Evaluation method for filtration and film-forming characteristics of thixotropic mud in pipe-jacking in confined aquifers

Abstract

The present invention provides a method for evaluating the thixotropic mud filtration and film-forming characteristics of a top pipe in a confined aquifer, comprising the following steps: S1 setting up a system; S2 laying a confined aquifer; S3 testing the initial permeability coefficient of the confined aquifer; S4 preparing a thixotropic mud slurry; S5 applying water pressure to the confined aquifer; S6 testing the thixotropic mud filtration and film-forming characteristics; S7 testing the permeability coefficient of the confined aquifer infiltration plus solid: water infiltrates unidirectionally from bottom to top in the soil body, and calculating the permeability coefficient of the confined aquifer infiltration plus solid; S8 evaluating the thixotropic mud filtration and film-forming characteristics: drawing the filtration depth during the thixotropic mud filtration loss process 、 Liquid level drop height 、 The relationship curve between liquid loss volume and loss time is established, and the fitting equation is established to obtain the loss rate of thixotropic mud. This method uses the combined test of thixotropic mud loss + film formation + seepage to comprehensively evaluate the thixotropic mud loss and film formation performance, optimize the mud formula, and improve the construction efficiency and drag reduction effect.

Description

Technical Field

[0001] The invention relates to the field of pipe jacking engineering, and in particular to a method for evaluating the filtration and film-forming characteristics of thixotropic mud for pipe jacking in a confined aquifer. Background Art

[0002] As a trenchless pipeline laying technology for underground projects similar to the shield method, pipe jacking construction has been widely used in urban subway entrances and exits, integrated pipe corridors, underground commercial streets and other projects in recent years because of its advantages such as no excavation of the road surface, small construction disturbance, and protection of urban landscape. However, during the pipe jacking construction process, the soil above the pipe jacking machine moves or compresses and deforms along the jacking direction due to excessive friction resistance between the pipe and the soil, which in turn causes the "back-soil effect" problem, which has become a major problem in pipe jacking construction. How to effectively reduce the friction resistance during pipe jacking construction is an important basic research topic in pipe jacking engineering.

[0003] In order to reduce the friction resistance between the pipeline and the soil, it is usually necessary to inject thixotropic mud into the outer wall of the pipeline. Thixotropic mud is a drag-reducing material with a special mineral structure and thixotropic properties. During the pipe jacking construction process, the thixotropic mud fills the 2-5 cm annular space between the pipeline and the soil. On the one hand, it can convert the dry friction between the jacking pipeline and the soil into liquid friction, thereby reducing the friction resistance of the jacking; on the other hand, it can fill the gap between the pipeline and the soil, thereby reducing the deformation of the soil and supporting the formation. When the thixotropic mud is stationary, the mud is in a gelled state. Once it is disturbed by the outside world, it becomes a fluid state. After the external factors stop acting, the aqueous solution becomes a gelled state again. This property is the unique thixotropy of the thixotropic mud. This property enables it to play a better drag reduction role, and can better control the formation pressure and pipeline stability during the pipe jacking process. Problems, greatly improve the efficiency of pipe jacking construction, and reduce the probability of accidents. Since pipe jacking construction is a new type of trenchless pipeline laying technology for underground projects, there are still many deficiencies in the evaluation of the thixotropic mud filtration and film-forming properties of the pipe wall. Currently, the thixotropic mud filtration and film-forming effect is mostly studied by pressurizing the filter loss meter to form a mud cake. The filtration time is relatively long and the seepage filtration process cannot be studied in combination with the soil properties.

[0004] Therefore, in order to determine the filtration effect of thixotropic mud for pipe jacking and explore its static filtration performance under different water content conditions in the soil, a method for evaluating the filtration and film-forming characteristics of thixotropic mud for pipe jacking in confined aquifers is needed to accurately measure the filtration and film-forming characteristics of thixotropic mud for pipe jacking in confined aquifers, which will provide important technical support for the subsequent research and construction of thixotropic mud filtration and film-forming effects of pipe jacking. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the thixotropic mud filtration and film-forming characteristics of a jacking pipe in a confined aquifer, which solves the problem of the urgent need for comprehensive consideration of the thixotropic mud filtration effect and permeability performance test in the jacking pipe thixotropic mud filtration performance test, and conducts analytical evaluation of the thixotropic mud filtration and permeability performance.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for evaluating the filtration and film-forming characteristics of thixotropic mud in a confined aquifer top pipe, comprising the following steps:

[0008] S1 Set up the system: Assemble the sample test cylinder, and connect the penetration test module, grouting pressure module and filtration loss measurement module to the sample test cylinder respectively;

[0009] S2 confined aquifer laying: lay the soil and pore water pressure sensor in the sample test tube, and sprinkle water to the water outlet after the soil is laid;

[0010] S3 Test of initial permeability coefficient of confined aquifer: The permeability test module is used to make water permeate from bottom to top in the soil, and the initial permeability coefficient of confined aquifer is calculated;

[0011] S4 thixotropic mud slurry preparation: prepare thixotropic mud and put the thixotropic mud into the slurry storage box;

[0012] S5: Applying water pressure to the confined aquifer: Using the grouting pressure module, the water above the soil is drained to the filtration loss measurement module, and the soil is in a stable confined water state;

[0013] S6 Thixotropic Mud Loss Film Formation Test: Use the grouting pressure module to fill the space above the soil in the sample test tube with thixotropic mud slurry, and the thixotropic mud loss penetrates into the soil;

[0014] S7 Confined aquifer infiltration plus solid permeability coefficient test: The permeability test module allows water to permeate from bottom to top in the soil, and the permeability coefficient of the confined aquifer infiltration plus solid is calculated;

[0015] Evaluation of S8 thixotropic mud filtration film-forming characteristics: Plotting the filtration depth of thixotropic mud during filtration 、 Liquid level drop height 、 The relationship curve between liquid loss volume and loss time was established, and the fitting equation was established to obtain the loss rate of thixotropic mud.

[0016] Furthermore, in the above-mentioned method for evaluating the thixotropic mud filtration film-forming characteristics of the confined aquifer top pipe, in the step S3, the water pressure of the lower water pressure controller is set to P 1. Set the water pressure of the upper water pressure controller to P 2, P 1> P 2. Use the lower and upper water pressure controllers to make the distilled water penetrate the soil from bottom to top in one direction, and record the pressure of the upper water pressure controller under stable conditions. The amount of distilled water flowing in during a period of timeV The initial permeability coefficient of the confined aquifer is calculated using the following formula: k i ;

[0017] Formula (1)

[0018] In formula (1), V for The amount of water flowing into the upper water pressure controller within a certain period of time; H 2 is the height of the soil; ρ is the density of distilled water; R 2 is the inner diameter of the pressure-bearing cylinder; is the pressure difference between the lower water pressure controller and the upper water pressure controller, ; The time when distilled water flows into the upper water pressure controller;

[0019] In step S4, red ink is added to the thixotropic mud to observe the filtration film-forming effect. The thixotropic mud is based on the mass of water, and the percentages of the remaining components relative to the mass of water are: 8.0%~10% bentonite, 0.20%~0.30% soda ash, 0.10%~0.20% carboxymethyl cellulose and 0.018%~0.072% polyacrylamide; in step S5, the pressure pump of the grouting pressure module provides the air pressure in the slurry storage box to be P 2. The water above the soil P 2, and then the pressure of the pressure pump of the filtration loss measurement module is started and controlled to P 2. Make the soil P 2 stable pressurized water state under pressure; in the step S6, the grouting pressure provided by the pressure pump of the grouting pressure module to the grout storage box is P 3. The pressure difference between the booster pump and the pressure pump is , ; By observing the readings of the first scale and the pore water pressure sensor, record the depth of thixotropic mud loss into the soil d , Thixotropic mud liquid level drop height h , Liquid volume in the drain tank V 1. After the thixotropic mud filtration is stable, use a steel ruler to measure the thickness of the thixotropic mud film on the soil. H In step S7, the water pressure of the water pressure controller is set to P 1. Set the water pressure of the upper water pressure controller to P 2. Record the upper water pressure controller in the stable state at ∆ t’ The amount of distilled water flowing in during a period of time The permeability coefficient of the confined aquifer infiltration solid is calculated using the following formula: :

[0020] Formula (2)

[0021] In formula (2), for The amount of water flowing into the upper water pressure controller within a certain period of time; It is the height of the soil after thixotropic mud filtration; ρ is the density of distilled water; R 2 is the inner diameter of the pressure-bearing cylinder; is the pressure difference between the lower water pressure controller and the upper water pressure controller, ; The time when distilled water flows into the upper water pressure controller;

[0022] In step S8, the filtration rate v It is calculated using the following formula:

[0023] Formula (3)

[0024] In formula (3), k i is the soil permeability coefficient; ; d is the thixotropic mud loss depth; n is the soil porosity; is the tortuosity coefficient of the flow path, which is taken as 1.5;

[0025] Comparison of soil permeability before and after thixotropic mud filtration k i and , evaluate the soil filtration reinforcement effect; in the step S3 and the step S7, the water pressure of the lower water pressure controller P 1. Water pressure on the water pressure controller P 2 satisfies the following relationship:

[0026] Formula (4).

[0027] Furthermore, in the above-mentioned method for evaluating the filtration loss and film-forming characteristics of thixotropic mud in top pipe of confined aquifer, different slurry ratios, different soil properties and different confining pressures are adjusted according to different control working conditions and steps S2 to S8 are repeated to conduct multiple comparative tests; when conducting multiple comparative tests, the sample test tube is connected to the grouting holes from top to bottom in sequence through a pressure-resistant hose, and the corresponding thixotropic mud is pressed between adjacent grouting holes each time, and a group of conditions with the fastest filtration loss rate and the largest film thickness is found to be the optimal condition.

[0028] Furthermore, in the above-mentioned method for evaluating the filtration and film-forming characteristics of thixotropic mud in a confined aquifer top pipe, the evaluation method is implemented using a test system, which includes a sample test cylinder, a permeability test module, a grouting and pressurizing module, a filtration loss measurement module, a data acquisition module and a computer, wherein the sample test cylinder contains soil; the permeability test module can provide a stable water pressure or a stable water volume for the soil; the grouting and pressurizing module can inject thixotropic mud into the space above the soil in the sample test cylinder, and the thixotropic mud can infiltrate into the soil after being injected into the sample test cylinder, and the thixotropic mud forms a mud skin on the surface of the soil after infiltrating into the soil; the filtration loss measurement module can measure the filtration loss of the thixotropic mud; the data acquisition module is used to collect test data, and the data acquisition module is connected to the computer.

[0029] Furthermore, in the above-mentioned method for evaluating the thixotropic mud filtration film-forming characteristics of the top pipe of the confined aquifer, the test system also includes a steel bracket, the sample test tube is placed on the steel bracket, the steel bracket includes a support disc and four support legs, the top of the support leg is connected to the support disc, and the angle between the axis of the support leg and the ground is α is 60°~80°, the thickness of the support disc d 1 is 10mm~15mm; the sample test cylinder includes a pressure cylinder, a top flange, a bottom flange, a first flange and a second flange, the bottom flange is connected to the lower end of the pressure cylinder, the first flange covers the lower end of the pressure cylinder, and the first flange and the bottom flange are connected by bolts; the top flange is connected to the upper end of the pressure cylinder, the second flange covers the upper end of the pressure cylinder, the second flange and the top flange are connected by bolts, and the first flange and the second flange can ensure the internal sealing of the sample test cylinder; the material of the sample test cylinder is acrylic, and the height of the pressure cylinder is H 1 is 200mm~400mm, inner diameter R 2 is 125mm, the thickness of the top flange d 2 is 10mm~15mm, the thickness of the bottom flange is consistent with the thickness of the top flange; the outer diameter of the top flange R1 is 150mm, the outer diameter of the bottom flange is consistent with the outer diameter of the top flange, and the diameter of the support disc is consistent with the outer diameter of the pressure cylinder; an annular first groove is provided at the relative position of the bottom flange and the first flange, and a first sealing ring is provided in the two first grooves, and the first sealing ring is used to seal between the bottom flange and the first flange; an annular second groove is provided at the relative position of the top flange and the second flange, and a second sealing ring is provided in the two second grooves, and the second sealing ring is used to seal between the top flange and the second flange; a first scale is vertically attached to the outer surface of the pressure cylinder, and the height of the soil in the sample test cylinder is H 2, H 2=(2 / 3~3 / 4) H 1; A circular third groove is arranged on the upper surface of the first flange, the axis of the third groove is colinear with the axis of the sample test cylinder, the inner diameter of the third groove is consistent with the inner diameter of the pressure cylinder, the third groove is paved with permeable stone, the thickness of the permeable stone is the same as the depth of the third groove, filter paper is arranged above the permeable stone, and the soil is laid on the filter paper; a filtration loss drain nozzle is arranged at the center of the first flange, the filtration loss drain nozzle is provided with a first self-locking valve, the support disc is provided with a through hole for the filtration loss drain nozzle to pass through, and the lower end of the filtration loss drain nozzle passes through the through hole and extends to the bottom of the support disc.

[0030] Furthermore, in the above-mentioned method for evaluating the thixotropic mud filtration film-forming characteristics of the top pipe of the confined aquifer, the permeability test module includes an upper water pressure controller and a lower water pressure controller, a water outlet is provided on the side wall of the pressure cylinder, a second self-locking valve is provided in the water outlet, and the upper water pressure controller is connected to the water outlet through the second self-locking valve; the distance between the upper surface of the soil body and the lower surface of the second flange is H 3. The distance between the water outlet and the lower surface of the second flange is H 4. H 4=1 / 2 H 3; The lower water pressure controller is connected to the filtration loss drainage nozzle through a first connecting pipe, and a first valve is provided on the first connecting pipe.

[0031] Furthermore, in the above-mentioned method for evaluating the thixotropic mud filtration film-forming characteristics of the top pipe of the confined aquifer, the grouting pressure module includes a pressure pump and a slurry storage box, the slurry storage box is a box structure with an open upper end, the material of the slurry storage box is stainless steel, and the length of the slurry storage box is L 1 is 100mm~150mm, width L 2 is 100mm~150mm, heightH 5 is 150mm~200mm; the upper end of the slurry storage box is covered with a first cover plate, and a third sealing ring is arranged at the connection between the first cover plate and the slurry storage box, and the first cover plate and the slurry storage box are connected by a first buckle; a grouting hole is arranged on the second flange, and a grouting hole is arranged on the side wall of the slurry storage box, and the grouting hole is connected to the grouting hole through a pressure-resistant hose, and a third self-locking valve is arranged in the grouting hole, and the third self-locking valve can be closed in time when the grouting needs to be ended; a pressurizing hole is arranged on the first cover plate, and the pressure pump is connected to the pressurizing hole through a pressure-resistant hose, and the pressure pump can apply air pressure to the slurry storage box, thereby pressing the thixotropic slurry into the sample test cylinder; a first pressure gauge is arranged on the first cover plate, and the first pressure gauge can display the pressure inside the slurry storage box.

[0032] Furthermore, in the above-mentioned method for evaluating the filtration and film-forming characteristics of thixotropic mud in a confined aquifer top pipe, a plurality of grouting holes are provided, and the plurality of grouting holes are evenly distributed vertically on the side wall of the slurry storage box, and the thixotropic mud in the slurry storage box between two adjacent grouting holes can just fill the space between the soil in the sample test cylinder and the second flange, and multiple comparative tests can be carried out using the plurality of grouting holes; when conducting multiple comparative tests, the sample test cylinder is connected to the plurality of grouting holes in sequence from top to bottom through a pressure-resistant hose, and the corresponding thixotropic mud between the adjacent grouting holes is pressed each time to ensure the consistency of the thixotropic mud performance; the distance between the centers of two adjacent grouting holes is d 3. d 3 satisfies the following formula:

[0033] Formula (5)

[0034] In formula (5), R 2 is the inner diameter of the pressure-bearing cylinder; H 3 is the distance between the upper surface of the soil and the lower surface of the second flange; L 1 is the length of the slurry storage box; L 2 is the width of the slurry storage box.

[0035] Further, in the above-mentioned method for evaluating the filtration film-forming characteristics of thixotropic mud in the top pipe of a confined aquifer, the filtration loss measurement module includes a pressure pump and a drainage box, the drainage box is a tank structure with an open upper end, the material of the drainage box is acrylic, the upper end of the drainage box is covered with a second cover plate, a fourth sealing ring is provided at the connection between the second cover plate and the drainage box, and the second cover plate is connected to the drainage box through a second buckle; a water storage hole is provided on the second cover plate, the water storage hole is connected to the filtration loss drainage nozzle through a second connecting pipe, and a second valve is provided on the second connecting pipe; a pressure hole is provided on the second cover plate, the pressure pump is connected to the pressure hole through a pressure-resistant hose, and the pressure pump can apply air pressure to the drainage box, thereby ensuring that the water pressure at the bottom of the soil body in the sample test cylinder is constant during the filtration loss process; a second pressure gauge is provided on the second cover plate, and the second pressure gauge can display the pressure inside the drainage box; a second scale is vertically attached to the side wall of the drainage box.

[0036] Furthermore, in the above-mentioned method for evaluating the filtration and film-forming characteristics of thixotropic mud in the top pipe of a confined aquifer, the data acquisition module includes a pore water pressure sensor and a data acquisition instrument, a plurality of the pore water pressure sensors are arranged on the inner wall of the pressure cylinder, a wire outlet hole is arranged on the side wall of the bottom flange, the data line of the pore water pressure sensor passes through the wire outlet hole and is connected to the data acquisition instrument, and the data acquisition instrument is connected to the computer; the pore water pressure sensors are evenly arranged in 3 to 5 circles from the upper end of the soil body to the lower end of the soil body, and a plurality of the pore water pressure sensors are arranged in each circle.

[0037] It can be seen from the analysis that the present invention discloses a method for evaluating the filtration and film-forming properties of thixotropic mud for pipe jacking in a confined aquifer. This method fills the gap in the analysis and evaluation of the filtration and film-forming properties of thixotropic mud for pipe jacking. This method adopts the combined test of filtration, film-forming and seepage of thixotropic mud for pipe jacking to comprehensively evaluate the filtration and film-forming properties of thixotropic mud, thereby optimizing the mud formula and improving the construction efficiency and drag reduction effect. When pipe jacking is carried out in a confined aquifer, the filtration and film-forming properties of thixotropic mud for pipe jacking are directly related to the quality of mud sleeve formation when thixotropic mud is used as a pipe jacking drag reduction material. A high-quality mud sleeve can effectively reduce the friction between the pipe jacking and the soil layer, significantly improving the construction efficiency; at the same time, it can reduce the pressure of groundwater on the pipe jacking, prevent groundwater from gushing into the pipe jacking working area, avoid engineering accidents such as water gushing and sand gushing, and thus improve the stability and safety of pipe jacking construction. This evaluation method can accurately evaluate the filtration and film-forming properties of thixotropic mud, and provide a scientific basis for optimizing the pipe jacking construction plan, determining mud ratio, grouting pressure and other parameters. At the same time, confined aquifers are usually closely related to the surrounding ecological environment. Evaluating the filtration and film-forming properties of thixotropic mud helps to select environmentally friendly mud materials and construction processes, reduce the impact on the groundwater environment, and protect the ecological balance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0039] Figure 1 The flowchart of the evaluation method according to one embodiment of the present invention is shown in FIG.

[0040] Figure 2 FIG. 1 is a schematic diagram of the structure of a testing system according to an embodiment of the present invention.

[0041] Figure 3 The figure is a schematic structural diagram of a steel support according to an embodiment of the present invention.

[0042] Figure 4 It is a schematic diagram of the exploded three-dimensional structure of a sample test tube according to an embodiment of the present invention.

[0043] Figure 5 It is a schematic diagram of the three-dimensional structure of a grouting pressure module according to an embodiment of the present invention.

[0044] Figure 6 The figure is a schematic diagram of the three-dimensional structure of a filtration loss measurement module according to an embodiment of the present invention.

[0045] Explanation of reference numerals: 1 sample test tube; 2 pressure tube; 3 top flange; 4 bottom flange; 5 first flange; 6 second flange; 7 first sealing ring; 8 second sealing ring; 9 first scale; 10 third groove; 11 permeable stone; 12 filter paper; 13 soil; 14 thixotropic mud; 15 filtration loss drain nozzle; 16 first self-locking valve; 17 supporting disc; 18 through hole; 19 supporting leg; 20 upper water pressure controller; 21 lower water pressure controller; 22 water outlet; 23 second self-locking valve; 24 first connecting pipe; 25 first valve; 26 pressure pump; 27 slurry storage box; 28 first cover plate; 29 first buckle; 30 grouting hole; 31 grouting hole; 32 pressure hole; 33 first pressure gauge; 34 pressure pump; 35 drainage box; 36 second cover plate; 37 second buckle; 38 water storage hole; 39 second connecting pipe; 40 second valve; 41 pressure hole; 42 second pressure gauge; 43 second scale; 44 pore water pressure sensor; 45 data line; 46 data acquisition instrument; 47 computer; 48 steel bracket; 49 bolt hole. DETAILED DESCRIPTION

[0046] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. Each example is provided by way of explanation of the present invention and does not limit the present invention. In fact, it will be clear to those skilled in the art that modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature shown or described as a part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desired that the present invention encompasses such modifications and variations within the scope of the appended claims and their equivalents.

[0047] In the description of the present invention, the terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention. The terms "connected", "connected" and "set" used in the present invention should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component; it can be a wired electrical connection, a radio connection, or a wireless communication signal connection. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0048] One or more examples of the present invention are shown in the accompanying drawings. The detailed description uses numbers and letter labels to refer to features in the drawings. Like or similar labels in the drawings and description have been used to refer to like or similar parts of the present invention. As used herein, the terms "first", "second", "third", etc. are used interchangeably to distinguish one component from another and are not intended to indicate the location or importance of individual components.

[0049] like Figures 1 to 6 As shown, according to an embodiment of the present invention, a method for evaluating the filtration loss and film-forming characteristics of thixotropic mud in a confined aquifer top pipe is provided, by which the permeability of the confined aquifer, the filtration loss characteristics and film-forming law of the thixotropic mud can be evaluated, such as Figure 1 As shown, the evaluation method includes the following steps:

[0050] S1 Set up the system: Assemble the sample test cylinder 1, and connect the penetration test module, grouting pressure module and filtration loss measurement module to the sample test cylinder 1 respectively.

[0051] Place the first flange 5 on the steel support 48, and make the lower end of the filtration loss drainage nozzle 15 pass through the through hole 18 of the supporting disc 17, place the permeable stone 11 and the filter paper 12 in the third groove 10 of the first flange 5 in sequence, place the first sealing ring 7 between the first groove of the first flange 5 and the first groove of the bottom flange 4, align the bolt holes 49 of the first flange 5 and the bottom flange 4, tighten the bolts and nuts symmetrically, connect the first flange 5 and the bottom flange 4 with the bolts and nuts, connect the grouting hole 30 of the second flange 6 with the grouting hole 31 of the slurry storage box 27 through a pressure-resistant hose and close the third self-locking valve, connect the upper water pressure controller 20 with the water outlet 22 of the sample test cylinder 1 and close the second self-locking valve 23, connect the lower water pressure controller 21 with the filtration loss drainage nozzle 15 of the sample test cylinder 1, and close the first self-locking valve 16 and the first valve 25.

[0052] S2: Laying of the confined aquifer: Laying the soil 13 and the pore water pressure sensor 44 in the sample test tube, and spraying water to the water outlet after the soil is laid.

[0053] The soil 13 for testing is laid in the sample test tube 1. While laying the soil 13, the pore water pressure sensor 44 is laid on the side wall of the pressure tube 2, and the data line 45 of the pore water pressure sensor 44 is connected to the data acquisition instrument 46. After the laying of the soil 13 is completed, water is sprinkled to the water outlet 22 to make the soil 13 form a pressurized aquifer, and the second sealing ring 8 is placed between the second groove of the second flange 6 and the second groove of the top flange 3, and the bolt holes 49 of the second flange 6 and the top flange 3 are aligned, and the bolts and nuts are tightened symmetrically to connect the second flange 6 and the top flange 3 with the bolts and nuts.

[0054] S3 Test of initial permeability coefficient of confined aquifer: water is allowed to permeate unidirectionally from bottom to top in the soil body 13 through the permeability test module, and the initial permeability coefficient of confined aquifer is calculated.

[0055] Open the first self-locking valve 16 and the first valve 25 of the filtration drain nozzle 15 and the second self-locking valve 23 of the water outlet 22, and set the water pressure of the water pressure controller 21 to P 1. Set the water pressure of the upper water pressure controller 20 to P 2, P 1> P 2. The distilled water is allowed to penetrate the soil 13 from bottom to top in one direction through the lower water pressure controller 21 and the upper water pressure controller 20. The upper water pressure controller 20 under the stable state has a certain time period ∆ t The amount of distilled water flowing in during a period of time V , the initial permeability coefficient of the confined aquifer is obtained by calculation k i .

[0056] The initial permeability coefficient of the confined aquifer is calculated using the following formula: k i :

[0057] Formula (1)

[0058] In formula (1), V for The amount of water flowing into the upper water pressure controller 20 during the time period; H 2 is the height of the soil body 13; ρ is the density of distilled water; R 2 is the inner diameter of the pressure-bearing cylinder 2; is the pressure difference between the lower water pressure controller 21 and the upper water pressure controller 20, ; It is the time for distilled water to flow into the upper water pressure controller 20.

[0059] S4: Preparation of thixotropic mud slurry: prepare thixotropic mud 14 and load the thixotropic mud 14 into the slurry storage box 27.

[0060] The slurry of thixotropic mud 14 is prepared according to the ratio, red ink is added to the thixotropic mud 14 to observe the filtration film-forming effect, the first buckle 29 between the first cover plate 28 and the slurry storage box 27 is opened, and the thixotropic mud 14 slurry is filled into the grouting hole 31 at the top of the slurry storage box 27. The thixotropic mud 14 is based on the mass of water, and the percentages of the remaining components relative to the mass of water are: 8.0%~10% bentonite, 0.20%~0.30% soda ash, 0.10%~0.20% carboxymethyl cellulose and 0.018%~0.072% polyacrylamide.

[0061] S5: applying water pressure to the confined aquifer: using the grouting pressurization module to drain the water above the soil body 13 to the filtration loss measurement module, and making the soil body 13 in a stable confined water state.

[0062] Close the first valve 25 of the lower water pressure controller 21, the first self-locking valve 16 of the filtration loss drainage nozzle 15, and the second self-locking valve 23 of the upper water pressure controller 20, connect the topmost grouting hole 31 of the slurry storage box 27 to the grouting hole 30 of the sample test tube 1 through a pressure-resistant hose, and start the pressure pump 26 to supply the grouting hole 31 of the slurry storage box 27 with the grouting hole 30 of the sample test tube 1. P 2 pressure, open the third self-locking valve of the grouting hole 31, the first self-locking valve 16 of the filtration loss drainage nozzle 15 and the second valve 40, so that the water above the soil 13 is P After the liquid level in the sample test tube 1 drops to the upper surface of the soil 13, the first self-locking valve 16 of the filtration loss drain nozzle 15 is immediately closed, and the pressure of the pressure pump 34 of the filtration loss measurement module is started and controlled. P2. After the pressure stabilizes, open the first self-locking valve 16 of the filtration drain nozzle 15 to make the soil 13 in the sample test tube 1 P 2 Stable pressurized water state under pressure.

[0063] S6 Thixotropic Mud Filtration Film Test: Use the grouting pressure module to fill the space above the soil in the sample test tube with thixotropic mud slurry, and the thixotropic mud filtration penetrates into the soil.

[0064] The pressure hose is transferred from the top grouting hole 31 to the secondary grouting hole 31, and the pressure pump 26 is controlled to provide the grout storage box 27 with P 3 grouting pressure, the pressure difference between the booster pump 26 and the pressure pump 34 is , When the slurry level in the slurry storage box 27 drops to the secondary grouting hole 31, the soil 13 in the sample test tube 1 is filled with thixotropic mud 14 slurry. At this time, the pressure pump 26 provides a stable pressure to the slurry storage box 27 and the sample test tube 1. P 3 pressure of air pressure, in P 3 The thixotropic mud 14 is filtered out and penetrates into the soil 13 under pressure.

[0065] By observing the readings of the first scale 9 and the pore water pressure sensor 44, the depth of the thixotropic mud 14 filtering into the soil 13 is recorded. d 、Thixotropic mud 14 Liquid level drop height h , the volume of liquid in the drain tank 35 V 1.

[0066] After the thixotropic mud 14 has stabilized in filtration, close the first self-locking valve 16 of the filtration drain nozzle 15, open the second flange 6, and use a steel ruler to measure the thickness of the film formed by the thixotropic mud 14 on the soil 13. H .

[0067] S7: Test of permeability coefficient of the infiltration and solid body of the confined aquifer: The permeability test module is used to make water permeate from bottom to top in the soil body 13, and the permeability coefficient of the infiltration and solid body of the confined aquifer is calculated.

[0068] Reinstall the second flange 6, close the grouting pressure module and the filtration measurement module, open the first self-locking valve 16 of the filtration drainage nozzle 15, the second self-locking valve 23 of the water outlet 22 and the first valve 25, and set the water pressure of the water pressure controller 21 to P 1. Set the water pressure of the upper water pressure controller 20 to P 2. The distilled water is made to permeate from bottom to top in the soil layer through the lower water pressure controller 21 and the upper water pressure controller 20. The upper water pressure controller 20 is recorded in the stable state. The amount of distilled water flowing in during a period of time , the permeability coefficient of the confined aquifer infiltration plus solid is obtained by calculation ;

[0069] The permeability coefficient of the confined aquifer infiltration solid is calculated using the following formula: :

[0070] Formula (2)

[0071] In formula (2), for The amount of water flowing into the upper water pressure controller 20 during the time period; is the height of the soil 13 after the thixotropic mud 14 has been filtered out; ρ is the density of distilled water; R 2 is the inner diameter of the pressure-bearing cylinder 2; is the pressure difference between the lower water pressure controller 21 and the upper water pressure controller 20, ; It is the time for distilled water to flow into the upper water pressure controller 20.

[0072] Comparison of the permeability coefficient of soil 13 before and after filtration of thixotropic mud 14 k i and , evaluate the soil 13 filtration reinforcement effect, when When the soil 13 is well reinforced by filtration.

[0073] Evaluation of S8 thixotropic mud filtration film-forming characteristics: Plot the filtration depth of thixotropic mud 14 during filtration d、 Liquid level drop height h、 Liquid loss volume V 1 and filtration time t The relationship curve was established, and the fitting equation was established to analyze and obtain the filtration rate of thixotropic mud 14 v .

[0074] Filtration rate v It is calculated using the following formula:

[0075] Formula (3)

[0076] In formula (3), k i is the soil 13 permeability coefficient; ; d is the filtration depth of thixotropic mud 14; n is the porosity of soil 13; is the tortuosity coefficient of the flow path, which is taken as 1.5.

[0077] Furthermore, in step S3 and step S7, the water pressure of the lower water pressure controller 21 isP 1 and water pressure of upper water pressure controller 20 P 2 satisfies the following relationship:

[0078] Formula (4)

[0079] According to different control working conditions, different slurry ratios, different soil 13 properties and different bearing pressures are adjusted and steps S2 to S8 are repeated to conduct multiple comparative tests. When conducting multiple comparative tests, the sample test tube 1 is connected to the grouting holes 31 from top to bottom in sequence through a pressure-resistant hose, and the corresponding thixotropic mud 14 is pressed into the adjacent grouting holes 31 each time. The optimal situation is the one with the fastest filtration rate and the largest film thickness.

[0080] The above-mentioned method for evaluating the thixotropic mud filtration and film-forming characteristics of the confined aquifer top pipe is implemented using a test system, such as Figure 2 As shown, the test system includes a sample test tube 1, a permeability test module, a grouting and pressurizing module, a filtration loss measurement module, a data acquisition module and a computer 47, wherein the sample test tube 1 contains a soil body 13; the permeability test module can provide a stable water pressure or a stable water volume for the soil body 13, and the permeability test module is used to test the permeability coefficient of the soil body 13; the grouting and pressurizing module can inject thixotropic mud 14 into the space above the soil body 13 in the sample test tube 1, and the thixotropic mud 14 can percolate into the interior of the soil body 13 after being injected into the sample test tube 1, and the thixotropic mud 14 forms a mud skin on the surface of the soil body 13 after percolated into the interior of the soil body 13, and the filtration loss characteristics of the thixotropic mud 14 affect the formation of the mud skin. In actual engineering, the filtration loss characteristics of the thixotropic mud 14 can affect the formation effect of the mud sleeve around the top pipe. The filtration loss measurement module can measure the filtration loss of the thixotropic mud 14; the data acquisition module is used to collect test data, and the data acquisition module is connected to the computer 47.

[0081] Furthermore, the test system further comprises a steel support 48, on which the sample test tube 1 is placed, and the steel support 48 can provide stable support for the sample test tube 1. Figure 3 As shown, the steel bracket 48 includes a support disc 17 and four support legs 19. The support disc 17 and the support legs 19 are made of stainless steel. The top of the support leg 19 is connected to the support disc 17 by welding or threading. The angle between the axis of the support leg 19 and the ground is α The angle of the support disc 17 is 60° to 80°, which can ensure that the sample test tube 1 remains stable when draining water or under air pressure. d 1 is 10 mm to 15 mm, ensuring that the steel support 48 can bear the weight of the sample test tube 1 and the objects inside the sample test tube 1.

[0082] like Figure 4As shown, the sample test cylinder 1 includes a pressure cylinder 2, a top flange 3, a bottom flange 4, a first flange 5 and a second flange 6. The pressure cylinder 2, the top flange 3 and the bottom flange 4 are an integrated structure. The bottom flange 4 is connected to the lower end of the pressure cylinder 2. The first flange 5 covers the lower end of the pressure cylinder 2. A plurality of bolt holes 49 are provided at corresponding positions of the first flange 5 and the bottom flange 4. The diameter of the first flange 5 is the same as the outer diameter of the bottom flange 4. The first flange 5 and the bottom flange 4 are connected by bolts and nuts. The top flange 3 is connected to the upper end of the pressure cylinder 2. The second flange 5 is connected to the bottom flange 4 by bolts and nuts. The flange 6 covers the upper end of the pressure tube 2, and a plurality of bolt holes 49 are provided at corresponding positions of the second flange 6 and the top flange 3. The diameter of the second flange 6 is the same as the outer diameter of the top flange 3. The second flange 6 and the top flange 3 are connected by bolts and nuts. The first flange 5 and the second flange 6 can ensure the internal sealing of the sample test tube 1. The sample test tube 1 is an I-shaped cylinder structure, and the material of the sample test tube 1 is acrylic (plexiglass). The use of acrylic material in the sample test tube 1 can intuitively observe the infiltration of the thixotropic mud 14 into the soil body 13 and the formation process of the mud skin.

[0083] Height of pressure tube 2 H 1 is 200mm~400mm, inner diameter R 2 is 125mm, the thickness of the top flange 3 d 2 is 10mm~15mm, the thickness of the bottom flange 4 is consistent with the thickness of the top flange 3; the outer diameter of the top flange 3 R 1 is 150mm, the outer diameter of the bottom flange 4 is consistent with the outer diameter of the top flange 3, the diameter of the support disc 17 is consistent with the outer diameter of the pressure-bearing cylinder 2, and the inner diameter of the bottom flange 4 and the inner diameter of the top flange 3 are consistent with the inner diameter of the pressure-bearing cylinder 2; an annular first groove is provided at the relative position of the bottom flange 4 and the first flange 5, and a first sealing ring 7 is provided in the two first grooves. The first sealing ring 7 is used to seal between the bottom flange 4 and the first flange 5, and an annular second groove is provided at the relative position of the top flange 3 and the second flange 6. A second sealing ring 8 is provided in the two second grooves. The second sealing ring 8 is used to seal between the top flange 3 and the second flange 6. The first sealing ring 7 can be pressed into the first grooves of the bottom flange 4 and the first flange 5 at the same time, and the second sealing ring 8 can be pressed into the second grooves of the top flange 3 and the second flange 6 at the same time, so that the sample test cylinder 1 remains sealed after being fastened with bolts, and no liquid will flow out from the gaps between the first flange 5, the second flange 6 and the pressure cylinder 2 when the sample test cylinder 1 is under pressure.

[0084] A first scale 9 is vertically attached to the outer surface of the pressure tube 2, and the filling height of the soil 13 in the sample test tube 1 can be accurately obtained through the first scale 9. Figure 2 As shown, the height of the soil 13 in the sample test tube 1 is H 2, H 2=(2 / 3~3 / 4) H 1; such as Figure 4 As shown, a circular third groove 10 is provided on the upper surface of the first flange 5, the axis of the third groove 10 is colinear with the axis of the sample test cylinder 1, the inner diameter of the third groove 10 is consistent with the inner diameter of the pressure cylinder 2, a permeable stone 11 is paved in the third groove 10, the thickness of the permeable stone 11 is the same as the depth of the third groove 10, a filter paper 12 is provided above the permeable stone 11, the diameter of the filter paper 12 is the same as the inner diameter of the pressure cylinder 2, the soil 13 is evenly laid on the filter paper 12, and the sample test cylinder 1 is composed of the permeable stone 11, the filter paper 12 and the filter paper 12. 1, filter paper 12, soil 13 and thixotropic mud 14; a loss drainage nozzle 15 is arranged at the center of the first flange 5, the loss drainage nozzle 15 is provided with a first self-locking valve 16, a support disc 17 is provided with a through hole 18 for the loss drainage nozzle 15 to pass through, the length of the loss drainage nozzle 15 is greater than the thickness of the support disc 17, the lower end of the loss drainage nozzle 15 passes through the through hole 18 and extends to the bottom of the support disc 17, and the loss drainage nozzle 15 is used for the water in the sample test tube 1 and the discharge of the loss liquid of the thixotropic mud 14.

[0085] Furthermore, the permeability test module includes an upper water pressure controller 20 and a lower water pressure controller 21. A water outlet 22 is provided on the side wall of the pressure tube 2. A second self-locking valve 23 is provided in the water outlet 22. The upper water pressure controller 20 is connected to the water outlet 22 through the second self-locking valve 23. The distance between the upper surface of the soil body 13 and the lower surface of the second flange 6 is H 3. The distance between the water outlet 22 and the lower surface of the second flange 6 is H 4. H 4=1 / 2 H 3; the lower water pressure controller 21 is connected to the filtration loss drain nozzle 15 through a first connecting pipe 24, and a first valve 25 is provided on the first connecting pipe 24.

[0086] Furthermore, if Figure 5 As shown, the grouting pressure module includes a pressure pump 26 and a slurry storage box 27. The slurry storage box 27 is a box structure with an open upper end. The material of the slurry storage box 27 is stainless steel. The length of the slurry storage box 27 is L 1 is 100mm~150mm, width L 2 is 100mm~150mm, height H5 is 150mm~200mm; the upper end of the slurry storage box 27 is covered with a first cover plate 28, and a third sealing ring is provided at the connection between the first cover plate 28 and the slurry storage box 27, and the third sealing ring can seal between the first cover plate 28 and the slurry storage box 27, and the first cover plate 28 and the slurry storage box 27 are connected by a first buckle 29; the first cover plate 28 and the box body of the slurry storage box 27 are sealed by the third sealing ring, and the first cover plate 28 and the box body of the slurry storage box 27 are further sealed and connected by the first buckle 29 in the middle, ensuring that the slurry storage box 27 can keep the box body stable and can stably transmit air pressure when receiving the pressure of the pressure pump 26.

[0087] A grouting hole 30 is provided on the second flange 6, and a grouting hole 31 is provided on the side wall of the slurry storage box 27. The grouting hole 30 is connected to the grouting hole 31 through a pressure-resistant hose. A third self-locking valve is provided in the grouting hole 31. The third self-locking valve can be closed in time when the grouting needs to be ended. When the pressure-resistant hose is not connected to the grouting hole 31, the third self-locking valve is automatically closed; a pressurizing hole 32 is provided on the first cover plate 28, and the pressure pump 26 is connected to the pressurizing hole 32 through a pressure-resistant hose. The pressure pump 26 can apply air pressure to the slurry storage box 27, thereby pressing the thixotropic mud 14 into the sample test tube 1; a first pressure gauge 33 is provided on the first cover plate 28, and the first pressure gauge 33 can display the pressure inside the slurry storage box 27, that is, the grouting pressure of the grouting pressure module. When the first pressure gauge 33 shows that the internal pressure of the slurry storage box 27 is stable at the set value, the third self-locking valve of the grouting hole 31 is opened to ensure that the thixotropic mud 14 in the slurry storage box 27 is pressed into the sample test tube 1 at a stable grouting pressure. When the pressure pump 26 pumps the thixotropic mud 14 from the slurry storage box 27 into the sample test tube 1 through the grouting hole 31, the pressure of the pressure pump 26 is kept unchanged until the thixotropic mud 14 above the grouting hole 31 connected to the pressure hose is completely injected into the sample test tube 1. At this time, the slurry storage box 27 no longer pumps the thixotropic mud 14 into the sample test tube 1, but pumps air pressure into the sample test tube 1 instead, so as to keep the thixotropic mud 14 in the sample test tube 1 percolating at a constant pressure.

[0088] Furthermore, a plurality of grouting holes 31 are provided, and the plurality of grouting holes 31 are evenly distributed vertically on the side wall of the slurry storage box 27, and the center line of the plurality of grouting holes 31 is perpendicular to the ground. The thixotropic mud 14 in the slurry storage box 27 between two adjacent grouting holes 31 can just fill the space between the soil 13 in the sample test cylinder 1 and the second flange 6, and multiple comparative tests can be carried out using the plurality of grouting holes 31; when conducting multiple comparative tests, the sample test cylinder 1 is connected to the plurality of grouting holes 31 in sequence from top to bottom through a pressure-resistant hose, and the corresponding thixotropic mud 14 between adjacent grouting holes 31 is pressed into each comparative test, so as to ensure the consistency of the performance of the thixotropic mud 14 in the multiple comparative tests, and ensure that the volume of the thixotropic mud 14 pressed into the sample test cylinder 1 is the same for each comparative test.

[0089] The distance between the centers of two adjacent grouting holes 31 is d 3. d 3 satisfies the following formula:

[0090] Formula (5)

[0091] In formula (5), R 2 is the inner diameter of the pressure-bearing cylinder 2; H 3 is the distance between the upper surface of the soil 13 and the lower surface of the second flange 6; L 1 is the length of the slurry storage box 27; L 2 is the width of the slurry storage box 27.

[0092] Furthermore, if Figure 6 As shown, the filtration loss measurement module includes a pressure pump 34 and a drainage box 35. The drainage box 35 is a pressure-resistant cylindrical tank structure with an open upper end. The drainage box 35 is made of acrylic (plexiglass). The upper end of the drainage box 35 is covered with a second cover plate 36. A fourth sealing ring is provided at the connection between the second cover plate 36 and the drainage box 35. The second cover plate 36 is connected to the drainage box 35 through a second buckle 37. The second cover plate 36 and the box body of the drainage box 35 are sealed by a fourth sealing ring, and the second cover plate 36 and the box body of the drainage box 35 are further sealed and connected by a second buckle 37. A water storage hole 38 is provided on the second cover plate 36, and the water storage hole 38 is connected to the filter through a second connecting pipe 39. The second connecting pipe 39 is provided with a second valve 40; the second cover plate 36 is provided with a pressure hole 41, and the pressure pump 34 is connected to the pressure hole 41 through a pressure-resistant hose. The pressure pump 34 can apply air pressure to the drainage box 35, thereby ensuring that the water pressure at the bottom of the soil 13 in the sample test cylinder 1 is constant during the filtration process; the second cover plate 36 is provided with a second pressure gauge 42, and the second pressure gauge 42 can display the pressure inside the drainage box 35, that is, the pressure of the pressurized aquifer in the sample test cylinder 1; the side wall of the drainage box 35 is vertically attached with a second ruler 43, and the volume of the liquid discharged from the sample test cylinder 1 can be quickly read through the second ruler 43 during the filtration process.

[0093] Furthermore, the data acquisition module includes a pore water pressure sensor 44 and a data acquisition instrument 46. A plurality of pore water pressure sensors 44 are arranged on the inner wall of the pressure cylinder 2. A wire outlet hole is arranged on the side wall of the bottom flange 4. The data line 45 of the pore water pressure sensor 44 passes through the wire outlet hole and is connected to the data acquisition instrument 46. The data acquisition instrument 46 is connected to the computer 47. The pore water pressure sensor 44 is evenly arranged in 3 to 5 circles from the upper end of the soil body 13 to the lower end of the soil body 13, and a plurality of pore water pressure sensors 44 are arranged in each circle.

[0094] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0095] A method for evaluating the filtration and film-forming properties of thixotropic mud for pipe jacking in confined aquifers fills the gap in the analysis and evaluation of the filtration and film-forming properties of thixotropic mud for pipe jacking. This method uses the combined test of filtration, film-forming and seepage of thixotropic mud for pipe jacking to comprehensively evaluate the filtration and film-forming properties of thixotropic mud, thereby optimizing the mud formula and improving the construction efficiency and drag reduction effect. When pipe jacking is carried out in confined aquifers, the filtration and film-forming properties of thixotropic mud for pipe jacking are directly related to the quality of mud jacket formation when thixotropic mud is used as a pipe jacking drag reduction material. High-quality mud jackets can effectively reduce the friction between the pipe jacking and the soil layer, significantly improving the construction efficiency; at the same time, it can reduce the pressure of groundwater on the pipe jacking, prevent groundwater from gushing into the pipe jacking working area, avoid engineering accidents such as water and sand gushing, and thus improve the stability and safety of pipe jacking construction. This evaluation method can accurately evaluate the filtration and film-forming properties of thixotropic mud, and provide a scientific basis for optimizing the pipe jacking construction plan, determining mud ratio, grouting pressure and other parameters. At the same time, confined aquifers are usually closely related to the surrounding ecological environment. Evaluating the filtration and film-forming properties of thixotropic mud helps to select environmentally friendly mud materials and construction processes, reduce the impact on the groundwater environment, and protect the ecological balance.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for evaluating the thixotropic mud filtration and film-forming properties of a confined aquifer top pipe, characterized in that: The steps include: S1 Set up the system: Assemble the sample test cylinder, and connect the penetration test module, grouting pressure module and filtration loss measurement module to the sample test cylinder respectively; S2 confined aquifer laying: lay the soil and pore water pressure sensor in the sample test tube, and sprinkle water to the water outlet after the soil is laid; S3 Test of initial permeability coefficient of confined aquifer: The permeability test module is used to make water permeate from bottom to top in the soil, and the initial permeability coefficient of confined aquifer is calculated; S4 thixotropic mud slurry preparation: prepare thixotropic mud and put the thixotropic mud into the slurry storage box; S5: Applying water pressure to the confined aquifer: Using the grouting pressure module, the water above the soil is drained to the filtration loss measurement module, and the soil is in a stable confined water state; S6 Thixotropic Mud Loss Film Formation Test: Use the grouting pressure module to fill the space above the soil in the sample test tube with thixotropic mud slurry, and the thixotropic mud loss penetrates into the soil; S7 Confined aquifer infiltration plus solid permeability coefficient test: The permeability test module allows water to permeate from bottom to top in the soil, and the permeability coefficient of the confined aquifer infiltration plus solid is calculated; Evaluation of S8 thixotropic mud filtration film-forming characteristics: Plotting the filtration depth of thixotropic mud during filtration 、 Liquid level drop height 、 The relationship curve between liquid loss volume and loss time was established, and the fitting equation was established to obtain the loss rate of thixotropic mud.

2. The method for evaluating the thixotropic mud filtration and film-forming properties of the top pipe in the confined aquifer according to claim 1, characterized in that: In step S3, the water pressure of the water pressure controller is set to P 1. Set the water pressure of the upper water pressure controller to P 2, P 1> P 2. Use the lower and upper water pressure controllers to make the distilled water penetrate the soil from bottom to top in one direction, and record the pressure of the upper water pressure controller under stable conditions. The amount of distilled water flowing in during a period of time V The initial permeability coefficient of the confined aquifer is calculated using the following formula: k i ; Formula (1) In formula (1), V for The amount of water flowing into the upper water pressure controller within a certain period of time; H 2 is the height of the soil; ρ is the density of distilled water; R 2 is the inner diameter of the pressure-bearing cylinder; is the pressure difference between the lower water pressure controller and the upper water pressure controller, ; The time when distilled water flows into the upper water pressure controller; In step S4, red ink is added to the thixotropic mud to observe the filtration film-forming effect. The thixotropic mud is based on the mass of water, and the percentages of the remaining components relative to the mass of water are: 8.0% to 10% bentonite, 0.20% to 0.30% soda ash, 0.10% to 0.20% carboxymethyl cellulose and 0.018% to 0.072% polyacrylamide; In step S5, the pressure pump of the grouting pressure module provides the gas pressure in the slurry storage box to be P 2. The water above the soil P 2, and then the pressure of the pressure pump of the filtration loss measurement module is started and controlled to P 2. Make the soil P 2 Stable confined water state under pressure; In step S6, the grouting pressure provided by the pressure pump of the grouting pressure module to the grout storage box is P 3. The pressure difference between the booster pump and the pressure pump is , ; By observing the readings of the first scale and the pore water pressure sensor, the depth of thixotropic mud loss into the soil is recorded. d , Thixotropic mud liquid level drop height h , Liquid volume in the drain tank V 1. After the thixotropic mud filtration is stable, use a steel ruler to measure the thickness of the thixotropic mud film on the soil. H ; In step S7, the water pressure of the water pressure controller is set to P 1. Set the water pressure of the upper water pressure controller to P 2. Record the upper water pressure controller in the stable state. The amount of distilled water flowing in during a period of time The permeability coefficient of the confined aquifer infiltration solid is calculated using the following formula: : Formula (2) In formula (2), for The amount of water flowing into the upper water pressure controller within a certain period of time; It is the height of the soil after thixotropic mud filtration; ρ is the density of distilled water; R 2 is the inner diameter of the pressure-bearing cylinder; is the pressure difference between the lower water pressure controller and the upper water pressure controller, ; The time when distilled water flows into the upper water pressure controller; In step S8, the filtration rate v It is calculated using the following formula: Formula (3) In formula (3), k i is the soil permeability coefficient; ; d is the thixotropic mud loss depth; n is the soil porosity; is the tortuosity coefficient of the flow path, which is taken as 1.5; Comparison of soil permeability before and after thixotropic mud filtration k i and , evaluate the soil filtration reinforcement effect; In step S3 and step S7, the water pressure of the lower water pressure controller P 1. Water pressure on the water pressure controller P 2 satisfies the following relationship: Formula (4).

3. The method for evaluating the thixotropic mud filtration and film-forming properties of the top pipe in the confined aquifer according to claim 2, characterized in that: According to different control working conditions, different slurry ratios, different soil properties and different bearing pressures are adjusted and steps S2 to S8 are repeated to perform multiple comparative tests; When conducting multiple comparative tests, the sample test tube is connected to the grouting holes from top to bottom in sequence through a pressure-resistant hose. Each time, the corresponding thixotropic mud is pressed into the adjacent grouting holes. The optimal situation is the one with the fastest filtration rate and the largest film thickness.

4. The method for evaluating the thixotropic mud filtration and film-forming characteristics of the top pipe in the confined aquifer according to claim 1, wherein the evaluation method is implemented by using a test system, and is characterized in that: The test system includes a sample test cylinder, a permeability test module, a grouting pressure module, a filtration loss measurement module, a data acquisition module and a computer, wherein: The sample test cylinder contains soil; The permeability test module can provide a stable water pressure or a stable water volume for the soil; The grouting and pressurizing module can inject thixotropic mud into the space above the soil in the sample test cylinder. After the thixotropic mud is injected into the sample test cylinder, it can infiltrate into the soil. After the thixotropic mud infiltrates into the soil, it forms a mud skin on the surface of the soil. The filtration loss measurement module can measure the filtration loss of the thixotropic mud; The data acquisition module is used to collect test data, and the data acquisition module is connected to the computer.

5. The method for evaluating the thixotropic mud filtration and film-forming characteristics of the top pipe in the confined aquifer according to claim 4, characterized in that: The test system also includes a steel support, the sample test cylinder is placed on the steel support, the steel support includes a support disc and four support legs, the top of the support leg is connected to the support disc, and the angle between the axis of the support leg and the ground is α is 60°~80°, the thickness of the support disc d 1 is 10mm~15mm; The sample test cylinder comprises a pressure-bearing cylinder, a top flange, a bottom flange, a first flange and a second flange, wherein the bottom flange is connected to the lower end of the pressure-bearing cylinder, the first flange covers the lower end of the pressure-bearing cylinder, and the first flange and the bottom flange are connected by bolts; The top flange is connected to the upper end of the pressure-bearing cylinder, the second flange covers the upper end of the pressure-bearing cylinder, the second flange and the top flange are connected by bolts, and the first flange and the second flange can ensure the internal sealing of the sample test cylinder; The material of the sample test tube is acrylic, and the height of the pressure tube is H 1 is 200mm~400mm, inner diameter R 2 is 125mm, the thickness of the top flange d 2 is 10 mm to 15 mm, and the thickness of the bottom flange is consistent with the thickness of the top flange; The outer diameter of the top flange R 1 is 150 mm, the outer diameter of the bottom flange is consistent with the outer diameter of the top flange, and the diameter of the support disc is consistent with the outer diameter of the pressure cylinder; An annular first groove is provided at the relative position of the bottom flange and the first flange, and a first sealing ring is provided in the two first grooves. The first sealing ring is used to seal between the bottom flange and the first flange. An annular second groove is provided at the relative position of the top flange and the second flange, and a second sealing ring is provided in the two second grooves, and the second sealing ring is used to seal between the top flange and the second flange; The outer surface of the pressure-bearing cylinder is vertically attached with a first scale. The height of the soil in the sample test cylinder is H 2, H 2=(2 / 3~3 / 4) H 1; A circular third groove is provided on the upper surface of the first flange, the axis of the third groove is colinear with the axis of the sample test cylinder, the inner diameter of the third groove is consistent with the inner diameter of the pressure cylinder, a permeable stone is paved in the third groove, the thickness of the permeable stone is the same as the depth of the third groove, a filter paper is provided above the permeable stone, and the soil is laid on the filter paper; A loss-liquid drainage nozzle is arranged at the center of the first flange, and the loss-liquid drainage nozzle is provided with a first self-locking valve. The support disc is provided with a through hole for the loss-liquid drainage nozzle to pass through, and the lower end of the loss-liquid drainage nozzle passes through the through hole and extends to the bottom of the support disc.

6. The method for evaluating the thixotropic mud filtration and film-forming characteristics of the top pipe in the confined aquifer according to claim 5, characterized in that: The penetration test module includes an upper water pressure controller and a lower water pressure controller. A water outlet is provided on the side wall of the pressure-bearing cylinder. A second self-locking valve is provided in the water outlet. The upper water pressure controller is connected to the water outlet through the second self-locking valve. The distance between the upper surface of the soil and the lower surface of the second flange is H 3. The distance between the water outlet and the lower surface of the second flange is H 4. H 4=1 / 2 H 3; The lower water pressure controller is connected to the filtration loss drain nozzle through a first connecting pipe, and a first valve is arranged on the first connecting pipe.

7. The method for evaluating the thixotropic mud filtration and film-forming characteristics of the top pipe in the confined aquifer according to claim 5, characterized in that: The grouting pressure module includes a pressure pump and a slurry storage box. The slurry storage box is a box structure with an open upper end. The material of the slurry storage box is stainless steel. The length of the slurry storage box is L 1 is 100mm~150mm, width L 2 is 100mm~150mm, height H 5 is 150mm~200mm; The upper end of the slurry storage box is covered with a first cover plate, a third sealing ring is provided at the connection between the first cover plate and the slurry storage box, and the first cover plate and the slurry storage box are connected by a first buckle; The second flange is provided with a grouting hole, the side wall of the slurry storage box is provided with a grouting hole, the grouting hole is connected to the grouting hole through a pressure-resistant hose, and a third self-locking valve is provided in the grouting hole, and the third self-locking valve can be closed in time when the grouting needs to be ended; A pressure hole is provided on the first cover plate, and the pressure pump is connected to the pressure hole through a pressure-resistant hose. The pressure pump can apply air pressure to the slurry storage box, thereby pressing the thixotropic slurry into the sample test cylinder; The first cover plate is provided with a first pressure gauge, and the first pressure gauge can display the pressure inside the slurry storage box.

8. The method for evaluating the thixotropic mud filtration and film-forming characteristics of the top pipe in the confined aquifer according to claim 7, characterized in that: The grouting holes are arranged in plurality, and the plurality of grouting holes are evenly distributed vertically on the side wall of the slurry storage box. The thixotropic slurry in the slurry storage box between two adjacent grouting holes can just fill the space between the soil in the sample test cylinder and the second flange. The plurality of grouting holes can be used to carry out multiple comparative tests. When conducting multiple comparative tests, the sample test tube is connected to the multiple grouting holes in sequence from top to bottom through a pressure-resistant hose, and the corresponding thixotropic mud between adjacent grouting holes is pressed each time to ensure the consistency of the thixotropic mud performance; The distance between the centers of two adjacent grouting holes is d 3. d 3 satisfies the following formula: Formula (5) In formula (5), R 2 is the inner diameter of the pressure-bearing cylinder; H 3 is the distance between the upper surface of the soil and the lower surface of the second flange; L 1 is the length of the slurry storage box; L 2 is the width of the slurry storage box.

9. The method for evaluating the thixotropic mud filtration and film-forming characteristics of the top pipe in the confined aquifer according to claim 5, characterized in that: The filtration loss measurement module includes a pressure pump and a drainage box. The drainage box is a tank structure with an open upper end. The material of the drainage box is acrylic. The upper end of the drainage box is covered with a second cover plate. A fourth sealing ring is provided at the connection between the second cover plate and the drainage box. The second cover plate is connected to the drainage box through a second buckle. The second cover plate is provided with a water storage hole, the water storage hole is connected to the filtration loss drain nozzle through a second connecting pipe, and the second connecting pipe is provided with a second valve; The second cover plate is provided with a pressure hole, the pressure pump is connected to the pressure hole through a pressure-resistant hose, and the pressure pump can apply air pressure to the drainage box, thereby ensuring that the water pressure at the bottom of the soil body in the sample test cylinder is constant during the filtration process; A second pressure gauge is provided on the second cover plate, and the second pressure gauge can display the pressure inside the drainage box; A second scale is vertically attached to the side wall of the drainage box.

10. The method for evaluating the thixotropic mud filtration and film-forming characteristics of the top pipe in the confined aquifer according to claim 5, characterized in that: The data acquisition module includes a pore water pressure sensor and a data acquisition instrument. A plurality of pore water pressure sensors are arranged on the inner wall of the pressure-bearing cylinder. A wire outlet hole is arranged on the side wall of the bottom flange. The data line of the pore water pressure sensor passes through the wire outlet hole and is connected to the data acquisition instrument. The data acquisition instrument is connected to the computer. The pore water pressure sensors are evenly arranged in 3 to 5 circles from the upper end of the soil body to the lower end of the soil body, and a plurality of the pore water pressure sensors are arranged in each circle.

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