CN113686727B - A variable pressure internal vibration close packing density measurement method - Google Patents

Abstract

The invention is thatThe method relates to the technical field of geotechnical tests, in particular to a variable pressure internal vibration close packing density measurement method; the scheme is that a counter-force frame and a spring are combined to replace a counterweight to load the top of a sample, so that the loading pressure is adjustable; a vibrator is arranged in the sample barrel to realize the internal vibration of the sample; measuring the height H of the vibration-finished sample by checking the spring rate K, filling the sample in the sample cylinder and determining the top pressure p of the applied sample ₀ Calculating the close 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 on-site pre-loading pressure; the method is suitable for field tight packing density test.

Description

A variable pressure internal vibration close packing density measurement method

Technical field

The present invention relates to engineering testing methods, in particular to non-cohesive soil geotechnical testing methods, specifically a variable pressure internal vibration close packing density measurement method.

Background technique

Existing methods for measuring the dry density of coarse-grained soil and large-grained soil include the surface vibration compactor method and the shaking table method. The loading pressures of these two methods are fixed loads, and the loading pressure values are different in different specifications. Some specifications take 18kPa, such as Highway Geotechnical Test Regulations (JTG3430-2020), and some specifications take 14kPa, such as Hydropower and Water Conservancy Engineering Coarse-Grained Soil Test Regulations. (DL/T5356-2006), and the measurement of packing density does not require top loading of the sample, such as gravel and pebbles for construction (GB/T 14685-2011). For coarse-grained soil and large-grained soil, the compacted dry density is related to factors such as gradation, moisture content, and loading pressure. The relationship between the compacted dry density and the loading pressure is that when the loading pressure increases from 7kPa to 200kPa, the compacted dry density increases first. then decrease. As a result, the following technical defects arise in actual engineering: First, it cannot be used in the field; second, the top pressure of the specimen cannot be applied according to the on-site preloading pressure; third, it cannot be used in the field. , the vibration table method requires a counterweight on the top of the test sample, and the top load is 18kPa. The inner diameter of the sample barrel is 152mm and 280mm, and the counterweights are 32kg and 111kg respectively. High counterweights pose safety hazards during vibration and also increase the number of test personnel. labor intensity.

Contents of the invention

The present invention overcomes the shortcomings of the prior art and proposes a variable pressure internal vibration close packing density measurement method for measuring cohesive soil free drainage coarse-grained soil and giant-grained soil.

In order to achieve the above objects, the present invention is achieved through the following technical solutions.

A variable pressure internal vibration close packing density measurement method. The specific measurement method includes the following steps:

a) Check the spring stiffness coefficient K: Apply pressure to the sample to be tested in the sample cylinder through an adjustable pressure device above the sample cylinder; a vibrator is fixed at the bottom of the sample cylinder, and the adjustable pressure device includes Hollow screw, the upper end of the hollow screw is connected to a turntable, the lower end is connected to the upper plate, and the lower plate is connected directly below the upper plate through a spring; a pressure detection device is placed in the sample tube, and the turntable is rotated to make the lower plate and The surface of the pressure detection device is closely attached. Turn the turntable to apply an initial load and then unload it. Insert the vernier depth gauge from the top hole of the hollow threaded rod into the bottom to contact the top surface of the lower plate. Record the initial reading L ₀ of the vernier depth gauge. Turn the turntable n times. Obtain the loading pressure p, insert the vernier depth gauge from the hollow threaded rod again and contact the top surface of the lower plate, record the reading L of the vernier depth gauge, and calculate the spring stiffness coefficient K:

K=p/(L ₀ -L)= p/（nx）（　）

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

The relationship formula (II) between the spring loading pressure and the number of turns n of the rotating turntable is obtained from the formula:

p=n(Kx)=K (L ₀ -L) (II).

b) Determine the top loading pressure p ₀ of the close packing density based on the on-site compaction preload pressure, and determine the number of turns n of the rotating turntable (7) according to formula (II).

c) After taking out the pressure detection device, load the sample into the sample cylinder, record the initial reading L ₀ of the vernier depth gauge according to the method in step a, then rotate the turntable n times, and measure the corresponding reading of the vernier depth gauge after the spring is compressed. L, calculate the actual loading pressure p ₁ according to formula (II); turn on the vibrator to vibrate the sample densely, then re-measure the reading L of the vernier depth gauge according to step a, and check the top load after the sample is vibrated according to formula (II) Pressure p ₂ ; the average value of p ₁ and p ₂ is _used as the actual loading pressure p on the top of the sample. It is required that the absolute value of the range between p _real and p ₀ does not exceed 10%; the vibration time is 5-8 minutes.

d) Determine the height H ₀ of the vibrated sample; calculate the close packing density ρ.

Preferably, the sample tube is fixed in the sleeve, and the sleeve includes an upper sleeve with upper and lower openings and a lower sleeve with upper openings. The sample sleeve has upper and lower openings, and the sample sleeve is sleeved on the upper sleeve and the lower sleeve. between sleeves; where the close packing density ρ is:

ρ=1.274M d /(D ² H ₀ -d ² h) (Ⅲ)

In the formula: M _d is the mass of the dried sample; D and d are the inner diameter of the sample cylinder and the outer diameter of the vibrator respectively; H ₀ is the height of the sample, and h is the height of the top of the vibrator relative to the bottom of the lower sleeve.

After measuring the height H ₀ of the vibrated sample, measure the moisture content of the sample; calculate the close packing density ρ of the sample according to formula (IV):

ρ=1.274M _f / ((D ² H ₀ -d ² h)·(1+0.01ω)) (IV)

In the formula: M _f is the mass of the air-dried sample; ω is the moisture content of the sample; D is the inner diameter of the sample cylinder; d is the outer diameter of the vibrator; H ₀ is the height of the sample.

Further, the number of the springs is ≥ 3, and the springs are evenly distributed around the center of the upper and lower plates to provide uniform pressure to the surface of the sample, and the pressure provided by the springs is ≥ 14 kPa.

Further, the top of the vibrator is ≥5cm lower than the top of the sample tube.

Further, the vibrator is an electric rod vibrator.

The beneficial effects produced by the present invention compared with the existing technology are:

(1) The present invention uses spring pressure and does not require a counterweight. The top loading pressure can be adjusted according to the on-site preloading pressure.

(2) The present invention can directly realize the internal vibration of the sample and is suitable for various complex environments.

(3) The present invention uses springs instead of counterweights to load the top of the sample, which reduces potential safety hazards in vibration and reduces the labor intensity of testers.

(4) The present invention does not require anchoring and is suitable for close packing density testing in the field.

Description of the drawings

Figure 1 is a schematic structural diagram of the packing density measuring device of the present invention.

Figure 2 is a schematic structural diagram of the upper sleeve of the packing density measuring device of the present invention.

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

Figure 4 is a schematic structural diagram of the lower sleeve of the packing density measuring device of the present invention.

In the figure, 1 is a fully threaded rod, 2 is a reserved threaded hole, 3 is a double-headed threaded rod, 4 is a reserved hole, 5 is a nut, 6 is an upper beam, 7 is a turntable, 8 is a hollow threaded rod, 9 To reserve threaded holes, 10 is the bearing, 11 is the top orifice, 12 is the upper plate, 13 is the spring, 14 is the rubber shield, 15 is the lower plate, 16 is the sample tube, 17 is the upper sleeve, 18 is On the lower sleeve, 19 is the power cord, 20 is the rubber sleeve, and 21 is the electric rod vibrator.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clear, the present invention will be further described in detail with reference to the embodiments and drawings. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention. The technical solution of the present invention will be described in detail below with reference to the embodiments and drawings, but the scope of protection is not limited by this.

Embodiment 1 is a method for measuring the close packing density of cohesive soil. Specifically, a variable pressure internal vibration close packing density measuring device is used for measurement. Specifically, the top pressure internal vibration method is used to measure the close packing density of granular soil.

As shown in Figure 1, it is a variable-pressure internal vibration close-packed density measuring device used in this method, which is used to measure free-draining coarse-grained soil and giant-grained soil in cohesive soil. The device mainly includes: electric rod vibrator 21. Sample cylinder 16, upper sleeve 17, lower sleeve 18, adjustable pressure device and vernier depth gauge.

As shown in Figure 3, the sample tube 16 is a cylindrical metal tube with no bottom and a wall thickness of not less than 5mm. The dimensions are selected according to Table 1.

As shown in Figures 2 and 4, the sleeve includes an upper sleeve 17 and a lower sleeve 18. The inner diameter of the upper sleeve 17 is consistent with the sample barrel 16, and is connected in a straight line with the inner wall of the sample barrel 16 after being tightly fixed. The inner diameter of the upper and lower sleeves matches the outer diameter of the sample barrel 16, the height is not less than 30mm, and the wall thickness is the same as the sample barrel 16. The upper sleeve 17 and the sample barrel 16 are connected using the "Γ" interface, and the upper and lower sleeves are connected to the sample barrel 16. After assembly, it is fixed by fully threaded rod 1.

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

Adjustable pressure device: including H-shaped beam reaction frame, turntable 7, hollow threaded rod 8, bearing 10, upper plate 12, spring 13, rubber guard 14, lower plate 15. The H-shaped crossbeam reaction frame is composed of a double-headed threaded rod 3, a nut 5 and a crossbeam 6. The double-headed threaded rod 3 is fixed on the lower sleeve 18 through the reserved threaded hole 2. The upper end of the double-ended threaded rod 3 is connected to the crossbeam 6 through bolts, the hollow threaded rod 8 passes through the reserved threaded hole 9 on the crossbeam 6, the lower end is connected to the bearing 10, and the upper end is connected to the turntable 7. The bearing 10 is fixed in the center opening of the upper plate 12, and the lower plate 15 is fixed under the upper plate through springs 13. The springs 13 are evenly distributed outside the centers of the upper and lower plates, 1/2 away from the center, and not less than 3 The spring 13 can provide a pressure of not less than 14kPa, and the spring 13 is connected to the upper and lower plates through bolts. The diameters of the upper and lower plates are the same and slightly smaller than the inner diameter of the sample barrel 16 and the sleeve. The stiffness is large enough so that the lower plate 15 can move freely within the sample barrel during the loading process.

Vernier depth gauge: The length meets the distance from the lower plate 15 to the top surface of the turntable 7 +3cm, and the accuracy is 0.02mm.

The specific measurement steps are as follows:

1. Taking the cohesionless soil with the maximum particle size of 20mm as an example, collect representative samples, use the standard sieving method (T0115-2007) to determine the particle percentage of each particle group, and use a 20mm standard square hole sieve to screen out particles larger than 20mm. particle size soil, and at the same time limit the mass percentage of dry particles passing the 0.075mm standard sieve to no more than 15%, thus obtaining granular soil with a particle size of 20mm~0.075mm, which should be properly stored for future use. Before the test, put the prepared granular soil into an oven, dry the soil sample at 105°C to 110°C, cool it to room temperature, stir evenly, and keep it dry.

2. Select a sample cylinder 16 with an effective volume of no less than ^2830cm3 , and select a sleeve 18 that matches the outer diameter of the sample cylinder 16. Fix the electric rod vibrator 21 to the center jack at the bottom of the lower sleeve 18 through the rubber sleeve 20. Put the sample tube 16 into the lower sleeve 18. The bottom of the sample tube 16 is in close contact with the lower sleeve 18. Weigh. Then the upper sleeve 17 is placed on top, and the upper and lower sleeves and the sample sleeve 16 are fixed through the fully threaded rod 1.

3. Install the adjustable pressure device: The H-shaped beam reaction frame of the adjustable pressure device is fixed in the reserved threaded hole 2 of the lower sleeve 18 through the double-headed threaded rod 3. The upper end of the double-ended threaded rod 3 is connected to the crossbeam 6 through bolts, the hollow threaded rod 8 passes through the reserved threaded hole 9 in the crossbeam 6, the lower end is connected to the bearing 10, and the upper end is connected to the turntable 7. Select the upper plate 12 and the lower plate 15 that match the inner diameter of the sample tube 16. The upper and lower plate diameters are slightly smaller than the inner diameter of the sample tube 16 by 2mm. The bearing 10 is fixed in the center opening of the upper plate 12. The lower plate 15 passes through the spring. 13 is fixed under the upper plate 12. The springs 13 are evenly distributed outside the center of the upper and lower plates, 1/2 away from the center, and there are no less than 3 springs. The springs 13 are connected to the upper and lower plates through bolts. The stiffness of the spring 13 is selected according to the on-site loading pressure, so that the loading pressure of the spring 13 meets the on-site pre-compaction pressure. The pitch of the hollow threaded rod 8 is x, in mm.

4. Check the stiffness coefficient K of spring 13. Place two load cells with the same specification and model symmetrically in the sample tube 16. Rotate the turntable 7 to make the lower plate 15 closely contact the surface of the sample load cell. Rotate the turntable 7 clockwise for 2 turns to apply the initial load, and then Rotate counterclockwise for 2 turns to unload, and the load cell reading returns to zero. The vernier depth gauge is inserted from the top hole 11 of the hollow threaded rod 8 to the bottom to contact the top surface of the lower plate 15. Record the initial reading L ₀ of the vernier depth gauge, in mm, and take out the vernier. Depth Gauges. Rotate the turntable 7 clockwise for n turns, record the load cell reading p, the loading pressure p is not less than the on-site preload pressure unit N, insert the vernier depth gauge again from the top hole 11 of the hollow threaded rod 8 to the bottom to contact the top surface of the lower plate 15 , record the reading L of the vernier depth gauge, in mm. Measure three times and use the average value to calculate the spring stiffness coefficient K, in N/mm.

K=p/(L ₀ -L)= p/(nx) (1)

In the formula: x is the pitch, mm.

From this, the relationship formula (2) between the spring loading pressure and the number of turns n of the rotating turntable 7 is obtained:

p=n(Kx)=K (L ₀ -L) (2)

5. Load the sample. Take the prepared dried sample and slowly fill the prepared sample into the test cylinder with a spatula or funnel. The height of the filling should be no less than 4cm and no higher than the height of the top surface of the electric rod vibrator 21, and no higher than the top of the sample cylinder. 1cm below, and pay attention to minimize the degree of particle separation, and smooth the surface of the sample.

6. Apply the pressure p ₀ on the top of the sample according to the pre-applied pressure on site, and determine the number of turns n of the rotating turntable (7) according to the formula (II). Install the upper sleeve 17 on the upper part of the sample tube 16, rotate the turntable 7 to make the lower disk 15 closely contact the surface of the sample, rotate the turntable 7 clockwise for 2 turns, apply the initial load, and then rotate counterclockwise for 2 turns to unload, and the vernier depth gauge Insert the hollow threaded rod 8 from the top opening 11 into the bottom contact with the top surface of the lower plate 15, and record the initial reading L ₀ of the vernier depth gauge. Turn the turntable 7 n times clockwise, and then use the vernier depth gauge to measure the corresponding length L after the spring is compressed. The actual loading pressure p ₁ at the top of the specimen can be determined from formula (2).

7. Connect the power supply through the power cord 19, turn on the vibrator switch, and start vibrating for 6 minutes.

8. After the vibration is completed, measure the spring expansion and contraction again. Use formula (2) to determine the top loading pressure p _{2 of the sample after vibration.} Take the average of p ₁ and p ₂ as the top loading pressure p _real . Calculate p _real and p The absolute value of the range of ₀ does not exceed 10%. If the requirements are met, proceed to the next step, otherwise retest.

9. Remove the upper sleeve 17. Place the straight steel bar at the 16 diameter position of the sample tube and measure the height of the sample after vibration. The readings should be measured from four positions evenly distributed on the surface of the sample and at least 15mm away from the cylinder wall and accurate to 0.5mm. Record and calculate the height H ₀ of the sample. Measure and record the mass of the entire sleeve, sample barrel 16 and the sample. After deducting the overall mass of the sleeve under the sample barrel 16, it is the sample mass M. When calculating the volume, the volume of the vibrating rod and the rubber sleeve should be deducted, and the close packing density ρ should be calculated according to formula (3) to 0.001.

ρ=1.274M _d /(D ² H ₀ -d ² h) (3)

In the formula: M _d is the mass of the dried sample, kg; D and d are the inner diameter of the sample cylinder 16 and the outer diameter of the electric rod vibrator 21, respectively, m; H ₀ is the height of the sample, m, h is vibration. The height of the top of the rod relative to the bottom of the lower sleeve 18.

10. Take out the dried sample again, repeat steps 6 to 9 two more times, and measure the close packing density ρ. Sufficient representative samples must be prepared during the test, and a single sample must not be repeatedly vibrated and compacted.

11. Take the average of the three measured close packing density as the close packing density value of the test report.

Example 3

This method is otherwise consistent with the method in Example 2, except for the following points:

(1) The sample is an air-dried sample; (2) After the vibration packing density test is completed, the sample is dried and the moisture content of the sample is measured; (3) The close packing density ρ of the sample is calculated according to formula (4).

ρ=1.274M _f /((D ² H ₀ -d ² h)(1+0.01ω)) (4)

In the formula: M _f is the mass of the air-dried sample, kg; ω is the moisture content of the sample, %; other symbols are the same as above.

The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be concluded that the specific embodiments of the present invention are limited to this. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the premise of the present invention, Below, several simple deductions or substitutions can be made, which should all be deemed to belong to the patent protection scope of the present invention as determined by the submitted claims.

Claims (6)

1. A variable pressure internal vibration close packing density measurement method, characterized in that the specific measurement method includes the following steps: a) Check the spring stiffness coefficient K: apply pressure to the sample to be tested in the sample cylinder (16) through an adjustable pressure device above the sample cylinder (16); the bottom of the sample cylinder (16) is fixed with vibration The adjustable pressure device includes a hollow screw (8). The upper end of the hollow screw (8) is connected to a turntable (7), and the lower end is connected to the upper plate (12). The lower plate (15) passes through a spring (13). ) is connected directly below the upper plate (12); place the pressure detection device in the sample tube (16), rotate the turntable (7) so that the lower plate (15) is in close contact with the surface of the pressure detection device, and rotate the turntable (7) ) After applying the initial load and then unloading, insert the vernier depth gauge from the top opening of the hollow threaded rod (8) into the bottom contact with the top surface of the lower plate (15), record the initial reading L ₀ of the vernier depth gauge, and rotate the turntable (7) n times , obtain the loading pressure p, insert the vernier depth gauge again from the hollow threaded rod (8) and contact the top surface of the lower plate (15), record the reading L of the vernier depth gauge, and calculate the spring stiffness coefficient K: K=p/(L ₀ -L)= p/（nx）（　） In the formula: x is the pitch of the hollow screw; The relationship formula (II) between the spring loading pressure and the number of turns n of the rotating turntable is obtained from the formula: p=n(Kx)=K (L ₀ -L) (II); b) Determine the top loading pressure p ₀ of the close packing density based on the on-site compaction preload pressure, and determine the number of turns n of the rotating turntable (7) according to formula (II); c) After taking out the pressure detection device, load the sample into the sample tube (16), record the initial reading L ₀ of the vernier depth gauge according to the method in step a, then turn the turntable (7) for n turns, and measure the corresponding value after the spring is compressed The reading L of the vernier depth gauge, calculate the actual loading pressure p ₁ according to formula (II); turn on the vibrator to vibrate the sample densely, then re-measure the reading L of the vernier depth gauge according to step a, and check it according to formula (II) The top loading pressure p ₂ after vibration of the sample; the average value of p ₁ and p ₂ is used as the actual loading pressure p _real at the top of the sample. It is required that the absolute value of the range between p _real and p ₀ does not exceed 10%; the vibration time is 5-8 minutes ; d) Determine the height H ₀ of the vibrated sample; calculate the close packing density ρ. 2. A variable pressure internal vibration close packing density measurement method according to claim 1, characterized in that the sample tube (16) is fixed in a sleeve, and the sleeve includes an upper sleeve (16) with upper and lower openings. 17) and a lower sleeve (18) with an upper opening, the sample barrel (16) has upper and lower openings, and the sample barrel (16) is nested between the upper sleeve (17) and the lower sleeve (18); The close packing density ρ is: ρ=1.274M d /(D ² H ₀ -d ² h) (Ⅲ) In the formula: M _d is the mass of the dried sample; D and d are the inner diameter of the sample cylinder (16) and the outer diameter of the vibrator respectively; H ₀ is the height of the sample, h is the top of the vibrator relative to the lower sleeve (18) The height of the bottom. 3. A method for measuring the close packing density of variable pressure internal vibration according to claim 1, characterized in that after measuring the height _H0 of the sample after vibration, the moisture content of the sample is measured; the sample is calculated according to formula (IV) Such close packing density ρ: ρ=1.274M _f / ((D ² H ₀ -d ² h)·(1+0.01ω)) (IV) In the formula: M _f is the mass of the air-dried sample; ω is the moisture content of the sample; D is the inner diameter of the sample cylinder; d is the outer diameter of the vibrator; H ₀ is the height of the sample. 4. A variable pressure internal vibration close packing density measurement method according to claim 1, characterized in that the number of the springs (13) is ≥ 3, and the springs (13) are evenly distributed around the centers of the upper and lower plates. Used to provide uniform pressure to the surface of the specimen, the pressure provided by the spring (13) is ≥14 kPa. 5. A variable pressure internal vibration close packing density measurement method according to claim 1, characterized in that the top of the vibrator is ≥5cm lower than the top of the sample tube (16). 6. A variable pressure internal vibration close packing density measurement method according to claim 1, characterized in that the vibrator is an electric rod vibrator.