit time is equal to the number of signals collected per unit time.

[0040] The piezoelectric element exciting element 2 and the piezoelectric element receiving element 3 both adopt one of a compression element, a bending element and a torsion shear element, and the compression element, the bending element and the torsion shear element are used to generate compression waves, shear waves and torsion shear waves respectively.

[0041] An embodiment of the present invention comprises the following steps:

[0042] Step S1, first set up a real-time stiffness measurement device: connect the signal generation system, the piezoelectric elastic wave velocity test system, the data acquisition system 6 and the post-processing analysis system 7 in sequence, and connect the signal generation system and the data acquisition system 6 at the same time, prepare a soil physical model 4, and bury the piezoelectric element excitation element 2 and the piezoelectric element receiving element 3 in the piezoelectric elastic wave velocity test system at a specified position in the soil physical model 4, and measure the distance between the piezoelectric element excitation element 2 and the piezoelectric element receiving element 3 at the same time;

[0043] Step S2, then, apply a load to the soil physical model 4, and start the function generator 1 in the signal generating system at the same time, the function generator 1 transmits a pulse signal to the piezoelectric element excitation element 2 and the data acquisition system 6, the piezoelectric element excitation element 2 generates a fluctuation under the excitation of the pulse signal, the fluctuation generated by the piezoelectric element excitation element 2 is transmitted to the piezoelectric element receiving element 3 through the soil of the soil physical model 4, the piezoelectric element receiving element 3 generates an electrical signal under the fluctuation and transmits the electrical signal to the signal amplifier 5, and then the signal amplifier 5 amplifies the electrical signal and transmits it to the data acquisition system 6;

[0044] Step S3 , finally, the data acquisition system 6 inputs the collected signals into the post-processing analysis system 7 , and the post-processing analysis system 7 analyzes and processes the input signals to obtain the real-time stiffness of the soil physical model 4 .

[0045] In step S3, the signal collected by the data acquisition system 6 includes the pulse signal directly emitted by the function generator 1, and the electrical signal generated by the pulse signal after passing through the piezoelectric elastic wave velocity test system. The pulse signal directly emitted by the function generator 1 is used as the initial pulse signal, and the electrical signal generated after passing through the piezoelectric elastic wave velocity test system is used as the electrical signal. The data acquisition system 6 inputs both the initial pulse signal and the electrical signal passing through the soil physical model 4 into the post-processing analysis system 7. The post-processing analysis system 7 is mainly composed of a filtering module, a window division module and a phase difference discrimination module connected in sequence. The data acquisition system 6 inputs the collected signal into the post-processing analysis system 7, and obtains the signal phase difference between the initial pulse signal and the electrical signal after filtering by the filtering module, intercepting by the window division module and by the phase difference discrimination module. Then, the elastic wave velocity and stiffness of the soil physical model 4 are obtained by combining the signal phase difference with the model stiffness inversion principle.

[0046] The filtering module is used to filter the input electrical signal / initial pulse signal, and the window division module is used to cut off the filtered electrical signal / initial pulse signal according to a preset width.

[0047] In step S3, the specific method of obtaining the stiffness of the soil physical model 4 by using the signal phase difference is as follows:

[0048] First, the signal phase difference between the initial pulse signal and the electrical signal collected by the data acquisition system 6 is obtained by using the cross-correlation function method or the peak-to-peak method. Then, the propagation time difference t between the wave excited by the piezoelectric element excitation element 2 and the wave received by the piezoelectric element receiving element 3 is obtained according to the signal phase difference. Then, the stiffness G of the soil physical model 4 is obtained according to the following formula:

[0049] G=ρ sat V s 2

[0050]

[0051] Among them, ρ sat is the saturated density of the soil physical model; V s is the elastic shear wave velocity; L is the distance between the piezoelectric element excitation element 2 and the piezoelectric element receiving element 3.

[0052] Specifically, the function generator 1 uses an instrument or circuit that can pulse and emit sine waves or square waves, and the pulse frequency and wave frequency of the function generator 1 can be adjusted to achieve higher precision. The piezoelectric element excitation element 2 and the piezoelectric element receiving element 3 are compression elements that can generate compression waves (longitudinal waves), or bending elements that can generate shear waves (transverse waves) and torsion shear elements that generate torsion shear waves; the signal amplifier 5 is a device or circuit that can amplify electrical signals. The data acquisition system 6 is a system or device that can collect and record voltage signals in real time; the sampling frequency of the data acquisition system 6 is not less than 10 kHz. The post-processing analysis system 7 includes a filtering module, a window division module, and a phase difference discrimination module, which includes a system, code or script that can intercept, filter and analyze the signal phase difference, and then the model stiffness can be obtained by using the model stiffness inversion principle based on the signal phase difference to obtain the elastic wave velocity, thereby obtaining the model stiffness.

[0053] like Figure 1 As shown, the device includes a signal generating system, a piezoelectric elastic wave velocity testing system, a data acquisition system 6 and a post-processing analysis system 7; a soil physical model 4 is installed in the piezoelectric elastic wave velocity testing system, and a function generator 1 in the signal generating system transmits a pulse signal to the input end of the piezoelectric elastic wave velocity testing system and the data acquisition system 6. The pulse signal in the piezoelectric elastic wave velocity testing system is transmitted to the data acquisition system 6 from the output end of the piezoelectric elastic wave velocity testing system after passing through the soil physical model 4. The data acquisition system 6 is used to collect the signal passing through the piezoelectric elastic wave velocity testing system and the pulse signal directly emitted by the function generator 1, and input the collected signal into the post-processing analysis system 7. The post-processing analysis system 7 is used to analyze and process the input signal to obtain the stiffness of the soil physical model 4.

[0054] The piezoelectric elastic wave velocity test system includes a piezoelectric element excitation unit 2, a piezoelectric element receiving unit 3, a soil physical model 4 and a signal amplifier 5; the piezoelectric element excitation unit 2 and the piezoelectric element receiving unit 3 are both buried in the soil physical model 4, and the function generator 1 in the signal generating system transmits a pulse signal to the piezoelectric element excitation unit 2 of the piezoelectric elastic wave velocity test system. The piezoelectric element excitation unit 2 generates fluctuations under the excitation of the pulse signal, and the fluctuations generated by the piezoelectric element excitation unit 2 are propagated to the piezoelectric element receiving unit 3 through the soil physical model 4. The piezoelectric element receiving unit 3 generates an electrical signal under the fluctuations and transmits the electrical signal to the signal amplifier 5, and then the signal amplifier 5 amplifies the electrical signal and transmits it to the data acquisition system 6.

[0055] like Figure 2 As shown, the post-processing analysis system 7 is mainly composed of a filtering module, a window division module and a phase difference discrimination module connected in sequence. The data acquisition system 6 inputs the collected signal into the post-processing analysis system 7, and obtains the signal phase difference after filtering by the filtering module, intercepting by the window division module and the phase difference discrimination module in sequence. Then, the elastic wave velocity and stiffness of the soil physical model 4 are obtained by combining the signal phase difference with the model stiffness inversion principle. The signal phase difference is the signal phase difference between the electrical signal generated after the piezoelectric elastic wave velocity test system and the pulse signal directly emitted by the function generator 1. The above two signals are collected by the data acquisition system 6.

[0056] The waveform of the pulse signal emitted by the function generator 1 is one of a sine wave and a square wave. The number of pulses emitted by the function generator 1 per unit time is equal to the number of signals collected per unit time.

[0057] The piezoelectric element exciting element 2 and the piezoelectric element receiving element 3 both adopt one of a compression element, a bending element and a torsion shear element, and the compression element, the bending element and the torsion shear element are used to generate compression waves, shear waves and torsion shear waves respectively.

[0058] An embodiment of the present invention comprises the following steps:

[0059] Step S1, first set up a real-time stiffness measurement device: connect the signal generation system, the piezoelectric elastic wave velocity test system, the data acquisition system 6 and the post-processing analysis system 7 in sequence, and connect the signal generation system and the data acquisition system 6 at the same time, prepare a soil physical model 4, and bury the piezoelectric element excitation element 2 and the piezoelectric element receiving element 3 in the piezoelectric elastic wave velocity test system at a specified position in the soil physical model 4, and measure the distance between the piezoelectric element excitation element 2 and the piezoelectric element receiving element 3 at the same time;

[0060] Step S2, then, apply a load to the soil physical model 4, and start the function generator 1 in the signal generating system at the same time, the function generator 1 transmits a pulse signal to the piezoelectric element excitation element 2 and the data acquisition system 6, the piezoelectric element excitation element 2 generates a fluctuation under the excitation of the pulse signal, the fluctuation generated by the piezoelectric element excitation element 2 is transmitted to the piezoelectric element receiving element 3 through the soil of the soil physical model 4, the piezoelectric element receiving element 3 generates an electrical signal under the fluctuation and transmits the electrical signal to the signal amplifier 5, and then the signal amplifier 5 amplifies the electrical signal and transmits it to the data acquisition system 6;

[0061] Step S3 , finally, the data acquisition system 6 inputs the collected signals into the post-processing analysis system 7 , and the post-processing analysis system 7 analyzes and processes the input signals to obtain the real-time stiffness of the soil physical model 4 .

[0062] In step S3, the signal collected by the data acquisition system 6 includes the pulse signal directly emitted by the function generator 1, and the electrical signal generated by the pulse signal after passing through the piezoelectric elastic wave velocity test system. The pulse signal directly emitted by the function generator 1 is used as the initial pulse signal, and the electrical signal generated after passing through the piezoelectric elastic wave velocity test system is used as the electrical signal. The data acquisition system 6 inputs both the initial pulse signal and the electrical signal passing through the soil physical model 4 into the post-processing analysis system 7. The post-processing analysis system 7 is mainly composed of a filtering module, a window division module and a phase difference discrimination module connected in sequence. The data acquisition system 6 inputs the collected signal into the post-processing analysis system 7, and obtains the signal phase difference between the initial pulse signal and the electrical signal after filtering by the filtering module, intercepting by the window division module and by the phase difference discrimination module. Then, the elastic wave velocity and stiffness of the soil physical model 4 are obtained by combining the signal phase difference with the model stiffness inversion principle.

[0063] The filtering module is used to filter the input electrical signal / initial pulse signal, and the window division module is used to cut off the filtered electrical signal / initial pulse signal according to a preset width.

[0064] In step S3, the specific method of obtaining the stiffness of the soil physical model 4 by using the signal phase difference is as follows:

[0065] First, the signal phase difference between the initial pulse signal and the electrical signal collected by the data acquisition system 6 is obtained by using the cross-correlation function method or the peak-to-peak method. Then, the propagation time difference t between the wave excited by the piezoelectric element excitation element 2 and the wave received by the piezoelectric element receiving element 3 is obtained according to the signal phase difference. Then, the stiffness G of the soil physical model 4 is obtained according to the following formula:

[0066] G=ρ sat V s 2

[0067]

[0068] Among them, ρ sat is the saturated density of the soil physical model; V s is the elastic shear wave velocity; L is the distance between the piezoelectric element excitation element 2 and the piezoelectric element receiving element 3.

[0069] Specifically, the function generator 1 uses an instrument or circuit that can pulse and emit sine waves or square waves, and the pulse frequency and wave frequency of the function generator 1 can be adjusted to achieve higher precision. The piezoelectric element excitation element 2 and the piezoelectric element receiving element 3 are compression elements that can generate compression waves (longitudinal waves), or bending elements that can generate shear waves (transverse waves) and torsion shear elements that generate torsion shear waves; the signal amplifier 5 is a device or circuit that can amplify electrical signals. The data acquisition system 6 is a system or device that can collect and record voltage signals in real time; the sampling frequency of the data acquisition system 6 is not less than 10 kHz. The post-processing analysis system 7 includes a filtering module, a window division module, and a phase difference discrimination module, which includes a system, code or script that can intercept, filter and analyze the signal phase difference, and then the model stiffness can be obtained by using the model stiffness inversion principle based on the signal phase difference to obtain the elastic wave velocity, thereby obtaining the model stiffness.

[0070] In specific implementation, Figure 1 As shown, a pair of piezoelectric bending elements are arranged in the soil physical model to monitor the change of soil shear wave velocity before and after the earthquake. The soil physical model is 74cm long, 34cm wide and 40cm deep. The piezoelectric bending element is arranged at a depth of 20cm in the soil physical model. A pair of piezoelectric bending elements includes a piezoelectric element excitation element 2 and a piezoelectric element receiving element 3. The distance between the piezoelectric element excitation element 2 and the piezoelectric element receiving element 3 is L = 10.03cm. The soil physical model is tested under a centrifugal acceleration of 50g. The saturation density ρ of the soil physical model sat 2000kg / m 3 .

[0071] In order to monitor the change of the stiffness of the model with time before and after the earthquake, the function generator 1 in the signal generation system is used to emit a pulse signal before the earthquake. The frequency of the pulse signal is f b =15Hz, which means that 15 stiffness (wave velocity) data of the model can be obtained within 1s. Each pulse signal is a sine wave, and the frequency of the sine wave can be selected according to the excitation element resonance frequency of the piezoelectric elastic wave velocity test system. In this embodiment, f=3k Hz is selected. After setting the pulse signal, turn on the data acquisition system to collect the pulse signal emitted by the function generator and the signal returned by the subsequent signal amplifier 5. In order to ensure that the collected data is not distorted and to facilitate post-processing, the data acquisition system collects at least 10-20 points for each waveform, so the acquisition frequency of the data acquisition system is set to 50k Hz in the embodiment.

[0072] The pulse signal is subsequently transmitted to the piezoelectric element excitation element of the piezoelectric elastic wave velocity test system. The piezoelectric element excitation element is stimulated by the pulse signal to generate mechanical vibration, and the shear wave generated by the mechanical vibration is transmitted to the piezoelectric element receiving element through the model soil. The piezoelectric element receiving element senses the mechanical vibration of the soil and generates a tiny electrical signal, which is transmitted to the data acquisition system through the signal amplifier 5. At this time, the data acquisition system will receive the following information: Figure 3 The signals of the two channels are shown.

[0073] The soil physical model is placed on the shaking table. After the above preparations are completed, the shaking table is controlled to apply seismic loads. At this time, the entire measurement device can monitor the stiffness changes of the model under seismic loads in real time. When the wave velocity of the model is stable, data collection and pulse excitation can be stopped.

[0074] The data acquisition system 6 receives the signal input as follows Figure 2 The post-processing analysis system shown. The post-processing analysis system includes a filtering module, a window division module and a phase difference discrimination module. After the signal is transmitted, the post-processing analysis system will first filter the collected signal using the filtering module. In this embodiment, a high-pass filter is used to process the signal. After the time-frequency analysis of the post-processing system, the filter cutoff frequency is automatically selected as 1000Hz. After the filtering is completed, it is necessary to enter the window division module to perform window interception on the collected signal. The width of the window is automatically calculated and processed by the post-processing system using the following formula:

[0075]

[0076] Where int means integer. In this embodiment, the width of each window is 3333 data points. The total number of windows is equal to the number of valid data finally monitored, which can be obtained by multiplying the acquisition time by the pulse excitation frequency. After the window division is completed, the post-processing analysis system will automatically save the excitation and reception signals of all windows and visualize the signals of each window, such as Figure 4 As shown, it is convenient to find out whether there are any abnormalities in the data.

[0077] The window data intercepted by the window division module is input into the phase difference determination module, and the phase difference determination module automatically obtains the time difference (ie, propagation time difference) between the excitation wave of the piezoelectric element excitation element 2 and the receiving wave of the piezoelectric element receiving element 3.

[0078] In this embodiment, the cross-correlation function method is used to obtain the signal phase difference between the initial pulse signal and the electrical signal, and then the real wave propagation time difference is obtained according to the sampling frequency. The final time difference t is as follows: Figure 5As shown. The cross-correlation function method is selected because the frequency components of the received waves at different times are roughly the same and the cross-correlation is strong. In other applications, the peak-to-peak method or the starting point method can also be used to distinguish the time difference. Then, according to the time difference obtained by the post-processing analysis system, the elastic shear wave velocity V of the soil is calculated by sampling the following formula: s :

[0079]

[0080] In this example, L = 10.03 cm. Finally, according to the principle of elastic mechanics, the stiffness G of the model soil at each moment is obtained using the following formula:

[0081] G=ρ sat V s 2

[0082] In the formula, the model saturation density ρ sat 2000kg / m 3 , V s is the elastic shear wave velocity. Figure 6 The evolution result of the stiffness of the soil of the monitoring model monitored in this embodiment. The test results show that before the earthquake, the stiffness of the soil was about 25MPa. During the earthquake, the piezoelectric element was excited by the earthquake and the shear wave velocity of the soil could not be measured. After the earthquake, due to the increase in pore water pressure, the effective stress of the model soil decreased. The stiffness of the soil was only about 50% of the original after the earthquake. As the earthquake ended, the excess pore water pressure gradually dissipated, the effective stress of the soil increased, and the stiffness of the model also gradually increased and finally returned to the level before the earthquake, which is consistent with the change pattern of the measured data at the Christchurch earthquake site in New Zealand and the Great East Japan Earthquake in 2011.

[0083] In order to verify the stability and accuracy of the device, the final stiffness of the model was measured using a traditional oscilloscope acquisition method in the embodiment. Due to the hypergravity time-shrinking effect, the entire process of soil stiffness recovery only lasts 20 seconds. If a traditional oscilloscope is used for data acquisition, only one valid data point can be captured, and the nonlinear recovery process of the model stiffness cannot be monitored. The embodiment uses the system and method of the present invention to monitor 15 data points per second, and a total of 300 data points are obtained within 20 seconds, realizing the full monitoring of the nonlinear recovery process of the model stiffness. If the frequency of the pulse signal is adjusted to f b=100Hz, then 2000 points can be obtained. In addition, the data acquisition system collected a total of 1 trillion data points within 20s. Manual processing will consume a huge amount of time and energy, and it is easy to make mistakes. However, the intelligent automatic post-processing system of the present invention only takes about 30s to process and automatically visualize such a large amount of data. Imagine if the data is collected for dozens of minutes, or a very large pulse signal frequency is used, the collected data may reach hundreds of millions of data points. Manual data processing is almost impossible, and the automatic intelligent processing system of the present invention has greater advantages.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A real-time measurement device for soil stiffness in a physical model test, characterized by: The invention comprises a signal generating system, a piezoelectric elastic wave velocity testing system, a data acquisition system (6) and a post-processing analysis system (7); a soil physical model (4) is installed in the piezoelectric elastic wave velocity testing system; a function generator (1) in the signal generating system transmits a pulse signal to an input end of the piezoelectric elastic wave velocity testing system and the data acquisition system (6); the pulse signal in the piezoelectric elastic wave velocity testing system passes through the soil physical model (4) and is transmitted from an output end of the piezoelectric elastic wave velocity testing system to the data acquisition system (6); the data acquisition system (6) is used to collect the signal passing through the piezoelectric elastic wave velocity testing system and the pulse signal directly emitted by the function generator (1), and input the collected signal into the post-processing analysis system (7); the post-processing analysis system (7) is used to analyze and process the input signal to obtain the stiffness of the soil physical model (4).

2. A real-time measurement device for soil stiffness in a physical model test according to claim 1, characterized in that: The piezoelectric elastic wave velocity test system comprises a piezoelectric element excitation element (2), a piezoelectric element receiving element (3), a soil physical model (4) and a signal amplifier (5); the piezoelectric element excitation element (2) and the piezoelectric element receiving element (3) are both buried in the soil physical model (4); a function generator (1) in a signal generation system transmits a pulse signal to the piezoelectric element excitation element (2) of the piezoelectric elastic wave velocity test system; the piezoelectric element excitation element (2) generates a wave under the stimulation of the pulse signal; the wave generated by the piezoelectric element excitation element (2) is transmitted to the piezoelectric element receiving element (3) via the soil physical model (4); the piezoelectric element receiving element (3) generates an electric signal under the wave and transmits the electric signal to the signal amplifier (5); the signal amplifier (5) amplifies the electric signal and transmits it to a data acquisition system (6).

3. The real-time measurement device for soil stiffness in a physical model test according to claim 1 is characterized by: The post-processing analysis system (7) is mainly composed of a filtering module, a window division module and a phase difference discrimination module connected in sequence. The data acquisition system (6) inputs the collected signal into the post-processing analysis system (7), and obtains the signal phase difference after filtering by the filtering module, intercepting by the window division module and the phase difference discrimination module in sequence. Then, the elastic wave velocity and stiffness of the soil physical model (4) are obtained by using the signal phase difference. The signal phase difference is the signal phase difference between the electrical signal generated after the piezoelectric elastic wave velocity test system and the pulse signal directly emitted by the function generator (1).

4. The real-time measurement device for soil stiffness in a physical model test according to claim 1 is characterized by: The pulse signal waveform emitted by the function generator (1) is one of a sine wave and a square wave, and the number of pulses emitted by the function generator (1) per unit time is equal to the number of signals collected per unit time.

5. The real-time measurement device for soil stiffness in a physical model test according to claim 2, characterized in that: The piezoelectric element excitation element (2) and the piezoelectric element receiving element (3) both adopt one of a compression element, a bending element and a torsion shear element, and the compression element, the bending element and the torsion shear element are used to generate compression waves, shear waves and torsion shear waves respectively.

6. A real-time measurement method for soil stiffness in a physical model test applied to the device described in any one of claims 1 to 5, characterized in that: The following steps are involved: Step S1, firstly, set up a real-time stiffness measurement device: connect the signal generation system, the piezoelectric elastic wave velocity test system, the data acquisition system (6) and the post-processing analysis system (7) in sequence, and connect the signal generation system and the data acquisition system (6) at the same time, prepare a soil physical model (4), bury the piezoelectric element excitation element (2) and the piezoelectric element receiving element (3) at a preset position in the soil physical model (4), and measure the distance between the piezoelectric element excitation element (2) and the piezoelectric element receiving element (3); Step S2, then, a load is applied to the soil physical model (4), and at the same time, a function generator (1) in the signal generating system is started, the function generator (1) transmits a pulse signal to the piezoelectric element excitation element (2) and the data acquisition system (6), the piezoelectric element excitation element (2) generates a fluctuation under the stimulation of the pulse signal, the fluctuation generated by the piezoelectric element excitation element (2) is transmitted to the piezoelectric element receiving element (3) through the soil of the soil physical model (4), the piezoelectric element receiving element (3) generates an electric signal under the fluctuation and transmits the electric signal to the signal amplifier (5), and then the signal amplifier (5) amplifies the electric signal and transmits it to the data acquisition system (6); Step S3: Finally, the data acquisition system (6) inputs the collected signals into the post-processing analysis system (7), and the post-processing analysis system (7) analyzes and processes the input signals to obtain the real-time stiffness of the soil physical model (4).

7. A real-time measurement method for soil stiffness in a physical model test according to claim 6, characterized in that: In step S3, the signal collected by the data acquisition system (6) includes a pulse signal directly emitted by the function generator (1) and an electrical signal generated by the pulse signal after passing through the piezoelectric elastic wave velocity test system. The post-processing analysis system (7) is mainly composed of a filtering module, a window division module and a phase difference discrimination module connected in sequence. The data acquisition system (6) inputs the collected signal into the post-processing analysis system (7), and the signal phase difference between the initial pulse signal and the electrical signal is obtained after filtering by the filtering module, intercepting by the window division module and by the phase difference discrimination module in sequence. Then, the elastic wave velocity and stiffness of the soil physical model (4) are obtained using the signal phase difference.

8. A real-time measurement method for soil stiffness in a physical model test according to claim 7, characterized in that: In step S3, the specific method of obtaining the stiffness of the soil physical model (4) by using the signal phase difference is as follows: First, the signal phase difference between the initial pulse signal and the electrical signal is obtained by using the cross-correlation function method or the peak-to-peak method. Then, the propagation time difference t between the wave excited by the piezoelectric element excitation element (2) and the wave received by the piezoelectric element receiving element (3) is obtained according to the signal phase difference. Then, the stiffness G of the soil physical model (4) is obtained according to the following formula: Among them, ρ sat is the saturated density of the soil physical model; V s is the elastic shear wave velocity; L is the distance between the piezoelectric element excitation element (2) and the piezoelectric element receiving element (3).

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