阅读说明：本技术 一种可变压振动最大干密度测量装置 (Variable-pressure vibration maximum dry density measuring device ) 是由 李建军 薛义飞 于 2021-07-16 设计创作，主要内容包括：本发明涉及土工试验技术领域,是一种可变压振动最大干密度测量装置；方案具体是采用反力架和弹簧的组合替代配重对试样顶部加载,实现加载压力可调节；通过校核弹簧刚度系数K、在试样筒内装填试样并确定施加试样顶部压力p-(0),测定振毕试样高度H-(0),计算试样的最大干密度ρ-(dmax)；本发明采用弹簧施压,不需要配重,可根据现场预加载压力调节顶部加载压力大小；用于测定无粘性土自由排水粗粒土和巨粒土的最大干密度；该装置可与振动台配合使用最大干密度,也可采用手动颠击法测量最大干密度。(The invention relates to the technical field of geotechnical tests, in particular to a device for measuring the maximum dry density of variable-pressure vibration; the scheme specifically comprises the steps that a counter-force frame and a spring are combined to replace a balance weight to load the top of a sample, so that the loading pressure is adjustable; by checking the spring rate K, filling the sample cylinder with the sample and determining the pressure p at the top of the sample 0 Measuring the height H of the sample after vibration 0 Calculating the maximum dry density rho of the sample dmax (ii) a The invention adopts the spring to apply pressure, does not need a counterweight, and can adjust the magnitude of top loading pressure according to the field preloading pressure; the method is used for measuring the maximum dry density of the cohesionless soil free-drainage coarse-grained soil and the giant-grained soil; the device can be matched with a vibration table to use the maximum dry density, and can also adopt a manual bumping method to measure the maximum dry density.)

1. The device for measuring the maximum dry density of variable-pressure vibration comprises a reaction frame, wherein a sleeve is fixed at the bottom of the reaction frame, and a sample cylinder (16) is fixed in the sleeve, and is characterized in that an adjustable pressure device is arranged right above the sample cylinder (16) and used for loading pressure on a sample to be measured in the sample cylinder (16); the adjustable pressure device comprises a hollow screw (8), and the hollow screw (8) is in threaded connection with a cross beam (6) of the reaction frame; the upper end of the hollow screw rod (8) is connected with a turntable (7), the lower end of the hollow screw rod is connected with an upper disc (12) through a bearing (10), and a lower disc (15) is connected under the upper disc (12) through a spring (13); the upper disc (12) and the lower disc (15) have the same diameter and can extend into the sample tube (16) along the inner wall; the number of the springs (13) is more than or equal to 3, the springs (13) are uniformly distributed on the periphery of the centers of the upper disc and the lower disc and are used for providing uniform pressure for the surface of a sample, and the pressure provided by the springs (13) is more than or equal to 14 kPa;

and the hollow screw (8) is used for placing a vernier depth gauge for depth measurement.

2. A variable pressure vibration maximum dry density measurement device according to claim 1, wherein the bearing (10) is fixed in a central opening of the upper disc (12).

3. The variable pressure vibration maximum dry density measuring device according to claim 1, wherein the reaction frame is an H-shaped beam reaction frame, the H-shaped beam reaction frame comprises a beam (6) and a double-threaded rod (3), the upper end of the double-threaded rod (3) is connected with the beam (6), and the lower end of the double-threaded rod is connected with the sleeve.

4. A variable pressure vibration maximum dry density measuring apparatus according to claim 3, wherein the sleeve comprises an upper sleeve (17) opened at the upper part and a lower sleeve (18) opened at the upper part, the sample tube (16) is sleeved between the upper sleeve (17) and the lower sleeve (18), and the lower sleeve (18) is fixed on the vibration table; the upper sleeve and the lower sleeve are assembled with the sample cylinder (16) and then fixed through a full threaded rod (1).

5. A variable pressure vibrating maximum dry density measuring device according to claim 4, wherein the lower end of the double-ended threaded rod (3) is connected to a lower sleeve (18).

6. A variable pressure vibration maximum dry density measuring device according to claim 3, wherein the periphery of the prepared hole (9) on the top surface of the beam (6) of the H-shaped beam reaction frame is embedded with a 360-degree dial (22), and the minimum index value is 1 degree.

7. A variable pressure vibration maximum dry density measuring device according to claim 1, wherein a guide rod (20) is arranged at the center of the spring (13) for controlling the vertical motion track of the lower disc (15) during vibration, the lower end of the guide rod (20) is fixed on the lower disc (15), and the upper end of the guide rod passes through the upper disc roller (21); the guide rod (20) is in sliding contact with the upper disc (12) through a roller (21) and is used for reducing the side friction of the guide rod (20); the rolling shaft (21) is fixedly embedded in a preformed hole of the upper disc (12).

Technical Field

The invention relates to engineering test equipment, in particular to geotechnical test equipment, and specifically relates to a variable-pressure vibration maximum dry density measuring device.

Background

The existing methods for measuring the dry density of coarse-grained soil and giant-grained soil comprise a surface vibration compactor method and a vibration table method. The two methods are all fixed loads, the loading pressures of different specifications are different in value, some methods adopt 18kPa, such as a road geotechnical test regulation (JTG 3430-2020), some methods also adopt 14kPa, such as a hydropower engineering coarse-grained soil test regulation (DL/T5356-2006), and the method also has the advantages that the top loading of a sample is not required for measuring the stacking compactness, such as gravel pebbles for construction (GB/T14685-. For coarse and large grained soils the compacted dry density is related to factors such as grading, moisture content, loading pressure, etc., the relationship between compacted dry density and loading pressure is such that as the loading pressure is increased from 7kPa to 200kPa, the compacted dry density increases first and then decreases. Thus, the following technical drawbacks arise in the actual engineering: firstly, the fixed pressure adopted in the indoor test cannot be matched with the grounding pressure of different construction machines on site, and the indoor test result cannot well guide the site construction; secondly, a test sample is loaded with sample cylinders with the internal diameters of 152mm and 280mm according to the top of 18kPa as a vibrating table method needs to be weighted on the top of the test sample, and the weights are respectively 32kg and 111 kg; thirdly, the high counter weight has potential safety hazard in vibration, and the labor intensity of testing personnel is also increased.

Disclosure of Invention

The invention overcomes the defects of the prior art and provides a variable-pressure vibration maximum dry density measuring device which is used for measuring cohesionless soil free-drainage coarse-grained soil and giant-grained soil.

In order to achieve the above object, the present invention is achieved by the following technical solutions.

A variable-pressure vibration maximum dry density measuring device comprises a reaction frame, wherein a sleeve is fixed at the bottom of the reaction frame, a sample cylinder is fixed in the sleeve, an adjustable pressure device is arranged right above the sample cylinder, and the adjustable pressure device is used for loading pressure on a sample to be measured in the sample cylinder; the adjustable pressure device comprises a hollow screw rod, and the hollow screw rod is in threaded connection with a cross beam of the reaction frame; the upper end of the hollow screw is connected with a turntable, the lower end of the hollow screw is connected with the upper disc through a bearing, and the lower disc is connected to the position right below the upper disc through a spring; the diameters of the upper disc and the lower disc are the same, and the upper disc and the lower disc can extend into the sample chamber along the inner wall of the sample chamber; the number of the springs is more than or equal to 3, the springs are uniformly distributed on the periphery of the centers of the upper disc and the lower disc and used for providing uniform pressure for the surface of a sample, and the pressure provided by the springs is more than or equal to 14 kPa; and the inside of the hollow screw is used for placing a vernier depth gauge for depth measurement.

Further, the bearing is fixed in the central opening of the upper disc.

Further, the reaction frame is an H-shaped beam reaction frame, the H-shaped beam reaction frame comprises a beam and a double-threaded rod, the upper end of the double-threaded rod is connected with the beam, and the lower end of the double-threaded rod is connected with the sleeve.

Furthermore, the sleeve comprises an upper sleeve with an upper opening and a lower sleeve with an upper opening, the sample cylinder is sleeved between the upper sleeve and the lower sleeve, and the lower sleeve is fixed on the vibration table; the upper sleeve and the lower sleeve are assembled with the sample cylinder and then fixed through a full threaded rod.

Furthermore, the lower end of the double-end threaded rod is connected with the lower sleeve.

Furthermore, a 360-degree dial scale is embedded on the periphery of a beam top surface preformed hole of the H-shaped beam reaction frame, and the minimum division value is 1 degree.

Furthermore, a guide rod is arranged at the center of the spring and used for controlling the vertical motion track of the lower disc in the vibration process, the lower end of the guide rod is fixed on the lower disc, and the upper end of the guide rod penetrates through the upper disc rolling shaft; the guide rod is in sliding contact with the upper disc through a rolling shaft and is used for reducing the side friction of the guide rod; the rolling shaft is fixedly embedded in the upper disc reserved hole.

A method for measuring maximum dry density of variable pressure vibration comprises the following steps:

a) checking the spring stiffness coefficient K: placing a pressure detection device in a sample cylinder, rotating a turntable to enable a lower disc to be closely attached to the surface of the pressure detection device, rotating the turntable to apply an initial load, then unloading, inserting a vernier depth gauge into a hole in the top of a hollow threaded rod, enabling the vernier depth gauge to be in bottom contact with the top surface of the lower disc, and recording an initial reading L of the vernier depth gauge₀Rotating the turntable for n circles to obtain loading pressure p, inserting the vernier depth gauge into the hollow threaded rod again and contacting the top surface of the lower disc, recording the reading L of the vernier depth gauge, and calculating the spring stiffness coefficient K:

K=p/(L₀-L)= p/（nx） （Ӏ）

in the formula: x is the pitch of the hollow screw.

Obtaining a relation formula (II) between the spring loading pressure and the number n of the rotating turnplate rotation numbers from the formula Ӏ:

p=n（Kx）=K (L₀-L) （Ⅱ）。

b) after the pressure detection device was taken out, the sample was filled in the sample cartridge, and the applied sample top pressure p: recording initial reading L of vernier depth gauge according to the method of step a₀Rotating the turntable for n circles, and measuring the reading L of the vernier depth gauge corresponding to the compressed spring; determination of the specimen top loading pressure p from equation (II)₁(ii) a Determining the sample top loading pressure p according to the step a after the sample is vibrated₂；p₁And p₂The average value of (d) is the top loading pressure p.

c) Measuring height H of sample after vibration₀(ii) a Calculating the maximum dry density ρ_dmax。

Further, maximum dry density ρ_dmaxComprises the following steps:

ρ_dmax=1.274M_d/（D²×H₀） （Ⅲ）

in the formula: m_dThe sample mass; d is the inner diameter of the sample cylinder; h₀Is the specimen height.

Further, the vibration of the sample is performed by vibration of a vibration table or manual vibration.

Further, the height H of the sample after the shaking is measured₀Then, measuring the water content of the sample; calculating the maximum dry density rho of the sample according to the formula (IV)_dmax：

ρ_dmax=1.274M _f /（H₀×D²×（1+0.01ω）） （Ⅳ）

In the formula: m _f Air-drying the sample quality; omega is the water content of the sample; d is the inner diameter of the sample cylinder; h₀Is the specimen height.

Compared with the prior art, the invention has the following beneficial effects:

(1) the invention adopts the spring to apply pressure, does not need a counterweight, and can adjust the top loading pressure according to the field preloading pressure.

(2) The invention can be directly used by matching with the existing vibrating table in a laboratory, thereby saving the cost.

(3) According to the invention, the spring is used for replacing the balance weight when the top of the sample is loaded, so that the potential safety hazard in vibration is reduced, and the labor intensity of testing personnel is reduced.

(4) The invention has simple structure and light weight, is suitable for field construction test, and can realize the maximum dry density test of the granular soil without a vibrating table.

Drawings

Fig. 1 is a schematic structural view of the dry density measuring apparatus according to the present invention.

Fig. 2 is a schematic structural view of an upper sleeve of the dry density measuring device of the present invention.

Fig. 3 is a schematic structural diagram of a sample cylinder of the dry density measuring device of the present invention.

Fig. 4 is a schematic view of the lower sleeve structure of the dry density measuring device of the present invention.

FIG. 5 is a schematic view of the dry density measurement device of the present invention at the beam dial.

FIG. 6 is a schematic view of the connection portion of the upper and lower plates of the dry density measuring apparatus according to the present invention.

In the figure, 1 is a full threaded rod, 2 is a reserved threaded rod, 3 is a double-threaded rod, 4 is a reserved hole, 5 is a nut, 6 is an upper beam, 7 is a rotary table, 8 is a hollow threaded rod, 9 is a reserved threaded hole, 10 is a bearing, 11 is a top orifice of the hollow threaded rod, 12 is an upper disc, 13 is a spring, 14 is a rubber shield, 15 is a lower disc, 16 is a sample cylinder, 17 is an upper sleeve, 18 is a lower sleeve, 19 is a vibrating table, 20 is a guide rod, 21 is a roller and 22 is a dial.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail with reference to the embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of the present invention are described in detail below with reference to the embodiments and the drawings, but the scope of protection is not limited thereto.

Example 1

As shown in fig. 1, the present embodiment is a vibration pressure-adjustable maximum dry density measuring apparatus for measuring cohesionless soil free-drainage coarse-grained soil and giant-grained soil, which mainly comprises: a vibration table 19, a sample cylinder 16, an upper sleeve 17, a lower sleeve 18, an adjustable pressure device and a vernier depth gauge.

A vibration table: the table size of the vibration table 19 is not less than 500mm × 500mm, and has sufficient rigidity. The frequency of the vibration table is adjustable from 30Hz to 50Hz, the double amplitude is adjustable from 0mm to 2mm, and the maximum load of the vibration table meets the quality requirements of the sample cylinder 16, the upper sleeve 17, the lower sleeve 18, the sample, the adjustable pressure device and the like. The vibration table 19 is fixed on the concrete foundation.

As shown in fig. 3, the sample tube 16 is a cylindrical metal tube with a wall thickness of not less than 5mm and the dimensions selected from table 1. The sample cartridge 16 is sealed at the bottom, but removable.

The sleeve comprises an upper sleeve 17 and a lower sleeve 18. As shown in fig. 2, the inner diameter of the upper sleeve 17 is matched with the sample tube 16, and is in linear connection with the inner wall of the sample tube 16 after being tightly fixed. As shown in FIG. 4, the lower sleeve 18 is fixed on the top of the vibrating table 19, the inner diameter of the sleeve is matched with the outer diameter of the sample tube 16, the height is not less than 30mm, the wall thickness is the same as that of the sample tube 16, the upper sleeve 17 is connected with the sample tube 16 by a 'gamma' interface, and the upper sleeve and the lower sleeve are fixed by a full threaded rod 1 after being assembled with the sample tube 16.

The adjustable pressure device comprises: comprises an H-shaped beam reaction frame, a turntable 7, a hollow threaded rod 8, a bearing 10, an upper disc 12, a spring 13, a rubber shield 14 and a lower disc 15. The H-shaped beam reaction frame consists of a double-threaded rod 3, a nut 5 and a beam 6, and the double-threaded rod 3 is fixed on the lower sleeve 18 through a reserved threaded hole 2. The lower sleeve 18 and the vibration table 19 are fixed in a reliable connection mode. The upper end of the double-threaded rod 3 is connected with the cross beam 6 through a bolt, the hollow threaded rod 8 penetrates through a reserved threaded hole 9 in the cross beam 6, the lower end of the hollow threaded rod is connected with a bearing 10, and the upper end of the hollow threaded rod is connected with the turntable 7. The bearing 10 is fixed in the central opening of the upper disc 12, the lower disc 15 is fixed under the upper disc through the spring 13, the springs 13 are uniformly distributed outside the centers of the upper disc and the lower disc, the distance from the centers of the upper disc and the lower disc is 1/2, no less than 3 springs 13 can provide pressure no less than 14kPa, and the springs 13 are connected with the upper disc and the lower disc through bolts. A guide rod 20 is arranged in the center of the spring 13, the lower end of the guide rod 20 is fixed on a lower disc, the upper end of the guide rod 20 penetrates through an upper disc roller 21, the roller 21 is fixedly embedded in a preformed hole of the upper disc 12, and the guide rod 20 is in sliding contact with the upper disc 12 through the roller 21. The diameters of the upper and lower disks are the same and slightly smaller than the inner diameters of the sample cylinder 16 and the sleeve, the rigidity is large enough, and the lower disk 15 can move freely in the sample cylinder in the loading process.

Vernier depth scale: the length of the rotary table meets the requirement that the distance between the lower disc 15 and the top surface of the rotary table 7 is plus 3cm, and the precision is 0.02 mm.

Example 2

Is a method for measuring the maximum dry density using the measuring device described in example 1: and (3) measuring the maximum dry density of the granular soil by matching with a vibration table.

The test procedure is carried out according to the shaking table method in T0132-1996 of road soil engineering test regulation (JTG 3430-2020).

1. The size of the selected table board is not less than 500mm multiplied by 500mm of the vibration table 19, the frequency of the vibration table 19 is adjustable from 30Hz to 50Hz, the double amplitude is adjustable from 0mm to 2mm, the table board of the vibration table 19 has enough rigidity, and the vibration table 19 is fixed on a concrete foundation.

2. And (2) collecting a representative sample, determining the particle percentage of each particle group by adopting a standard screening method (T0115-2007), screening out the granular soil with the particle size of more than 20mm by using a standard square-hole sieve with the diameter of 20mm, and limiting the mass percentage of dry particles passing through the standard sieve with the diameter of 0.075mm to be not more than 15%, so as to obtain the granular soil with the particle size of 20 mm-0.075 mm, and storing the granular soil properly for later use. Before the test, the prepared granular soil is put into an oven, the soil sample is dried at the temperature of 105-110 ℃, cooled to room temperature, uniformly stirred, roughly divided into three parts, and kept dry.

3. The sample tube 16 with the inner diameter of 152mm is selected, and the lower sleeve 18 matched with the outer diameter of the sample tube 16 is selected at the same time, and the mass of the sample tube 16 is weighed. The lower sleeve 18 is fixed with the vibrating table 19, the sample tube 16 is placed in the lower sleeve 18, the bottom of the sample tube 16 is closely attached to the lower sleeve 18, then the upper sleeve 17 is placed at the top, and the whole fixing is carried out through the full threaded rod 1.

4. And selecting the top loading pressure of the sample, and installing an adjustable pressure device. The H-shaped beam reaction frame of the pressure-adjustable device is fixed in a reserved threaded hole 2 of a lower sleeve 18 through a double-threaded rod 3, and the lower sleeve 18 and a vibrating table 19 are fixed in a reliable connection mode. The upper end of the double-threaded rod 3 is connected with the cross beam 6 through a bolt, the hollow threaded rod 8 penetrates through a reserved threaded hole 9 of the cross beam 6, the lower end of the hollow threaded rod is connected with a bearing 10, and the upper end of the hollow threaded rod is connected with the turntable 7. An upper disc 12 and a lower disc 15 which are matched with the inner diameter of a sample cylinder 16 are selected, the diameter of the upper disc and the lower disc is slightly smaller than the inner diameter of the sample cylinder 16 by 2mm, a bearing 10 is fixed in a central opening of the upper disc 12, the lower disc 15 is fixed below the upper disc 12 through a spring 13, the springs 13 are uniformly distributed on the outer sides of the centers of the upper disc and the lower disc at a distance of 1/2 from the center and not less than 3, the springs 13 are connected with the upper disc and the lower disc through bolts, and a guide rod 20 is arranged in the center of each spring 13. The stiffness of the spring 13 is selected according to the field loading pressure so that the loading pressure of the spring 13 meets the field pre-compaction pressure. The pitch of the hollow threaded rod 8 is x in mm.

5. The stiffness coefficient K of the spring 13 is checked. Placing a force measuring sensor in the center of a sample cylinder 16, rotating a turntable 7 to enable a lower disc 15 to be closely attached to the surface of the force measuring sensor of the sample, rotating the turntable 7 clockwise for 2 circles to apply initial load, then anticlockwise rotating for 2 circles to unload, enabling the reading of the force measuring sensor to return to zero, inserting a vernier depth gauge into a hole in the top of a hollow threaded rod 8, enabling the vernier depth gauge to be inserted into the bottom of the hole to be in contact with the top surface of the lower disc, and recording the initial reading L of the vernier depth gauge₀And the unit mm, taking out the vernier depth gauge. And rotating the turntable 7 clockwise for N circles, recording the reading p of the force measuring sensor, enabling the loading pressure p to be not less than the unit N of the field preloading pressure, inserting the vernier depth gauge into the top hole 11 of the hollow threaded rod 8 again, enabling the vernier depth gauge to contact the top surface of the lower disc at the bottom, and recording the reading L of the vernier depth gauge in unit mm. The measurements were thus carried out 3 times, and the spring rate K in N/mm was calculated using the average value.

K=p/(L₀-L)= p/（nx） （1）

In the formula: x is the pitch, mm.

The relation formula (2) between the spring loading pressure and the number n of the rotation turns of the rotating disk 7 is obtained:

p=n（Kx）=K (L₀-L) （2）

6. and (6) filling the sample. Taking a portion of the prepared dried sample, slowly filling the prepared sample into a test cylinder with a spatula or funnel, and taking care to minimize particle separation (preferably the filling amount is such that the sample after compacting is equal to or slightly lower than 1/3; and (4) smoothing the surface of the sample. The wall of the test tube can then be tapped several times with a rubber hammer or the like to allow the sample to sink.

7. Applying a sample top pressure p according to the magnitude of the on-site pre-applied pressure₀And determining the estimated number n of the rotation turns of the turntable 7 according to the formula (2). Installing an upper sleeve 17 on the upper part of a sample cylinder 16, rotating the rotary table 7 to enable the lower disc 15 to be closely attached to the surface of a sample, rotating the rotary table 7 clockwise for 2 circles, applying an initial load, then rotating counterclockwise for 2 circles for unloading, inserting a vernier depth gauge into the top opening 11 of the top of the hollow threaded rod 8, enabling the vernier depth gauge to be in contact with the top surface of the lower disc 15 at the bottom, and recording an initial reading L of the vernier depth gauge₀. The rotary table 7 is rotated clockwise for n turns, and then the vernier depth gauge is used to measure the length L corresponding to the compressed spring. The actual loading pressure p of the top of the sample can be determined by the formula (2)₁。

8. And opening a switch of the vibration table to start vibration, wherein the vibration time is 6 min.

9. Measuring the spring expansion amount again after the vibration is finished, and determining the top loading pressure p of the sample after the vibration according to the formula (2)_2，Get p₁And p₂As the actual top loading pressure p_{Fruit of Chinese wolfberry}Calculating p_{Fruit of Chinese wolfberry}And p₀The absolute value of the range difference is not more than 10 percent, the requirement is met, the next step is carried out, and otherwise, the test is carried out again. .

10. And repeating the 6 th step to the 8 th step, and carrying out vibration compaction on the samples on the second layer and the third layer.

11. The upper sleeve 17 is removed. A straight steel strip is placed on the diameter position of the sample cylinder 16, and the height of the sample after the vibration is finished is measured. Preferably, the readings are at least four and are uniformly distributed on the surface of the sampleMeasuring to 0.5mm at a distance of 15mm from the cylinder wall, recording and calculating the height H of the sample₀。

12. The sample cylinder 16 and the sample are taken out and weighed. Deducting the mass of the sample tube 16 to obtain the mass M of the sample_dCalculating the maximum dry density rho according to the formula (3)_dmaxCalculated to 0.001.

ρ_dmax=1.274M_d/（D²×H₀） （3）

In the formula: m_dKg for the dried sample mass; d is the inner diameter of the sample cylinder, m; h₀Is the sample height, m.

13. Taking out the dried sample again, repeating the steps 6-12 for 2 times, and measuring the maximum dry density rho_dmax. In the test, enough representative samples must be prepared and the individual samples must not be repeatedly vibrocompacted.

14. The maximum dry density values determined in three runs were averaged to give the maximum dry density value reported in the test.

Example 3

In-situ measurement of maximum dry density by manual bumping

The method is consistent with the loading device adopted by the vibration table method of the embodiments 1 and 2, and the measuring steps are basically consistent, and the differences are that:

1. in order to test the compact packing density of the granular soil under the condition that no vibration table is arranged on the site, an H-shaped beam reaction frame of the pressure-adjustable device is directly connected with a lower sleeve 18 through a double-threaded rod 3.

2. The sample bumping and compacting method refers to a method for measuring the maximum dry density by using crushed stone pebbles for construction (GB/T14685-. In example 2, after the first charge, a round bar of 16mm diameter was placed under the lower sleeve 18, and the sample container 16 and the adjustable pressure device were pressed together, and the two were alternately flipped left and right 25 times. The second layer is loaded and the second layer is similarly compacted (but the direction of the round bar under the lower sleeve 18 is perpendicular to that of the first layer) after filling, and then the third layer is loaded and the third layer is similarly compacted (but the direction of the round bar under the lower sleeve is parallel to that of the first layer) after filling.

Example 4:

the rest of this case is the same as the embodiments 1 and 2, except that: (1) air-drying the sample; (2) after the vibration stacking density test is finished, drying the sample, and measuring the water content of the sample; (3) calculating the maximum dry density rho of the sample according to the formula (4)_dmax。

ρ_dmax=1.274M _f /（H₀×D²×（1+0.01ω）） (4)

In the formula: m _f Kg for air-dried sample mass; omega is the water content,%; the other symbols are as above.

While the invention has been described in further detail with reference to specific preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.