Laboratory calibration method for reducing flow velocity of recovery force nozzle of gravity anchor

Abstract

The invention relates to the technical field of ocean engineering, in particular to a laboratory calibration method for reducing the flow velocity of a gravity anchor recovery force nozzle. The method comprises the following steps: S1, obtaining a field soil body needing gravity anchor recovery operation through a thin-wall soil sampler, and preparing a triaxial test sample; s2, calculating confining pressure and axial pressure according to field conditions; s3, the prepared sample is installed on a triaxial apparatus, the calculated confining pressure and axial pressure are applied, initial back pressure is applied through a back pressure system of the triaxial apparatus, and the water injection amount changing along with time is recorded; s4, performing a multi-pressure-difference test and fluid viscosity correction based on the initial back pressure applied in S3; and S5, according to a test result, carrying out actual working condition flow velocity conversion. The back pressure value is changed, the corresponding water injection rate and time are recorded, and the flow velocity is corrected in combination with factors such as fluid viscosity, so that the accuracy of an experimental result is improved, and a scientific basis is provided for optimizing a nozzle design.

Description

Technical Field

[0001] The present invention relates to the field of marine engineering technology, in particular to a laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle. Background Art

[0002] In marine engineering, especially deep-sea development, anchor foundations often need to be recycled and reused. For example, starting anchors used in submarine pipeline laying, including gravity anchors and suction anchors, are often required for retrieving these anchor foundations. Retrieving these anchor foundations requires appropriate lifting equipment, but the capacity of these lifting equipment is often limited due to the operating environment. To enable the recovery of large gravity anchors using smaller lifting equipment, jetting lines can be installed on the anchors to reduce the force required to recover them.

[0003] To reduce the recovery force, water jet pipes and water jet holes are typically deployed to disrupt the contact surface between the gravity anchor and the soil. This reduces the top suction force and skirt friction during the gravity anchor recovery process, thereby lowering recovery costs. When laying pipes and designing water jet holes, properly evaluating the flow rate of the water jet holes is crucial for ensuring a reasonable assessment of the water jet pipe's ability to break through the soil and completing the design of the water jet piping.

[0004] In an existing laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle, inaccurate measurements can occur when measuring soil parameters due to limitations in experimental equipment precision or operational errors. Fluid viscosity and nozzle geometry significantly affect flow rate, but in practice, accurately determining these parameters and making effective corrections is difficult. When considering different pump performance, nozzle sizes, and on-site construction conditions, converting data obtained under laboratory conditions to parameters under actual working conditions involves certain uncertainties and errors. In summary, a laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle is provided. Summary of the Invention

[0005] The purpose of the present invention is to provide a laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle, so as to solve the problem raised in the above background technology that in an existing laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle, when measuring soil parameters, due to the accuracy limitations of the experimental equipment or operating errors, the measurement results may be inaccurate, and the fluid viscosity and nozzle geometry have a significant impact on the flow rate, but in actual operation, it is more difficult to accurately determine these parameters and make effective corrections. When it comes to different water pump performance, nozzle sizes and on-site construction conditions, there are certain uncertainties and errors in converting the data obtained under laboratory conditions into parameters under actual working conditions.

[0006] To achieve the above object, the present invention provides a laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle, comprising the following steps:

[0007] S1. Use a thin-wall soil sampler to obtain the on-site soil that needs to be recovered by the gravity anchor and prepare the triaxial test specimen;

[0008] S2. Calculate the confining pressure and axial pressure according to the site conditions;

[0009] S3. Install the prepared specimen on the triaxial apparatus, apply the calculated confining pressure and axial pressure, apply the initial back pressure through the back pressure system of the triaxial apparatus, and record the water injection volume changing with time;

[0010] S4, based on the initial back pressure applied in S3, conduct multiple pressure differential tests and fluid viscosity correction;

[0011] S5. According to the test results, the actual working flow rate is converted.

[0012] As a further improvement of the present technical solution, in S1, the specific steps of preparing the triaxial test specimen are as follows:

[0013] Measure soil parameters and calculate relevant sample data;

[0014] The sample data include sample volume, internal friction angle, cohesion and saturation;

[0015] Calculate the sample volume:

[0016]

[0017] Where, V represents the sample volume; D represents the diameter; H represents the height;

[0018] Calculate the internal friction angle through direct shear test:

[0019]

[0020] Where φ represents the internal friction angle; τ 峰值 represents the peak shear stress; σ n represents the normal stress;

[0021] Calculate the cohesion through triaxial compression test:

[0022]

[0023] Where c represents cohesion; σ1 represents the maximum principal stress; σ3 represents the minimum principal stress; (σ1-σ3) 破坏 Indicates soil damage;

[0024] Calculate saturation:

[0025]

[0026] Where S r represents saturation; w represents water content; G s represents the specific gravity of soil particles; e represents the porosity ratio.

[0027] As a further improvement of this technical solution, in S2, the specific calculation steps for calculating the confining pressure and axial pressure according to the on-site conditions are as follows:

[0028] Confining pressure calculation:

[0029] σ h =(1-sinφ)·σ v +c·tanφ;

[0030] Where σ h represents horizontal stress; σ v represents vertical stress;

[0031] Axial compression calculation:

[0032]

[0033] Where M is the mass of the gravity anchor; A is the area of the anchor top; and g is the acceleration due to gravity.

[0034] As a further improvement of the present technical solution, in S3, the prepared sample is mounted on a triaxial apparatus, the calculated confining pressure and axial pressure are applied, an initial back pressure is applied through the back pressure system of the triaxial apparatus, and the specific steps of recording the water injection volume changing with time are as follows:

[0035] S3.1. Install the specimen in the pressure chamber of the triaxial apparatus to ensure tightness.

[0036] S3.2. Apply confining pressure and axial pressure through the hydraulic system to maintain the stress stability time;

[0037] S3.3. Apply initial back pressure through the back pressure system of the triaxial apparatus, perform permeability coefficient correction, and record the water injection volume that changes with time.

[0038] As a further improvement of the present technical solution, in S3.3, the specific process of applying the initial back pressure through the back pressure system of the triaxial apparatus, performing permeability coefficient correction, and recording the water injection volume changing with time is as follows:

[0039] The initial back pressure P is applied by the back pressure system of the triaxial apparatus. 反 ;

[0040] Record the change of water injection volume over time during the back pressure application process and calculate the permeability coefficient:

[0041]

[0042] Where, k represents the permeability coefficient; Q represents the water injection volume; t represents the time; ΔP represents the pressure difference; L represents the cross-sectional area;

[0043] Permeability correction:

[0044] k 修正 =k 干燥 ·(1+0.5·S r );

[0045] Where k 修正 represents the permeability coefficient after saturation correction; k 干燥 Indicates the permeability coefficient in dry state.

[0046] As a further improvement of the present technical solution, in S4, the specific steps of performing the multi-pressure differential test and fluid viscosity correction based on the initial back pressure applied in S3 are as follows:

[0047] S4.1. Adjust the pressure difference by adjusting the back pressure;

[0048] S4.2. Test the flow rate and introduce fluid viscosity to optimize and correct the flow rate.

[0049] As a further improvement of the present technical solution, in S4.2, the specific steps of testing the flow rate and introducing the fluid viscosity to optimize and correct the flow rate are as follows:

[0050] The test flow rate is:

[0051]

[0052] Where, v represents the test flow rate; d represents the nozzle diameter;

[0053] Considering that fluid viscosity has an impact on flow rate, fluid viscosity is introduced to optimize flow rate;

[0054] The flow rate correction formula is:

[0055]

[0056] Where v′ represents the corrected flow velocity; C d represents the flow coefficient; μ represents the fluid viscosity; l represents the nozzle length; ρ represents the fluid density.

[0057] As a further improvement of the present technical solution, in S5, the specific steps of converting the flow rate under actual working conditions according to the test results are as follows:

[0058] S5.1. Calculate the maximum flow rate of the test pump and the maximum flow rate of the on-site pump based on the test conditions and on-site parameters, and calculate the flow rate ratio;

[0059] S5.2. Use the flow rate ratio to convert the test flow rate to the actual flow rate.

[0060] As a further improvement of the present technical solution, in S5.1, the maximum flow rate of the test water pump and the maximum flow rate of the on-site water pump are calculated respectively according to the test conditions and on-site parameters. The specific process of calculating the flow rate ratio is:

[0061] Based on the reference flow rate under standard conditions, calculate the maximum flow rate of the test water pump:

[0062]

[0063] Where, v0 represents the maximum flow rate of the test water pump; v 基准 Indicates a reference flow rate based on standard conditions; C d，试验 Indicates the flow coefficient of the nozzle under test conditions; C d，实际 Indicates the discharge coefficient of the nozzle in actual application;

[0064] According to the fluid viscosity correction, calculate the maximum flow rate of the on-site water pump:

[0065]

[0066] Where, v 实际 Indicates the maximum flow rate of the on-site water pump; K represents a constant related to the water pump characteristics; l 实际 Indicates the effective length of the actual nozzle; d 实际 Indicates the actual nozzle diameter; ΔP 实际 Indicates the pressure difference in actual operation;

[0067] The flow rate ratio is obtained by the maximum flow rate of the on-site water pump and the maximum flow rate of the test water pump:

[0068]

[0069] Where R represents the flow rate ratio.

[0070] As a further improvement of the present technical solution, in S5.2, the calculation process of converting the test flow rate into the actual flow rate using the flow rate ratio is as follows:

[0071] The test flow rate is scaled up to the actual working conditions by the flow rate ratio R, taking into account the differences in the performance of the on-site pump and the geometry of the nozzle:

[0072] v 实际 =R·v0.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] 1. This laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle ensures that the simulated soil stress state closely matches the actual state through proper sampling and specimen preparation. Calculating the confining and axial pressures based on field conditions ensures consistency between the experimental conditions and the actual state, thereby enhancing the application value of the experimental results. Applying initial back pressure through the triaxial apparatus's back pressure system and recording the water injection volume over different time periods facilitates the assessment of the soil's permeability and deformation characteristics under varying pressure conditions.

[0075] 2. In this laboratory calibration method for reducing the flow rate of the gravity anchor recovery nozzle, by changing the back pressure value and recording the corresponding water injection volume and time, and combining factors such as fluid viscosity to correct the flow rate, it not only improves the accuracy of the experimental results, but also provides a scientific basis for optimizing the nozzle design. By using the data obtained from the test and the calculated flow rate ratio, the flow rate under laboratory conditions is converted into the flow rate under actual working conditions, thereby improving construction efficiency and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 The figure is a flow chart of the overall method of the present invention. DETAILED DESCRIPTION

[0077] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0078] Example:

[0079] See also Figure 1 As shown, this embodiment provides a laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle, comprising the following steps:

[0080] S1. Use a thin-wall soil sampler to obtain the on-site soil that needs to be recovered by the gravity anchor and prepare the triaxial test specimen;

[0081] In this example, the specific steps for preparing the triaxial test specimen are as follows:

[0082] Measure soil parameters and calculate relevant sample data;

[0083] The sample data include sample volume, internal friction angle, cohesion and saturation;

[0084] Calculate the sample volume:

[0085]

[0086] Where, V represents the sample volume; D represents the diameter; H represents the height;

[0087] Calculate the internal friction angle through direct shear test:

[0088]

[0089] Where φ represents the internal friction angle; τ 峰值 represents the peak shear stress; σ n represents the normal stress;

[0090] Calculate the cohesion through triaxial compression test:

[0091]

[0092] Where c represents cohesion; σ1 represents the maximum principal stress; σ3 represents the minimum principal stress; (σ1-σ3) 破坏 Indicates soil damage;

[0093] Calculate saturation:

[0094]

[0095] Where S r represents saturation; w represents water content; G s represents the specific gravity of soil particles; e represents the porosity ratio.

[0096] Specifically, in a laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle, the steps of obtaining on-site undisturbed soil samples through a thin-walled soil sampler and preparing triaxial test specimens ensure the authenticity and representativeness of the experimental materials. The specific steps include measuring soil parameters (such as sample volume, internal friction angle, cohesion and saturation), which are crucial for accurately simulating the mechanical properties of soil under actual working conditions. Calculating the sample volume, determining the internal friction angle through a direct shear test, calculating the cohesion using a triaxial compression test, and calculating the saturation based on the moisture content and specific gravity of the soil particles provide basic data for the subsequent accurate calculation of the confining pressure and axial pressure, thereby ensuring the effective simulation of the actual engineering stress environment under laboratory conditions and improving the scientific nature and reliability of the entire calibration process. This process not only enhances the accuracy of the experimental results, but also provides solid data support for optimizing nozzle design and construction parameters.

[0097] S2. Calculate the confining pressure and axial pressure according to the site conditions;

[0098] In this example, based on the site conditions, the specific calculation steps for calculating the confining pressure and axial pressure are as follows:

[0099] Confining pressure calculation:

[0100] σ h =(1-sinφ)·σv +c·tanφ;

[0101] Where σ h represents horizontal stress; σ v represents vertical stress;

[0102] Axial compression calculation:

[0103]

[0104] Where M is the mass of the gravity anchor; A is the area of the anchor top; and g is the acceleration due to gravity.

[0105] Specifically, in a laboratory calibration method for reducing the flow rate of the gravity anchor recovery nozzle, the specific steps of calculating the confining pressure and axial pressure based on the field conditions played a key role. Calculating the horizontal stress and using the formula to determine the vertical stress can accurately simulate the stress state of the soil in the actual project. These calculations are based on the internal friction angle and cohesion of the soil, as well as the mass and top surface area of the gravity anchor, ensuring that the laboratory test conditions are as close to the actual situation as possible. This not only improves the accuracy and reliability of the experimental results, but also provides a solid basic data support for subsequent multi-pressure differential tests, fluid viscosity corrections, and actual working condition flow rate conversion, thereby effectively guiding the design and optimization of gravity anchor recovery operations.

[0106] S3. Install the prepared specimen on the triaxial apparatus, apply the calculated confining pressure and axial pressure, apply the initial back pressure through the back pressure system of the triaxial apparatus, and record the water injection volume changing with time;

[0107] In this example, the prepared specimen is mounted on a triaxial apparatus, the calculated confining pressure and axial pressure are applied, and an initial back pressure is applied through the triaxial apparatus's back pressure system. The specific steps for recording the time-varying water injection volume are as follows:

[0108] S3.1. Install the specimen in the pressure chamber of the triaxial apparatus to ensure tightness.

[0109] S3.2. Apply confining pressure and axial pressure through the hydraulic system to maintain the stress stability time;

[0110] S3.3. Apply initial back pressure through the back pressure system of the triaxial apparatus, perform permeability coefficient correction, and record the water injection volume that changes with time.

[0111] In this example, the initial back pressure is applied through the back pressure system of the triaxial apparatus, and the permeability coefficient is corrected. The specific process of recording the water injection volume over time is as follows:

[0112] The initial back pressure P is applied by the back pressure system of the triaxial apparatus. 反 ;

[0113] Record the change of water injection volume over time during the back pressure application process and calculate the permeability coefficient:

[0114]

[0115] Where, k represents the permeability coefficient; Q represents the water injection volume; t represents the time; ΔP represents the pressure difference; L represents the cross-sectional area;

[0116] Permeability correction:

[0117] k 修正 =k 干燥 ·(1+0.5·S r );

[0118] Where k 修正 represents the permeability coefficient after saturation correction; k 干燥 Indicates the permeability coefficient in dry state.

[0119] Specifically, in a laboratory calibration method for reducing the flow rate of the gravity anchor recovery nozzle, step S3 plays an important role in simulating the actual soil stress state and evaluating its permeability characteristics by installing the prepared specimen on a triaxial apparatus and applying the calculated confining pressure and axial pressure, and then using the back pressure system of the triaxial apparatus to apply the initial back pressure and record the injection volume that changes with time. Specifically, by applying the initial back pressure and recording the change of the injection volume with time, the permeability coefficient can be calculated, and a more accurate permeability coefficient can be obtained through saturation correction. This process not only ensures the consistency between the soil stress state under experimental conditions and the actual situation, but also provides key soil permeability data, which is crucial for accurately simulating and optimizing the fluid flow behavior in the gravity anchor recovery operation. These data lay the foundation for further multi-pressure differential testing, fluid viscosity correction and actual working condition flow rate conversion, thereby improving the scientificity and practicality of the entire calibration method.

[0120] S4, based on the initial back pressure applied in S3, conduct multiple pressure differential tests and fluid viscosity correction;

[0121] In this example, the specific steps for performing a multi-pressure differential test and fluid viscosity correction based on the initial back pressure applied by S3 are as follows:

[0122] S4.1. Adjust the pressure difference by adjusting the back pressure;

[0123] Among them, the back pressure is adjusted so that the pressure difference ΔP=P 反 -σ h ;

[0124] S4.2. Test the flow rate and introduce fluid viscosity to optimize and correct the flow rate.

[0125] In this example, the specific steps for testing the flow rate and introducing fluid viscosity to optimize the flow rate are as follows:

[0126] The test flow rate is:

[0127]

[0128] Where, v represents the test flow rate; d represents the nozzle diameter;

[0129] Considering that fluid viscosity has an impact on flow rate, fluid viscosity is introduced to optimize flow rate;

[0130] The flow rate correction formula is:

[0131]

[0132] Where v′ represents the corrected flow velocity; C d represents the flow coefficient; μ represents the fluid viscosity; l represents the nozzle length; ρ represents the fluid density.

[0133] Specifically, in a laboratory calibration method for reducing the flow rate of a gravity anchor recovery force nozzle, step S4 performs multiple pressure difference tests and fluid viscosity corrections based on the initial back pressure applied by S3, which plays a key role in accurately evaluating and optimizing the flow rate. By adjusting the back pressure to make the pressure difference, and testing the flow rate under different pressure difference conditions, the fluid viscosity is introduced to correct the flow rate, and the correction formula is used to consider the influence of factors such as fluid viscosity and nozzle geometry, so as to obtain more accurate flow rate data. This process not only improves the accuracy of the experimental results, but also provides a reliable basis for subsequent actual working condition flow rate conversion, ensuring that the test results under laboratory conditions can be effectively applied to actual engineering design and operation, optimize nozzle performance, and reduce gravity anchor recovery force. This step is a key link in achieving high-precision flow rate control and optimization in the entire calibration method.

[0134] S5. According to the test results, the actual working flow rate is converted.

[0135] In this example, based on the test results, the specific steps for converting the flow rate to the actual working condition are as follows:

[0136] S5.1. Calculate the maximum flow rate of the test pump and the maximum flow rate of the on-site pump based on the test conditions and on-site parameters, and calculate the flow rate ratio;

[0137] In this example, the maximum flow rate of the test water pump and the maximum flow rate of the on-site water pump are calculated based on the test conditions and on-site parameters. The specific process of calculating the flow rate ratio is as follows:

[0138] Based on the reference flow rate under standard conditions, calculate the maximum flow rate of the test water pump:

[0139]

[0140] Where, v0 represents the maximum flow rate of the test water pump; v 基准 Indicates a reference flow rate based on standard conditions; C d，试验 Indicates the flow coefficient of the nozzle under test conditions; C d，实际 Indicates the discharge coefficient of the nozzle in actual application;

[0141] According to the fluid viscosity correction, calculate the maximum flow rate of the on-site water pump:

[0142]

[0143] Where, v 实际 Indicates the maximum flow rate of the on-site water pump; K represents a constant related to the water pump characteristics; l 实际 Indicates the effective length of the actual nozzle; d 实际 Indicates the actual nozzle diameter; ΔP 实际 Indicates the pressure difference in actual operation;

[0144] The flow rate ratio is obtained by the maximum flow rate of the on-site water pump and the maximum flow rate of the test water pump:

[0145]

[0146] Where R represents the flow rate ratio.

[0147] S5.2. Use the flow rate ratio to convert the test flow rate to the actual flow rate.

[0148] In this example, the calculation process for converting the test flow rate to the actual flow rate using the flow rate ratio is:

[0149] The test flow rate is scaled up to the actual working conditions by the flow rate ratio R, taking into account the differences in the performance of the on-site pump and the geometry of the nozzle:

[0150] v 实际 =R·v0.

[0151] Specifically, in a laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle, the role of step S5 in converting the actual working condition flow rate according to the test results is to ensure that the data obtained under laboratory conditions can accurately reflect and be applied to the actual engineering environment. Specifically, by calculating the maximum flow rate of the test water pump and the maximum flow rate of the on-site water pump and obtaining the flow rate ratio, the flow rate data under the test conditions can be converted into the flow rate in actual operation. The maximum flow rate of the test water pump is calculated based on the reference flow rate under standard conditions, and the maximum flow rate of the on-site water pump is calculated based on the fluid viscosity correction. Subsequently, using the flow rate ratio, the test flow rate is proportionally scaled to the actual working conditions, taking into account the performance of the on-site water pump and the geometric differences of the nozzle, and finally the actual flow rate is obtained. This process not only improves the practical application value of the experimental results, but also provides a scientific basis for optimizing nozzle design, selecting a suitable water pump and setting reasonable operating parameters, thereby effectively guiding the design and implementation of the gravity anchor recovery operation. This step is a key link in achieving a seamless transition from the laboratory to the actual project, ensuring the reliability and efficiency of the design scheme.

[0152] Application examples:

[0153] S1. Use a thin-wall soil sampler to obtain the on-site soil that needs to be recovered by the gravity anchor and prepare the triaxial test specimen:

[0154] Original soil samples were collected from the site using a thin-walled soil sampler, and triaxial test specimens were prepared according to the Standard for Geotechnical Test Methods (GB / T50123-2019).

[0155] The measured soil parameters include sample volume, internal friction angle, cohesion and saturation.

[0156] S2. Calculate the confining pressure and axial pressure according to the site conditions:

[0157] Horizontal and vertical stresses are calculated based on soil parameters to ensure simulation of stress states in actual projects.

[0158] S3. Install the prepared specimen on the triaxial apparatus, apply the calculated confining pressure and axial pressure, and apply the initial back pressure through the back pressure system of the triaxial apparatus. Record the water injection volume that changes with time:

[0159] Install the specimen in the pressure chamber of the triaxial apparatus to ensure tightness.

[0160] Apply confining pressure and axial pressure and maintain stabilization time.

[0161] Apply initial back pressure and record the change of water injection volume over time, calculate the permeability coefficient and make corrections.

[0162] S4: Based on the initial back pressure applied in S3, perform a multi-pressure differential test and fluid viscosity correction:

[0163] Adjust the back pressure to change the pressure differential.

[0164] Test the flow rate under different pressure difference conditions and introduce fluid viscosity to correct the flow rate. Use the formula to calculate the corrected flow rate.

[0165] S5. According to the test results, the actual working flow rate conversion is performed:

[0166] Calculate the maximum flow rate of the test water pump and the maximum flow rate of the on-site water pump to obtain the flow rate ratio.

[0167] Use the flow rate ratio to convert the test flow rate to the actual operating flow rate.

[0168] Through the above steps, the laboratory can accurately simulate and evaluate the soil mechanical properties and fluid flow behavior in actual engineering projects, thereby optimizing the nozzle design and flow rate control in gravity anchor retrieval operations.

[0169] The basic principles, main features, and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited to the above-described embodiments. The above-described embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention claimed.

Claims

1. A laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle, characterized by: The following steps are involved: S1. Use a thin-wall soil sampler to obtain the on-site soil that needs to be recovered by the gravity anchor and prepare the triaxial test specimen; S2. Calculate the confining pressure and axial pressure according to the site conditions; S3. Install the prepared specimen on the triaxial apparatus, apply the calculated confining pressure and axial pressure, apply the initial back pressure through the back pressure system of the triaxial apparatus, and record the water injection volume changing with time; S4, based on the initial back pressure applied in S3, conduct multiple pressure differential tests and fluid viscosity correction; S5. According to the test results, the actual working flow rate is converted.

2. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 1, characterized in that: In S1, the specific steps of preparing the triaxial test specimen are: Measure soil parameters and calculate relevant sample data; The sample data include sample volume, internal friction angle, cohesion and saturation; Calculate the sample volume: Where, V represents the sample volume; D represents the diameter; H represents the height; Calculate the internal friction angle through direct shear test: Where φ represents the internal friction angle; τ 峰值 represents the peak shear stress; σ n represents the normal stress; Calculate the cohesion through triaxial compression test: Where c represents cohesion; σ1 represents the maximum principal stress; σ3 represents the minimum principal stress; (σ1-σ3) 破坏 Indicates soil damage; Calculate saturation: Where S r represents saturation; w represents water content; G s represents the specific gravity of soil particles; e represents the porosity ratio.

3. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 1, characterized in that: In S2, the specific steps for calculating the confining pressure and axial pressure according to the on-site conditions are as follows: Confining pressure calculation: s h =(1-sinφ)·σ v +c·tanφ; Where, σ h represents horizontal stress; σ v represents vertical stress; Axial compression calculation: Where M is the mass of the gravity anchor; A is the area of the anchor top; and g is the acceleration due to gravity.

4. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 1, characterized in that: In S3, the prepared sample is mounted on the triaxial apparatus, the calculated confining pressure and axial pressure are applied, and the initial back pressure is applied through the back pressure system of the triaxial apparatus. The specific steps of recording the water injection volume changing with time are as follows: S3.

1. Install the specimen in the pressure chamber of the triaxial apparatus to ensure tightness. S3.

2. Apply confining pressure and axial pressure through the hydraulic system to maintain the stress stability time; S3.

3. Apply initial back pressure through the back pressure system of the triaxial apparatus, perform permeability coefficient correction, and record the water injection volume that changes with time.

5. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 4, characterized in that: In S3.3, the specific process of applying the initial back pressure through the back pressure system of the triaxial apparatus, performing the permeability coefficient correction, and recording the water injection volume changing with time is as follows: The initial back pressure P is applied by the back pressure system of the triaxial apparatus. 反 ; Record the change of water injection volume over time during the back pressure application process and calculate the permeability coefficient: Where, k represents the permeability coefficient; Q represents the injection volume; t represents the time; ΔP represents the pressure difference; L represents the cross-sectional area; Permeability correction: k 修正 =k 干燥 ·(1+0.5·S r ); Where k 修正 represents the permeability coefficient after saturation correction; k 干燥 Indicates the permeability coefficient in dry state.

6. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 1, characterized in that: In S4, the specific steps of performing the multi-pressure differential test and fluid viscosity correction based on the initial back pressure applied in S3 are as follows: S4.

1. Adjust the pressure difference by adjusting the back pressure; S4.

2. Test the flow rate and introduce fluid viscosity to optimize and correct the flow rate.

7. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 1, characterized in that: In S4.2, the specific steps of testing the flow rate and introducing the fluid viscosity to optimize and correct the flow rate are: The test flow rate is: Where, v represents the test flow rate; d represents the nozzle diameter; Considering that fluid viscosity has an impact on flow rate, fluid viscosity is introduced to optimize flow rate; The flow rate correction formula is: Where v′ represents the corrected flow velocity; C d represents the flow coefficient; μ represents the fluid viscosity; l represents the nozzle length; ρ represents the fluid density.

8. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 1, characterized in that: In S5, according to the test results, the specific steps for converting the flow rate under actual working conditions are as follows: S5.

1. Calculate the maximum flow rate of the test pump and the maximum flow rate of the on-site pump based on the test conditions and on-site parameters, and calculate the flow rate ratio; S5.

2. Use the flow rate ratio to convert the test flow rate to the actual flow rate.

9. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 8, characterized in that: In S5.1, the maximum flow rate of the test water pump and the maximum flow rate of the on-site water pump are calculated based on the test conditions and on-site parameters. The specific process of calculating the flow rate ratio is: Based on the reference flow rate under standard conditions, calculate the maximum flow rate of the test water pump: Where, v0 represents the maximum flow rate of the test water pump; v 基准 Indicates a reference flow rate based on standard conditions; C d试验 Indicates the flow coefficient of the nozzle under test conditions; C d实际 Indicates the discharge coefficient of the nozzle in actual application; According to the fluid viscosity correction, calculate the maximum flow rate of the on-site water pump: Where, v 实际 Indicates the maximum flow rate of the on-site water pump; K represents a constant related to the water pump characteristics; l 实际 Indicates the effective length of the actual nozzle; d 实际 Indicates the actual nozzle diameter; ΔP 实际 Indicates the pressure difference in actual operation; The flow rate ratio is obtained by the maximum flow rate of the on-site water pump and the maximum flow rate of the test water pump: Where R represents the flow rate ratio.

10. The laboratory calibration method for reducing the flow rate of a gravity anchor recovery nozzle according to claim 9, characterized in that: In S5.2, the calculation process for converting the test flow rate to the actual flow rate using the flow rate ratio is: The test flow rate is scaled up to the actual working conditions by the flow rate ratio R, taking into account the differences in the performance of the on-site pump and the geometry of the nozzle: v 实际 =R·v0。

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