Measurement and calculation method of modulus - type intelligent compaction measurement index with low variability

Abstract

The present invention discloses a method for measuring and calculating a modulus - type intelligent compaction measurement index with low variability. The core of this method lies in being able to make full use of all non - void data points within the calculation interval, and then calculating the stiffness coefficient by the least - squares method. The vibration modulus index obtained by such conversion has greatly improved resistance to signal random errors and has strong stability. This index has good adaptability in the case of strong variability in practice, and can also reduce the interference of its own volatility when evaluating compaction uniformity.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent compaction detection for road engineering, and particularly relates to a method for measuring and calculating a modulus - type intelligent compaction measurement index with low variability. Background Technique

[0002] Intelligent compaction detection technology is to equip a series of sensors on compaction equipment to detect the dynamic response of the compaction equipment (mainly the centroid acceleration of the steel wheel of a vibratory roller), and then, based on the relationship between the dynamic response and the compaction quality of the material, extract corresponding intelligent compaction measurement indexes to reflect the compaction quality. Compared with the traditional compaction degree detection methods in road engineering, intelligent compaction detection technology has the advantages of being real - time, comprehensive, and non - destructive.

[0003] The core of intelligent compaction detection technology lies in extracting appropriate compaction measurement indexes based on the measured dynamic response. Early compaction indexes were all harmonic ratio - type indexes, such as CMV, CCV, etc. These indexes are all dimensionless parameters without clear physical meanings, and their relationship with compaction quality depends on empirical relationships. Subsequently, with the proposal of stiffness coefficient indexes (tangent stiffness k a and secant stiffness k b ), it marked the transition of compaction indexes to mechanical indexes. On this basis, the stiffness coefficient k a can be further transformed into the vibration modulus E vib , and E vib is the only absolute compaction index related only to the properties of the compacted material among the currently commonly used indexes, and has the same physical meaning as the resilient modulus commonly used in engineering, so it has great application value. However, the current E vib index is too sensitive to the measurement error of the dynamic response, resulting in a strong volatility in the index calculation result. In the case of strong variability in actual engineering, the measured value of the index is not stable and it is difficult to reflect the actual stiffness of the compacted material. Therefore, the present invention attempts to modify the calculation method to provide a modulus - type index with low variability. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for measuring and calculating a modulus - type intelligent compaction measurement index with low variability to ensure the adaptability of the vibration modulus index in the case of strong variability in practice, and at the same time avoid the interference of the index's own volatility during the evaluation of compaction uniformity.

[0005] In order to achieve the above - mentioned technical purpose, the following steps are used to measure and calculate the vibration modulus:

[0006] A method for measuring and calculating a modulus - type intelligent compaction measurement index with low variability adopts the following steps:

[0007] Step 1: Collect the original signal: Using the acceleration sensor and position sensor on the central axis of the roller's vibrating drum, collect the vertical acceleration of the steel wheel vibration and the phase of the steel wheel eccentric block. At the same time, calculate the jump vibration measurement value RMV index based on the collected acceleration signal. Monitoring the RMV index is to prevent the roller from experiencing severe jump vibration, which may cause adverse effects such as damage to the compacted material. The calculation formula for this index is as follows:

[0008]

[0009] In the formula, A ω represents the fundamental frequency component in the acceleration signal frequency spectrum diagram after Fourier transform, and A 0.5ω represents the sub-harmonic component of 0.5 times the fundamental frequency;

[0010] The RMV index value in the formula should be close to zero. Otherwise, the amplitude of the roller should be reduced;

[0011] Step 2: Calculate the velocity and displacement signals by back-calculation based on the acceleration measurement results: During the calculation, first select a certain length of calculation interval, usually 0.5 s or 1 s. Use the average value method to remove the DC component in the original acceleration signal within the interval, and then use the processed acceleration result to obtain the velocity and displacement signals through numerical integration. During the integration, only integrate the data points of a single period each time, and then correct the integration constant according to the principle that the integration area of a single period is zero. Finally, splice the integration results of each period within the interval;

[0012] Step 3: Calculate the contact force between the steel wheel and the compacted structure: First, determine the phase of the exciting force according to the monitoring result of the eccentric block position sensor on the central axis. The exciting force is the vertical component of the centrifugal force when the eccentric block rotates. After determining the position of the eccentric block, the magnitude or phase of the exciting force can be determined. Then, calculate the contact force between the vibrating drum and the compacted structure according to the following formula:

[0013]

[0014] In the formula, F c represents the contact force, and F e represents the peak value of the exciting force, represents the phase of the exciting force at zero time, ω represents the exciting frequency, m d and m f respectively represent the mass of the vibrating drum and the mass of the frame allocated to the vibrating drum, and a represents the vertical acceleration of the vibrating drum, with upward being positive;

[0015] Step 4: Calculate the stiffness coefficient k c: Make full use of all non - debonding data points within the selected calculation interval in Step 2. The so - called "make full use" is in contrast to the existing stiffness coefficient calculation methods. Generally, the existing ka and kb only utilize 1 - 4 points, but actually, the number of data points in a contact state within a cycle is much more than this. According to the relationship between the contact force and the vertical displacement and velocity of the vibrating wheel, and with the help of the least - square principle for calculation. Each time, a cycle of data is selected for calculation, and finally, the results of each cycle within the calculation interval are averaged to obtain k. c ;

[0016] Step 5: Calculate the vibration modulus E vib (k c ): Convert the k c value obtained in Step 4 into the vibration modulus E vib (k c ).

[0017] As a further preferred solution, the calculation method of the stiffness coefficient k c in Step 4 is as follows:

[0018] F c = k c x + c s v

[0019] In the formula, x and v respectively represent the vertical displacement and velocity of the vibrating wheel, with downward being positive, and c s represents the damping coefficient; assuming the contact force is zero, substitute all non - debonding data points within a single cycle into the above formula, and a series of over - determined equations can be obtained. Solve this system of equations according to the least - square principle, and the stiffness coefficient k c can be obtained.

[0020] As a further preferred solution, the conversion relationship between k c and E vib (k c ) in Step 5 is as follows:

[0021]

[0022] In the formula, ν represents the Poisson's ratio of the compacted material, and l and R respectively represent the width and radius of the vibrating wheel. Using the above relationship and through the iterative method, the E vib (k c ) index can be obtained.

[0023] Beneficial effects:

[0024] The present invention provides a new calculation method for the stiffness coefficient and converts it into the vibration modulus. Compared with the existing vibration modulus index, E vib (k cIt can make full use of all data points within the calculation interval except for voids, which greatly improves the effective data utilization rate of the index and rapidly reduces its sensitivity to accidental errors. Therefore, the E vib (k c ) index in the present invention has higher stability. On the one hand, it can adapt to the strong variability in practice and can make a relatively accurate judgment on the actual compaction quality. On the other hand, it can also play a huge role in the evaluation of compaction uniformity and can avoid misjudgment of the unevenness of compaction degree due to the volatility of the index itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the frequency spectrum of the acceleration signal after Fourier transform;

[0026] Figure 2 It is a schematic diagram of the finite element model of vibratory compaction;

[0027] Figure 3 It is a schematic diagram of the acceleration signal obtained by finite element simulation;

[0028] Figure 4 It is a schematic diagram of the velocity and displacement signals obtained by double integration;

[0029] Figure 5 It is a schematic diagram of the calculation principle of the stiffness coefficient k c ;

[0030] Figure 6 It is an example of the stability comparison of different vibration modulus indexes. SPECIFIC EMBODIMENTS

[0031] The content of the present invention will be further clarified below in conjunction with specific embodiments and the accompanying drawings of the specification.

[0032] By means of finite element simulation, the accuracy of the index in the present invention is verified, and at the same time, its stability advantage is explained. A finite element model of vibratory compaction is established based on the assumption of plane strain, as Figure 2 shown. The selection of relevant parameters of the compaction wheel refers to the XCMG XS263J single-drum vibratory roller. The main working parameters of this type of roller are shown in Table 1 (weak vibration mode). The assumption of pure elasticity is used for the compaction material, and the calculation accuracy of the finite element model is verified using the Lundberg theoretical solution.

[0033] Table 1 Calculation results of E vib (k c )

[0034]

[0035]

[0036] Taking the case where the modulus of the compacted material is 100 MPa as an example, Figure 3 The calculation results of the centroid acceleration signal of the compaction wheel obtained by finite element simulation are given (sampling frequency 1000 Hz, and the calculation interval is taken as 0.5 s). Refer to Step 2 to perform double integration on the acceleration signal. The integration of discrete data can adopt the trapezoidal formula method. To avoid the accumulation of random errors caused by long-interval integration, only approximately one cycle of data points is selected for calculation each time. In this example, each time 3 data points are selected. After the integration is completed, the integration constant of the result needs to be corrected. According to the principle that the integration area of a single cycle is zero, the trapezoidal formula is also used to calculate the integration area of the signal points within a single excitation cycle. Note that the excitation cycle may not be an integer multiple of the sampling cycle. For example, in this example, the excitation cycle contains 31 sampling cycles and 0.25 residual cycles. The integration area of the residual cycle is calculated by means of linear interpolation. After the calculation is completed, dividing the integration area by the cycle length can obtain the average amplitude of the signal, and subtracting this value from the signal data points can complete the correction of the integration constant. Finally, the calculation results of each cycle are spliced in sequence to obtain the complete integrated waveform within the calculation interval, as Figure 4 shown. After that, refer to Step 3 to calculate the contact force signal (the phase of the excitation force signal in the finite element is known). Substitute the displacement, velocity, and contact force data obtained in Steps 2 and 3 into the expression in Step 4 (note that the data points with zero contact force need to be removed, and these points represent the state where the compaction wheel is in a void state), and a series of overdetermined equations are obtained, which are solved using the least squares method to obtain the stiffness coefficient k c . Note that only the data points of one cycle are calculated each time, and then the k c values of each cycle within the calculation interval are averaged. The result obtained in this example is 80.97 MN / m. Finally, substitute this value into the expression in Step 5, and the vibration modulus E vib (k c ) can be obtained through iterative operations, which is 94.50 MPa.

[0037] Referring to the above method, Table 2 gives the calculation results of E vib (k c ) under different compacted material modulus conditions, and compares them with the actual input modulus of the compacted material in the finite element. It can be seen that the relative errors between the calculated values of E vib (k c ) and the actual modulus are all within 10%, meeting the requirements of engineering accuracy, which is the basis for this index to be put into use in engineering.

[0038] The stability of this index is described below. The existing k a and k b two kinds of stiffness coefficients can utilize very limited data points during calculation. ka Only the points near the zero point of the displacement in the loading section can be utilized, k b Only the point with the maximum displacement can be utilized. The limitation on the number of calculation points results in k a and k b The vibration modulus (E vib (k a ) and E vib (k b )) converted from it are easily affected by accidental errors and have strong volatility. While the k c stiffness in the present invention fits the contact force-displacement hysteresis curve by solving an overdetermined system of equations, essentially using an approximate ellipse, as Figure 5 shown. Such an approach can make full use of all data points except for the voids within one cycle, so the stability is greatly improved. Taking the two cases where the input modulus of the compacted material is 100 MPa and 120 MPa as examples, Figure 6 the results of three vibration moduli calculated based on data of different cycles within a calculation interval of 0.5 s are given. It can be seen that the volatility of E vib (k c ) is much lower than other indicators. When the modulus is 100 MPa, the standard deviation of E vib (k c ) is only 0.49 MPa, while the standard deviation of E vib (k a ) is about 15 times that of it, and the standard deviation of E vib (k b ) is also nearly 7.5 times that of it; when the modulus is 120 MPa, the standard deviation of E vib (k c ) is 0.98 MPa, and the standard deviations of E vib (k a ) and E vib (k b ) are 7.03 and 4.01 MPa respectively, and there are also obvious differences.

[0039] Table 2 Calculation results of E vib (k c ) under different moduli of compacted materials

[0040]

[0041] Finally, it should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be implemented by using the existing technology.

Claims

1. A method for measuring and calculating a modulus - type intelligent compaction measurement index with low variability, characterized in that, Adopt the following steps: Step 1: Collect the original signal: Use the acceleration sensor and position sensor on the central axis of the vibrating wheel of the roller to collect the vertical acceleration of the steel wheel vibration and the phase of the eccentric block of the steel wheel. At the same time, calculate the jump vibration measurement value RMV index according to the collected acceleration signal. The calculation formula of this index is as follows: where A ω represents the fundamental frequency component in the acceleration signal spectrogram after Fourier transform, and A 0.5ω represents the sub-harmonic component of 0.5 times the fundamental frequency; The RMV index value in the formula should be close to zero; otherwise, the amplitude of the roller should be reduced. Step 2: Calculate the speed and displacement signals by back-calculating based on the acceleration measurement results: When calculating, first select a certain length of calculation interval, choose 0.5 s or 1 s. In the interval, use the average value method to remove the DC component in the original acceleration signal, and then use the processed acceleration result to obtain the speed and displacement signals through numerical integration. When integrating, only integrate the data points of a single cycle each time, and then correct the integration constant according to the principle that the integral area of a single cycle is zero. Finally, splice the integration results of each cycle in the interval in sequence. Step 3: Calculate the contact force between the steel wheel and the compaction structure: First, determine the phase of the exciting force according to the monitoring result of the eccentric block position sensor on the central axis, and then calculate the contact force between the vibrating wheel and the compaction structure according to the following formula: In the formula, F c represents the contact force, and F e represents the peak value of the exciting force, represents the phase of the exciting force at the zero moment, ω represents the exciting frequency, m d and m f respectively represent the mass of the vibrating wheel and the mass of the frame allocated to the vibrating wheel, and a represents the vertical acceleration of the vibrating wheel, with upward being positive; Step 4: Calculate the stiffness coefficient k c : Make full use of all the non-void data points within the selected calculation interval in Step 2. According to the relationship between the contact force and the vertical displacement and velocity of the vibrating wheel, calculate using the least squares principle. Each time, select the data of one period for calculation, and finally take the average of the results of each period within the calculation interval to obtain k c ; The calculation method of the stiffness coefficient k in step 4 c is as follows: The specific calculation formula is as follows: F c = k c x + c s v where x and v represent the vertical displacement and velocity of the vibrating wheel respectively, with the downward direction being positive, and c s represents the damping coefficient; assuming the contact force is zero, substituting all the data points within a single period except for the voiding into the above equation, a series of overdetermined equations can be obtained. Solving this system of equations according to the least squares principle can yield the stiffness coefficient k c ; Step 5: Calculate the vibration modulus E vib (k c ):Convert the k c value obtained in Step 4 to the vibration modulus E vib (k c ).

2. The measurement and calculation method of the modulus class intelligent compaction measurement index with low variability according to claim 1, characterized in that: k in step 5 c and E vib (k c ) The conversion relationship is as follows: In the formula, ν represents the Poisson's ratio of the compacted material, l and R respectively represent the width and radius of the vibrating wheel. Using the above relationship and through the iterative method, E can be obtained. vib (k c ) index.

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