Method and system for testing dynamic elastic modulus of granular filler of railroad bed

Abstract

The invention discloses a method and a system for testing the dynamic elastic modulus of a railway bed granular filler, relates to the field of railway bed engineering, and solves the technical problem that the conventional method cannot be used for effectively and dynamically testing the railway bed granular filler. The method comprises the steps that a test material forming test piece is tested, the test comprises different loading sequences, different confining pressure and vertical load are applied to each loading sequence, the confining pressure is static air pressure, the vertical load is m times of dynamic repeated load, and the single dynamic load is composed of load pulse and interval, setting a plurality of load pulse loading durations and intermittent durations to simulate load conditions of different train speeds and roadbed depths, recording vertical stress and deformation as test data in the test process, and then processing the test data to obtain a dynamic elastic modulus; compared with the prior art, the stress-strain curve obtained by the method has higher goodness of fit with the roadbed response when the train passes by actually, and the guidance value of the test result on engineering practice is remarkably improved.

Description

Technical Field

[0001] The invention relates to the field of railway roadbed engineering, and in particular to a method and system for testing the dynamic elastic modulus of railway roadbed granular filler. Background Art

[0002] The elastic modulus is the core parameter that characterizes the deformation characteristics of materials under stress conditions, and directly reflects the material's ability to resist elastic deformation. In railway subgrade engineering, the elastic modulus is not only a key indicator for evaluating the mechanical properties of fillers, but also an important basis for subgrade structure design, construction quality control, and long-term service performance prediction. As the foundation layer of the track structure, the railway subgrade must withstand the long-term repeated effects of train dynamic loads. The accuracy of its dynamic elastic modulus is directly related to the smoothness of the track, driving safety, and maintenance costs. However, there are still significant gaps in the test methods for the dynamic elastic modulus of granular fillers in the existing railway specifications, resulting in the design parameter values ​​relying on experience or methods in the highway field, which makes it difficult to truly reflect the particularity of railway loads.

[0003] The loads borne by railway subgrades have significant dynamic characteristics: the train wheel loads have a short action time (usually milliseconds), high frequency, and the load amplitude shows a nonlinear distribution with changes in vehicle speed and axle weight. In addition, the stress state at different depths of the subgrade is significantly different. The shallow layer is more affected by the instantaneous impact effect, while the deep layer needs to consider long-term cumulative deformation. Although the existing "Highway Subgrade Design Code" (JTG D30-2015) proposes a dynamic rebound modulus test method, its loading waveform (half-haversine pulse) does not match the transient impact characteristics of railway loads, and the loading parameters are fixed (single frequency and intermittent time), which cannot cover the complex and changeable working conditions in railway engineering.

[0004] At present, the dynamic modulus test of granular fillers at home and abroad is mainly concentrated in the field of highways, and the method has the following shortcomings: The loading waveform does not match the actual load: Highway specifications use a semi-haver waveform to simulate vehicle loads, while railway loads are closer to Gaussian pulses (high instantaneous peak and fast decay). Existing methods cannot accurately simulate the dynamic response characteristics of train wheel loads. The current method uses the ratio of the peak stress to the rebound strain of a single cycle loading as the modulus value, ignoring the nonlinear hysteresis behavior of the material during loading (such as plastic deformation accumulation and stress path dependence).

[0005] However, the current railway subgrade design specifications have not yet included laboratory test standards for dynamic elastic modulus, and design parameters are mostly based on static tests or empirical formulas, which makes it difficult to meet the stringent requirements of high-speed and heavy-load railways for subgrade performance. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method and system for testing the dynamic elastic modulus of railway roadbed granular filler, which solves the technical problem that the existing method cannot accurately simulate the dynamic response characteristics of train wheel loads, making it impossible to conduct effective dynamic tests on the railway roadbed.

[0007] A method for testing the dynamic elastic modulus of railway roadbed granular filler comprises: testing a test specimen, wherein the test comprises different loading sequences, each loading sequence applies different confining pressures and vertical loads, the confining pressure is static air pressure, the vertical load is m times of dynamic repeated load, a single dynamic load consists of load pulses and intervals, a variety of load pulse loading durations and interval durations are set to simulate load conditions of different train speeds and roadbed depths, vertical stress and deformation are recorded as test data during the test, and then the test data are processed to obtain the dynamic elastic modulus.

[0008] Furthermore, the load pulse is a Gaussian pulse, and its mathematical expression is: , where a is the pulse waveform width (loading time), P max is the peak value of the pulse load.

[0009] Furthermore, the test data includes the vertical stress and deformation of the last five times of each loading sequence, and the data reading interval should be less than 1 / 10 of the pulse waveform width.

[0010] Furthermore, the processing of the test data includes: fitting the single cycle data using an ellipse equation, calculating the angle θ between the line connecting the two foci of the ellipse and the X-axis, and taking the slope E=tanθ as the dynamic elastic modulus.

[0011] Furthermore, the elliptical equation is used to fit the single cycle data, and the expression is as follows:

[0012] And meet , to ensure that the regression equation is an ellipse; where: ε is the deformation (strain), σ is the vertical stress, and A, B, C, D, E, and F are regression coefficients.

[0013] Furthermore, the angle between the two foci and the X-axis is calculated by using the regression ellipse equation. The slope of is taken as the dynamic elastic modulus of the railway roadbed granular filler, and the calculation formula is as follows:

[0014] Furthermore, setting the load pulse loading duration and intermittent duration includes setting 5 pulse loading durations of 0.1s, 0.2s, 0.3s, 0.4s, and 0.5s, and the corresponding intermittent durations are 0.2s, 0.4s, 0.6s, 0.8s, and 1.0s, respectively.

[0015] Furthermore, the test specimen preparation process includes: selecting railway roadbed granular filler as the test material, including graded crushed stone, natural gravel, crushed coal gangue and soil, and loose granular materials solidified without any binder, and then forming the test specimen in accordance with the relevant provisions of Appendix A "Standard Test Method for Dynamic Rebound Modulus of Roadbed Soil" of "Highway Roadbed Design Code" (JTGD30-2015).

[0016] Furthermore, the test is carried out using a closed-loop electro-hydraulic servo-driven three-axis device.

[0017] A railway roadbed granular filler dynamic elastic modulus test system comprises: a test device, a data acquisition module and a data analysis module, wherein the test device is used to apply different loading sequences to a test material forming specimen, each loading sequence applies different confining pressures and vertical loads, the confining pressure is static air pressure, the vertical load is m times of dynamic repeated load, a single dynamic load consists of a load pulse and an interval, a variety of load pulse loading durations and interval durations are set to simulate load conditions of different train speeds and roadbed depths, the data acquisition module records vertical stress and deformation as test data during the test, and the data analysis module is used to process the test data to obtain the dynamic elastic modulus.

[0018] The beneficial effects of the present invention include: The present invention provides a test method for railway roadbed granular filler, using Gaussian pulse It replaces the traditional half-haversine waveform, whose characteristics of high instantaneous peak value and fast decay are closer to the impact effect of train wheel load. Compared with the traditional rebound modulus calculation method, the elastic modulus calculation method proposed in this invention comprehensively considers the stress-strain characteristics of roadbed granular filler during loading and unloading, and can be better used for structural analysis and engineering design.

[0019] The present invention can better simulate the stress and deformation characteristics of roadbed filling materials under different vehicle speeds and roadbed depths by setting 5 groups of loading time combinations (0.1-0.5 s) and intermittent time (0.2-1.0 s), covering the typical working conditions in railway engineering.

[0020] The present invention effectively characterizes the nonlinear hysteresis behavior of the material by fitting an elliptical equation based on single-cycle stress-strain data and calculating the dynamic elastic modulus by the slope of the focal line. Compared with the highway dynamic rebound modulus test method, this method comprehensively considers the stress and deformation characteristics of granular fillers during loading and unloading, and the test results are more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of a single dynamic loading process involved in an embodiment of the present application.

[0022] Figure 2This is a schematic diagram of the single dynamic loading stress-strain data regression and elastic modulus calculation results involved in the embodiments of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0024] Example 1 The present invention relates to a test method for dynamic elastic modulus of railway roadbed granular filler, which is suitable for testing the dynamic elastic modulus of railway roadbed granular filler. The specific process comprises the following steps: 1. Preparation of test specimens The test material specimens are railway roadbed granular fillers, including graded crushed stone, natural gravel, crushed coal gangue and soil, etc., loose granular materials that are not solidified with any binder are formed into specimens in accordance with the relevant provisions of Appendix A "Standard Test Method for Dynamic Rebound Modulus of Roadbed Soil" of "Highway Roadbed Design Code" (JTGD30-2015).

[0025] 2. Set the loading pulse Step 2: A closed-loop electro-hydraulic servo dynamic triaxial device is used. The test consists of different loading sequences. Each loading sequence applies different confining pressures and vertical loads. The confining pressure is static air pressure, and the vertical load is 100 dynamic repeated loads. The loading sequence can be referred to Table 1. The preload is a further compaction of the specimen, and it also ensures that the material and the test equipment are in full contact and stable. The single dynamic load consists of a load pulse and an interval. Five pulse loading durations are set (0.1s, 0.2s, 0.3s, 0.4s, and 0.5s), and the corresponding interval times are 0.2s, 0.4s, 0.6s, 0.8s, and 1.0s, respectively, to simulate the load conditions of different train speeds and roadbed depths, such as Figure 1 As shown; Table 1 Loading sequence of dynamic triaxial test

[0026] 3. Set the loading waveform The load pulse adopts Gaussian waveform, and its mathematical expression is: , where a is the pulse waveform width (loading time) and Pmax is the peak value of the pulse load (maximum axial dynamic stress).

[0027] 4. Calculation of dynamic elastic modulus The vertical stress and deformation of the last five times of each loading sequence (100 dynamic repeated loads) were recorded, and the data reading frequency was no less than 50 acquisition points for each dynamic loading cycle, such as Figure 2 As shown. The elliptical equation is used to fit the single cycle data, and the equation form is as follows: Aε 2 +Bεσ+Cσ 2 +Dε+Eσ+F=0 Where: ε is deformation (strain), σ is vertical stress, A, B, C, D, E, and F are regression coefficients.

[0028] Least squares regression can be used, but restrictions need to be added , to ensure that the regression equation is an ellipse.

[0029] The angle between the two foci and the X-axis using the regression ellipse equation The slope of is taken as the dynamic elastic modulus of the railway roadbed granular filler, and the calculation formula is as follows:

[0030] The dynamic elastic modulus testing and analysis method of railway roadbed granular filler proposed in the present invention is consistent with the specimen preparation process and equipment requirements of Appendix A "Standard Test Method for Dynamic Rebound Modulus of Roadbed Soil" of "Highway Roadbed Design Code" (JTGD30-2015). Different loading time combinations are innovatively proposed, and Gaussian pulses are used as loading waveforms. The slope of the angle θ between the two-focus connection line and the X-axis based on the regression ellipse equation is proposed as the dynamic elastic modulus value of the railway roadbed granular filler, and the stress and deformation characteristics of the material during loading and unloading are comprehensively considered.

[0031] Example 2 A dynamic elastic modulus test system for railway roadbed granular filler. It should be understood that the system corresponds to the above-mentioned method embodiment and can execute each step involved in the method embodiment. The specific functions of the system can be found in the description above. To avoid repetition, the detailed description is appropriately omitted here.

[0032] A railway roadbed granular filler dynamic elastic modulus test system comprises: a test device, a data acquisition module and a data analysis module, wherein the test device is used to apply different loading sequences to a test material forming specimen, each loading sequence applies different confining pressures and vertical loads, the confining pressure is static air pressure, the vertical load is m times of dynamic repeated load, a single dynamic load consists of a load pulse and an interval, a variety of load pulse loading durations and interval durations are set to simulate load conditions of different train speeds and roadbed depths, the data acquisition module records vertical stress and deformation as test data during the test, and the data analysis module is used to process the test data to obtain the dynamic elastic modulus.

[0033] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A test method for dynamic elastic modulus of railway roadbed granular filler, characterized in that: include: The test specimens were tested, including different loading sequences. Each loading sequence applied different confining pressures and vertical loads. The confining pressure was static air pressure, and the vertical load was m times of dynamic repeated load. A single dynamic load consisted of load pulses and intervals. A variety of load pulse loading durations and interval durations were set to simulate the load conditions of different train speeds and roadbed depths. During the test, the vertical stress and deformation were recorded as test data, and then the test data were processed to obtain the dynamic elastic modulus.

2. The method for testing the dynamic elastic modulus of railway roadbed granular filler according to claim 1, characterized in that: The load pulse is a Gaussian pulse, and its mathematical expression is: , where a is the pulse waveform width, P max is the peak value of the pulse load.

3. The method for testing the dynamic elastic modulus of railway roadbed granular filler according to claim 1, characterized in that: The test data include the vertical stress and deformation of the last five times of each loading sequence, and the data reading interval should be less than 1 / 10 of the pulse waveform width.

4. The method for testing the dynamic elastic modulus of railway roadbed granular filler according to claim 1, characterized in that: The processing of the test data includes: fitting the single cycle data with an ellipse equation, calculating the angle θ between the line connecting the two foci of the ellipse and the X-axis, and taking the slope E=tanθ as the dynamic elastic modulus.

5. The method for testing the dynamic elastic modulus of railway roadbed granular filler according to claim 4, characterized in that: The elliptical equation is used to fit the single cycle data, and the expression is as follows: ； And meet , to ensure that the regression equation is an ellipse; Where: ε is deformation, σ is vertical stress, A, B, C, D, E, and F are regression coefficients.

6. The method for testing the dynamic elastic modulus of railway roadbed granular filler according to claim 5, characterized in that: The angle between the two foci and the X-axis using the regression ellipse equation The slope of is taken as the dynamic elastic modulus value of the railway roadbed granular filler, and the calculation formula is as follows:

7. The method for testing the dynamic elastic modulus of railway roadbed granular filler according to claim 1, characterized in that: Setting various load pulse loading durations and intermittent durations includes setting 5 pulse loading durations of 0.1s, 0.2s, 0.3s, 0.4s, and 0.5s, and the corresponding intermittent durations are 0.2s, 0.4s, 0.6s, 0.8s, and 1.0s respectively.

8. The method for testing the dynamic elastic modulus of railway roadbed granular filler according to claim 1, characterized in that: The preparation process of the test specimen includes: selecting railway roadbed granular filler as test material, including graded crushed stone, natural gravel, crushed coal gangue and soil, and using loose granular materials solidified by no binder, and then forming the test specimen according to regulations.

9. The method for testing the dynamic elastic modulus of railway roadbed granular filler according to claim 1, characterized in that: The application of different confining pressures and vertical loads is performed by a closed-loop electro-hydraulic servo-driven three-axis device.

10. A railway roadbed granular filler dynamic elastic modulus test system, characterized in that: The method for testing the dynamic elastic modulus of railway roadbed granular filler for implementing any one of claims 1 to 9 comprises: testing equipment, a data acquisition module and a data analysis module, wherein the testing equipment is used to apply different loading sequences to the test material molded specimens, each loading sequence applies different confining pressures and vertical loads, the confining pressure is static air pressure, the vertical load is m times of dynamic repeated load, a single dynamic load consists of a load pulse and an interval, a variety of load pulse loading durations and interval durations are set to simulate the load conditions of different train speeds and roadbed depths, the data acquisition module records the vertical stress and deformation as test data during the test, and the data analysis module is used to process the test data to obtain the dynamic elastic modulus.

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