Optimization method for seepage flow velocity under complex stratum and steady-state flow field

Abstract

The invention provides a method for optimizing the seepage flow velocity in a complex stratum and a steady-state flow field, and belongs to the technical field of dam leakage detection, and the method comprises the following steps: S1, obtaining an optimization coefficient through an experiment exploration mode; the in-hole horizontal flow velocity expression is optimized based on the optimization coefficient, and an optimized horizontal seepage flow expression is obtained; s2, holes are dug in the dam, the permeability coefficient of each soil layer in the holes in the dam is obtained, and the horizontal seepage flow velocity of each soil layer in the holes is calculated based on the optimized horizontal seepage expression in the S1; and S3, acquiring actual parameters of the dam by adopting a finite element model, inputting the actual parameters into the finite element model, and verifying the accuracy of the horizontal seepage flow velocity of the hole in the step S2. According to the method, the horizontal seepage flow velocity can be accurately calculated.

Description

Technical Field

[0001] The present invention belongs to the technical field of detecting dike leakage, and particularly relates to an optimization method for seepage flow velocity under complex strata and steady flow fields. Background Art

[0002] Dike leakage is extremely harmful and is related to flood control safety and the service life of the project. Leakage detection can promptly detect potential hazards and prevent dangers such as piping and soil erosion. It can provide accurate basis for dike maintenance, early warning of possible collapse risks, avoid floods raging, and ensure the safety of the lives and property of the people around, which is of great significance for the stable operation of water conservancy facilities.

[0003] The traditional single-hole tracer method has limitations in measuring flow velocity. It does not consider the influence of formation conditions, especially the effect of the formation permeability coefficient on the tracer. In actual situations, the diffusion of the tracer is significantly affected by the formation permeability coefficient. The larger the permeability coefficient, the more significant the diffusion effect of the tracer.

[0004] Taking a specific example to illustrate, assume that the flow velocity in the monitoring hole of the traditional single-hole tracer method is V1. Due to the influence of the permeability coefficient in actual situations, the diffusion rate of the tracer in the hole will change, and the actual flow velocity is V2. Moreover, the larger the permeability coefficient, the greater the error between the actual flow velocity V2 and the flow velocity V1 in the monitoring hole of the single-hole tracer method. This leads to inaccurate flow velocity measured by the traditional single-hole tracer method, and further results in inaccurate leakage detection results. Summary of the Invention

[0005] In order to overcome the above problems, the present invention proposes an optimization method for seepage flow velocity under complex strata and steady flow fields, which can solve the technical problem of accurately exploring dike leakage under the influence of different permeability coefficients.

[0006] To achieve the above object, the present invention adopts the following technical content:

[0007] An optimization method for seepage flow velocity under complex strata and steady flow fields, comprising the following steps:

[0008] S1: Obtain an optimization coefficient through experimental exploration; optimize the horizontal flow velocity expression in the hole based on the optimization coefficient to obtain an optimized horizontal seepage expression;

[0009] S2: Dig holes on the dike, obtain the permeability coefficients of each soil layer in the holes on the dike, and calculate the horizontal seepage flow velocities of each soil layer in the hole based on the optimized horizontal seepage expression in S1;

[0010] S3: Adopt a finite element model, obtain the actual parameters of the dike and input them into the finite element model to verify the accuracy of the horizontal seepage flow velocity of the hole in S2.

[0011] Further, step S1 includes the following steps:

[0012] S1.1: Calculate the horizontal flow velocity V inside the g-th hole d,g ; The formula is:

[0013]

[0014] In formula (1), r0 represents the radius of the hole in the soil body during the experiment; α represents the correction coefficient; N g,0 represents the conductivity at the initial moment of the g-th hole; N g,t represents the conductivity of the g-th hole at time t; t0 represents the time difference from the initial moment to time t;

[0015] S1.2: Based on the soil layer permeability coefficient, establish an "optimization coefficient"; based on the "optimization coefficient", establish a formula for the "optimized horizontal seepage velocity";

[0016] The formula is:

[0017]

[0018] In formula (2), k g represents the permeability coefficient of the soil body where the g-th hole is located during the experiment; V f，g is the "optimized horizontal seepage velocity" of the g-th hole during the experiment; is the "optimization coefficient" of the g-th hole during the experiment.

[0019] Furthermore, step S2 includes the following steps:

[0020] S2.1: Dig holes at the dam site, and divide the excavated soil layer in the hole into multiple modules according to a set length;

[0021] S2.2: Use geotechnical experiments to obtain the permeability coefficient of each module;

[0022] S2.3: Use formula (2) to calculate the "optimized horizontal seepage velocity" of different modules in this hole.

[0023] Furthermore, in step S1, by means of particle size distribution, 8 kinds of soil bodies with different permeability coefficients are configured. For the holes dug on each soil body, each hole is a round hole and has the same diameter.

[0024] The diameters of the holes dug on both are the same, reducing the variables between the experiment and the actual dam hole digging, and making the calculated horizontal seepage velocity more accurate.

[0025] Furthermore, in step S2, the soil body in the hole at the dam site is divided into multiple modules with a length of 1 m; the soil layer with a depth of 3 - 28 m is intercepted, and the optimized horizontal seepage velocity of each module at this 3 - 28 m depth is calculated.

[0026] For the soil mass excavated from the hole, due to human interference, the top and bottom ends of the collected samples are greatly affected, prone to deformation or the sampled soil layer is incomplete. The soil layer in the middle section has greater representativeness and less possibility of being disturbed. Therefore, the soil layer with a depth of 3 - 28 m is used to calculate the "optimized horizontal seepage velocity" to avoid human interference in the results.

[0027] Adopting the above technical solution, the beneficial effects that can be achieved are as follows:

[0028] The horizontal flow velocity in the hole can be optimized using Equation (2), so as to obtain a more accurate horizontal seepage velocity. Equation (2) takes into account the influence of the permeability coefficient on the horizontal seepage velocity, introduces the permeability coefficient to obtain the "optimized horizontal seepage expression", reflects the influence of the permeability coefficient on the horizontal seepage velocity, and makes the data more in line with the real data. Description of the Drawings

[0029] Figure 1 is the flow chart of this method;

[0030] Figure 2 is the geometric model diagram of finite element modeling;

[0031] Figure 3 is the mesh division diagram;

[0032] Figure 4 is the comparison diagram of the optimized horizontal seepage velocity and the velocity after finite element simulation;

[0033] Figure 5 is the display diagram of the leakage results of 29 holes in the dam. Detailed Implementation Modes

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] An optimization method for seepage velocity under complex strata and steady flow fields includes the following steps:

[0036] S1: Obtain the optimization coefficient through experimental exploration; optimize the horizontal flow velocity expression in the hole based on the optimization coefficient to obtain the optimized horizontal seepage expression;

[0037] S1 specifically includes the following steps:

[0038] S1.1: By means of particle size distribution, eight different soil bodies are made in a laboratory environment. The permeability coefficients of each soil body are different, and the porosity of each soil body is kept the same to control variables. A hole of the same specification is drilled in each soil body, and the holes of each soil body are numbered, denoted as 1 - 8.

[0039] All of the above holes are round holes with a diameter of 75 cm and a depth of 50 cm.

[0040] S1.2: Based on the single - hole tracer method (existing method), experiments are carried out respectively under the known steady - state horizontal seepage velocity (steady - state flow field), and the horizontal flow velocities inside the above - mentioned holes are measured respectively.

[0041] The meaning of the steady - state horizontal seepage velocity (steady - state flow field) is that in a single experiment, the horizontal seepage velocity remains steady without sudden changes.

[0042] The principle of measuring the horizontal flow velocity inside the hole by the single - hole tracer method is as follows: By injecting a saturated sodium chloride solution (tracer) into the hole, as the horizontal seepage scours the sodium chloride solution, the concentration of the sodium chloride solution will change, which will cause its conductivity to change. By monitoring the change of the conductivity of the saturated sodium chloride solution over time and relying on the existing formula for the flow velocity inside the hole (Equation (1)), the horizontal flow velocity inside the corresponding hole is calculated.

[0043] The specific process of S1.2 is as follows:

[0044] Suppose in a certain experiment, the single - hole tracer method is used to measure the horizontal flow velocity inside the g - th hole; a known steady - state horizontal seepage velocity is set before the experiment;

[0045] Let the horizontal flow velocity inside the g - th hole be denoted as V d,g , where g ∈ [1, 8]; let the steady - state horizontal seepage velocity in this experiment be denoted as V p，g .

[0046] According to the existing expression for the horizontal flow velocity inside the hole, the horizontal flow velocity V d,g inside the g - th hole is:

[0047]

[0048] In Equation (1), r0 represents the radius of the hole on the soil body in the experiment, that is, 75 / 2 cm = 37.5 cm mentioned above. α represents the correction coefficient, which is a fixed value and is artificially set to 2; N g,0 represents the conductivity at the initial moment (0 moment) of the g - th hole; N g,t represents the conductivity of the g - th hole at the t - th moment (set to the 15th minute); t0 represents the time difference from the initial moment to the t - th moment, that is, 15 min.

[0049] Also, since the steady-state horizontal seepage velocity at the g-th side hole is a known quantity, the calculated horizontal velocity V in the g-th hole d,g and the known horizontal seepage velocity V p,g at this time, as well as the corresponding permeability coefficient k of the soil layer represented by the g-th g are recorded in Table 1.

[0050] Table 1 Data of the in-hole velocity under the permeability coefficients of different soil layers

[0051]

[0052] S1.3: Determine the "optimization coefficient" according to the data in Table 1, and optimize the in-hole horizontal velocity expression based on the "optimization coefficient" to obtain the optimized horizontal seepage expression;

[0053] From the first four rows of Table 1, it can be seen that k g and λ g are roughly linearly related. Therefore, the data of the above two in Table 1 are fitted by linear fitting, and the fitted straight line is:

[0054] m = 11.269n + 1 (2)

[0055] In Equation (2), n represents the value of k g ; m represents the value of λ g .

[0056] From the data in Table 1, since Therefore, if it is necessary to calculate V f，g , and thus indirectly represent V p，g , then it is necessary to multiply the "optimization coefficient" on the basis of V d，g calculated by Equation (1). The optimization coefficient is 1 / m obtained by substituting k g into Equation (2). Combining with the straight-line equation of Equation (2), that is, the "optimization coefficient" is:

[0057] So far, the formula for V f，g is derived as:

[0058]

[0059] The calculation process is illustrated by the data in the last row of Table 1:

[0060] Taking the data in the second column of Table 1 as an example, when V d,1 = 9.824×10 -3 (i.e., ), substituting the permeability coefficient k1 = 0.0072 of the soil layer into Equation (3), we get V

[0061] V f,1= 9.824 * 10 -3 / 1.0811368 = 9.0867 * 10 -3 。

[0062] Since V d,1 = 9.824 * 10 -3 and V p,1 = 9.219 * 10 -3 has a difference greater than the difference between V f,1 = 9.0867 * 10 -3 and V p,1 = 9.219 * 10 -3 it shows that in the laboratory environment, using formula (3) can optimize the horizontal flow velocity in the hole.

[0063] However, since S1 only shows feasibility in the laboratory environment and does not show feasibility in actual situations, it is necessary to prove that formula (3) is still applicable to actual dams.

[0064] The proof process of this solution is divided into two parts. First, for the actual dam, the horizontal seepage velocity needs to be calculated using formula (3). Then, the horizontal seepage velocity of the dam also needs to be simulated using the finite element model, and the results of the two are compared. If the results of the two are relatively close, it indicates that formula (3) in S1 has high accuracy; otherwise, the accuracy is insufficient.

[0065] S2: Calculation of the horizontal seepage velocity of the actual dam.

[0066] S2 specifically includes the following steps:

[0067] S2.1: The dam is the dam of a certain actual location, and holes are dug at the positions on the dam that need to be detected;

[0068] The borehole diameter is 75 cm, the same as the specification in the experiment, the borehole depth is 30 m; the hole interval is 30 m. In this solution, a total of 29 holes are excavated.

[0069] S2.2: Based on the single-hole tracer method, measure the horizontal flow velocity in each hole.

[0070] Assume that the 29 holes are numbered. Taking hole No. 1 as an example:

[0071] Use the single-hole tracer method for hole No. 1 to measure the horizontal flow velocity in the hole; assume that the horizontal flow velocity in hole No. 1 measured is V1.

[0072] S2.3: Then obtain the permeability coefficient of the soil excavated from the corresponding hole in S2.2.

[0073] Taking hole No. 1 as an example again:

[0074] In this embodiment, the soil body from the 3m depth to the 28m depth of the No. 1 hole is intercepted, and the soil body of each 1m is used as a "module". The permeability coefficients of each "module" are different. Geotechnical experiments are carried out on each module respectively to obtain the permeability coefficient of each module. The permeability coefficient of each module is denoted as S i (i ∈ [1, 25]);

[0075] S2.4: Obtain the "optimized horizontal seepage velocity" corresponding to each module in each hole based on Equation (3).

[0076] Taking the No. 1 hole as an example again:

[0077] Among them, the "optimized horizontal seepage velocity" V2 of module 1 is:

[0078] The "optimized horizontal seepage velocity" V of module i i is:

[0079] S3: Finite element model analysis.

[0080] Because the dam in S2 is an actual existing dam, a geometric model is established based on the actual existing dam, as shown in Figure 2 .

[0081] Figure 2 The relevant parameter settings in it are shown in Table 2.

[0082] Table 2 Dam dimensions

[0083]

[0084] Perform Figure 2 mesh generation, and after meshing, it is shown in Figure 3 .

[0085] In the finite element software, different parameter settings are carried out for different regions, and the parameter settings are shown in Table 3.

[0086] Table 3 Model parameter settings

[0087]

[0088] Establish the equation of the finite element model:

[0089] ∫v([B] T [C][B])dv{H} = {q}∫ A ( <n> T )dA (4)

[0090] In Equation (4), v is the horizontal seepage velocity; [B] is the head gradient matrix, including boundary conditions; [C] is the permeability coefficient matrix of grid cells; {H} is the nodal head vector; {q} is the velocity of the three sides of grid cells; <n>is the interpolation function vector; A is the area of the grid cell.

[0091] Taking Hole No. 1 as an example, determine the position of Hole No. 1 in the finite element model, and then input the corresponding head gradient matrix [B], grid cell permeability coefficient matrix [C], and {H} as the nodal head vector in the actual dam's Hole No. 1 into the finite element model software as actual parameters. The finite element model software can calculate the horizontal seepage velocities at different depths according to Equation (4).

[0092] Taking Hole No. 1 as an example, compare the horizontal seepage velocities from 3m to 28m deep in the finite element model with the "optimized horizontal seepage velocity" calculated by Equation (3) in S2. The comparison results are shown in Figure 4 .

[0093] From Figure 4 , it can be seen that the "optimized horizontal seepage velocity" calculated by Equation (3) is close to the result simulated by the finite element model, indicating that Equation (3) has high accuracy.

[0094] After knowing the accurate horizontal seepage velocity, it is possible to judge whether the dam is leaking according to the set seepage velocity threshold. If the horizontal seepage velocity is greater than the set threshold, the dam leaks at that position. The judgment results are shown in Figure 5 . Orange in the figure indicates general leakage (flow velocity greater than 1*10 -4 cm / s), and red indicates severe leakage (flow velocity greater than 1*10 -3 cm / s).

[0095] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can make various changes and modifications without departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.< / n> < / n>

Claims

1. An optimization method for seepage flow velocity under complex strata and steady flow fields, characterized in that, It includes the following steps: S1: Obtain the optimization coefficient through experimental exploration; optimize the expression of the horizontal flow velocity in the hole based on the optimization coefficient to obtain the optimized horizontal seepage expression; S2: Dig holes in the dam to obtain the permeability coefficients of each soil layer in the holes on the dam, and calculate the horizontal seepage velocities of each soil layer in the hole based on the optimized horizontal seepage expression in S1; S3: Use a finite element model, input the actual parameters of the dam into the finite element model, and verify the accuracy of the horizontal seepage velocity of the hole in S2.

2. The optimization method of seepage velocity under complex strata and steady flow field according to claim 1, characterized in that, Step S1 includes the following steps: S1.1: Calculate the horizontal flow velocity V inside the g-th hole d,g ; The formula is: In Equation (1), r0 represents the pore radius on the soil mass in the experiment; α represents the correction coefficient; N g,0 represents the conductivity at the initial moment of the g-th pore; N g,t represents the conductivity of the g-th pore at time t; t0 represents the time difference from the initial moment to time t; S1.2: Establish the "optimization coefficient" based on the soil layer permeability coefficient; establish the formula for the "optimized horizontal seepage velocity" based on the "optimization coefficient"; The formula is: In Equation (2), k g represents the permeability coefficient of the soil mass where the g-th hole is located in the experiment; V f，g is the "optimized horizontal seepage velocity" of the g-th hole in the experiment; is the "optimization coefficient" of the g-th hole in the experiment.

3. The optimized method for seepage flow velocity under complex strata and steady flow fields according to claim 2, characterized in that, The following steps are included in step S2: S2.1: Dig holes on the dam site, and divide the excavated soil layer in the hole into multiple modules according to the set length; S2.2: Use geotechnical experiments to obtain the permeability coefficient of each module; S2.3: Calculate the "optimized horizontal seepage velocity" of different modules in the hole using formula (2).

4. An optimization method for seepage velocity under complex strata and steady flow fields according to claim 3, characterized in that In step S1, 8 kinds of soils with different permeability coefficients are configured by means of particle size distribution. The holes dug on each soil body are all circular holes with the same diameter.

5. The optimization method of seepage velocity under complex strata and steady flow field according to claim 4, characterized in that, In step S2, the soil body in the hole on the dam site is divided into multiple modules with a length of 1 m; the soil layer with a depth of 3 - 28 m is intercepted, and the optimized horizontal seepage velocities of each module at the depth of 3 - 28 m are calculated.

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