A test method for determining the dirt rate of a ballast

Abstract

The application discloses a test method for determining the dirtiness of a ballast bed, and comprises the following steps: screening the size of ballast particles according to the particle size range of the ballast; selecting the screening rate of ballast particles with different particle size ranges according to the ballast grading requirement; uniformly mixing the ballast particles with different screening rates; performing a drainage method test on the mixed ballast by layer compaction in a container to obtain the void ratio of the ballast pile under the grading condition; and filling the mixed ballast into a ballast box by layer compaction to perform a ballast box vibration test to obtain the dirtiness of the ballast bed. The application not only provides a new idea for determining the existing numerical simulation dirtiness of the ballast bed, but also provides a practical method and a theoretical reference for the performance evaluation and service performance prediction of the ballast bed.

Description

TECHNICAL FIELD

[0001] The present application relates to a test method for determining the fouling rate of a ballast bed, belonging to the technical field of railway transportation. BACKGROUND

[0002] Ballast track is one of the most widely used forms of railway structure in China. As an important part of ballast track, the service state of ballast bed affects the line stability and safe operation of ballast track. Ballast bed is composed of graded ballast, and there are gaps between the ballast particles, which are beneficial to drainage and dispersion of the train impact load transmitted from the upper sleepers. During the long-term service of the ballast bed, coal ash, slag and sandstone will enter the interior of the ballast bed through the gaps between the ballast particles, gradually developing into fouling of the ballast bed, forming a fouling ballast bed. The fouling changes the original contact form between the ballast particles, which will affect the service state and mechanical properties of the ballast bed, and indirectly affect the maintenance and repair of the railway line and the safe operation of the train. Therefore, it is very important to study the mechanical properties of the fouling ballast bed.

[0003] At present, in the numerical simulation of fouling ballast bed, most scholars in the study regard the fouling rate of the whole ballast bed as uniform, that is, all the gaps between the ballast particles are filled with fouling particles or all the gaps between the ballast particles are filled with a fixed proportion. However, in actual experience, the fouling degree at different depths in the ballast bed should be inconsistent. The results simulated by the existing numerical simulation method will have a large difference from the actual situation.

[0004] Based on the above problems, it is necessary to provide a test method for determining the fouling rate of a ballast bed. SUMMARY

[0005] The present application provides a test method for determining the fouling rate of a ballast bed. The fouling rate of the ballast bed at different depths can be determined by the drainage method test and the ballast box vibration test. Based on the test results, a more realistic discrete element model of the fouling ballast bed is established in the discrete element software.

[0006] The technical scheme of the present application is: a test method for determining the fouling rate of a ballast bed, comprising:

[0007] Screening the size of the ballast particles according to the particle size range of the ballast;

[0008] Selecting the screening rate of the ballast particles of different particle size ranges according to the ballast grading requirements; mixing the ballast particles of different screening rates uniformly;

[0009] Compacting the mixed ballast in layers in the container 2 to perform the drainage method test, and obtaining the void ratio of the ballast pile 1 under this grading condition;

[0010] The mixed ballast is layered and compacted into the ballast box 5 for a ballast box vibration test to obtain a dirty ballast bed rate.

[0011] Further comprising generating the dirty ballast particles in the ballast voids in the discrete element software according to the obtained dirty ballast bed rate, with ball units as the dirty ballast particles, the generated ball units having independent continuous id numbers, and modeling different ballast beds with different dirty rates by deleting the kth ball unit id every k id numbers, so that the dirty rate k can be determined accordingly.

[0012] The mixed ballast is layered and compacted into the container 2 for a drainage method test to obtain the void ratio of the ballast pile 1 under this grading condition, comprising:

[0013] The ballast is filled and compacted in n layers in the container 2, with a filling height of H2; wherein H2

[0014] Water is injected into the container 2, and the volume v w of water injected into the container 2 when the water level reaches H2 is recorded.

[0015] According to the volume proportion of water, the void ratio β of the ballast pile 1 is calculated.

[0016] The void ratio β is expressed as follows:

[0017]

[0018] In the formula, β is the void ratio of the ballast pile; v w is the volume of water when the water injection height in the container 2 reaches H2; v t1 is the internal volume of the container 2 at a height of H2.

[0019] The mixed ballast is layered and compacted into the ballast box 5 for a ballast box vibration test to obtain a dirty ballast bed rate, comprising:

[0020] n / 2n sample boxes with the same size and open top are made, the inner wall size of the sample box is L4, W4, H4, the wall thickness of the sample box is T1, and the volume of the sample box is denoted as v q .

[0021] The ballast is filled into the sample box.

[0022] The ballast is filled into the ballast box 5 in n layers and compacted, with the first layer at the bottom and the nth layer at the top, and the sample boxes of different layers are staggered in the length and height directions, and the upper and lower sample boxes are coplanar; the internal volume of the ballast box at a height of H2 is denoted as v t2 .

[0023] According to the void ratio β, the void volume v of the ballast pile in the ballast box is calculated v = β · v t2 ;

[0024] Sand particles 4 are uniformly spread on the surface of the ballast pile to simulate ballast beds with different levels of contamination; the mass of the sand particles 4 is calculated according to the void ratio and different levels of contamination;

[0025] In the vibration duration range, vibration tests at a preset frequency are carried out according to the step length; the vibration duration is 0 min-S min;

[0026] After each vibration test at each level of contamination, the sampling box in the ballast pile is taken out, the weight of the sand particles in the sampling box is recorded, the test results are observed, and if the difference between the weight of the sand particles when the vibration duration is S1 min and the weight of the sand particles when the vibration duration is S2 min is within a preset range, it is considered that the internal ballast bed has reached a stable state, and the weight m of the sand particles in the sampling box at this time is recorded 1～n , the volume percentage of the sand particles in the sampling box is calculated, and the volume percentage of the lower layer sand particles is gradually subtracted to obtain the volume percentage of the sand particles in the current layer, which is the ballast contamination rate of the current layer; wherein S2

[0027] A T2-thick bottom ballast 3 is laid at the bottom of the ballast box 5.

[0028] L3 / L4 = W3 / W4, n < W3 / W4 < L3 / Rmax, n = H2 / (H4+T1), 1mm ≤ T1 ≤ 1.5mm, Rmax represents the maximum ballast particle size, the inner wall size of the ballast box is L3, W3 and H3 in length, width and height, respectively, and H2 < H3.

[0029] The beneficial effects of the present application are: the present application not only provides a new idea for determining the existing contaminated ballast bed numerical simulation contamination rate research, but also provides a practical method and theoretical reference for performance evaluation and service performance prediction of ballast bed. Specifically: the present application measures the void ratio of the selected special graded ballast pile by drainage method test, simulates the contamination particles with sand particles, uses the sampling box arranged at different depths in the ballast pile, and obtains the contamination rate at different depths of the contaminated ballast bed under different levels of contamination through the ballast box vibration test, which is more in line with the real situation of contamination particle distribution in the contaminated ballast bed, and the modeling in the discrete element software PFC2D can make the modeling result closer to the actual situation. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The flowchart of the present application;

[0031] Figure 2 The cross-sectional view of the drainage method for measuring the void ratio of the ballast pile provided by the present application;

[0032] Figure 3 A cross-sectional schematic diagram of the ballast box vibration test provided by the present invention;

[0033] Figure 4 This is a schematic diagram illustrating the modeling approach in the discrete element software PFC2D provided by the present invention.

[0034] Figure 5 This is the modeling model of the present invention in the discrete element software PFC2D;

[0035] The labels in the diagram are as follows: 1-ballast pile, 2-container, 3-bottom ballast, 4-sand, 5-ballast box, 6-vibration motor, 7-first sampling box, 8-second sampling box, 9-third sampling box, 10-fourth sampling box, 11-ballast, 12-dirty particles. Detailed Implementation

[0036] The invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of the invention is not limited to the description.

[0037] Example 1: As Figures 1-5 As shown, a test method for determining the dirt rate of ballast track includes: sieving ballast particles according to their size range; selecting the sieving rate of ballast particles in different size ranges based on ballast gradation requirements; mixing ballast particles with different sieving rates evenly; compacting the mixed ballast in layers within a square container 2 made of acrylic sheet and conducting a drainage test to obtain the porosity of the ballast pile 1 under this gradation condition; and compacting the mixed ballast in layers into a ballast box 5 and conducting a ballast box vibration test to obtain the dirt rate of the ballasted track track.

[0038] Furthermore, the step of compacting the mixed ballast in layers within a square container 2 made of acrylic sheet and conducting a drainage test to obtain the porosity of the ballast pile 1 under this gradation condition includes:

[0039] The ballast is filled and compacted in n layers inside container 2, with a filling height of H2; where H2 w Based on the volume ratio of water, the porosity β of ballast pile 1 was calculated.

[0040] Furthermore, the porosity β is expressed as follows:

[0041]

[0042] In the formula, β is the porosity of the ballast pile; v w v is the volume of water when the water level in container 2 reaches H2; t1 Let H2 be the internal volume of container 2 at height H2.​

[0043] Further, the mixed ballast is layered and compacted into the ballast box 5 for a ballast box vibration test to obtain the dirty rate of the ballast bed, including: making n / 2n sample boxes with the same size and open top, the inner wall size of the sample box is L4, W4, H4, the wall thickness of the sample box is T1, and the volume of the sample box is v q ; the ballast is filled into the sample box; the ballast is filled into the ballast box 5 in n layers and compacted, the lowest layer is the first layer, and the uppermost layer is the nth layer, the sample boxes of different layers are staggered in the length and height directions, and the upper and lower sample boxes are coplanar; the volume of the ballast inside the ballast box at the height of H2 is v t2 ; according to the void ratio β, the void volume v v of the ballast pile in the ballast box is calculated t2 ; sand particles 4 are uniformly spread on the surface of the ballast pile to simulate ballast beds with different degrees of dirt; wherein the mass of the sand particles 4 is calculated according to the void ratio and different degrees of dirt; within the vibration duration range, vibration tests are carried out at a preset frequency according to the step length; wherein the vibration duration is 0min-Smin; after each vibration test of each degree of dirt, the sample box in the ballast pile is taken out, the weight of the sand particles in the sample box is recorded, the test result is observed, and if the difference between the weight of the sand particles when the vibration duration is S1min and the weight of the sand particles when the vibration duration is S2min is within the preset range, it is considered that the internal state of the dirty ballast bed has reached a stable state, the weight m 1～n of the sand particles in the sample box at this time is recorded, the volume percentage of the sand particles in the sample box is calculated, and the volume percentage of the sand particles in the lower layer is subtracted layer by layer to obtain the volume percentage of the sand particles in the layer, which is the ballast bed dirty rate of the layer; wherein S2<S1<S, and S2 and S1 are separated by one step length.

[0044] Further, a T2-thick bottom ballast 3 is laid at the bottom of the ballast box 5.

[0045] Further, L3 / L4=W3 / W4, n

[0046] Further, the following describes the optional specific embodiments of the present application:

[0047] Step 1: using standard test sieve (GB / T6003.1-2012) to screen different particle size range of ballast specified in the special grade gradation ballast, a total of five kinds of particle size range of ballast, respectively: particle size less than 22.5mm, particle size greater than or equal to 22.5mm less than 31.5mm, particle size greater than or equal to 31.5mm less than 40mm, particle size greater than or equal to 40mm less than 50mm, particle size greater than or equal to 50mm less than 63mm.

[0048] Step 2: according to the industry standard "railway ballast" TB / T2140-2008 in the special grade gradation ballast particle size specified sieve percentage, select: 22.5mm square hole sieve sieve rate of 2%, 31.5mm square hole sieve sieve rate of 20%, 40mm square hole sieve sieve rate of 50%, 50mm square hole sieve sieve rate of 90%, 63mm square hole sieve sieve rate of 100%, with particle size less than 22.5mm ballast weight as 20kg for reference, according to the proportion of the remaining four kinds of particle size range of ballast weight respectively: particle size greater than or equal to 22.5mm less than 31.5mm ballast weight for 180kg, particle size greater than or equal to 31.5mm less than 40mm ballast weight for 300kg, particle size greater than or equal to 40mm less than 50mm ballast weight for 400kg, particle size greater than or equal to 50mm less than 63mm ballast weight for 100kg, then mix them thoroughly.

[0049] Step 3: as Figure 2 The profile diagram of measuring the void ratio of ballast pile by drainage method is shown, which comprises the following steps:

[0050] Step 1: make a container 2 made of transparent acrylic plate with inner wall length, width and height of L1, W1 and H1 respectively, the thickness of acrylic plate is 5mm, which ensures that the container is water tight and leakproof;

[0051] Step v: fill the ballast in n layers in the acrylic plate container 2 and compact it, the filling height is H2; H2 < H1;

[0052] Step 3: fill water in the container and record the volume v of water injected into the container when the water level reaches H2 w ;

[0053] Step 4: according to the volume ratio of water, the void ratio β of ballast pile can be calculated.

[0054] Step 4: as Figure 3 The profile diagram of ballast box vibration test is shown, which comprises the following steps:

[0055] Step 1: make a ballast box 5 with iron plate, the inner wall size of ballast box 5 is L3, W3 and H3 in length, width and height respectively, and the wall thickness is 10mm;

[0056] Step 2: Make n / 2n sampling boxes with the same size of top opening, the inner wall size of the sampling box is L4, W4, H4, the wall thickness of the sampling box is T1, and the volume of the sampling box is v q ; L3 / L4=W3 / W4, n

[0057] Step 3: Fill the ballast into the sampling box and mark different colors for subsequent test to calculate the sand content in the sampling box;

[0058] Step 4: In order to avoid the influence of boundary effect on the result, lay T2-thick bottom ballast on the bottom of the ballast box;

[0059] Step 5: Fill the ballast into the ballast box in n layers and compact, the lowest is the first layer and the uppermost is the n-th layer, the sampling boxes in different layers are staggered in the length and height directions, and the upper sampling box in the adjacent two layers is coplanar with the top of the lower sampling box; the internal volume of the ballast box at H2 height is v t2 ; It should be noted that if the number of sampling boxes is n and the value of n is 4, the four sampling boxes are staggered in the length and height directions as shown in Figure 3 , that is, the first sampling box 7, the second sampling box 8, the third sampling box 9 and the fourth sampling box 10 are arranged; if the number of sampling boxes is 2n, each group of sampling boxes is n, and the value of n is 4, two groups are arranged in the width direction. Figure 3 If the value of H2 is 350mm, the thickness of each layer of ballast is 87.5mm.

[0060] Step 6: According to the void ratio β of the ballast bed, the void volume v v of the ballast pile in the ballast box is calculated. t2 The sand particles are uniformly spread on the surface of the ballast pile to simulate the invasion of the ballast bed, and four different degrees of pollution are simulated, and the weight of the sand particles under four different degrees of pollution 0.2, 0.4, 0.6 and 0.8 is calculated according to the void volume, and the weight of the sand particles required by the four degrees of pollution is 0.2·v v ·ρ 沙 , 0.4·v v ·ρ 沙 , 0.6·v v ·ρ 沙 , 0.8·v v ·ρ 沙 , wherein ρ 沙 is the density of the sand particles, and the density of the sand particles used in the present application is 1627kg / m 3 .

[0061] Step ⑦: using the vibration motor 5, at the middle position above the ballast pile, vibration test is carried out at a frequency of 30 Hz in a vibration duration range according to a step length; wherein the vibration duration is 0-5 min; in the embodiment of the present application, the step length is 5 min; in the embodiment of the present application, the vibration duration is 0 min, 5 min, 10 min, 15 min, 20 min and 25 min respectively;

[0062] Step ⑧: after each vibration test of each degree of contamination, the sampling box in the ballast pile is taken out, the weight of the sand particles in the sampling box is recorded, the test result is observed, if the weight of the sand particles when the vibration duration is S1 min and the weight of the sand particles when the vibration duration is S2 min differ by no more than 10%, it is considered that the inside of the contaminated track bed has reached a stable state, and the weight m of the sand particles in the sampling box at this time is recorded; 1～n the volume percentage of the sand particles in the sampling box is calculated, and the volume percentage of the sand particles in the lower layer is subtracted layer by layer to obtain the volume percentage of the sand particles in the current layer, that is, the contamination rate of the track bed in the current layer; wherein S2

[0063] It should be noted that if the number of sampling boxes is n, after each vibration test of each degree of contamination, the sampling boxes in each layer are taken out for calculation of the weight of the sand particles in the sampling box, after the calculation is completed, the next data statistics is carried out by re-considering the steps ④-⑧ in step 4. If the number of sampling boxes is 2n, after each vibration test of each degree of contamination, a group of sampling boxes in each layer are taken out for calculation of the weight of the sand particles in the sampling box, after the calculation is completed, the next data statistics is carried out by re-considering the steps ④-⑧ in step 4. Through field experiments, the measurement speed is faster when the number of sampling boxes is 2n than when the number of sampling boxes is n.

[0064] The following is an example of 4 layers to give the expression of the contamination rate of the ballast pile.

[0065] The specific formula is as follows:

[0066] The contamination rate of the first layer of ballast pile is:

[0067] The contamination rate of the second layer of ballast pile is:

[0068] The contamination rate of the third layer of ballast pile is:

[0069] The contamination rate of the fourth layer of ballast pile is:

[0070] Contamination rate except the first layer

[0071] Step 5: Calculate the ballast contamination rate of different layers according to the above steps, as shown in the following table: Figure 4 As shown in the figure, ball units are generated as dirty particles 12 in the voids of ballast 11 in discrete element software PFC. The generated ball units have independent continuous id numbers. Every k id number is deleted in the form of the kth ball unit id to realize the modeling of different ballast contamination rates. Then the contamination rate k can be determined in this way. For each layer of ballast pile, k is determined according to the above method. The dirty particles are sand particles.

[0072] Step 6: According to the requirements in the industry standard "High-speed Railway Design Specification" TB 10621-2014, a two-dimensional numerical model of the ballast bed is established in the discrete element software PFC. This model includes the base surface layer, the ballast layer and the sleeper. Among them, the ballast layer selects the six typical broken stone ballast in the experiment to obtain its contour profile by 3D scanning. The profile is imported into PFC as a clump particle template to generate special gradation ballast layer. Then, the method in step 5 is used to fill the ballast layer with ball units as dirty particles to establish a numerical model of the dirty ballast bed, as shown in the figure. Figure 5 According to the k value of each layer of ballast pile determined in step 5, the modeling of different ballast contamination rates is carried out.

[0073] Further, the L1, W1, H1 of the container made of acrylic plate used in the experiment are 2500mm, 500mm, 500mm respectively. H2 is 350mm. The inner wall dimensions L3, W3, H3 of the ballast box are 1000mm, 700mm, 550mm respectively. Four sampling boxes are printed by a 3D printer, and the inner wall dimensions of the sampling box are 150mm, 105mm, 86mm. The wall thickness of the sampling box is 1.5mm. T2 is 20mm. The ballast in container 2 and ballast box 5 is filled in four layers, and the thickness of each layer is 87.5mm, and the thickness of four layers is 350mm.

[0074] The specific embodiments of the application are described in detail above in combination with the drawings, but the application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the purpose of the application.

Claims

1. A test method for determining the dirt rate of a track bed, characterized in that, Comprising: Sieving the size of ballast particles according to the ballast particle size range; Selecting the sieve passing rate of ballast particles in different particle size ranges according to the ballast gradation requirements; mixing the ballast particles with different sieve passing rates evenly; Layering and compressing the mixed ballast in the container (2) for the drainage method test to obtain the void ratio of the ballast pile (1) under this gradation condition; Layering and compressing the mixed ballast into the ballast box (5) for the ballast box vibration test to obtain the fouling rate of the ballasted track bed; The step of layering and compressing the mixed ballast into the ballast box (5) for the ballast box vibration test to obtain the fouling rate of the ballasted track bed includes: Construct n / 2n identical sampling boxes with open tops. The inner wall dimensions of each sampling box are L4, W4, and H4, respectively, and the wall thickness is T1. Denote the volume of each sampling box as... ; Filling the sampling box with ballast; The ballast is filled into the ballast box (5) in n layers and compacted. The bottom layer is the first layer and the top layer is the nth layer. The sampling boxes of different layers are staggered along the length and height directions, and the sampling boxes of the upper and lower layers are coplanar. The internal volume of the ballast box at height H2 is recorded as . ; Based on porosity Calculate the void volume of the ballast pile inside the ballast box. ; Uniformly sprinkling sand grains (4) on the surface of the ballast pile to simulate the track beds with different fouling degrees; wherein, the mass of the sand grains (4) is calculated according to the void ratio according to different fouling degrees; Performing vibration tests at preset frequencies according to the step size within the vibration duration range; wherein, the vibration duration is 0 min - S min; After each vibration test for each level of contamination, the sampling box was removed from the ballast pile, and the weight of the sand particles in the sampling box was recorded. The test results were observed. If the difference between the weight of the sand particles at vibration time S1min and the weight of the sand particles at vibration time S2min was within the preset range, it was considered that the contaminated ballast bed had reached a stable state, and the weight of the sand particles in the sampling box at this time was recorded. The volume percentage of sand particles in the sampling box is calculated, and the volume percentage of sand particles in the lower layer is subtracted layer by layer to obtain the volume percentage of sand particles in this layer, which is the dirt rate of the track bed in this layer; where S2 < S1 < S, and S2 and S1 are separated by one step size. Wherein, H2 is the filling height of the ballast.

2. The test method for determining the dirt rate of a track bed according to claim 1, characterized in that, This also includes generating contamination particles in the ballast voids using ball elements in discrete element method software, based on the obtained contamination rate of the ballbed. Each generated ball element has an independently and consecutively numbered ID. Modeling of ballast beds with different contamination rates is achieved by deleting the ID of the kth ball element for every k IDs. The contamination rate is then calculated. k can be determined from this.

3. The test method for determining the dirt rate of a track bed according to claim 1, characterized in that, The step of layering and compressing the mixed ballast in the container (2) for the drainage method test to obtain the void ratio of the ballast pile (1) under this gradation condition includes: Filling and compressing the ballast in the container (2) in n layers at the filling height of H2; wherein, H2 < H1, and H1 is the height of the container (2); Fill container (2) with water and record the volume of water poured into container (2) when the water level reaches H2. ; Based on the volume ratio of water, the porosity of the ballast pile (1) was calculated. .

4. The test method for determining the dirt rate of a track bed according to claim 3, characterized in that, porosity The expression is as follows: ； In the formula, The porosity of the ballast pile; The volume of water when the water level in container (2) reaches H2; Let H2 be the internal volume of container (2) at height H2.

5. The test method for determining the dirt rate of a track bed according to claim 1, characterized in that, Laying a bottom ballast (3) with a thickness of T2 at the bottom of the ballast box (5).

6. The test method for determining the dirt rate of a track bed according to claim 1, characterized in that, L3 / L4 = W3 / W4, n < W3 / W4 < L3 / Rmax, n = H2 / (H4 + T1), 1 mm ≤ T1 ≤ 1.5 mm, Rmax represents the maximum ballast particle size, and the inner wall dimensions of the ballast box are L3, W3, and H3 respectively, and H2 < H3.

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