阅读说明：本技术 一种可变压内部振动紧密堆积密度测量方法 (Variable-pressure internal vibration compaction packing density measurement method ) 是由 李建军 刘钰浩 张帅 耿少波 冯浩 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,是一种可变压内部振动紧密堆积密度测量方法；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；在试样筒内设置振动器,实现试样的内部振动；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,测定振毕试样高度H-(0),计算试样的紧密堆积密度ρ；本发明直接实现试样的内部振动,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；适宜野外现场紧密堆积密度测试。(The invention relates to the technical field of geotechnical tests, in particular to a method for measuring variable-pressure internal vibration compaction packing density; 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; a vibrator is arranged in the sample cylinder to realize the internal vibration of the sample; checking the spring stiffness coefficient K, filling the sample in the sample cylinder, determining the top pressure p of the sample, and measuring the height H of the sample after finishing vibration 0 Calculating the compact packing density rho of the sample; the invention directly realizes the internal vibration of the sample, adopts the spring to apply pressure, does not need a counterweight, and can adjust the top loading pressure according to the site preloading pressure; the method is suitable for field compact packing density test.)

1. A variable-pressure internal vibration compaction packing density measurement method is characterized by comprising the following steps:

a) checking the spring stiffness coefficient K: loading pressure on a sample to be tested in the sample cylinder (16) through an adjustable pressure device above the sample cylinder (16); a vibrator is fixed at the bottom in the sample cylinder (16), the pressure-adjustable device comprises a hollow screw (8), the upper end of the hollow screw (8) is connected with a turntable (7), the lower end of the hollow screw is connected with an upper disc (12), and a lower disc (15) is connected to the position right below the upper disc (12) through a spring (13); placing a pressure detection device in a sample cylinder (16), rotating a rotary table (7) to enable a lower disc (15) to be closely attached to the surface of the pressure detection device, rotating the rotary table (7) to apply initial load and then unloading, inserting a vernier depth gauge into a hole in the top of a hollow threaded rod (8) and enabling the vernier depth gauge to be in contact with the top surface of the lower disc (15), and recording initial reading L of the vernier depth gauge₀And rotating the turntable (7) for n circles to obtain loading pressure p, inserting the vernier depth gauge into the hollow threaded rod (8) again and contacting the top surface of the lower disc (15), 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 screw 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) determining a compacted bulk density top loading pressure p from a field compaction preload pressure₀Determining the number n of rotation turns of the rotating turntable (7) by a formula (II);

c) after the pressure measuring device is removed, a sample is filled in the sample cylinder (16), and the initial reading L of the vernier depth gauge is recorded according to the method of step a₀Then the rotating disc (7) is rotated for n circles, the reading L of the vernier depth gauge corresponding to the compressed spring is measured, and the actual loading pressure p is calculated according to the formula (II)₁(ii) a Starting a vibrator to vibrate and densify the sample, then measuring the reading L of the vernier depth gauge again according to the step a, and checking the top loading pressure p of the sample after vibration according to the formula (II)₂；p₁And p₂Is taken as the actual loading pressure p on the top of the test specimen_{Fruit of Chinese wolfberry}Requires p_{Fruit of Chinese wolfberry}And p₀The absolute value of the range difference is not more than 10%; the vibration time is 5-8 min;

d) measuring height H of sample after vibration₀(ii) a The close packing density ρ is calculated.

2. The variable pressure internal vibration compaction packing density measurement method according to claim 1, wherein a sample tube (16) is fixed in a sleeve, the sleeve comprises an upper sleeve (17) with an upper opening and a lower sleeve (18) with an upper opening, the sample tube (16) is opened up and down, and the sample tube (16) is sleeved between the upper sleeve (17) and the lower sleeve (18);

the close packing density ρ is:

ρ=1.274Md/(D²H₀-d²h) （Ⅲ）

in the formula: m _d Drying the sample mass; d and D are respectively the inner diameter of the sample cylinder (16) and the outer diameter of the vibrator; h₀For the height of the sample, h is the top end of the vibrator relative to the lower sleeve: (18) The height of the bottom.

3. The method of claim 1, wherein the height H of the vibrated sample is determined₀Then, measuring the water content of the sample; and (3) calculating the compact packing density rho of the sample according to the formula (IV):

ρ=1.274M_f/（（D² H₀-d² h）·（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; d is the outer diameter of the vibrator; h₀Is the specimen height.

4. The method for measuring the variable-pressure internal vibrating-compacting packing density according to claim 1, wherein 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 and lower disks for providing uniform pressure to the surface of the sample, and the pressure provided by the springs (13) is more than or equal to 14 kPa.

5. The method of claim 1, wherein the top of the vibrator is not less than 5cm below the top of the sample container (16).

6. The variable pressure internal vibratory compaction density measurement method according to claim 1, wherein the vibrator is an electric bar vibrator.

Technical Field

The invention relates to an engineering test method, in particular to a cohesionless soil test method, and specifically relates to a variable-pressure internal vibration compaction packing density measurement method.

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: thus, the following technical drawbacks arise in the actual engineering: first, it cannot be used in the field; second, sample top pressure cannot be applied based on the field preload pressure; thirdly, a test sample top is weighted according to the vibrating table method, 18kPa is loaded on the top, the inner diameter is 152mm, the inner diameter is 280mm, and the weights are respectively 32kg and 111 kg; 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 internal vibration compaction packing density measuring method 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 internal vibration compaction packing density measuring method comprises the following steps:

a) checking the spring stiffness coefficient K: loading pressure on a sample to be tested in the sample cylinder through an adjustable pressure device above the sample cylinder; a vibrator is fixed at the bottom in the sample cylinder, the pressure-adjustable device comprises a hollow screw, the upper end of the hollow screw is connected with a turntable, the lower end of the hollow screw is connected with an upper disc, and a lower disc is connected under the upper disc through a spring; in the sample cylinderPlacing a pressure detection device, rotating the rotary table to make the lower disc closely attached to the surface of the pressure detection device, rotating the rotary table to apply an initial load, unloading the pressure detection device, inserting the vernier depth gauge into the hollow threaded rod from the top opening of the hollow threaded rod to make the vernier depth gauge contact with the top surface of the lower disc at the bottom, 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) determining a compacted bulk density top loading pressure p from a field compaction preload pressure₀And the number n of the rotation turns of the rotating turntable (7) is determined by the formula (II).

c) After the pressure detection device is taken out, a sample is filled in the sample cylinder, and the initial reading L of the vernier depth gauge is recorded according to the method of the step a₀Rotating the turntable for n turns, measuring the reading L of the vernier depth gauge after the spring is compressed, and calculating the actual loading pressure p according to the formula (II)₁(ii) a Starting a vibrator to vibrate and densify the sample, then measuring the reading L of the vernier depth gauge again according to the step a, and checking the top loading pressure p of the sample after vibration according to the formula (II)₂；p₁And p₂Is taken as the actual loading pressure p on the top of the test specimen_{Fruit of Chinese wolfberry}Requires p_{Fruit of Chinese wolfberry}And p₀The absolute value of the range difference is not more than 10%; the vibration time is 5-8 min.

d) Measuring height H of sample after vibration₀(ii) a The close packing density ρ is calculated.

Preferably, the sample cylinder is fixed in the sleeve, the sleeve comprises an upper sleeve with an upper opening and a lower sleeve with an upper opening, the sample cylinder is opened up and down, and the sample cylinder is sleeved between the upper sleeve and the lower sleeve; wherein the close packing density ρ is:

ρ=1.274Md/(D²H₀-d²h) （Ⅲ）

in the formula: m _d Drying the sample mass; d and D are the inner diameter of the sample cylinder and the outer diameter of the vibrator respectively; h₀The height of the sample is h, and the height of the top end of the vibrator relative to the bottom of the lower sleeve is h.

Measuring height H of sample after vibration₀Then, measuring the water content of the sample; and (3) calculating the compact packing density rho of the sample according to the formula (IV):

ρ=1.274M_f/（（D² H₀-d² h）·（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; d is the outer diameter of the vibrator; h₀Is the specimen height.

Furthermore, 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 the sample, and the pressure provided by the springs is more than or equal to 14 kPa.

Furthermore, the top of the vibrator is more than or equal to 5cm lower than the top of the sample cylinder.

Further, the vibrator is an electric rod vibrator.

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 directly realize the internal vibration of the sample and is suitable for various complex environments.

(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 does not need anchoring and is suitable for testing the field compact packing density.

Drawings

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

Fig. 2 is a schematic structural view of an upper sleeve of the bulk density measuring apparatus according to the present invention.

Fig. 3 is a schematic structural view of a sample cartridge of the bulk density measuring apparatus according to the present invention.

Fig. 4 is a schematic view of the lower sleeve structure of the bulk 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, 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 power cord, 20 is a rubber sleeve, and 21 is an electric rod vibrator.

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 is a method for measuring cohesive soil compact bulk density, specifically using a variable pressure internal vibration compact bulk density measuring device, specifically a top pressure internal vibration method to determine the compact bulk density of granular soil.

As shown in figure 1, the variable-pressure internal vibration compaction packing density measuring device adopted by the method is used for measuring cohesionless soil free-drainage coarse-grained soil and giant-grained soil, and the device mainly comprises: an electric rod vibrator 21, a sample tube 16, an upper sleeve 17, a lower sleeve 18, an adjustable pressure device and a vernier depth gauge.

As shown in fig. 3, the sample tube 16 is a cylindrical metal tube without a lower bottom, has a wall thickness of not less than 5mm, and has the dimensions selected according to table 1.

As shown in fig. 2 and 4, the sleeve includes an upper sleeve 17 and a lower sleeve 18. 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. The inner diameter of the upper sleeve and the lower sleeve is matched with the outer diameter of the sample cylinder 16, the height is not less than 30mm, the wall thickness is the same as that of the sample cylinder 16, the upper sleeve 17 is connected with the sample cylinder 16 through a gamma interface, and the upper sleeve and the lower sleeve are assembled with the sample cylinder 16 and then fixed through a full threaded rod 1.

Electric bar vibrator: the diameter of the cylindrical vibrator is 30 mm-50 mm, the length of the cylindrical vibrator is at least 5cm lower than the height of the sample cylinder 16, the vibration frequency is adjustable from 30Hz to 60Hz, the radius of vibration action is not less than 300mm, and the distance from the outer wall of the rod type vibrator to the inner wall of the sample cylinder is not less than. As shown in fig. 4, the electric rod vibrator 21 is fixed at the bottom of the lower sleeve 18 through a rubber sleeve 20 and is connected with an external power supply through a power cord 19, and the power supply adopts 380V and 50 Hz.

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 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. 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.

The specific measurement steps are as follows:

1. taking 20mm inviscid soil as an example of the maximum size fraction, collecting a representative sample, determining the particle percentage of each particle group by adopting a standard screening method (T0115-2007), screening out the particle soil with the particle size larger than 20mm by using a 20mm standard square-hole screen, and simultaneously limiting the mass percentage of dry particles passing through a 0.075mm standard screen to be not more than 15%, so that the particle soil with the particle size of 20 mm-0.075 mm is obtained, and the particle soil is properly stored for later use. Before testing, the prepared granular soil is put into an oven, the soil sample is dried at 105-110 ℃, cooled to room temperature, uniformly stirred and kept dry.

2. The effective volume is not less than 2830cm³And a lower sleeve 18 is selected to match the outer diameter of the sample tube 16. An electric rod type vibrator 21 is fixed to a central insertion hole in the bottom of a lower sleeve 18 through a rubber sleeve 20, a sample cylinder 16 is placed in the lower sleeve 18, the bottom of the sample cylinder 16 is tightly attached to the lower sleeve 18, the integral mass of the sample cylinder 16 and the lower sleeve 18 is weighed, then an upper sleeve 17 is placed on the top, and the upper sleeve, the lower sleeve and the sample cylinder 16 are fixed through a full threaded rod 1.

3. 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. 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, and the spring 13 is connected with the upper disc and the lower disc through bolts. 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.

4. The stiffness coefficient K of the spring 13 is checked. Two force sensors with the same specification and model are symmetrically arranged in a sample cylinder 16, a rotary table 7 is rotated to enable a lower disc 15 to be closely attached to the surface of the sample force sensor, the rotary table 7 is rotated clockwise for 2 circles to apply initial load, then the rotary table is rotated anticlockwise for 2 circles to unload, and the force sensors readThe number is reset to zero, the vernier depth gauge is inserted into the top hole 11 of the hollow threaded rod 8, the bottom of the vernier depth gauge is contacted with the top surface of the lower disc 15, and the initial reading L of the vernier depth gauge is recorded₀And 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 transducer, 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 15 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）

5. and (6) filling the sample. And (3) taking the prepared dried sample, slowly filling the prepared sample into a sample cylinder by using a small shovel or a funnel, wherein the height of the filler is not less than 4cm higher than the top surface of the electric rod type vibrator 21 and not more than 1cm lower than the upper edge of the sample cylinder, and the particle separation degree is minimized by paying attention to the filler, so that the surface of the sample is leveled.

6. Applying a sample top pressure p according to the magnitude of the on-site pre-applied pressure₀And the number n of the rotation turns of the rotating turntable (7) is determined by the formula (II). 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。

7. The power supply is connected through a power line 19, a vibrating rod switch is turned on, vibration is started, and the vibration time is 6 min.

8. 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 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.

9. 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. The reading is preferably measured and accurate to 0.5mm from four positions which are uniformly distributed on the surface of the sample and are at least 15mm away from the cylinder wall, and the height H of the sample is recorded and calculated₀. And measuring and recording the mass of the whole sleeve, the sample cylinder 16 and the sample, and deducting the whole sleeve mass under the sample cylinder 16 to obtain the sample mass M. When the volume is calculated, the volume of the vibrating rod and the volume of the rubber sleeve are deducted, and the compact packing density rho is calculated to be 0.001 according to the formula (3).

ρ=1.274M _d /(D²H₀-d²h) (3)

In the formula: m _d Kg for the dried sample mass; d and D are the inner diameter of the sample cylinder 16 and the outer diameter, m, of the electric rod vibrator 21, respectively; h₀The height of the sample, m, h, is the height of the tip of the vibrating rod relative to the bottom of the lower sleeve 18.

10. And taking out the dried sample again, repeating the steps 6-9 for 2 times, and determining the compact packing density rho. In the test, enough representative samples must be prepared and the individual samples must not be repeatedly vibrocompacted.

11. The three measurements of the close-packing density were averaged to give the test reported close-packing density value.

Example 3

The method is otherwise identical to that of example 2, except for the following points:

(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) and (4) calculating the compact packing density rho of the sample according to the formula (4).

ρ=1.274M _f /（（D² H₀-d² h）（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.