Large-scale relative density test method and test device for coarse aggregates

Abstract

The invention discloses a large-scale coarse aggregate relative density test method and a test device thereof. The method comprises the following steps: firstly, adopting a design grading envelope, detecting grading by using a rolling test or filling, correcting the design grading envelope according to a maximum particle size normalization method to obtain an objective grading range which simultaneously considers grading coarsest aggregates and grading curve rules, and determining test grading; secondly, a density barrel device and a test sample loading method are selected, and the layered sample loading problem and the size effect problem are considered at the same time; thirdly, selecting a test compaction machine type selection and compaction parameter determination method, and considering the requirement of the particle breakage rate in the test process; according to the large-scale relative density test method for the coarse aggregates, the requirement on the compaction quality control precision of a rock-fill dam can be met, and a basis is provided for the compaction design and the compaction quality control of the coarse aggregates.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water conservancy civil engineering, and uses numerical test and physical test means to determine the relative density test results of coarse-grained materials. The research results can be directly applied to the filling design and compaction quality evaluation of coarse-grained materials. BACKGROUND

[0002] The compaction of cohesionless coarse-grained soil is mainly completed by rearrangement of particles and local damage of contact points. With the development of thin-layer compaction technology of heavy vibration roller, the maximum particle size of dam sand gravel material and rockfill material has reached 600-800 mm, and the maximum particle size of indoor relative density test can only be within 100 mm due to the test conditions.

[0003] Low et al. and Shi Yanwen obtained the linear relationship between coarse-grained material and compaction dry density in semi-logarithmic coordinate system by indoor test using similar gradation method, which can extrapolate the maximum dry density of field coarse-grained material gradation. However, for rockfill dams using thin-layer compaction technology, the test dry density gradually stabilizes with the increase of the maximum particle size, and the maximum dry density obtained by extrapolation method does not match the test results.

[0004] Researchers proposed large-scale density bucket method based on sand gravel material with maximum particle size of about 300 mm, and specified the corresponding test procedures and detection technical regulations. There are still the following problems:

[0005] (1) As a kind of granular material, the physical and mechanical properties of coarse-grained material are closely related to the gradation. How to select the test gradation consistent with the filling conditions is the basis for ensuring that the relative density test results objectively reflect the actual situation of dam site;

[0006] (2) The size effect of density bucket test, i.e. the ratio of diameter to diameter and the ratio of diameter to height, has a great influence on the dry density test results. The existing experience cannot guarantee the stability and reliability of the test results;

[0007] (3) Unlike the small particle size scale test in the laboratory which can be fully mixed by hand, when conducting density bucket test, the reasonable spatial position of super-large particle size coarse-grained material in the density bucket must be solved to ensure the stability and reliability of the test results;

[0008] (4) Using construction vibration roller as the compaction tool of large-scale density bucket, there is a lack of specification and basis for vibration roller compaction equipment and method;

[0009] (5) There is a lack of research data on the influence of coarse-grained material particle crushing on density bucket test results, and the allowable range of coarse-grained material particle crushing during density bucket test needs to be specified.

[0010] In 1945, Terzaghi proposed the compaction theory of coarse-grained soil, and the relative density index should be used to measure the well-drained coarse-grained soil. Due to the difficulty of large-scale relative density test of rockfill material on site, the papers of , , can only use porosity as the transition standard for compaction of rockfill dam, but the porosity standard only specifies the compaction standard of the worst gradation, which is difficult to guarantee the filling quality of the rockfill dam. A reliable large-grained coarse-grained material relative density test method is needed for water conservancy and hydropower engineering dam. SUMMARY

[0011] The purpose of the application is to solve the above technical problems by combining numerical test with physical test to study large-scale density barrel test, so as to provide a practical large-scale relative density test method for the design of large-scale relative density of coarse-grained material and the control of compaction quality.

[0012] To achieve the above purpose, the application adopts the following technical solutions:

[0013] A large-scale relative density test method for coarse-grained material, comprising the following steps:

[0014] Step 1: Determine the preliminary range of the engineering coarse-grained material using gradation by using the particle size outer package method, and correct the gradation curve by using the maximum particle size normalization method to obtain the objective gradation curve, and then determine the test gradation;

[0015] Step 2: According to the objective gradation curve determined in step 1, select multiple representative gradation curves as the relative density test gradation by interpolation method;

[0016] Step 3: Determine the height-diameter ratio and diameter-diameter ratio of the density barrel that can eliminate the size effect through numerical test;

[0017] Step 4: Based on the height-diameter ratio and diameter-diameter ratio of the density barrel determined in step 3, compare different sample loading methods through numerical test to determine the sample loading method that can obtain stable test results;

[0018] Step 5: Based on the height-diameter ratio and diameter-diameter ratio of the density barrel determined in step 3, select the coarse-grained soil test gradation, and make the test device with a bottom density steel barrel upper connecting sleeve ring;

[0019] Step 6: Based on the sample loading method determined in step 4, layer loading in the density barrel;

[0020] Step 7: After loading, the minimum dry density of the sample is measured by using the sand pouring method or the water pouring method;

[0021] ​​​​​​Step 8, remove the surface sleeve, fill the density barrel with the gradation material similar to the test gradation using the similar method, and use heavy vibratory roller for traveling vibratory compaction and fixed-point micro-vibratory compaction;

[0022] Step 9, after the density barrel compaction is completed, the test dry density after compaction is calculated;

[0023] Step 10, repeat steps 2 to 9 to obtain multiple sets of density barrel test results, screen the gradation of the coarse aggregate in the density barrel in step 9, and calculate the particle breakage rate, if the particle breakage rate is less than 10%, the test dry density obtained in step 9 is the maximum dry density of the test gradation.

[0024] Beneficial effects:

[0025] The present application adopts the particle size normalization method to correct the design gradation envelope, and obtains the objective gradation range considering the coarsest particles and the gradation curve law through the compaction test or filling detection gradation.

[0026] Multiple representative gradation curves are selected using the interpolation method to ensure that the test gradation covers the actual gradation range on site, thereby improving the representativeness and accuracy of the test. The proposed relative density field large-scale test method avoids the problem that the maximum dry density test result does not match the field caused by the traditional extrapolation method, and provides a reliable basis for the compaction quality evaluation.

[0027] In an alternative embodiment, the multiple representative gradation curves in step 2 include an upper envelope, an optimal gradation line, an upper average gradation, an average line, a lower average gradation, a lower envelope, and a lower envelope extension, a total of seven.

[0028] Beneficial effects: according to According to the specifications such as SL274-2020, the upper envelope of the filling rockfill or gravel material generally does not exceed the range, but the lower envelope may exceed the range, and the present application adds the optimal gradation line, which greatly improves the accuracy of the equal relative density line of the fine particle content P5-dry density-relative density composition three-factor graph, and is beneficial to more accurate implementation of the dam compaction quality evaluation.

[0029] In an alternative embodiment, in step 3, the diameter ratio is not less than 4.0, and the height-diameter ratio is not less than 2.0.

[0030] Beneficial effects: according to the numerical test results, when the diameter ratio is not less than 4.0 and the height-diameter ratio is not less than 2.0, the minimum porosity result of the relative density test is closest to the theoretical value, and the error is controlled within 3%, which ensures that the engineering precision requirements are met.

[0031] In an alternative embodiment, step 4 is repeated for each sampling method for not less than 50 groups.

[0032] Beneficial effects: through not less than 50 groups of repeated tests, it is convenient to obtain statistically significant test results, so as to overcome the dispersion problem of relative density test results.

[0033] In an alternative embodiment, the net height of the barrel body of the density barrel in step 5 is 70-90 cm, and a sleeve with the same diameter and a height of 20-30 cm is installed at the upper part.

[0034] Beneficial effects: after the minimum dry density measurement is completed, the upper part of the density barrel can be filled with the same gradation sample, so as to ensure the consistency of the gradation during the maximum dry density test.

[0035] In an alternative embodiment, the layer-by-layer filling in step 6 is as follows: from bottom to top, at least four layers are formed, the first layer is filled with particles with a particle size of less than 100 mm, and the average layer thickness is 5 cm; the second to fourth layers are filled with particles with a particle size of not less than 100 mm, and the layer thickness of each layer is between 15-35 cm, and the large-diameter particles are arranged staggered between layers.

[0036] Beneficial effects: through the above-mentioned layer-by-layer filling method, it is ensured that particles of different particle sizes are close to the optimal arrangement position, and more objective minimum dry density and maximum dry density test results are obtained.

[0037] In an alternative embodiment, the number of rolling passes at which the dynamic rolling settlement rate reaches 95% is determined as the number of rolling passes of the test traveling vibration roller in step 8, and the length of time of the fixed-point micro-vibration roller compaction is not less than 15 minutes.

[0038] Beneficial effects: traveling vibration roller compaction at a certain speed can effectively reduce particle crushing on the basis of compaction, and facilitate the adjustment of particle position, so the traveling vibration roller compaction is used for basic compaction in the present application. Then, the length of time of the fixed-point micro-vibration roller compaction is 15 minutes, which ensures that the compaction is close to the theoretically most dense state.

[0039] In an alternative embodiment, the Marsal formula is used to calculate the particle crushing rate in step 10, and the allowable range of Marsal particle crushing rate at which the gradation of coarse aggregate does not change significantly is 0-10%.

[0040] Beneficial effects: particle crushing factors have two main influences on the relative density test method proposed in the present application, one is that excessive crushing rate leads to partial compaction power loss, affects the compaction effect, and causes the maximum dry density test result to be low; the other is that the difference between the test gradation and the filling gradation after compaction is too large, which reduces the gradation representativeness of the test result. A large amount of test data shows that when the crushing rate is less than 10%, the measured dry density test result is relatively stable.

[0041] The application further discloses a test device for implementing the coarse-grained large-scale relative density test method, which comprises a density barrel and a sleeve.

[0042] The density barrel is provided with a first fixing ring, and the sleeve is provided with a second fixing ring; when the sleeve is sleeved on the density barrel, the sleeve is fixed on the density barrel through the first fixing ring and the second fixing ring.

[0043] Beneficial effects: The fixing rings are arranged to organically connect the density barrel and the sleeve, facilitate sample loading after the minimum dry density test, and facilitate the sleeve to be pulled out after sample loading to perform the maximum dry density test.

[0044] In an alternative embodiment of the test device, the density barrel is provided with a first lifting hook, and / or the sleeve is provided with a second lifting hook.

[0045] Beneficial effects: Since the thickness of the steel plate of the density barrel is generally greater than 14 mm, the self weight is relatively high, and manual installation is difficult, the two sets of lifting hooks are arranged to facilitate mechanized construction and improve the test efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 It is a structural schematic view of a coarse-grained soil field relative density test device;

[0047] Among them, 1 is a density barrel; 2 is a sleeve; 11 is a first fixing ring; 12 is a first lifting hook; 21 is a second fixing ring; and 22 is a second lifting hook.

[0048] Figure 2 It is a size effect diagram of the minimum porosity of the coarse-grained relative density numerical test;

[0049] Figure 3 It is a variation coefficient diagram of the coarse-grained relative density numerical test results;

[0050] Figure 4 It is a DSX filling gravel material grading curve diagram;

[0051] Figure 5 It is a normalized curve of the rolling test and the filling grading;

[0052] Figure 6 It is a S3 material field gravel relative density test grading (dmax=300 mm) curve diagram of the DSX;

[0053] Figure 7 It is a three-factor diagram of the field relative density test of the gravel material;

[0054] Figure 8 It is a design optimization envelope rockfill material field large-scale relative density test grading;

[0055] Figure 9 Three-factor graph for designing field relative density test of graded rockfill material for rolling method 1;

[0056] Figure 10 Three-factor graph for designing field relative density test of graded rockfill material for rolling method 2;

[0057] Figure 11 Three-factor graph for designing field relative density test of graded rockfill material for rolling method 3;

[0058] Figure 12 Comparison graph of gradation before and after field relative density test of average graded rockfill material. DETAILED DESCRIPTION

[0059] The present application will be further illustrated by the following specific examples and the accompanying drawings, which are intended to be illustrative only and not limiting of the scope of the present application, and modifications of the present application by those skilled in the art after reading the present application will fall within the scope of the appended claims.

[0060] The present application is a large-scale relative density test method for coarse granular material with a particle size range of 60mm to 800mm, comprising the following steps:

[0061] Step 1, select the particle size envelope method, plot the exploration data of the stockyard on the gradation curve graph with the particle size di as the horizontal coordinate and the percentage P of the mass of particles less than the particle size di as the vertical coordinate, determine the gradation range according to the envelope contour line, the finest one is the upper envelope line and the coarsest one is the lower envelope line, and determine the preliminary range of the engineering use gradation.

[0062] In order to fit the field gradation rule and correct the gradation curve, the particle size of the gradation is normalized. The particle size data of each gradation of the sand and gravel material is divided by the maximum particle size of the gradation, and according to the test maximum particle size range, the test gradation is restored.

[0063] Considering the influence of dry density size effect, when the maximum particle size of the rockfill material reaches 400mm, the dry density test value is basically stable, and the similar method can be used to normalize the gradations with different maximum particle sizes to dmax=400mm.

[0064] Step 2, according to the normalized and optimized gradation curve, select the relative density test gradation by interpolation method. Considering the influence of particle crushing, according to the maximum particle size gradation, determine the test gradation, including seven gradation curves, respectively, the upper envelope line, the optimal gradation line, the upper average gradation, the average line, the lower average gradation, the lower envelope line and the lower envelope line expansion. The maximum dry density test and the minimum dry density test gradation are consistent.

[0065] Step 3, carry out the packing test of different particle size groups and triaxial test of target gradation. The inter-particle friction coefficient and anti-rotation coefficient are determined by the packing test, and the particle elastic modulus and stiffness ratio are determined by the triaxial test.

[0066] The particle numerical test model is established, and the results of the packing test and the indoor large-scale triaxial test are simulated to calibrate the particle parameters and the contact parameters between particles.

[0067] The test gradation that meets the engineering requirements is selected, and the numerical relative density test is carried out. The maximum dry density is determined by the vibration table method, and the change rate of porosity per second is less than 2% as the test end standard. In order to obtain the height-diameter ratio and diameter-diameter ratio of the density bucket that basically eliminates the size effect, the diameter-diameter ratio and height-diameter ratio of the density bucket are changed, and multiple numerical experiments are carried out.

[0068] For the large-scale density bucket test on site, the diameter of the density bucket is controlled within 2.0 m according to the width of the heavy roller.

[0069] The maximum particle size dmax of the test dam material is 400 mm. If the test error is controlled within 5%, and considering the site test conditions and test precision requirements, the minimum diameter-diameter ratio and height-diameter ratio are generally selected as 4.0 and 2.0 respectively, which can meet the requirements of the dam engineering coarse-grained soil density bucket test.

[0070] Step 4, based on step 3, the same sample is used for numerical test of different sample preparation methods, and the stable test result of the sample preparation method is obtained to guide the actual sample preparation. Three representative methods are selected for the actual test, which are "mixed sample preparation", "3-layer mixed sample preparation", and "large-to-small sample preparation". For these three sample preparation methods, the same sample is tested multiple times, and the coefficient of variation and average porosity of the results are compared.

[0071] The test results show that the porosity of "layered sample preparation" is lower and the dispersion is relatively small; the dispersion of "mixed sample preparation" is larger. In the relative density test, "layered sample preparation" is the best choice.

[0072] Step 5, determine the density bucket test device: based on step 4, make the device with a bottom density steel bucket and an upper connecting sleeve ring. The diameter and height of the density bucket are measured multiple times at different positions with a steel tape or a steel ruler, the average value is calculated to obtain the volume, and the water filling method is used for verification.

[0073] Step 6, based on step 3, layered sample. According to the grading requirements, the test material of each particle size group is weighed, and the particles below 100 mm are stirred uniformly and placed in the barrel, and the particles above 100 mm are placed manually; from bottom to top, it is divided into the first layer, the second layer, the third layer and the fourth layer. The first layer is about 5 cm thick, and the particle size distribution is selected below 100 mm; the second to fourth layers are between 15-35 cm thick, and the particle size distribution is basically evenly distributed in each layer, starting from 100 mm, and grading by 100 mm. After the minimum dry density is determined, the test material is uniformly and loosely filled on the top of the density barrel, about 20 cm higher than the top of the density barrel (for a barrel diameter of 50 cm), and the test material with the same type and grading is filled around the density barrel, with the height being flush with the test material. During the rolling process, appropriate material is added according to the settlement of the barrel top to avoid direct contact between the roller and the density barrel.

[0074] Step 7, determine the method for measuring the minimum dry density: select the sand pouring method or water pouring method to measure the volume from the top of the filler to the top of the barrel.

[0075] (1)

[0076] V is the volume of the density barrel, V is the volume of the sand pouring or water pouring.

[0077] Step 8, remove the surface sleeve, fill the perimeter of the density barrel with similar graded material, and select heavy vibration compaction.

[0078] The test compaction machinery can select a vibration roller with the same vibration force, vibration frequency and amplitude as the actual construction. According to the heavy vibration roller used in construction, a vibration roller with a weight of more than 32 tons can be selected.

[0079] The difference between the 36-ton vibration roller and the 32-ton vibration roller is very small, and the application accuracy can meet the requirements.

[0080] Start the selected vibration roller outside the field at the predetermined speed, amplitude and frequency, travel at a speed of 2-3 km / h, and roll according to the "advance and retreat method", with 2 passes of advance and retreat. Then move the vibration roller in and out within the range of each density barrel for 15 minutes.

[0081] Based on the principle that the settlement rate of the test material obtained by the rolling test is basically stable, different vibration roller models are used for rolling tests on the rockfill material, and the rolling passes are determined when the settlement after rolling is more than 95% and the rolling layer thickness is basically unchanged.

[0082] Rolling layer deformation fitting formula:

[0083] (2)

[0084] The test results are compiled into the following table, which shows that the deformation is stable when the vibration roller is rolled 26 times.

[0085] Table 3 Real-time average settlement and deformation trend of the rolling test pile

[0086] Step 9, after the rolling is completed, the test material on the top and around the density barrel is manually excavated to about 5 cm below the barrel opening, and the lower part of the sample is prevented from being disturbed. The sample volume is measured by the water filling method or the sand filling method, and the compaction density is calculated by combining the excavated material quality.

[0087] (3)

[0088] wherein, is the mass of the coarse-grained material poured into the density barrel, m is the mass of the excavated material, V is the volume of the density barrel, is the sand filling or water filling volume.

[0089] Step 10, according to the Soil Test Specification SL237-006-1999, the particle size distribution analysis test uses the sieve analysis method. The sample excavated from the test pit during the field density determination is sieved on site through the round-hole standard soil sieve (with sieve hole sizes of 100, 80, 60, 40, 20, 10, and 5 mm, respectively). For particles larger than 100 mm, a steel round collar is used to measure and distinguish them one by one, and the color of the particles is also considered. Next, about 5 kg of particles with diameters less than 5 mm are sampled, dried in the laboratory, and sieved using a standard vibrating sieve machine. The particle size distribution curve of the soil sample is redrawn.

[0090] The allowable range of particle breakage of coarse-grained material during the density barrel test is specified. The breakage rate of the gradation is calculated using the Marsal formula:

[0091] The sum of the positive values (4)

[0092] (5)

[0093] In the above formula: is the particle breakage rate; is the difference in the content of each particle size group before and after the test; are the contents of each particle size group before and after the test, respectively.

[0094] If the breakage rate is less than 10%, the test dry density obtained is the maximum dry density of the test gradation.

[0095] For example, Figure 1As shown, a device for testing the in-situ relative density of large-diameter coarse-grained soil includes a density bucket 1 and a sleeve 2. The density bucket 1 is a steel bucket with a bottom, and the sleeve 2 is a steel ring. The density bucket 1 is provided with a first fixing ring 11 and a first lifting hook 12, and the sleeve 2 is provided with a second fixing ring 21 and a second lifting hook 22. When the sleeve 2 is sleeved on the density bucket 1, the sleeve 2 is fixed on the density bucket 1 by the first fixing ring 11 and the second fixing ring 21.

[0096] As shown in the structural diagram of the device for testing the in-situ relative density of coarse-grained soil, Figure 1 As shown in the structural diagram of the device for testing the in-situ relative density of coarse-grained soil,

[0097] Example 1:

[0098] Using the numerical test method, the test gradation refers to the design gradation of the LW main heap, and the particle size fractal dimension D is 2.545. According to formula (6), the maximum particle size dmax is calculated as Six groups of gradations with particle sizes of 60mm, 100mm, 150mm, 200mm, 300mm and 500mm are respectively used for numerical tests.

[0099] (6)

[0100] In the above formula: is the percentage content of the mass of particles smaller than the particle size of the i-th group; is the particle size of the i-th group, with units of mm; is the maximum particle size of the test gradation, with units of mm, and D is the particle size fractal dimension of the gradation.

[0101] The mesoscopic parameters of the rockfill particles are selected as follows:

[0102] Table 1: Particle mesoscopic parameters for numerical tests

[0103] In order to determine the size of the density bucket, a gradation width (dmax / dmin) of 18.0 is selected for testing.

[0104] In order to quantitatively reflect the size effect corresponding to different diameter ratios and height-diameter ratios, the test porosity corresponding to a diameter ratio of 8.0 and a height-diameter ratio of 4.0 is selected as the reference porosity, and it is considered that the porosity under this test condition basically eliminates the size effect.

[0105] As shown in the structural diagram of the device for testing the in-situ relative density of coarse-grained soil, Figure 2 As shown in the structural diagram of the device for testing the in-situ relative density of coarse-grained soil,

[0106] In order to determine the sample loading method, hundreds of tests are involved, and the numerical test is carried out with a gradation width of 10.0 considering the calculation efficiency and accuracy.

[0107] Table 2 Test methods for different sample loading methods

[0108] like Figure 3 The coefficient of variation of the numerical test results shows that the "layered sample" has lower porosity and relatively smaller dispersion, while the "mixed sample" has greater dispersion. In the relative density test, the "layered sample" is the optimal choice.

[0109] Example 2:

[0110] The gravel used for the large-scale relative density test on site was selected from the S3 natural quarry of DSX.

[0111] Step 1: Using pit tracing, compaction tests, or filling gradation data, the maximum particle size normalization method is used to correct the design gradation envelope.

[0112] like Figure 4 The filling gradation shown has a relatively small maximum particle size, ranging from 150 to 500 mm, with an average value of about 270 mm.

[0113] like Figure 5 To utilize Figure 4 The maximum particle size dmax of each filling gradation is normalized, and the curve obtained is determined by the envelope.

[0114] Step 2, for a gradation with a maximum particle size of 300mm, according to Figure 5 The normalized gradation envelope was obtained by using the similarity method to obtain the upper and lower envelopes of the test. Three gradation curves were interpolated and two gradation curves were expanded outwards for on-site density barrel tests.

[0115] Table 4. Grating of Gravel in Field Relative Density Test

[0116] The on-site relative density test gradation of gravel at S3 quarry (dmax=300mm) is as follows: Figure 6 As shown.

[0117] Step 3: Design the density barrel dimensions.

[0118] Table 5. Density Barrel Design for On-site Relative Density Test

[0119] Maximum particle size of gradation / mm Density barrel size Sleeve barrel size Number of density barrels 60、100 50 cm x 50 cm -- 2 150、300 120 cm x 80 cm 120 cm x 25 cm 2 200、250、300、400 160 cm x 80 cm 160 cm x 25 cm 5 500、600 240 cm x 80 cm 240 cm x 25 cm 1 800 320 cm x 80 cm 320 cm x 25 cm 1

[0120] Step 4: Select the density bin size and perform layered sample loading according to the following method as an example.

[0121] The maximum particle size is 300mm and 400mm (barrel diameter x barrel height: 1.6m x 0.8m, sleeve 1.6m x 0.25m):

[0122] According to the grading requirements, each particle size group test material is weighed, and the 100mm or less particle size group is uniformly stirred;

[0123] The sample is loaded in four layers:

[0124] The first layer is about 5cm thick, and the 100mm or less particle size group is uniformly and loosely filled in the density barrel. When loading, the sample is gently placed into the barrel to prevent impact and vibration;

[0125] The second layer is about 30cm thick. First, 1 / 3 of the total mass of the 400-300mm particle size group is placed in the density barrel in a rotational symmetry, taking care to maintain a certain distance from the barrel wall. Then, 1 / 3 of the total mass of the 300-200mm particle size group is placed, taking care to prevent arching. Next, 1 / 3 of the total mass of the 200-100mm particle size group is placed. Then, the 100mm or less particle size group is uniformly and loosely filled to cover all the 200-100mm particles that have been placed, taking care to reserve space for the 400-300mm and 300-200mm particle size group of the next layer. The total height is about 35cm;

[0126] The third layer is about 30cm thick, and the sample loading method is the same as the second layer. Care should be taken to place the 400-300mm and 300-200mm particle size group of the next layer in a staggered manner, and the total height is about 65cm;

[0127] The fourth layer is about 35cm thick, and the sample loading method is the same as the second layer. Care should be taken to place the 400-300mm and 300-200mm particle size group of the next layer in a staggered manner, and the total height is about 100cm;

[0128] Step 5: The volume from the top of the filler to the top of the barrel is measured using the water filling method or sand filling method, and the minimum dry density is calculated.

[0129] Step 6: After the minimum dry density is determined, the test material with similar type and grading is used to fill the density barrel around the barrel, with the height being level with the test material in the barrel. Then, the sleeve is pulled out smoothly using an excavator. A 36t vibrating roller is selected, and the vibrating roller is rolled for 26 times, with a fixed-point micro-rolling for 15 minutes. Care should be taken to supplement the material on the top of the barrel in a timely manner during the rolling process.

[0130] Step 7: The test material in the barrel is completely excavated, the mass of the test sample in the density barrel is weighed, and the particle analysis is performed using the sieve analysis method. The results of the field relative density test of the sand and gravel material with dmax=300mm are shown in Figure 7 and Table 6.

[0131] Table 6 Results of field relative density test of sand and gravel material with dmax=300mm

[0132] Gradation name Lower envelope spread Lower envelope Lower average line Average gradation Upper average line Upper envelope Upper envelope spread P5 value (%) 14.1 15.6 17.9 19.5 23.7 27.8 31.9 36.5 Minimum dry density (g / cm 3 )]]> 1.994 2.011 2.054 2.058 2.050 2.034 1.989 1.935 Maximum dry density (g / cm 3 )]]> 2.372 2.393 2.421 2.420 2.412 2.396 2.355 2.313 Dr=0.9 2.328 2.348 2.379 2.378 2.370 2.354 2.312 2.269

[0133] Step 8, sieve the gradation after the relative density test, and calculate the Marsal breakage rate of the sand-gravel material according to formula (4), which is 2.49% and 2.41% respectively, meeting the requirement that the breakage rate is not greater than 10%.

[0134] Table 7 Gradation statistics of dam material before and after the relative density test

[0135] Example 3

[0136] The test material is taken from the Biyinggou blasting material yard of LW, which is located near the rolling test field. The hornblende schist rockfill material selected for this experiment has an average bulk density of 2.975.

[0137] Step 1, use the on-site rolling test data to optimize or correct the rockfill material gradation design envelope by the normalization method.

[0138] Table 8 Optimized design gradation envelope of rockfill material

[0139] Step 2, determine the on-site relative density test gradation, and the maximum particle size of the test gradation is 400 mm.

[0140] Table 9 On-site relative density test gradation within the design envelope of rockfill material

[0141] The on-site large-scale relative density test gradation of the rockfill material in the design optimized envelope is shown in Table 9. Figure 8

[0142] Step 3, design the density bucket size.

[0143] Table 11 Design of density bucket for on-site relative density test

[0144] Step 4, according to the gradation curve, mix the materials and perform layer-by-layer sampling. The thickness of the first layer is about 5 cm, and the thickness of the second to fourth layers is about 23 cm.

[0145] Step 5, measure the volume from the top surface of the material to the bucket opening using the sand pouring method, and calculate the minimum dry density.

[0146] Step 6, continue to uniformly and loosely fill the test material on the top of the density bucket, and perform the maximum dry density test sampling.

[0147] Step 7, measure the volume from the top surface of the compacted sample to the top of the bucket using the sand pouring method, measure the maximum dry density, and perform particle analysis.​

[0148] Rolling method 1: 32t vibratory roller compaction 16 times, each bucket of micro-roller 15 min;

[0149] Rolling method 2: 36t vibratory roller compaction 16 times, each bucket of micro-roller 15 min;

[0150] Rolling method 3: 36t vibratory roller compaction 26 times, each bucket of micro-roller 15 min;

[0151] The three rolling methods of the design grading of the rockfill material are shown in the three-factor graph of the field relative density test. Figures 9-11

[0152] The heavy vibratory roller type is changed from 32t vibratory roller to 36t vibratory roller, and the lower envelope line with the same vibration time is used: 2.585 g / cm 3 to 2.604 g / cm 3 , increased by 0.7%; the average grading: 2.646 g / cm 3 to 2.689 g / cm 3 , increased by 1.4%; the upper envelope line: 2.638 g / cm 3 to 2.681 g / cm 3 , increased by 1.5%.

[0153] Step 8: The fragmentation rate analysis is performed on the relative density test.

[0154] As shown in Figure 12 , the grading comparison graph before and after the field relative density test of the average grading rockfill material under the three rolling test methods. It can be seen that the Marsal fragmentation rate of the grading obtained by the three rolling test methods is not high, but the particle fragmentation of the 36t vibratory roller test is more obvious. The fragmentation rate is 6.89% when the 36t vibratory roller is used and the vibratory roller compaction is 26 times, which is less than the specified fragmentation rate requirement. At this time, the data processing of the dry density of the grading curve with the maximum particle size of 400mm is performed, and the maximum dry density of the test grading can be obtained.​

Claims

1. A method for testing the relative density of coarse-grained materials, characterized in that, Includes the following steps: Step 1: Use the particle size distribution method to determine the preliminary range of the gradation of the coarse aggregate used in the project, and use the maximum particle size normalization method to correct the gradation curve to obtain the objective gradation curve, and then determine the experimental gradation. Step 2: Based on the objective gradation curve determined in Step 1, select multiple representative gradation curves as the relative density test gradation using interpolation. Step 3: Through numerical experiments, determine the height-to-diameter ratio and diameter-to-diameter ratio of the density barrel that can eliminate the size effect; Step 4: Based on the height-to-diameter ratio and diameter-to-diameter ratio of the density barrel determined in Step 3, different sample loading methods are compared through numerical experiments to determine the sample loading method that can obtain stable test results. Step 5: Based on the height-to-diameter ratio and diameter-to-diameter ratio of the density cylinder determined in Step 3, select the coarse-grained soil test gradation and construct a test device with a bottom density steel cylinder and an upper connecting collar. Step 6: Based on the sample loading method determined in Step 4, perform stratified sample loading in the density container; Step 7: After loading the sample, determine the minimum dry density of the sample using the sand filling method or the water filling method. Step 8: Remove the surface sleeve, fill the area around the density barrel with gradation material prepared by similar method according to the test gradation, and use heavy vibratory rollers for traveling vibration compaction and fixed-point micro-vibratory compaction. Step 9: After the density barrel compaction is completed, calculate the test dry density after compaction; Step 10: Repeat steps 2 to 9 to obtain multiple sets of density barrel test results. Screen the gradation of coarse material in the density barrel in step 9 and calculate the particle breakage rate. If the particle breakage rate is less than 10%, the test dry density obtained in step 9 is the maximum dry density of the test gradation.

2. The method for testing the relative density of coarse-grained materials according to claim 1, characterized in that, The representative gradation curves in step 2 include the upper envelope curve, the optimal gradation curve, the upper average gradation curve, the average curve, the lower average gradation curve, the lower envelope curve, and the lower envelope curve expansion, totaling seven curves.

3. The method for testing the relative density of coarse-grained materials according to claim 1, characterized in that, In step 3, the diameter-to-diameter ratio is not less than 4.0, and the height-to-diameter ratio is not less than 2.

0.

4. The method for testing the relative density of coarse-grained materials according to claim 1, characterized in that: In step 4, at least 50 repeated tests are conducted for each sample loading method.

5. The method for testing the relative density of coarse-grained materials according to claim 2, characterized in that: In step 5, the net height of the density barrel is 70-90cm, and a sleeve of the same diameter with a height of 20-30cm is installed on the top.

6. The method for testing the relative density of coarse-grained materials according to claim 1, characterized in that: The layered sample preparation in step 6 is as follows: it is divided into at least four layers from bottom to top. The first layer is filled with particles with a diameter of less than 100 mm and an average layer thickness of 5 cm. The second to fourth layers are filled with particles with a diameter of not less than 100 mm and each layer is between 15-35 cm thick, with large-diameter particles placed alternately between layers.

7. The method for testing the relative density of coarse-grained materials according to claim 1, characterized in that: In step 8, the number of rolling passes with a dynamic settlement rate of 95% is determined as the number of test vibratory rolling passes, and the duration of the fixed-point micro-vibratory rolling is not less than 15 minutes.

8. The method for testing the relative density of coarse-grained materials according to claim 1, characterized in that: In step 10, the Marsal formula is used to calculate the particle breakage rate, and the allowable range of Marsal particle breakage rate is determined to be 0~10% when the coarse particle gradation does not change significantly.

9. A testing apparatus for implementing the coarse-grained material large relative density test method according to any one of claims 1-8, comprising a density barrel (1) and a sleeve (2), characterized in that: The density barrel (1) is a bottomed steel barrel, and the sleeve (2) is a steel ring that is detachably fitted on top of the density barrel (1). The density barrel (1) is provided with a first fixing ring (11), and the sleeve (2) is provided with a second fixing ring (21). When the sleeve (2) is fitted onto the density barrel (1), the sleeve (2) is fixed onto the density barrel (1) by the first fixing ring (11) and the second fixing ring (21).

10. The test apparatus according to claim 9, characterized in that: The density barrel (1) is provided with a first hook (12), and / or the sleeve (2) is provided with a second hook (22).

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