A pipe jacking mud permeability testing instrument and experimental method

Abstract

The present invention discloses a pipe jacking mud permeability testing instrument and an experimental method, wherein: the first cylinder and the second cylinder both include a pipe body with openings at both ends and an upper end cover and a lower end cover with sealing covers arranged at both ends of the pipe body, each end cover is provided with a branch pipe connected with the pipe body, and the upper end cover and the lower end cover of the first cylinder are provided with a first valve and a second valve on the branch pipes, respectively, and the upper end cover and the lower end cover of the second cylinder are provided with a third valve and a fourth valve on the branch pipes, respectively, and the pipe body of the first cylinder is connected with a plurality of pressure gauges; in the equipment frame, the upper crossbeam is provided with two fastening bolts threadedly connected thereto, the first cylinder and the second cylinder are both vertically arranged on the lower crossbeam, and the top surfaces of the upper end covers of the two are respectively pressed downward by two fastening bolts; and a pressure source connected with the branch pipe on the upper end cover of the second cylinder is also included. The present invention can quantitatively analyze the permeability of pipe jacking mud under different conditions, and solves the problem that the permeability of pipe jacking mud in different formations cannot be calculated.

Description

Technical Field

[0001] The invention relates to the technical field of trenchless pipe jacking engineering, and in particular to a pipe jacking mud permeability testing instrument and an experimental method. Background Art

[0002] Trenchless construction methods are the laying, repairing and replacing of underground pipelines without excavation. Among them, the pipe jacking method is widely used in the construction of underground facilities such as water supply and drainage pipelines, integrated pipe galleries, and underground passages due to its advantages of fast construction speed, small impact on the surrounding environment, and large laying depth. Since the beginning of the new century, with the maturity of domestic pipe jacking technology and the accumulation of construction experience, pipe jacking has gradually moved away from the construction of urban pipelines in single strata and developed towards the direction of large sections in complex strata.

[0003] Lubricating mud is an important part of the field of pipe jacking engineering technology. However, many pipe jacking mud penetration test devices can only target single formation conditions, making it difficult to accurately simulate the actual situation of mud penetration during the actual jacking process and unable to calculate the mud penetration in different formations. Therefore, it is necessary to develop a quantitative method to analyze the permeability of pipe jacking mud and solve the problem that the permeability of pipe jacking mud in different formations cannot be calculated. Summary of the invention

[0004] The purpose of the present invention is to provide a pipe jacking mud permeability testing instrument and experimental method in view of the existing technical status, which solves the problem that the pipe jacking mud permeability in different strata cannot be calculated and is conducive to the development of pipe jacking construction technology.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A pipe jacking mud permeability testing instrument comprises a first cylinder, a second cylinder and an equipment frame, wherein the first cylinder serves as a permeation container, the second cylinder serves as a liquid storage container, and both the first cylinder and the second cylinder are fixed on the equipment frame;

[0007] The first cylinder and the second cylinder both include a tube body with openings at both ends and an upper end cover and a lower end cover with sealing covers disposed at both ends of the tube body. The tube body is made of a transparent material. The upper end cover and the lower end cover are both provided with branch pipes connected to the tube body. The upper end cover and the lower end cover of the first cylinder are provided with a first valve and a second valve on the branch pipes respectively. The upper end cover and the lower end cover of the second cylinder are provided with a third valve and a fourth valve on the branch pipes respectively. The tube body of the first cylinder is connected with a plurality of pressure gauges, which are distributed longitudinally on the tube body of the first cylinder.

[0008] The equipment frame is provided with an upper crossbeam and a lower crossbeam, the upper crossbeam is provided with two fastening bolts threadedly connected thereto, the first cylinder and the second cylinder are both vertically arranged on the lower crossbeam, and the top surfaces of the upper end covers of the two cylinders are respectively pressed downward by the two fastening bolts;

[0009] It also includes a pressure source connected to the branch pipe on the upper end cover of the second cylinder, and the pressure source is used to supply pressure to the second cylinder.

[0010] Furthermore, the pressure source includes a nitrogen cylinder and a pressure regulating valve, and the nitrogen cylinder, the pressure regulating valve, and a branch pipe on the lower end cover of the second cylinder are connected in sequence.

[0011] Furthermore, the pressure regulating valve includes a primary pressure reducing valve and a secondary pressure reducing valve connected in series.

[0012] Furthermore, the top of the upper end cover is a truncated cone structure.

[0013] Furthermore, the top surface of the upper end cover is provided with a positioning groove matching the fastening bolt.

[0014] Furthermore, the lower cross beam is provided with two positioning plates matching the lower end cover, and the two positioning plates are respectively located directly below the two fastening screws provided on the upper cross beam.

[0015] A pipe jacking mud permeability test experimental method, using the pipe jacking mud permeability test experimental device, comprises the following steps:

[0016] S1. Preparation of sand layer saturated with test fluid

[0017] S1.1. Set a first sand-blocking belt at the bottom of the first cylinder, then fill the sand sample above the first sand-blocking belt, and make the pressure gauges on the tube body of the first cylinder within the sand sample elevation;

[0018] injecting a test liquid into the second cylinder;

[0019] Connect the branch pipe on the lower end cover of the second cylinder to the branch pipe on the lower end cover of the first cylinder through a pipeline;

[0020] S1.2. Open the first valve, the second valve and the third valve. Under the action of the position head difference, the test liquid penetrates into the sand sample in the first cylinder from bottom to top through the pipeline until the liquid level in the first cylinder is flush with the top surface of the sand sample. Close the first valve, the second valve and the third valve, and the preparation of the saturated sand layer containing the test liquid is completed;

[0021] S2. Test mud anti-seepage experiment

[0022] S2.1. Fill the upper space of the sand sample in the first cylinder with test mud;

[0023] replacing the test fluid in the second cylinder with test mud;

[0024] Connect the branch pipe on the lower end cover of the second cylinder to the branch pipe on the upper end cover of the first cylinder through a pipeline, and then connect the branch pipe on the lower end cover of the first cylinder to the collection container through the pipeline;

[0025] S2.2. Open the first valve, the second valve, the third valve and the fourth valve, and open the pressure regulating valve at the same time, so that the pressure of the nitrogen bottle acts on the test mud in the second cylinder, and the test mud is pressed from the second cylinder into the first cylinder, and penetrates through the saturated sand layer containing the test liquid. The test liquid and the test mud in the saturated sand layer containing the test liquid flow into the collection container, and a sand layer containing the test mud is formed at the same time. The test mud anti-seepage test is completed, and the first valve, the second valve, the third valve, the fourth valve and the pressure regulating valve are closed;

[0026] S3. Formation water back pressure experiment

[0027] S3.1. Draw out the test mud above the sand sample in the first cylinder, then set a second sand blocking belt above the sand sample and fill it with test mud;

[0028] replacing the test slurry in the second cylinder with the test fluid;

[0029] Connect the branch pipe on the lower end cover of the second cylinder to the branch pipe on the lower end cover of the first cylinder through a pipeline, and then connect the branch pipe on the upper end cover of the first cylinder to the collection container through the pipeline;

[0030] S3.2. Open the first valve, the second valve, the third valve and the fourth valve, and open the pressure regulating valve at the same time, so that the pressure of the nitrogen bottle acts on the test liquid in the second cylinder. The test liquid is pressed from the second cylinder into the first cylinder, and penetrates through the sand layer containing the test mud. The test liquid and the test mud in the sand layer containing the test mud flow into the collection container. The formation water back pressure experiment is completed, and the first valve, the second valve, the third valve, the fourth valve and the pressure regulating valve are closed.

[0031] Furthermore, the first sand-blocking belt includes a filter pad, a filter screen and a gravel layer which are sequentially arranged from bottom to top.

[0032] Furthermore, the second sand-blocking belt includes a filter screen, a filter pad and an elastic gasket which are arranged in sequence from bottom to top.

[0033] Furthermore, in step S1.1, the steps of filling the sand sample are as follows: pouring the sand sample in layers, and compacting each layer of the sand sample after pouring.

[0034] The beneficial effects of the present invention are:

[0035] The present invention uses the first cylinder as a permeation container and the second cylinder as a liquid storage container, and can sequentially carry out preparation of a sand layer saturated with a test liquid, a test mud impermeability test and a formation water back pressure test, and based on different sand sample ratios, different test liquids, different test muds, different pressures and different states of simulated formations, conduct a comprehensive jacking mud permeability test experiment, can quantitatively analyze the permeability of the jacking mud under different conditions, solves the problem that the permeability of the jacking mud in different formations cannot be calculated, and is conducive to the development of jacking construction technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the structure of the pipe jacking mud permeability testing instrument of the present invention (including the preparation of the sand layer saturated with the test liquid);

[0037] Figure 2 for Figure 1 An enlarged structural diagram of the first cylinder;

[0038] Figure 3 for Figure 1 An enlarged structural diagram of the second cylinder;

[0039] Figure 4 It is a structural schematic diagram of the pipe jacking mud permeability testing instrument of the present invention (test mud anti-permeability experiment);

[0040] Figure 5 for Figure 4 An enlarged structural diagram of the first cylinder;

[0041] Figure 6 It is a structural schematic diagram of the pipe jacking mud permeability testing instrument of the present invention (formation water back pressure experiment);

[0042] Figure 7 for Figure 6 Schematic diagram of the enlarged structure of the first cylinder.

[0043] Marking instructions: 1. Equipment frame, 1-1. Upper crossbeam, 1-2. Lower crossbeam, 2. First cylinder, 3. Second cylinder, 4. Fastening bolts, 5. Positioning plate, 6. Pressure regulating valve, 7. Nitrogen bottle, 8. Pipe body, 9. Upper end cover, 10. Lower end cover, 11. Branch pipe, 11-1. First valve, 11-2. Second valve, 11-3. Third valve, 11-4. Fourth valve, 12. Pressure gauge, 13. Permeable stone, 14. Filter pad, 15. Filter screen, 16. Gravel layer, 17. Collection container, 18. Elastic gasket. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings.

[0045] Embodiment 1:

[0046] See also Figure 1-3 As shown, a pipe jacking mud permeability testing instrument includes a first cylinder 2, a second cylinder 3 and an equipment frame 1. The first cylinder 2 serves as a permeability container for setting a simulated soil layer, and the second cylinder 3 serves as a liquid storage container for containing test mud or test liquid (formation water). The first cylinder 2 and the second cylinder 3 are both fixed on the equipment frame 1.

[0047] The first cylinder 2 and the second cylinder 3 each include a tube body 8 with openings at both ends, and an upper end cover 9 and a lower end cover 10 provided as sealing covers at both ends of the tube body 8 .

[0048] In order to observe the state of the test mud in the first cylinder 2 and the second cylinder 3, the tube body 8 is made of a transparent material. The two ends of the tube body 8 are not sealed, which is convenient for taking out the sand sample and cleaning and maintaining the equipment. In this embodiment, the tube body 8 is made of acrylic material with high transparency.

[0049] The upper end cover 9 and the lower end cover 10 are both provided with a branch pipe 11 connected to the tube body 8, and the upper end cover 9 and the lower end cover 10 of the first cylinder 2 are respectively provided with a first valve 11-1 and a second valve 11-2, and the upper end cover 9 and the lower end cover 10 of the second cylinder 3 are respectively provided with a third valve 11-3 and a fourth valve 11-4.

[0050] According to the experimental requirements, the design of the upper end cover 9 and the lower end cover 10 is as follows:

[0051] The upper end covers 9 of the first cylinder 2 and the second cylinder 3 are both concave and provided with a layer of sealing rubber ring;

[0052] The first cylinder 2, as a permeation container, needs to be filled with sand and grouted at the same time, so it not only needs to have a high sealing performance, but also should be easy to take out the sand sample and clean up the soil residue. Therefore, the lower end cover 10 of the first cylinder 2 is concave and is provided with a layer of sealing rubber ring;

[0053] As the second cylinder 3 is a liquid storage container, its sealing requirement is very high. Therefore, the lower end cover 10 of the second cylinder 3 is designed to be convex inwards and is provided with two layers of sealing rubber rings. After the lower end cover 10 is assembled with the tube body 8, it is difficult to fall off, and the problem of grout leakage will not occur during the grouting process.

[0054] The test mud and the test liquid will flow between the first cylinder 2 and the second cylinder 3. The upper end cover 9 and the lower end cover 10 need to be connected to different pipelines, so each valve is switched frequently. Therefore, each valve uses a ball valve and a quick-release connection method to facilitate experimental operation.

[0055] A plurality of pressure gauges 12 are connected to the tube body 8 of the first cylinder 2, and the pressure gauges 12 are distributed longitudinally on the tube body 8 of the first cylinder 2. This embodiment abandons the use of a pore water pressure sensor that needs to be connected to a data line, and selects a more reliable electronic digital pressure gauge to monitor the pressure of the simulated formation in the first cylinder 2 in real time. In order to prevent the test hole of the pressure gauge 12 from being blocked by sand samples or test mud, a permeable stone 13 is set at the connection between the pressure gauge 12 and the first cylinder 2 to play a role in blocking mud and sand.

[0056] Specifically, three electronic digital pressure gauges, upper, middle and lower, are installed outside the tube body 8 of the first cylinder 2 to display the pressure at three different positions in the simulated soil layer in real time.

[0057] An upper crossbeam 1-1 and a lower crossbeam 1-2 are provided in the equipment frame 1, and the upper crossbeam 1-1 is provided with two fastening bolts 4 threadedly connected thereto. The first cylinder 2 and the second cylinder 3 are both vertically arranged on the lower crossbeam 1-2, and the top surfaces of the upper end covers 9 of the two are pressed downwards by two fastening bolts 4 respectively.

[0058] The second cylinder 3 further comprises a pressure source connected to the branch pipe 11 on the upper end cover 9 of the second cylinder 3 , and the pressure source is used to supply pressure to the second cylinder 3 .

[0059] In the instrument, the upper end cover 9 and the lower end cover 10 of the first cylinder 2 and the second cylinder 3 will bear the force of the pressure source and the test liquid and the test mud, and the first cylinder 2 and the second cylinder 3 are fixed by pressing down with the tightening bolts 4, so that the force of the pressure source and the test liquid and the test mud can be transferred to the equipment frame 1, ensuring that there is no air leakage or liquid leakage during the experiment. In order to ensure the bearing capacity, in this embodiment, the equipment frame 1 is made of solid cast iron.

[0060] As one embodiment, the pressure source includes a nitrogen cylinder 7 and a pressure regulating valve 6, and the nitrogen cylinder 7, the pressure regulating valve 6, and the branch pipe 11 on the upper end cover 9 of the second cylinder 3 are connected in sequence. Preferably, the pressure regulating valve 6 includes a primary pressure reducing valve and a secondary pressure reducing valve connected in series (not shown in the figure).

[0061] The pressure regulating valve 6 can reduce the inlet pressure of the secondary pressure reducing valve, ensuring that the output pressure of the nitrogen bottle 7 will not increase sharply due to operational errors. However, the disadvantage is that there are many rubber pipe interfaces connecting the two pressure reducing valves, which are prone to leakage. In order to avoid this problem, thread sealant is used to seal the interface.

[0062] In the above technical solution, it is preferred that the top of the upper end cover 9 is a truncated cone structure, which is conducive to evenly distributing the force of the fastening bolts 4 to the upper end cover 9.

[0063] Further preferably, a top surface of the upper end cover 9 is provided with a positioning groove (not shown in the figure) matching the fastening bolt 4 for positioning the fastening bolt 4 and the upper end cover 9 .

[0064] More preferably, two positioning plates 5 matching the lower end cover 10 are provided on the lower crossbeam 1 - 2 , and the two positioning plates 5 are respectively located directly below the two fastening screws 4 provided on the upper crossbeam 1 - 1 , for positioning the lower crossbeam 1 - 2 and the lower end cover 10 .

[0065] It is necessary that the lower cross beam 1 - 2 and the positioning plate 5 should be designed with openings for the branch pipe 11 on the lower end cover 10 to pass through.

[0066] The fastening bolts 4 and the upper end cover 9 as well as the lower cross beam 1 - 2 and the lower end cover 10 are positioned to control the positions of the upper end cover 9 and the lower end cover 10 , so as to quickly install the first cylinder 2 and the second cylinder 3 vertically.

[0067] Embodiment 2:

[0068] See also Figure 1-7 As shown, a pipe jacking mud permeability test experimental method, using the above-mentioned pipe jacking mud permeability test experimental device, includes the following steps:

[0069] S1. Preparation of sand layer saturated with test fluid (i.e. simulated soil layer in initial state)

[0070] S1.1. A first sand-blocking belt is arranged at the bottom of the first cylinder 2, and then a sand sample is filled above the first sand-blocking belt, and the pressure gauge 12 on the tube body 8 of the first cylinder 2 is placed within the sand sample elevation;

[0071] During the experiment, the sand sample is easy to flow and block the seepage holes under the pressure of the test mud. Therefore, before preparing the saturated sand layer containing the test liquid, it is necessary to set the first sand blocking belt at the bottom of the first cylinder 2. Specifically, the first sand blocking belt is a multi-layer sand blocking belt, including a filter pad 14, a filter screen 15 and a gravel layer 16 arranged from bottom to top; the steps of filling the sand sample are as follows: pour the sand sample in layers, and compact each layer of sand sample (thickness controlled at 20-30mm) after pouring, and the purpose of using quantitative and fixed volume sand filling is to ensure that the porosity of the sand layers of the same grade filled in is roughly the same;

[0072] Injecting the test liquid into the second cylinder 3;

[0073] Connect the branch pipe 11 on the lower end cover 10 of the second cylinder 3 to the branch pipe 11 on the lower end cover 10 of the first cylinder 3 through a pipeline;

[0074] S1.2. Open the first valve 11-1, the second valve 11-2 and the third valve 11-3. Under the action of the position head difference, the test liquid penetrates into the sand sample in the first cylinder 2 from bottom to top through the pipeline until the liquid level in the first cylinder 2 is flush with the top surface of the sand sample. Close the first valve 11-1, the second valve 11-2 and the third valve 11-3, and the preparation of the saturated sand layer containing the test liquid is completed.

[0075] S2. Test mud anti-seepage experiment

[0076] S2.1, fill the upper space of the sand sample in the first cylinder 2 with test mud;

[0077] Replace the test liquid in the second cylinder 3 with the test mud. In this step, the original second cylinder 3 can be cleaned and then injected with the test mud, or a new second cylinder 3 can be directly used for replacement;

[0078] Connect the branch pipe 11 on the lower end cover 10 of the second cylinder 3 to the branch pipe 11 on the upper end cover 9 of the first cylinder 2 through a pipeline, and then connect the branch pipe 11 on the lower end cover 10 of the first cylinder 2 to the collection container 17 through a pipeline;

[0079] S2.2. Open the first valve 11-1, the second valve 11-2, the third valve 11-3 and the fourth valve 11-4, and open the pressure regulating valve 6 at the same time, so that the pressure of the nitrogen bottle 7 acts on the test mud in the second cylinder 3. The test mud is pressed from the second cylinder 3 into the first cylinder 2, and penetrates through the saturated sand layer containing the test liquid. The test liquid and the test mud in the saturated sand layer containing the test liquid flow into the collecting container 17, and a sand layer containing the test mud is formed at the same time. The test mud anti-seepage experiment is completed, and the first valve 11-1, the second valve 11-2, the third valve 11-3 and the fourth valve 11-4 and the pressure regulating valve 6 are closed.

[0080] During the mud anti-permeability test, the readings of each pressure gauge 12, the test mud leakage (with the use of an electronic balance) and the mud cake formation process are recorded in real time by video recording to complete the collection of experimental data. Through the obtained experimental data, the test mud penetration law is quantitatively analyzed and the test mud anti-permeability is accurately analyzed.

[0081] S3. Formation water back pressure experiment

[0082] S3.1. Draw out the test mud above the sand sample in the first cylinder 2, then set a second sand blocking belt above the sand sample and fill it with the test mud;

[0083] During the experiment, in order to simulate the formation water infiltration from bottom to top, a second sand-blocking belt needs to be arranged above the sand sample to prevent the sand from passing through and prevent relative sliding between the simulated formation and the pipe body 8. Specifically, the second sand-blocking belt is a multi-layer sand-blocking belt, including a filter screen 15, a filter pad 14 and an elastic gasket 18 arranged in sequence from bottom to top;

[0084] Replace the test slurry in the second cylinder 3 with the test liquid;

[0085] Connect the branch pipe 11 on the lower end cover 10 of the second cylinder 3 to the branch pipe 11 on the lower end cover 10 of the first cylinder 2 through a pipeline, and then connect the branch pipe 11 on the upper end cover 9 of the first cylinder 2 to the collection container 17 through a pipeline;

[0086] S3.2. Open the first valve 11-1, the second valve 11-2, the third valve 11-3 and the fourth valve 11-4, and open the pressure regulating valve 6 at the same time, so that the pressure 7 of the nitrogen bottle 7 acts on the test liquid in the second cylinder 3. The test liquid is pressed from the second cylinder 3 into the first cylinder 2, penetrates through the sand layer containing the test mud, and the test liquid and the test mud in the sand layer containing the test mud flow into the collecting container 17. The formation water back pressure experiment is completed, and the first valve 11-1, the second valve 11-2, the third valve 11-3 and the fourth valve 11-4 and the pressure regulating valve 6 are closed.

[0087] During the formation water back pressure experiment, the pressure readings, the amount of formation water intrusion (using an electronic balance) and the process of mud skin destruction were recorded in real time by video recording.

[0088] It should be noted that the test liquid, test mud and sand sample are prepared according to the experimental requirements and the control experiment is carried out. For example:

[0089] 1. Conduct water penetration experiments in saturated sand samples with three particle sizes: fine sand, medium sand, and coarse sand. Record the permeability and pressure changes of the simulated formation. This experimental group serves as the control group.

[0090] 2. Under salt invasion conditions, the anti-permeability performance test of ordinary lubricating mud in saturated sand samples with three particle sizes: fine sand, medium sand, and coarse sand. This experimental group serves as the control group of the anti-salt mud experiment.

[0091] 3. Experiment on the anti-seepage performance of salt-resistant lubricating mud in saturated sand samples with three particle sizes: fine sand, medium sand and coarse sand under salt invasion conditions.

[0092] In general, the present invention uses the first cylinder 2 as a permeation container and the second cylinder 3 as a liquid storage container, and can sequentially carry out preparation of a sand layer saturated with a test liquid, test mud impermeability test and formation water back pressure test, and based on different sand sample ratios, different test liquids, different test muds, different pressures and different states of simulated formations (initial state, intermediate state), conduct a comprehensive jacking mud permeability test experiment, which can quantitatively analyze the permeability of jacking mud under different conditions, solve the problem that the permeability of jacking mud in different formations cannot be calculated, and is conducive to the development of jacking construction technology.

[0093] Of course, the above are only preferred embodiments of the present invention, and are not intended to limit the scope of use of the present invention. Therefore, any equivalent changes made to the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A pipe jacking mud permeability testing instrument, characterized in that: It includes a first cylinder, a second cylinder and an equipment frame, the first cylinder is used as a permeation container, the second cylinder is used as a liquid storage container, and the first cylinder and the second cylinder are both fixed on the equipment frame; The first cylinder and the second cylinder both include a tube body with openings at both ends and an upper end cover and a lower end cover with sealing covers disposed at both ends of the tube body. The tube body is made of a transparent material. The upper end cover and the lower end cover are both provided with branch pipes connected to the tube body. The upper end cover and the lower end cover of the first cylinder are provided with a first valve and a second valve on the branch pipes respectively. The upper end cover and the lower end cover of the second cylinder are provided with a third valve and a fourth valve on the branch pipes respectively. The tube body of the first cylinder is connected with a plurality of pressure gauges, which are distributed longitudinally on the tube body of the first cylinder. The equipment frame is provided with an upper crossbeam and a lower crossbeam, the upper crossbeam is provided with two fastening bolts threadedly connected thereto, the first cylinder and the second cylinder are both vertically arranged on the lower crossbeam, and the top surfaces of the upper end covers of the two cylinders are respectively pressed downward by the two fastening bolts; It also includes a pressure source connected to the branch pipe on the upper end cover of the second cylinder, and the pressure source is used to supply pressure to the second cylinder.

2. The pipe jacking mud permeability testing instrument according to claim 1, characterized in that: The pressure source comprises a nitrogen cylinder and a pressure regulating valve, and the nitrogen cylinder, the pressure regulating valve and a branch pipe on the lower end cover of the second cylinder are connected in sequence.

3. The pipe jacking mud permeability testing instrument according to claim 2, characterized in that: The pressure regulating valve comprises a primary pressure reducing valve and a secondary pressure reducing valve connected in series.

4. The pipe jacking mud permeability testing instrument according to claim 1, characterized in that: The top of the upper end cover is a truncated cone structure.

5. A pipe jacking mud permeability testing instrument according to claim 1 or 4, characterized in that: The top surface of the upper end cover is provided with a positioning groove matching the fastening bolt.

6. The pipe jacking mud permeability testing instrument according to claim 1, characterized in that: The lower cross beam is provided with two positioning plates matching the lower end cover, and the two positioning plates are respectively located directly below the two fastening screws provided on the upper cross beam.

7. A pipe jacking mud permeability test experimental method, using a pipe jacking mud permeability test instrument according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Preparation of sand layer saturated with test fluid S1.

1. Set a first sand-blocking belt at the bottom of the first cylinder, then fill the sand sample above the first sand-blocking belt, and make the pressure gauges on the tube body of the first cylinder within the sand sample elevation; injecting a test liquid into the second cylinder; Connect the branch pipe on the lower end cover of the second cylinder to the branch pipe on the lower end cover of the first cylinder through a pipeline; S1.

2. Open the first valve, the second valve and the third valve. Under the action of the position head difference, the test liquid penetrates into the sand sample in the first cylinder from bottom to top through the pipeline until the liquid level in the first cylinder is flush with the top surface of the sand sample. Close the first valve, the second valve and the third valve, and the preparation of the saturated sand layer containing the test liquid is completed; S2. Test mud anti-seepage experiment S2.

1. Fill the upper space of the sand sample in the first cylinder with test mud; replacing the test fluid in the second cylinder with test mud; Connect the branch pipe on the lower end cover of the second cylinder to the branch pipe on the upper end cover of the first cylinder through a pipeline, and then connect the branch pipe on the lower end cover of the first cylinder to the collection container through the pipeline; S2.

2. Open the first valve, the second valve, the third valve and the fourth valve, and open the pressure regulating valve at the same time, so that the pressure of the nitrogen bottle acts on the test mud in the second cylinder, and the test mud is pressed from the second cylinder into the first cylinder, and penetrates through the saturated sand layer containing the test liquid. The test liquid and the test mud in the saturated sand layer containing the test liquid flow into the collection container, and a sand layer containing the test mud is formed at the same time. The test mud anti-seepage test is completed, and the first valve, the second valve, the third valve, the fourth valve and the pressure regulating valve are closed; S3. Formation water back pressure experiment S3.

1. Draw out the test mud above the sand sample in the first cylinder, then set a second sand blocking belt above the sand sample and fill it with test mud; replacing the test slurry in the second cylinder with the test fluid; Connect the branch pipe on the lower end cover of the second cylinder to the branch pipe on the lower end cover of the first cylinder through a pipeline, and then connect the branch pipe on the upper end cover of the first cylinder to the collection container through the pipeline; S3.

2. Open the first valve, the second valve, the third valve and the fourth valve, and open the pressure regulating valve at the same time, so that the pressure of the nitrogen bottle acts on the test liquid in the second cylinder. The test liquid is pressed from the second cylinder into the first cylinder, and penetrates through the sand layer containing the test mud. The test liquid and the test mud in the sand layer containing the test mud flow into the collection container. The formation water back pressure experiment is completed, and the first valve, the second valve, the third valve, the fourth valve and the pressure regulating valve are closed.

8. A pipe jacking mud permeability test experimental method according to claim 7, characterized in that: The first sand-blocking belt comprises a filter pad, a filter screen and a gravel layer which are arranged in sequence from bottom to top.

9. A pipe jacking mud permeability test experimental method according to claim 7, characterized in that: The second sand blocking belt comprises a filter screen, a filter pad and an elastic gasket which are arranged in sequence from bottom to top.

10. A pipe jacking mud permeability test experimental method according to claim 7, characterized in that: In step S1.1, the steps of filling the sand sample are as follows: pour the sand sample in layers, and compact each layer of the sand sample after pouring.

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