Method for detecting seepage flow rate of earth-rock dam based on single-hole dilution method

Abstract

The application provides a soil and rock embankment leakage flow rate detection method based on a single-hole dilution method, and breaks through the traditional technical bottleneck through multiple technical innovations: a precise tracer solution configuration is adopted, the injection mode is reasonable, forced convection mixing of the borehole water column is realized by using a pneumatic stirring mode, uniform diffusion of the tracer is realized, the water layering problem caused by manual stirring is completely eliminated, and the physical reliability of the conductivity decay curve is ensured; on the basis of the traditional dilution curve model, a borehole radius correction factor and a non-Darcy effect correction term are introduced, and an optimized flow rate formula is constructed, which compresses the error of more than 30% of the traditional method to within 5%, and significantly improves the accuracy of the vertical seepage profile output. The integrated closed-loop analysis of "tracer stratified injection-pneumatic homogeneous mixing-multi-node synchronous monitoring-flow field intelligent inversion" is realized, the dual defects of operation dispersion and theoretical limitation of the traditional single-hole method are overcome, and a quantifiable and reproducible quantitative diagnostic tool for embankment leakage channel positioning is provided.

Description

TECHNICAL FIELD

[0001] The present application mainly relates to the technical field of earth-rock dam leakage detection, and particularly relates to a method for detecting earth-rock dam leakage flow rate based on single-hole dilution method. BACKGROUND

[0002] In current earth-rock dam leakage detection, the single-hole dilution method is widely used due to low cost, good site adaptability, direct determination of seepage velocity, and no need for parameter conversion. The single-hole dilution method is a technical method for quantitatively determining the groundwater seepage velocity by monitoring the change rule of the concentration of a tracer in a borehole with time. The principle is based on the convection-diffusion process of the tracer in the aquifer and the law of conservation of mass. However, in actual detection, the method has the following technical bottlenecks:

[0003] The initial mixing uniformity is insufficient. The simple liquid injection method (such as pouring a whole tank) and manual stirring easily cause uneven distribution of the tracer or stratification of the water column, which affects the reliability of the conductivity decay curve. The operation process is discrete and inefficient. The concentration of the tracer is estimated by relying on manual experience. The injection depth is not accurately controlled. The stirring intensity and time lack quantitative standards. Human errors are easily introduced in the connection of each link. The existing seepage flow rate calculated based on the dilution curve ignores the geometric distortion (local flow rate amplification effect) and non-Darcy seepage (inertial resistance change under high Reynolds number) caused by the borehole, resulting in systematic distortion of the flow rate calculation results. SUMMARY

[0004] To solve the problems of the prior art, the present application provides a method for detecting earth-rock dam leakage flow rate based on single-hole dilution method, which provides a quantifiable and reproducible quantitative diagnostic tool for dam leakage channel positioning.

[0005] The technical scheme of the present application is as follows:

[0006] The method for detecting earth-rock dam leakage flow rate based on single-hole dilution method comprises the following steps:

[0007] S1, a monitoring array equipped with multiple conductivity-temperature composite sensors is vertically placed in a borehole water column, and is fixed at a predetermined position. The depth position of each sensor from the borehole mouth is accurately recorded. The conductivity and water temperature of the water body at different depths in the borehole are read, and the conductivity at the standard temperature is corrected. The average value of the conductivities at all depths is calculated as the background value of the conductivity at the temperature corrected position.

[0008] S2, an experiment is conducted to establish the relationship between the conductivity and the concentration, to obtain the relationship between the conductivity at the standard temperature and the concentration of the tracer solution. The required mass of the tracer solution is calculated based on the target conductivity, and the tracer solution is prepared.

[0009] S3, inject the prepared tracer solution into the borehole;

[0010] S4, deliver compressed air to the borehole for aeration mixing, so that the tracer solution diffuses in the whole water column to form a uniform flow field;

[0011] S5, re-vertically place the monitoring array in the water column and accurately fix it at the same depth position in step S1, record the conductivity and water temperature of all sensors at set time intervals during the dilution process, and stop recording when the dilution process tends to be stable;

[0012] S6, temperature correct the conductivity recorded in step S5 to obtain the conductivity at standard temperature, based on the dilution curve, introduce the borehole radius correction factor and non-Darcy effect correction term to establish the corrected flow velocity formula, calculate the flow velocity at each position based on the corrected flow velocity formula, and output the seepage velocity data along the borehole depth distribution.

[0013] Further, in step S1, the conductivity temperature correction uses the following formula (1):

[0014] K 25 = K / [1+ D ( T -25)](1);

[0015] In the formula, K 25 is the corrected conductivity of the water body at 25℃ standard temperature, D is the temperature coefficient; T is the water temperature of the water column in the borehole, K is the conductivity of the water body in the borehole.

[0016] Further, in step S2, the specific process of establishing the conductivity-concentration relationship by experiment is as follows:

[0017] 1) In the laboratory, use the water source near the borehole to prepare tracer solutions with different concentrations;

[0018] 2) Measure the conductivity value and the corresponding tracer solution concentration of each solution at standard temperature;

[0019] 3) Establish the relationship between the conductivity and the concentration of the tracer solution at standard temperature by linear regression (2):

[0020] K 25示踪剂 = a · C + b (2);

[0021] In the formula, K25示踪剂 is the conductivity of tracer at standard temperature of 25℃; C is the concentration of tracer solution; a is the proportionality coefficient; b is the background conductivity.

[0022] Further, in step S2, the required tracer solution mass calculation process is as follows:

[0023] 1) Calculate the target concentration according to formula (2) and the target conductivity, formula (3) as follows:

[0024] C target K 25 target b a (3);

[0025] 2) Measure the water level depth in the borehole and calculate the water column volume, formula (4) as follows:

[0026] V= πr 2 H (4);

[0027] Calculate the required tracer solution mass, formula (5) as follows:

[0028] m C target C b M NaCl (5);

[0029] In the formula, C target is the target concentration of tracer solution, K 25 target is the target conductivity, K 25 target N K 25 b N is the target multiple, K 25 b is the conductivity background value calculated in step S1, V is the water column volume of the borehole, H is the water level depth in the borehole, r is the borehole radius, m is the required tracer solution mass, C _​​​​​​​​​​​​​​​​​b the average background concentration in the borehole, M NaCl the molar mass of the tracer solution.

[0030] Further, the step S3 is specifically as follows:

[0031] Slowly lower the end of the tracer injection conduit into the borehole and keep it at about 0.5 m from the bottom of the borehole;

[0032] Test the pipeline pressure to confirm that the system has no leakage;

[0033] Open the valve of the tracer injection conduit and start injecting the prepared tracer solution at a stable low speed of no more than 5 L / min, divide the tracer solution into four equal parts and inject 25% of the total amount each time, before each injection, adjust the depth of the conduit to the predetermined position for injection, and the injection positions are respectively at 0.5 m from the bottom of the borehole, 1 / 4 of the water column depth from the bottom of the borehole, 1 / 2 of the water column depth from the bottom of the borehole, and 3 / 4 of the water column depth from the bottom of the borehole.

[0034] After completing the four injections, pull the tracer injection conduit out of the borehole.

[0035] Further, the step S4 is specifically as follows:

[0036] Arrange the annular flexible nylon aeration pipe in the borehole to ensure that it covers the entire water column depth, fix the aeration pipe bottom with additional weights, arrange the exhaust holes at a certain distance apart, connect the compressed air source to the aeration pipe, and deliver compressed air at a flow rate of 30-50 L / min for aeration and stirring, continue aeration and stirring for 8-10 minutes to ensure that the tracer solution is uniformly dispersed in the entire water column to form a uniform flow field, after aeration is completed, first close the compressed air source and slowly pull out the aeration pipe.

[0037] Further, in step S6, the corrected flow rate formula (6) is as follows:

[0038] v 修正 = β · K · πr / (2 α 1 t )·ln( G 25_0 / K 25 _ t ) (6);

[0039] wherein the borehole radius correction factor β The expression (7) is as follows:

[0040] β= (1 + (1 + 2 r L n (7) ;

[0041] Non-Darcy effect correction term K Expression (8) is as follows:

[0042] G = 1 + (1 + 2 a R e (8) ;

[0043] In the formula, G 25_0 is the conductivity at time t = 0 in step S5; t K 25 _ t is the conductivity at time t = t in step S5; t t is the measurement time; r is the radius of the borehole; α 1 is a correction coefficient, L is the characteristic length of the aquifer, n is an empirical index, a 2 is an empirical coefficient, and Re is the Reynolds number.

[0044] Advantages of the present application:

[0045] The present application provides a soil and rock dam leakage flow rate detection method based on a single-hole dilution method, which breaks through the traditional technical bottleneck through multiple technical innovations: precise tracer solution configuration is adopted, injection methods are reasonable, forced convection mixing of the borehole water column is realized by using a pneumatic stirring method, uniform diffusion of the tracer is realized, the water layering problem caused by manual stirring is completely eliminated, and the physical reliability of the conductivity decay curve is ensured; on the basis of the traditional dilution curve model, a borehole radius correction factor and a non-Darcy effect correction term are introduced, and an optimized flow rate formula is constructed, which compresses the error of more than 30% of the traditional method to within 5%, significantly improving the accuracy of the vertical seepage profile output. The integration of "tracer stratified injection-pneumatic homogeneous mixing-multi-node synchronous monitoring-flow field intelligent inversion" realizes an integrated closed loop analysis, and overcomes the dual defects of operation dispersion and theoretical limitation of the traditional single-hole method, providing a quantifiable and reproducible quantitative diagnostic tool for dam leakage channel positioning. BRIEF DESCRIPTION OF DRAWINGS

[0046] K is a flowchart of the present application;

[0047] Figure 1 is a tracer solution concentration and conductivity relationship curve schematic diagram of the present application;

[0048] Figure 2 ​​​​​Fig. 2 is a schematic diagram of the distribution curve of the flow rate in the two boreholes of the present application. DETAILED DESCRIPTION

[0049] The present application is further illustrated with reference to the accompanying drawings and specific examples. It is to be understood that these examples are only used to illustrate the present application and not intended to limit the scope of the present application. Furthermore, it is to be understood that those skilled in the art can make various modifications or changes to the present application after reading the content of the present application, and these equivalent forms also fall within the scope defined by the present application.

[0050] The present embodiment provides a soil and rock dam leakage flow rate detection method based on single-hole dilution method, and the main flow is as shown in Fig. 1. Figure 3

[0051] The leakage flow rate detection method proposed in the present embodiment is mainly realized by the following leakage flow rate detection device. The device mainly includes a tracer injection module, a pneumatic stirring module, a monitoring array, and an intelligent analysis platform.

[0052] Tracer injection module: The module is composed of a liquid storage tank, a pressure-resistant conduit system (including sectional valves), a pressure test unit, and a cleaning unit. The liquid storage tank is used to store the pre-configured tracer solution; the pressure-resistant conduit is equipped with an adjustable-depth injection inlet valve at the end, which realizes accurate stratified injection; the pressure test unit detects the system tightness by pressurizing to 0.5 MPa and maintaining pressure; the cleaning unit thoroughly flushes the pipeline with high-pressure clean water after injection to prevent residual contamination.

[0053] Pneumatic stirring module: The module includes a flexible ring-shaped aeration pipe (with uniform air outlet holes and bottom counterweight) and a compressed air pump (flow rate 30-50 L / min). The aeration pipe covers the entire water column depth of the borehole, and the bottom counterweight ensures underwater stability; the air pump provides a constant compressed air flow, which forms a micro-bubble group through the air outlet holes.

[0054] Monitoring array: The module is composed of a multi-node conductivity-temperature composite sensor array, an adjustable interval fixed support, a depth encoder, and a data acquisition terminal. The sensor spacing can be dynamically adjusted according to the water column height; the depth encoder accurately records the position of each node from the orifice; the data acquisition terminal stores the original conductivity and water temperature data in real time.

[0055] ​Intelligent Analysis Platform: This platform integrates data preprocessing, model calculation, and visualization systems, including a conductivity-temperature correction algorithm, a seepage velocity correction model, a profile mapping module, and a human-computer interaction interface. Its functions cover accurate calculation of seepage velocity and visualization of two-dimensional flow velocity profiles: First, the original conductivity values ​​are uniformly corrected to the 25℃ standard value; second, based on the borehole radius correction factor β and the non-Darcy effect correction term γ, the traditional dilution curve model is optimized to eliminate geometric distortion and inertial effect errors; finally, a seepage velocity profile map along the borehole depth is output, revealing the spatial distribution characteristics of seepage channels in earth-rock dams.

[0056] Figure 1 The diagram shown is a flowchart of the main operation of the seepage velocity detection method for earth-rock dams based on the single-hole dilution method proposed in this embodiment. The specific process and principle are as follows:

[0057] (1) Measure the background value of electrical conductivity in the borehole

[0058] A monitoring array equipped with multiple conductivity-temperature composite sensors is vertically placed into the borehole water column and fixed in a predetermined position (the sensor spacing can be adjusted according to the height of the water column in the borehole), accurately recording the depth of each sensor from the surface of the borehole opening.

[0059] After turning on the data acquisition system and waiting for the sensor readings to stabilize (reading change <1% for 3 consecutive minutes), measure the conductivity of the water at different depths within the borehole. Figure 1 and water temperature T .

[0060] Using formula (1), the measured depths are... K Corrected to the conductivity value at the standard temperature of 25°C.

[0061] K 25 = K / [1+ K ( T -25)](1;

[0062] In the formula: D 25 The conductivity is the electrical conductivity at a standard temperature of 25°C. K Temperature coefficient; T This refers to the water temperature of the water column inside the borehole.

[0063] Calculate the conductivity at all depths D 25 The average value is used as the temperature-corrected baseline conductivity value at that borehole location. K 25 _ b .

[0064] (2) Prepare tracer solution

[0065] Target tracer solution concentration setting: in order to make the average conductivity in the borehole significantly increase after the tracer solution injection (usually the target is to increase 5-10 times), set the target conductivity at 25°C standard temperature K 25 _ target = N · K 25 _ b ( N Target multiple).

[0066] Establish the conductivity-concentration relationship (as shown in K ):

[0067] ① In the laboratory, use the water source near the borehole (or similar water quality) to prepare tracer solutions of different concentrations.

[0068] ② Measure the conductivity value of each concentration of tracer solution at 25°C Figure 2 25示踪剂 and the corresponding tracer solution concentration C .

[0069] ③ Through linear regression, establish the relationship between the conductivity of the tracer solution at 25°C standard temperature and the concentration (2):

[0070] K 25示踪剂 = a · C + b (2);

[0071] In the formula: K 25示踪剂 is the conductivity of the tracer solution at 25°C standard temperature (μS / cm); C is the concentration of the tracer solution (mol / L); a is the proportionality coefficient; b is the background conductivity (μS / cm), approximately equal to K 25 _ b .

[0072] Calculate the mass of the required tracer solution:

[0073] ① Target concentration: according to formula (2) and target conductivity K 25 _ target , calculate the target concentration of the tracer solution, formula (3) as follows:

[0074] C _ target =( K 25 _target - b ) / a (3);

[0075] 2. Drilling water column volume: measure the water level depth in the drilling and the drilling radius H , calculate the water column volume, formula (4) as follows: r

[0076] V= πr 2 H (4);

[0077] 3. The tracer solution mass m that needs to be increased, the calculation formula (5) as follows:

[0078] m = ( C _ target - C _ b ) · V · M NaCl (5);

[0079] In the formula: C _ b The average background concentration in the drilling; V is the water column volume (L) in the drilling; M NaCl The molar mass of the tracer.

[0080] (3) Tracer solution injection

[0081] The end of the conduit is connected to the outlet valve of the liquid storage tank. Slowly lower the end of the conduit into the drilling and keep it about 0.5 m from the bottom of the hole (avoid direct insertion into the sediment to cause disturbance);

[0082] Pipeline pressure test: close the conduit end valve, test the ground connection pipeline to 0.5 MPa, and keep the pressure for 15 minutes without pressure drop, to confirm that the system has no leakage.

[0083] Inject tracer solution: open the valve and start injecting the prepared tracer solution at a stable low speed not greater than 5 L / min. Divide the tracer solution into four equal parts and inject 25% of the total amount each time. Before each injection, adjust the conduit depth to the predetermined position for injection. The injection positions are about 0.5 m from the bottom of the hole, 1 / 4 water column depth from the bottom of the hole, 1 / 2 water column depth from the bottom of the hole, and 3 / 4 water column depth from the bottom of the hole, respectively. After completing the four injections, first close the outlet valve of the liquid storage tank, then close the injection inlet valve at the end of the conduit, slowly and evenly pull the tracer injection conduit out of the drilling, and immediately flush the entire injection pipeline system with sufficient clean water to prevent residual tracer from contaminating subsequent tests or equipment.

[0084] (4) Stir the water body​

[0085] The annular flexible nylon aeration pipe is arranged in the borehole, ensuring covering the whole water column depth, and the aeration pipe bottom is fixed with additional weight. The air exhaust holes are arranged at a certain distance between the aeration pipes, and the compressed air source (air pump) is connected to the aeration pipe system. The compressed air is delivered at a flow rate of 30-50 L / min to carry out aeration stirring. The aeration stirring is continued for 8-10 minutes to ensure that the tracer solution is uniformly diffused in the whole water column to form a uniform flow field. After the aeration is completed, the air pump is first turned off, and the aeration pipe is slowly pulled out to avoid disturbing the water body.

[0086] (5) Measurement of conductivity change over time

[0087] Immediately after the stirring is stopped, the monitoring array is re-vertically placed in the water column and accurately fixed at the same depth position recorded in step (1).

[0088] The data acquisition system is started, and the recording interval (such as every 1 minute) is set to automatically record the conductivity values and water temperature at all sensor positions.

[0089] The monitoring is continued, and when the continuous conductivity change rate of all monitoring points is less than 0.5% / h, it is considered that the dilution process tends to be stable, and the recording is stopped.

[0090] (6) Seepage flow rate calculation and analysis

[0091] Data preprocessing: for the conductivity values measured at all times and all depths, the formula (1) is applied for temperature correction to obtain the conductivity at the standard temperature of 25°C.

[0092] Seepage flow rate correction:

[0093] Currently, the seepage flow rate is commonly calculated based on the dilution curve (conductivity-time decay model) (formula (9)), but this formula does not consider the influence of the borehole itself on the water flow velocity field, resulting in distortion of the measured flow rate.

[0094] v = πr 2 / (2 α 1 t )·ln( K 25_0 / K 25 _ t )(9);

[0095] In the formula: K 25_0 is the conductivity at time t =0; K 25 _t t t conductivity at time t; t t r r α 1

[0096] To reduce the deviation of the estimated flow velocity caused by the local velocity amplification and non-Darcy seepage (inertial effect) of the borehole itself, the borehole radius correction factor β and the non-Darcy effect correction term K are introduced into the formula (6) to establish the corrected flow velocity formula.

[0097] The borehole radius correction factor β , which is related to the borehole radius r and the characteristic length of the aquifer L , is used to correct the local flow field distortion caused by the borehole, and the expression (7) is as follows:

[0098] β = 1+ r / L ) n (7);

[0099] In the formula: n is an empirical index (usually 1-2)

[0100] The non-Darcy effect correction term G is introduced when the seepage velocity is high and the Reynolds number G exceeds the critical value Re crit , which corrects the inertial term influence, and the formula (8) is as follows:

[0101] Re = 1+ a 2· R e (8);

[0102] In the formula: a 2 is an empirical coefficient, G is the Reynolds number.

[0103] Finally, the corrected seepage flow velocity formula (6) is as follows:

[0104] v 修正 = β · Re · πr / (2 α 1 t )·ln( G 25_0 / K 25 _t ) (6);

[0105] Calculation and output:

[0106] The position information of each sensor is recorded by the intelligent analysis platform, and the flow rate at each position is calculated by using the built-in algorithm (formula (6)), to obtain the corrected flow rate corresponding to the depth of each sensor. Subsequently, the platform outputs the seepage velocity profile along the depth of the borehole, realizing the detection of the seepage flow rate of the earth and rockfill dam.

[0107] K Figure 3 As shown in FIG. 6, which is a schematic diagram of the distribution curve of the seepage flow rate in two boreholes output by the method of the present embodiment, the corresponding relationship between the depth of the borehole and the seepage flow rate can be determined intuitively, and the output result has very high precision.

Claims

1. A method for detecting seepage velocity in earth-rock dams based on single-hole dilution, characterized in that, Includes the following steps: S1. Vertically place the monitoring array equipped with multiple conductivity-temperature composite sensors into the borehole water column, fix it at the predetermined position, accurately record the depth of each sensor from the surface of the borehole opening, read the sensor data to obtain the conductivity and water temperature of the water at different depths in the borehole, correct it to the conductivity at the standard temperature, and calculate the average conductivity at all depths as the temperature-corrected baseline conductivity value at the borehole location. S2. The experiment establishes the conductivity-concentration relationship, obtains the relationship between conductivity and tracer solution concentration at standard temperature, calculates the required tracer solution mass based on the target conductivity, and prepares the tracer solution. S3. Inject the prepared tracer solution into the borehole; S4. Compressed air is supplied into the borehole for aeration and stirring, so that the tracer solution diffuses throughout the water column to form a uniform flow field. S5. Place the monitoring array back vertically into the water column and fix it precisely at the same depth position as in step S1. Record the conductivity and water temperature of all sensors during the dilution process at the set time intervals. Stop recording after the dilution process tends to stabilize. S6. Perform temperature correction on the conductivity recorded in step S5 to obtain the conductivity at standard temperature. Based on the dilution curve, introduce the borehole radius correction factor and the non-Darcy effect correction term to establish the corrected flow velocity formula. Calculate the flow velocity at each location based on the corrected flow velocity formula and output the seepage velocity data distributed along the borehole depth. In step S6, the corrected flow velocity formula (6) is as follows: v 修正 = β · γ · πr / (2 α 1 t )·ln( κ 25_0 / κ 25 _ t )（6） Among them, the borehole radius correction factor β The expression (7) is as follows: β =(1+ r / L ) n （7） Non-Darcy effect correction term γ Expression (8) is as follows: γ =1+ a 2· R e（8） In the formula, κ 25_0 For the time in step S5 t Conductivity at 0; κ 25 _ t For the time in step S5 t conductivity at that time; t For measuring time; r The radius of the borehole; α 1 is the correction factor. L The characteristic length of the aquifer. n It is an experience index. a 2 is the empirical coefficient, and Re is the Reynolds number.

2. The method for detecting seepage velocity in earth-rock dams based on single-hole dilution method according to claim 1, characterized in that, In step S1, the conductivity temperature correction is performed using the following formula (1): κ 25 = κ / [1+ δ ( T -25)]（1） In the formula, κ 25 The corrected conductivity of water at a standard temperature of 25°C. δ Temperature coefficient; T The water temperature of the water column inside the borehole. κ The electrical conductivity of the water in the borehole.

3. The method for detecting seepage velocity in earth-rock dams based on single-hole dilution method according to claim 1, characterized in that, In step S2, the specific process of establishing the conductivity-concentration relationship is as follows: 1) In the laboratory, tracer solutions of different concentrations were prepared using water source near the borehole; 2) Measure the conductivity of each solution and the corresponding tracer solution concentration at the standard temperature; 3) Establish the relationship between conductivity and concentration of tracer solution at standard temperature using linear regression (2): κ 25示踪剂 = a · C + b （2） In the formula: κ 25示踪剂 The conductivity of the tracer at a standard temperature of 25°C; C The concentration of the tracer solution; a This is the proportionality coefficient; b The background conductivity is given.

4. The method for detecting seepage velocity in earth-rock dams based on single-hole dilution method according to claim 3, characterized in that, The calculation process for the required tracer solution mass in step S2 is as follows: 1) Calculate the target concentration based on formula (2) and the target conductivity. Formula (3) is as follows: C _ target =（ κ 25 _ target - b ） / a （3） 2) Calculate the water column volume by measuring the water level depth and borehole radius, using formula (4) as follows: V= πr 2 H （4） The required increase in tracer solution mass is calculated using formula (5) as follows: m =（ C _ target - C _ b ）·V· M NaCl （5） In the formula, C _ target To determine the target concentration of the tracer solution, κ 25 _ target For the target conductivity, κ 25 _ target = N · κ 25 _ b N is the target multiple. κ 25 _ b The conductivity background value calculated in step S1, where V is the borehole water column volume. H This represents the water level depth inside the borehole. r Where is the borehole radius, m For the required tracer solution mass, C _ b This represents the average background concentration within the borehole. M NaCl This represents the molar mass of the tracer solution.

5. The method for detecting seepage velocity in earth-rock dams based on single-hole dilution method according to claim 1, characterized in that, The specific process of step S3 is as follows: The tracer injection catheter is slowly lowered into the borehole and kept at a distance of about 0.5m from the bottom of the hole. The pipeline pressure was tested to confirm that there were no leaks in the system; Open the valve of the tracer injection conduit and start injecting the prepared tracer solution at a stable low speed of no more than 5 L / min. Divide the tracer solution into four equal parts for injection, injecting 25% of the total amount each time. Before each injection, adjust the conduit depth to the predetermined position for injection. The injection positions are 0.5 m from the bottom of the borehole, 1 / 4 water column from the bottom of the borehole, 1 / 2 water column from the bottom of the borehole, and 3 / 4 water column from the bottom of the borehole. After four injections, the tracer injection catheter is withdrawn from the borehole.

6. The method for detecting seepage velocity in earth-rock dams based on single-hole dilution method according to claim 1, characterized in that, The specific process of step S4 is as follows: Arrange the annular flexible nylon aeration tube inside the borehole to ensure coverage of the entire water column depth. Add a counterweight to the bottom of the aeration tube for fixation. Arrange exhaust holes at certain intervals in the aeration tube. Connect the compressed air source to the aeration tube and deliver compressed air at a flow rate of 30–50 L / min for aeration and stirring. Continue aeration and stirring for 8–10 minutes to ensure that the tracer solution is evenly diffused throughout the water column to form a uniform flow field. After aeration, first turn off the compressed air source and slowly pull out the aeration tube.

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