CN204314191U - The device of Fast Measurement coarse-grained soil infiltration coefficient - Google Patents

Abstract

A device for quickly measuring the permeability coefficient of coarse-grained soil, the device is composed of: a cylindrical soil sample cylinder (1) without a bottom and a cover, and the soil sample cylinder (1) is placed on a circular permeable plate (2) , the circular permeable plate (2) is placed in the water collection container (4) through the support frame (3). The device is easy to construct, can quickly and conveniently measure the permeability coefficient of coarse-grained soil, and is especially suitable for use on construction sites.

Description

Device for Quickly Measuring Coarse Grained Soil Permeability Coefficient

technical field

The utility model relates to a device for measuring the permeability coefficient of coarse-grained soil, which belongs to the technical field of soil engineering.

Background technique

When the pores in the soil are connected with each other, water-permeable channels can be formed. Although these channels are very irregular and often narrow, water can flow through the soil along these channels by gravity. The phenomenon of water flowing in soil pores is called water seepage; the property that soil can be permeated by water is called soil permeability or water permeability, which is one of the mechanical properties of soil. The soil permeability coefficient is a parameter to evaluate the soil permeability. The larger the soil permeability coefficient, the stronger the water permeability; otherwise, the weaker it is.

The permeability coefficient of coarse-grained soil is about 10 ^-2 ~ 10 ^-4 cm/s, which is a kind of material with good water permeability. Its permeability coefficient can be directly measured by means of permeameter, that is, constant head permeability test: coarse After the granular soil is layered and saturated in the cylindrical permeameter, water is injected into the permeameter from the upper part. For the water level difference (water pressure difference) Δh of the piezometric tube, divide the water level difference Δh by the vertical distance L between the two piezometric tubes on the side wall of the permeameter to obtain the head loss per unit process, that is, the hydraulic gradient i; Take and measure the amount of seepage water q flowing out of the water outlet of the lower part of the permeameter per unit time, and calculate the permeability coefficient k by Darcy's law q=k·i·A. (where A is the cross-sectional area of the inner chamber of the permeameter). This method has accurate test results and is widely used in indoor laboratory tests. But it has the following problems: a special penetrometer is required, and the test is inconvenient. Due to the small aperture of the two piezometric tubes on the side wall, the seepage water infiltrates into the piezometric tube slowly, and it takes a long time for the water level of the two piezometric tubes to rise to the stable water point of equilibrium, resulting in a long test time. It cannot meet the requirements of simple and rapid determination of the permeability coefficient of coarse-grained soil on the field engineering site.

Utility model content

The purpose of this utility model is to provide a device for quickly measuring the permeability coefficient of coarse-grained soil. The device is easy to construct and can quickly and conveniently measure the permeability coefficient of coarse-grained soil, and is especially suitable for use on the construction site.

The technical scheme adopted by the utility model to realize the purpose of the invention is: a device for quickly measuring the permeability coefficient of coarse-grained soil, which is composed of: a cylindrical soil sample cylinder with no bottom and no cover, and the soil sample cylinder is placed in a circular On the permeable plate, the circular permeable plate is placed in the water collection container through the support frame.

The operating steps of measuring the permeability coefficient of coarse-grained soil with the utility model are:

a. Test preparation

The coarse-grained soil is layered and saturated in the soil sample cylinder, and the saturated coarse-grained soil sample to be tested is obtained in the soil sample cylinder; then the soil sample cylinder is placed on the circular permeable plate, and at the same time, the circular permeable The plate is placed in the water collection container through the support frame;

b. Penetration test

Use a dropper to evenly drip water on the upper surface of the coarse-grained soil sample in the soil sample cylinder until a water film is formed on the upper surface of the coarse-grained soil sample, and keep the water film through continuous dripping; The soil sample infiltrates downwards and drips into the water collection container through the circular permeable plate;

c. Determination of permeability coefficient

While the penetration test is being carried out, collect and measure the water volume in the water collection container within the specified time t; this operation is repeated until the difference between the water volumes measured for four consecutive times is less than the set threshold; then, the The average value Q of the four measured water quantities is obtained, and the permeability coefficient k of the coarse-grained soil sample is measured by k=Q/(A·t). In the formula: A is the cross-sectional area of the inner cavity of the soil sample cylinder.

Further, the soil sample cylinder of the present invention is placed on the circular permeable plate in such a way that the bottom of the soil sample cylinder is fixedly connected to the circular permeable plate; the support frame is a tripod fixedly connected to the circular permeable plate.

Compared with the measuring device whose parts are separated from each other, the measuring device whose parts are fixedly connected to each other, the soil sample cylinder will move together with other parts during sample preparation, which is not convenient and flexible enough, and the portability is not enough; but the step of assembling parts is omitted during operation, Save measurement time, better repeatability and reproducibility.

The principle of measuring the permeability coefficient of coarse-grained soil with the utility model is:

The flow of water in soil follows the energy equation of hydraulics, namely the famous Bernoulli equation. According to this equation, the total water head h at a point in the soil relative to an arbitrarily determined datum is:

h=z+h _w +h _v

In the formula: z——position water head, that is, the height between the point and the datum level;

h _w ——Pressure water head, that is, the liquid column height of the open piezometric tube at this point;

h _v ——dynamic head, that is, the height at which water is sprayed vertically upwards into the air at this point.

The dynamic head h _v is proportional to the square of the velocity. Since the seepage velocity of water in the soil is generally very small, h _v can be ignored. In this way, the total head h≈z+h _w .

If there is a total head difference in the soil, i.e. head loss, water will flow from the height of the total head along the pore channels in the soil to the lower part of the total head. )calculate.

$\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;h</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: Δh—head loss;

L - process.

The flow of water in the soil is mostly slow, belongs to laminar flow, conforms to Darcy's law, and satisfies the relationship of formula (2).

q＝k·A·i (2) In the formula: q——the amount of water passing through the cross-section of the soil per unit time;

A - the cross-sectional area of the soil;

i—hydraulic gradient;

k——permeability coefficient.

Therefore, the permeability coefficient k=q/(A·i) of coarse-grained soil can be determined by Darcy's law.

In this utility model, since the thickness of the free liquid surface on the upper surface of the sample is only 1 mm, there is almost no hydrostatic pressure, the upper surface pressure head h _w1 ≈ 0, and the upper surface total water head h ₁ is approximately equal to the position water head z ₁ , namely h ₁ ≈z ₁ ; there is almost no hydrostatic pressure on the lower surface of the sample due to the free flow of liquid, so the lower surface pressure head h _w2 ≈0, and the total lower surface water head h ₂ is approximately equal to the position water head z ₂ , that is, h ₂ ≈z ₂ . Therefore, the water head loss on the upper and lower surfaces of the sample Δh=h ₁ -h ₂ ≈z ₁ -z ₂ ＝H, the hydraulic gradient Among them, H is the height of the sample and the flow of seepage in this test. It can be seen that in this device, the hydraulic gradient i=1 along the seepage path of the soil sample is a constant value and has nothing to do with the properties of the soil sample. When the seepage is stable, the seepage flow rate q can be obtained from the volume Q of seepage water collected within a certain period of time t: q=Q/t, and then the permeability coefficient of the sample is calculated by Darcy's law:

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; q</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; t</span>}}$

Compared with the prior art, the beneficial effects of the utility model are:

1. The soil sample cylinder in the test device is an upper and lower bottomless cylinder, and there is no pressure measuring hole and pressure measuring tube on the side wall, and there is no need to set the inlet and outlet water level adjustment mechanism of the sample. The test preparation and test operation are very simple. It only needs a cylindrical appliance without a bottom and no cover, a water-permeable plate, a water collection container, and a support frame that can support the plate in the water collection container. It can even be temporarily assembled and constructed on site. The permeability coefficient of coarse-grained soil can also be measured without special equipment at the engineering site.

2. The existing device needs to measure the hydraulic gradient i along the process through piezometric tubes, but in the utility model, based on the fact that there is no pressure head on the top and bottom surfaces of the soil sample, only the position head, and the seepage path is the overall height of the soil sample. Therefore, the hydraulic gradient i≈1 is deduced, and there is no need to read the water head loss at two points in the soil sample during the seepage process through the piezometric tube, and the test operation is more convenient; The slow infiltration of seepage water and the process of rising the water level to the stable water point of equilibrium greatly shorten the test time and meet the requirements of rapid determination of the permeability coefficient of coarse-grained soil in field projects. Its measurement results are within the same evaluation level as the measurement results of existing methods.

Below in conjunction with accompanying drawing and specific embodiment the utility model is described in further detail.

Description of drawings

Fig. 1 is a schematic cross-sectional structure diagram of an embodiment of the utility model.

5 in the figure is the coarse-grained soil sample to be tested.

Detailed ways

Embodiment one

Fig. 1 shows, a kind of specific embodiment of the present utility model is, a kind of device of measuring the permeability coefficient of coarse-grained soil rapidly, and its composition is: the soil sample tube 1 of cylindrical shape and without bottom and cover, soil sample tube 1 Placed on the circular water permeable plate 2, the circular water permeable plate 2 is placed in the water collection container 4 through the support frame 3.

The operation steps of measuring the permeability coefficient of coarse-grained soil with the device of this example are:

a. Test preparation

The coarse-grained soil is layered and saturated in the soil sample cylinder 1, and a saturated coarse-grained soil sample 5 to be measured is obtained in the soil sample cylinder 1; then the soil sample cylinder 1 is placed on the circular permeable plate 2, At the same time, the circular permeable plate 2 is placed in the water collection container 4 through the support frame 3;

b. Penetration test

After water seepage, use a dropper to evenly drip water on the upper surface of the coarse-grained soil sample 5 in the soil sample cylinder 1 until a water film is formed on the upper surface of the coarse-grained soil sample 5, and keep the water film by continuously dripping; at the same time, the soil sample cylinder 1 The water inside continuously infiltrates downward through the coarse-grained soil sample 5, and drips into the water collection container 4 through the circular permeable plate 2;

c. Determination of permeability coefficient

While the penetration test is being carried out, collect and measure the water volume in the water collection container 4 within the specified time t; repeat this operation until the difference between the water volumes measured for four consecutive times is less than the set threshold; then, The water quantity measured four times is averaged Q, and by k=Q/(A t), the permeability coefficient k of the coarse-grained soil sample 5 is recorded, in the formula: A is the cross-section of the soil sample cylinder 1 cavity area.

Test verification:

Using the device and operating steps of this example, the permeability coefficient of a coarse-grained soil sample was measured, and the test results are shown in Table 3. The parameters of the coarse-grained soil sample are shown in Table 1, and the particle size composition is shown in Table 2.

The test data and results of measuring the permeability coefficient of the same coarse-grained soil sample using the existing standard constant head permeability test are shown in Table 4.

Since the water permeability of the soil is judged by the order of magnitude difference of the permeability coefficient, the permeability coefficient measured by the utility model is 4.60×10 ^-4 cm/s, while the permeability coefficient measured by the existing method is 5.62× 10 ^-4 cm/s. The measurement results of the two methods belong to the same evaluation level (magnitude), and the measurement error meets the engineering requirements.

Table 1 Samples and penetration test parameters

Table 2 Particle size composition of samples

Table 3 Test data and results of the utility model

Table 4 Standard constant water head test data and results

Embodiment two

Fig. 1 shows, a kind of specific embodiment of the present utility model is, a kind of device of measuring the permeability coefficient of coarse-grained soil rapidly, and its composition is: the soil sample tube 1 of cylindrical shape and without bottom and cover, soil sample tube 1 Placed on the circular water permeable plate 2, the circular water permeable plate 2 is placed in the water collection container 4 through the support frame 3.

The soil sample cylinder 1 in this example is placed on the circular permeable plate 2 in the following manner: the bottom of the soil sample cylinder 1 is fixedly connected to the circular permeable plate 2; the support frame 3 is fixedly connected to the circular permeable plate 2 tripod.

The operation steps of measuring the permeability coefficient of coarse-grained soil with the device of this example are:

a. Test preparation

The coarse-grained soil is layered and saturated in the soil sample cylinder 1, and a saturated coarse-grained soil sample 5 to be measured is obtained in the soil sample cylinder 1;

b. Penetration test

After water seepage, use a dropper to evenly drip water on the upper surface of the coarse-grained soil sample 5 in the soil sample cylinder 1 until a water film is formed on the upper surface of the coarse-grained soil sample 5, and keep the water film by continuously dripping; at the same time, the soil sample cylinder 1 The water inside continuously infiltrates downward through the coarse-grained soil sample 5, and drips into the water collection container 4 through the circular permeable plate 2;

c. Determination of permeability coefficient

While the penetration test is being carried out, collect and measure the water volume in the water collection container 4 within the specified time t; repeat this operation until the difference between the water volumes measured for four consecutive times is less than the set threshold; then, The water quantity measured four times is averaged Q, and by k=Q/(A t), the permeability coefficient k of the coarse-grained soil sample 5 is recorded, in the formula: A is the cross-section of the soil sample cylinder 1 cavity area.

Claims (2)

1. A device for quickly measuring the permeability coefficient of coarse-grained soil, which consists of: a cylindrical soil sample cylinder (1) without bottom and cover, and the soil sample cylinder (1) is placed on the circular permeable plate (2) , the circular permeable plate (2) is placed in the water collection container (4) through the support frame (3). 2. The device for quickly measuring the permeability coefficient of coarse-grained soil according to claim 1, characterized in that: the soil sample cylinder (1) is placed on the circular permeable plate (2) in the following manner: soil sample The bottom of the cylinder (1) is fixedly connected to the circular permeable plate (2); the support frame (3) is a tripod fixedly connected to the circular permeable plate (2).