A method for measuring the permeability coefficient of fine-grained soil by driving out air and variable head

Abstract

The present invention discloses a method for measuring the permeability coefficient of fine-grained soil by gas-driven variable head, which includes the following steps: S1. Prepare the test device and the specimen, install and adjust the test equipment; S2. Estimate the end time corresponding to the lowest position of the test; S3. Fill the variable head pipe with water to the required position, and record the water head after the water head is stable; S4. Open the seepage valve to start the test, record the start time, and after reaching the predetermined time or water head position, stop the water head supply, and record the end time and the water head data; S5. Calculate the permeability coefficient of the fine-grained soil according to the test data, obtain the expression of the permeability coefficient k<subgt;T< / subgt; of the specimen before the specimen discharges water, and substitute the test data for the calculation of k<subgt;T< / subgt>. The present invention can greatly save the test time, and in cooperation with the traditional variable head test, can greatly improve the test efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of fine-grained soil permeability testing in geotechnical engineering, and in particular to a method for measuring the permeability coefficient of fine-grained soil by air displacement and variable water head. Background Art

[0002] In existing variable head tests for fine-grained soils, the sample must be degassed before testing can begin, and the degassing and testing process often takes dozens of hours.

[0003] Existing testing technologies require degassing and waiting for a stable seepage flow to form within the sample before testing can begin. This is extremely time-consuming, so a more time-saving testing method is needed. Summary of the Invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0005] To achieve the above object, the present invention proposes a method for measuring the permeability coefficient of fine-grained soil by air displacement and water head variation, comprising the following steps:

[0006] S1. Prepare the test equipment and samples, install and adjust the test equipment;

[0007] S2, estimate the end time corresponding to the lowest position of the test;

[0008] S3. Flush the variable head pipe to the required position and record the water head after it stabilizes.

[0009] S4. Open the seepage valve to start the test, record the start time, and when the predetermined time or water head position is reached, stop the water head supply and record the end time and water head data;

[0010] S5. Calculate the permeability coefficient of fine-grained soil based on the test data. Before the test piece is exposed to water, obtain the expression for the permeability coefficient of the test piece and substitute the test data for k. T Calculation.

[0011] The present invention can greatly save test time and, when combined with the traditional variable water head test, can greatly improve test efficiency.

[0012] Optionally, in S1 , when installing and debugging the test equipment, it is necessary to remove the air at the bottom of the infiltration container for holding the fine-grained soil sample and prepare clean water as the water head.

[0013] Furthermore, in step S2, when estimating the end time corresponding to the lowest test position, it is necessary to first estimate the lowest test position. The estimation steps are as follows:

[0014] At time 0, the seepage surface is at the bottom of the specimen, and the distance from the water column surface in the variable-head tube to the top of the specimen is h1; at time t, the seepage surface is at a distance l from the bottom of the specimen, and the distance from the water column surface in the variable-head tube to the top of the specimen is h. According to the relationship that the amount of water infiltrated into the specimen is equal to the amount of water level drop in the variable-head tube, we can obtain:

[0015] nAl=a(h1 - h),

[0016] where n is the porosity; A is the cross-sectional area of the specimen; the range of l is l ≤ L, and L is the seepage path, which is the height of the specimen;

[0017] Therefore, we get:

[0018] Furthermore, in S4, at the start of the experiment, the ambient temperature of the permeation container needs to be recorded, and at predetermined intervals, the ambient temperature of the permeation container is detected and recorded.

[0019] Furthermore, in the said S5, the steps for calculating the permeability coefficient of fine-grained soil based on the test data include:

[0020] S51. Using Darcy's law to perform formula substitution and integration on the permeability coefficient k of the specimen T to obtain the expression of the permeability coefficient k of the specimen T ;

[0021] S52. According to the test content, numerically select the seepage path L of the specimen, the distance h1 from the water column surface in the variable-head tube to the top of the specimen, and the distance h from the water column surface in the variable-head tube to the top of the specimen in the expression, and further simplify the k T expression obtained in S51, and then the final k T expression can be obtained by substituting the test data.

[0022] Furthermore, in S51, according to Darcy's law v = k T i, the seepage velocity within the time micro-segment dt is and the seepage gradient is Therefore, we get:

[0023] Combined with the formula nAl = a(h1 - h) simultaneously, we obtain and substitute it into , and through integration, we can obtain:

[0024]

[0025] Furthermore, using the said the permeability coefficient of the specimen is obtained before the specimen discharges water, and its limiting condition is

[0026] Further, in S52, in the experiment, since L is usually taken as 4 cm and h1 can reach 200 cm, h1 is approximately used for L + h, and an approximate expression for the permeability coefficient is obtained.

[0027]

[0028] If the value of h approaches h1, then h can be approximately used for L + h, 0 can be used for h - h1, and the expression of k T is further simplified to:

[0029]

[0030] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0031] The above-mentioned and / or additional aspects and advantages of the present invention will become apparent and be easily understood from the following description of the embodiments in conjunction with the drawings, where:

[0032] Figure 1 is a schematic diagram of the method steps of a method for measuring the permeability coefficient of fine-grained soil by gas-driving variable head according to the present invention;

[0033] Figure 2 is a schematic diagram of the specific steps of S5 of a method for measuring the permeability coefficient of fine-grained soil by gas-driving variable head according to the present invention. Detailed Embodiments

[0034] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0035] The present invention provides a method for measuring the permeability coefficient of fine-grained soil by gas-driving variable head, which will be elaborated in detail below with reference to Figures 1 to 2 for elaboration.

[0036] A method for measuring the permeability coefficient of fine-grained soil by gas-driving variable head includes the following steps:

[0037] S1. Prepare the test device and the specimen, and install and adjust the test equipment;

[0038] S2. Estimate the end time corresponding to the lowest position of the test;

[0039] S3. Flush the variable head tube to the required position, and record the water head after the water head is stable;

[0040] S4. Open the seepage valve to start the test, record the start time. After reaching the predetermined time or water head position, stop the water head supply, and record the end time and water head data.

[0041] S5. Calculate the permeability coefficient of fine-grained soil based on the test data. Before the specimen discharges water, obtain the expression of the specimen's permeability coefficient, and substitute the test data for the calculation of k. T Calculation.

[0042] The present invention can greatly save the test time. In cooperation with the traditional variable water head test, it can greatly improve the test efficiency.

[0043] It should be noted that in S1, when installing and debugging the test equipment, it is necessary to remove the air at the bottom of the permeation container for holding the fine-grained soil sample, and prepare clear water as the water head. In S4, at the start of the experiment, it is necessary to record the ambient temperature of the permeation container, and detect and record the ambient temperature of the permeation container at predetermined intervals.

[0044] In the calculation, in S2, when estimating the end time corresponding to the lowest test position, it is necessary to first estimate the lowest test position. The estimation steps are as follows:

[0045] At the moment of 0, the seepage surface is at the bottom of the specimen, and the distance between the water column surface in the variable water head tube and the top of the specimen is h1; at the moment of t, the seepage surface leaves the bottom of the specimen by a distance of l, and the distance between the water column surface in the variable water head tube and the top of the specimen is h. According to the relationship that the amount of water infiltrated into the specimen is equal to the amount of water level drop in the variable water head tube, the following can be obtained:

[0046] nAl = a(h1 - h),

[0047] where n is the porosity; A is the cross-sectional area of the specimen; the range of l is l ≤ L, and L is the seepage path, that is, the height of the specimen;

[0048] Therefore, the following can be obtained:

[0049] In the said S5, the steps for calculating the permeability coefficient of fine-grained soil according to the test data include:

[0050] S51. Use Darcy's law to perform formula substitution and integration on the permeability coefficient k of the specimen, and obtain the expression of the specimen's permeability coefficient k. T For the calculation, T Expression;

[0051] S52. According to the test content, select the numerical values of the seepage path L of the specimen, the distance h1 between the water column surface in the variable water head tube and the top of the specimen, and the distance h between the water column surface in the variable water head tube and the top of the specimen in the expression, and further simplify the k expression obtained in S51, so as to substitute the test data to obtain the final k expression. T Expression, T Expression.

[0052] Specifically, in S51, according to Darcy's law v = ki, the seepage velocity within a small time interval dt is T and the seepage gradient is Therefore, it is obtained that: And by combining with the formula nAl = a(h1 - h), it is obtained that

[0053] and substituting it into and integrating, it can be obtained that: in

[0054]

[0055] Moreover, by using the the permeability coefficient of the specimen is obtained before the specimen discharges water, and its limiting condition is

[0056] In the said S52, since in the experiment, L is usually taken as 4 cm and h1 can reach 200 cm, so h1 is approximately taken as L + h to obtain an approximate expression of the permeability coefficient

[0057]

[0058] If the value of h approaches h1, then h can be approximately taken as L + h, 0 can be taken as h - h1, then the expression of k T is further simplified to:

[0059]

[0060] After the simplification is completed, substituting the corresponding data of each physical quantity according to the experimental data can obtain the value of k T of.

[0061] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0062] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0063] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for measuring the permeability coefficient of fine-grained soil by driving gas and variable head, characterized in that, It includes the following steps: S1. Prepare the test device and specimens, install and adjust the test equipment; S2. Estimate the end time corresponding to the lowest test position; S3. Fill the variable-head tube with water to the required position, and record the water head after the water head is stable; S4. Open the seepage valve to start the test, record the start time, and after reaching the predetermined time or water head position, stop the water head supply, and record the end time and water head data; S5. Calculate the permeability coefficient of fine-grained soil based on the test data, obtain the expression of the permeability coefficient of the specimen before the specimen discharges water, and substitute the test data for calculation; In S5, the steps for calculating the permeability coefficient of fine-grained soil based on the test data include: S51. Substitute the formula and integrate the permeability coefficient of the specimen using Darcy's law to obtain the expression of the permeability coefficient of the specimen ; S52. According to the test content, select the seepage path of the specimen in the expression , the distance between the water column surface in the variable-head tube and the top of the specimen and the distance between the water column surface in the variable-head tube and the top of the specimen for numerical selection, and further simplify the expression obtained in S51, then the test data can be substituted to obtain the final expression; In S51, according to Darcy's law , the seepage velocity within a micro-time segment is , and the seepage gradient is . Therefore, it is obtained that: ; Combined with the formula , we get , and substitute it into . By integrating, we can obtain: ； By using the the permeability coefficient of the test piece is obtained before the water outlet of the test piece, and its limiting condition is ; In S52, during the experiment, it is usually taken as 4 cm, which can reach 200 cm. Therefore, using the approximation , an approximate expression for the permeability coefficient is obtained ； If tends to , then can be approximated by , approximated by 0 , then The expression of 。 2. The variable-head measuring method for the permeability coefficient of fine-grained soil by gas displacement according to claim 1, wherein In S1, when installing and debugging the test equipment, it is necessary to remove the air at the bottom of the permeameter for containing the fine-grained soil sample, and prepare clear water as the water head.

3. The variable-head measurement method for the permeability coefficient of fine-grained soil by gas displacement according to claim 1, characterized in that, In S2, when estimating the end time corresponding to the lowest test position, it is necessary to first estimate the lowest test position, and the estimation steps are as follows: At time 0, the seepage surface is at the bottom of the specimen, and the distance from the water column surface in the variable-head tube to the top of the specimen is ; at time, the seepage surface leaves the bottom of the specimen by distance, and the distance from the water column surface in the variable-head tube to the top of the specimen is . According to the relationship that the amount of water infiltrated into the specimen is equal to the amount of water level drop in the variable-head tube, we can obtain: ， Among them, is the porosity; is the cross-sectional area of the specimen; The range of , is the seepage path, which is the height of the specimen; Therefore, it is obtained that: .

4. The variable-head measurement method for the permeability coefficient of fine-grained soil by gas displacement according to claim 1, characterized in that, In S4, at the start of the experiment, it is necessary to record the ambient temperature of the permeameter, and detect and record the ambient temperature of the permeameter at predetermined intervals.

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