A structural soft soil vacuum preloading field model test device and method

Abstract

The application discloses a structural soft soil vacuum preloading field model test device and method, and relates to the field of engineering construction. The test device comprises a sampling ring cutter barrel, a cutting and lifting plate, an upper sealing cover, water permeable stones, drainage plates, a connecting hose, a suction pump, a monitoring device, a flexible sealing film, a heap loading weight and the like. The thin-walled ring cutter barrel with blades is slowly pressed into the structural soft soil, the soil body is lifted by the cutting and lifting plate and placed on the water permeable stones on the site, the drainage plates and the monitoring device are arranged by using the cutting tool, the disturbance of the test to the structural soft soil is minimized, and thus the optimal vacuum preloading reinforcement scheme closer to the actual situation of the engineering site is obtained. The test device has a flexible structure and can be applied to the field model test of the large-volume soft soil in different modes such as vacuum preloading, heap loading preloading, vacuum-heap loading combined preloading and the like. The test device can meet the requirements of different drainage channel designs, different vacuum environment designs and different monitoring scheme designs, and thus the beneficial effects of improving the engineering quality and saving the funds are achieved.

Description

Technical Field

[0001] This invention relates to the field of foundation treatment technology, and in particular to an apparatus and method for conducting in-situ model tests of vacuum preloading on structural soft soil. Background Technology

[0002] In the field of foundation treatment technology, vacuum preloading is a commonly used method for reinforcing soft soil subgrades. The essence of vacuum preloading is to accelerate the drainage of internal moisture from soft soil foundations (high water content, highly compressible soils) by "vacuuming + establishing drainage channels" (supplemented by surcharge pressurization when necessary), thereby achieving rapid soil consolidation, improving bearing capacity, and reducing post-construction settlement. In engineering practice, vacuum preloading technology is complex, involving multiple parameters such as drainage channel design (drainage board material, diameter, depth, spacing, etc.), vacuum environment design (vacuuming pressure, sealing method), surcharge design (surcharge pressure, surcharge rate), and reinforcement status monitoring design (sensor type, installation method). Different combinations of parameters form multiple vacuum preloading design schemes. To ensure that foundation treatment projects meet the requirements of schedule, economic rationality, safety, and convenience, indoor tests or on-site model tests need to be conducted before construction. Comparative tests should be carried out on multiple vacuum preloading design schemes, and the reinforcement effect should be verified and analyzed to select the optimal vacuum preloading design scheme to guide on-site construction.

[0003] Laboratory tests are suitable for small-scale tests on non-structural soils, including sampling and transportation in their natural state, indoor preparation (indoor re-sampling, paving after disturbance, etc.), and laboratory testing. For structural soft soils, due to significant changes in properties before and after disturbance, laboratory test results often differ markedly from in-situ vacuum preloading results, thus failing to effectively guide engineering implementation. In-situ model tests, which maximize the preservation of the test samples' natural state and complete the entire process from sampling to testing, are large-scale tests and are the ideal method for vacuum preloading model tests of structural soft soils.

[0004] Structural soft soil is a special type of soft soil foundation, widely distributed in overseas engineering projects, especially in soft soil areas rich in volcanic ash. The characteristic of structural soft soil is that it possesses a certain structure, i.e., a certain strength, in its natural state; however, its drainage and consolidation properties change significantly after disturbance. Studies have shown that the strength of structural soft soil can decrease by up to 90% and the consolidation coefficient by 90%–95% after disturbance. Therefore, traditional sampling and preparation methods for vacuum preloading laboratory tests or field model tests on structural soft soil often suffer from significant differences between the test soil and the soil layers at the engineering site due to sampling disturbance issues. This leads to severely distorted test results when implemented on-site, greatly impacting subsequent project progress and costs.

[0005] A search of existing technical literature revealed no devices or methods for field model tests of vacuum preloading in structural soft soil. CN101603308B proposed a safe construction method for surcharge preloading on strongly structural soft soil. Its essence lies in achieving safe construction through dynamic monitoring and dynamic design adjustments, which is fundamentally different from conducting field model tests before construction. CN103823039 designed a combined vacuum preloading-surcharge-dynamic compaction consolidation apparatus. Its essence lies in using structural design to enable different external force application methods in the indoor test device to simulate different test schemes. It is mainly aimed at soft soil that can be disturbed and re-prepared, which is significantly different from the test object of structural soft soil. C N205776419U discloses an indoor model test apparatus, in which a sand layer, a soft soil layer and a drainage sand cushion layer are laid in sequence in the inner tank. This is clearly an indoor re-preparation method, which is significantly different from the field sampling apparatus and preparation method of this application. CN204163070U discloses an inner and outer sleeve type soil sampling method, which requires transportation and re-preparation, and the sampling volume is small (small inner diameter and height), which can only meet the needs of indoor testing. This is significantly different from the large-volume samples of field model tests, and the required sampling process is significantly different (e.g., large-volume samples cannot be extracted by vacuum alone).

[0006] Therefore, how to maintain the natural characteristics of large-volume structural soft soil, reduce experimental disturbance, and carry out on-site model tests of vacuum preloading has become a technical problem that urgently needs to be solved by researchers in this field. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a field model test device and method for vacuum preloading of structural soft soil. This device can be used for the entire process of large-volume structural soft soil sampling and preparation, vacuum preloading comparison test, reinforcement effect monitoring, and reinforcement effect verification. It can maintain the original structure of large-volume structural soft soil to the greatest extent, thereby providing support for the selection of subsequent vacuum preloading model test schemes and on-site engineering implementation.

[0008] A field model test device for vacuum preloading of structural soft soil includes a sampling ring cutter cylinder, a cutting lifting plate, permeable stones, a drainage board, a vacuum pump, and a monitoring device, as well as a sealing unit. The sampling ring cutter cylinder is a thin-walled annular structure with an open lower end and a thin-walled, sharpened edge. The drainage board and the monitoring unit are axially arranged inside the sampling ring cutter cylinder, wherein the drainage board is connected to the vacuum pump located outside the sampling ring cutter cylinder via a connecting hose. The cutting lifting plate and permeable stones alternately cover and support the lower opening of the sampling ring cutter cylinder according to the test progress. The sealing unit seals the top opening of the sampling ring cutter cylinder.

[0009] Preferably, the sealing unit includes an upper sealing cover used in the vacuum pre-compression test, and a flexible sealing membrane and a load used in the surcharge pre-compression or vacuum-surcharge combined pre-compression test. The upper sealing cover is a rigid structure and is threadedly connected to the outer wall of the top opening of the sampling ring knife cylinder. A one-way exhaust valve is provided in the middle of the upper sealing cover.

[0010] The flexible sealing membrane is a flexible structure that seals and covers the top opening of the sampling ring cutter tube. A load is placed on the flexible sealing membrane to provide experimental load for the soil inside the sampling ring cutter tube.

[0011] Preferably, the one-way exhaust valve is connected from the inside of the sampling ring barrel to the outside and cuts off in the reverse direction.

[0012] Preferably, the drainage board is a porous, interconnected plastic structure. After the structural soft soil sample is prepared, the drainage board is placed in the structural soft soil using a cutting tool. The number, diameter, and spacing of the drainage boards need to be configured according to the test plan.

[0013] Preferably, the vacuum pump is equipped with a water vapor separation device, which can apply vacuum negative pressure to the surface of structural soft soil while collecting moisture;

[0014] Preferably, the monitoring device includes a pore water pressure gauge, a stratified settlement gauge, and a water level sensor; according to the experimental design, after the large-volume structural soft soil sample is prepared, the monitoring device is placed in the structural soft soil using a cutting tool, and the data generated by the monitoring device is used to evaluate the vacuum preloading effect.

[0015] Preferably, the cutting lifting plate is a plate-shaped structure, with a cutting edge on one side for cutting, and lifting holes around the perimeter of the cutting lifting plate.

[0016] A test method for a field model test device for vacuum preloading of structural soft soil includes the following steps:

[0017] S1: Sampling ring cutter tube prepares large-volume structural soft soil samples; after removing surface debris, the sampling ring cutter tube and the upper sealing cap are sealed, and then slowly pressed into the structural soft soil layer using mechanical force or manual force. During the pressing process, the sampling ring cutter tube, due to its thin-walled and bladed structure, can minimize disturbance to the structural soft soil; at the same time, the one-way exhaust valve is in the open state to discharge excess gas in the sampling ring cutter tube, ensuring that the structural soft soil enters the sampling ring cutter tube smoothly;

[0018] S2: Lifting and pulling large-volume structural soft soil samples; when the sampling ring tube is filled with structural soft soil, the cutting edge of the pre-installed lifting plate is inserted into the bottom of the sampling ring tube, completely covering the bottom of the sampling ring tube. Then, the sampling ring tube is lifted out using lifting machinery and placed on the permeable stone on site. The lifting plate is then removed, and the permeable stone supports and covers the lower opening of the sampling ring tube, forming a drainage channel at the bottom of the sampling ring tube. The permeability of the permeable stone is selected based on the permeability characteristics of the underlying soil layer of the actual structural soft soil stratum, choosing the permeable stone that best approximates the actual drainage conditions. The lifting plate is then removed from between the soil sample and the permeable stone, and a seal is set between the sampling ring tube and the permeable stone.

[0019] S3: Drainage board and monitoring device installation; Remove the upper sealing cover and use a cutting tool to install the drainage board and monitoring device inside the structural soft soil;

[0020] S4: Repeat S1-S3 to prepare multiple samples for comparative experiments;

[0021] S5:

[0022] When using only the vacuum pre-pressure mode: reseal the upper sealing cover and connect the one-way exhaust valve, connecting hose, and vacuum pump in sequence to form an upper drainage channel and provide vacuum negative pressure;

[0023] When using surcharge preloading or vacuum-surcharge combined preloading: wrap the connecting hose inside the flexible sealing membrane, and place the surcharge weight on the flexible sealing membrane at the same time;

[0024] S6: According to the designed vacuum preloading reinforcement scheme, start the vacuum pump, set up the load in stages, and simultaneously start the monitoring device to record the vacuum preloading process data until the design requirements are met.

[0025] S7: Samples are taken and laboratory tests are conducted on the reinforced structural soft soil to verify and compare the reinforcement effects, thereby selecting the most economical and reasonable reinforcement scheme that meets the foundation design requirements.

[0026] The advantages and technical effects of this invention are as follows:

[0027] 1. This invention uses a thin-walled, bladed ring cutter to slowly press into structural soft soil, and uses a cutting lifting plate to extract a large volume of soil, which is then placed on permeable stones on site. At the same time, a drainage board and monitoring device are installed using the cutting tool to minimize the disturbance of the large volume of structural soft soil to the test, thereby obtaining an optimal vacuum preloading reinforcement scheme that is closer to the actual situation on the engineering site.

[0028] 2. The test method of this invention adopts a large-size sampling ring cutter cylinder, a cutting lifting plate and other disturbance reduction schemes, which can avoid the interference of local heterogeneity of structural soft soil and small-size samples on the test results;

[0029] 3. The test device of the present invention has a flexible structure and can be applied to field model tests of different methods such as vacuum preloading, surcharge preloading, and vacuum-surcharge combined preloading. It can meet the requirements of different drainage channel designs, different vacuum environment designs, and different monitoring scheme designs, thereby achieving the beneficial effects of improving project quality, meeting schedules, and saving costs. Attached Figure Description

[0030] Figure 1 , 2 This is a schematic diagram of the experimental apparatus before sample preparation according to the present invention;

[0031] Figure 3 This is a schematic diagram showing the lifting state during sample preparation according to the present invention;

[0032] Figure 4 This is a schematic diagram of the structure of the test device before removing the cutting plate according to the present invention;

[0033] Figure 5 This is a schematic diagram of the experimental apparatus used for vacuum preloading after sample preparation in this invention;

[0034] Figure 6 This is a schematic diagram of the test device structure when the sample is prepared and subjected to surcharge preloading according to the present invention;

[0035] In the diagram: 1. Upper sealing cap; 2. Sampling ring cutter barrel; 3. One-way exhaust valve; 4. Connecting hose; 5. Structural soft soil; 6. Drainage board; 7. Permeable stone; 8. Vacuum pump; 9. Flexible sealing membrane; 10. Loaded load; 11. Monitoring device; 12. Cutting lifting plate; 13. Sealing strip. Detailed Implementation

[0036] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0037] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] A field model test device for vacuum preloading of structural soft soil includes a sampling ring cutter barrel, a cutting lifting plate 12, an upper sealing cover, permeable stones, a drainage board, a connecting hose, a vacuum pump, a monitoring device, a flexible sealing membrane, and a load.

[0039] The sampling ring cutter 2 is a thin-walled ring-shaped structure with a blade at the lower end, which can avoid sampling disturbance when cutting structural soft soil; the sampling ring cutter 2 can adopt a large-size structure according to the soil conditions on site and the test design to meet the requirements of large-volume sample preparation; the sampling ring cutter 2 is threadedly connected to the upper sealing cover 1.

[0040] The upper sealing cover 1 is equipped with a sealing ring, which can form an upper sealed structure with the sampling ring tube 2; the upper sealing cover 1 is equipped with a one-way exhaust valve 3, which can discharge moisture and gas in the sampling ring tube 2 during the sampling process. At the same time, after the sampling is completed, when the sampling ring tube 2 is moved, the soil is adsorbed in the ring tube due to the vacuum sealing effect.

[0041] The cutting lifting plate 12 has a cutting edge on one side for cutting, and lifting holes are provided around the perimeter;

[0042] The permeable stone 7 has a porous structure and can be replaced with permeable stones 7 of different permeability according to the actual conditions of the underlying soft soil strata. The permeable stone 7 can serve as a drainage channel in the lower part during the vacuum preloading stage to discharge the water generated in the lower part due to vacuum preloading, surcharge preloading, or vacuum-surcharge combined preloading.

[0043] The drainage board 6 is a porous, interconnected plastic structure that can be placed inside the structural soft soil after the sample is prepared using a cutting tool. The number, diameter, and spacing of the drainage boards 6 can be flexibly configured according to the test plan.

[0044] One end of the connecting hose 4 is connected to the one-way exhaust valve 3, and the other end is connected to the vacuum pump 8. It serves as a vacuum pre-pressure pumping and drainage channel.

[0045] The vacuum pump 8 is equipped with a water vapor separation device, which can apply vacuum negative pressure to the surface of structural soft soil while collecting moisture;

[0046] The monitoring device 11 includes, but is not limited to, sensors such as pore water pressure gauges, stratified settlement gauges, and water level gauges; according to the experimental design, after the structural soft soil samples are prepared, the monitoring device 11 is placed in the structural soft soil using a cutting tool; the data generated by the monitoring device 11 can be used to evaluate the effect of vacuum preloading.

[0047] The flexible sealing membrane 9 is an airtight flexible sealing material that can ensure vacuum sealing while transmitting the pressure of the loaded heavy object 10.

[0048] The surcharge load 10 can apply surcharge preloading to the structural soft soil according to the surcharge preloading design;

[0049] A test method for vacuum preloading model of structural soft soil includes the following steps:

[0050] S1: Sampling ring cutter 2 prepares structural soft soil samples. After removing surface debris, the sampling ring cutter 2 and the upper sealing cap 1 are sealed. The sample is then slowly pressed into the structural soft soil layer using mechanical force or manual force. During the pressing process, the sampling ring cutter 2, due to its thin-walled and bladed structure, can minimize disturbance to the structural soft soil. At the same time, the one-way exhaust valve 3 is in the open state to discharge excess gas from the sampling ring cutter 2, ensuring that the structural soft soil can smoothly enter the sampling ring cutter 2.

[0051] S2: Pull and lift large-volume structural soft soil samples; when the sampling ring tube 2 is filled with structural soft soil, insert the cutting edge of the pre-installed lifting plate 12 with lifting wire into the bottom of the sampling ring tube 2, completely covering the bottom of the sampling ring tube 2, and then use lifting machinery to lift the sampling ring tube 2 and place it on the permeable stone 7 on site to form a drainage channel at the bottom; the permeability of the permeable stone 7 can be selected based on the permeability characteristics of the soil layer below the actual stratum of the structural soft soil, and the permeable stone that is closest to the actual drainage conditions can be selected; the cutting lifting plate 12 is pulled out from between the soil sample and the permeable stone 7, and a sealing strip 13 is set between the sampling ring tube 2 and the permeable stone 7;

[0052] S3: Installation of drainage board 6 and monitoring device 11. Remove the upper sealing cover 1 and use a cutting tool to install drainage board 6 and monitoring device 11 inside the structural soft soil.

[0053] S4: Repeat S1-S3 to prepare multiple samples for comparative experiments.

[0054] S5: When only the vacuum pre-pressure mode is used, reseal the upper sealing cover 1, and connect the one-way exhaust valve 3, connecting hose 4, and vacuum pump 8 in sequence to form an upper drainage channel and provide vacuum negative pressure.

[0055] When using surcharge preloading or vacuum-surcharge combined preloading, the connecting hose 4 is wrapped inside the flexible sealing membrane 9, and the surcharge weight 10 is placed on the flexible sealing membrane 9.

[0056] S6: According to the designed vacuum preloading reinforcement scheme, start the vacuum pump 8, and set the load 10 in stages. Simultaneously start the monitoring device 11 and record the vacuum preloading process data until the requirements of the scheme design are met.

[0057] S7: Samples are taken and laboratory tests are conducted on the reinforced structural soft soil to verify and compare the reinforcement effects, thereby selecting the most economical and reasonable reinforcement scheme that meets the foundation design requirements.

[0058] To more clearly illustrate the specific embodiments of the present invention, an example is provided below:

[0059] The present invention provides a field model test device and test method for vacuum preloading of structural soft soil, the specific test procedure of which is as follows:

[0060] S1: Sampling ring cutter barrel is used to prepare structural soft soil samples.

[0061] To verify the degree of disturbance caused by the sampling method of this invention to structural soft soil, comparative experiments were conducted on soft soil samples taken before and after sampling at similar locations within the sampling ring. The results show that, after excluding accidental factors such as the inherent heterogeneity of the soft soil and other inherent differences, the sampling disturbance caused by the method of this invention to structural soft soil is extremely small (the difference in indicators is generally within 5%), indicating that the experimental conclusions of this method can be more realistically applied to engineering practice.

[0062] Table 1 Comparative Analysis of Sampling Disturbance Degree of Structural Soft Soil Using the Method of the Present Invention

[0063] Moisture content w (%) 246 242 -1.63％ <![CDATA[Unit weight γ (kN / m 3 )]]> 11.3 11.3 0.00％ Porosity e 5.828 5.749 -1.36％ <![CDATA[Liquid Limit W L (%)]]> 199 209 5.03％ <![CDATA[Plastic Limit W P (%)]]> 116 120 3.45％ <![CDATA[Compression coefficient α (MPa -1 )]]> 5.6 5.8 3.57％

[0064] S2: Pulling up structural soft soil samples.

[0065] S3: Drainage board and monitoring device installation. Remove the upper sealing cap and use a cutting tool to install the drainage board and monitoring device inside the structural soft soil.

[0066] S4: Repeat S1-S3 to prepare multiple samples for comparative experiments.

[0067] S5: When using only the vacuum pre-pressure mode, reseal the upper sealing cover and connect the one-way exhaust valve, connecting hose, and vacuum pump in sequence to form an upper drainage channel and provide vacuum negative pressure.

[0068] When using surcharge preloading or vacuum-surcharge combined preloading, the connecting hose is wrapped inside a flexible sealing membrane, and a surcharge weight is placed on the flexible sealing membrane.

[0069] S6: According to the designed vacuum preloading reinforcement scheme, start the vacuum pump, set up the load in stages, and simultaneously start the monitoring device to record the vacuum preloading process data until the design requirements are met.

[0070] S7: Samples are taken and laboratory tests are conducted on the reinforced structural soft soil to verify and compare the reinforcement effects, thereby selecting the most economical and reasonable reinforcement scheme that meets the foundation design requirements.

[0071] Comparative tests and effects of different vacuum preloading design schemes

[0072] The effects of tests with different vacuum pressures and different drainage board spacings were analyzed. The changes in soil moisture content before and after vacuuming are shown in the table below.

[0073] Table 4. Changes in moisture content before and after the experiment.

[0074] Moisture content before experiment 256.7％ 306.4％ 242％ Moisture content after the test 138.1-150.2％ 167.7-128.2％ 124.5-155.3％

[0075] Note: Cumulative vacuuming time: #2 121h, #3 174h, #4 174h

[0076] Finally, any aspects not fully described in this invention utilize existing mature products and technologies.

[0077] In the description of this specification, references to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example that are included in the embodiments or examples of the present invention.

[0078] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A test method for a field model test device for vacuum preloading of structural soft soil, characterized in that, Includes the following steps: S1: Sampling ring cutter tube for preparing large-volume structural soft soil samples; After removing surface soil and sealing the sampling ring and top cap, the sample ring is slowly pressed into the structural soft soil layer using mechanical or manual force. During the pressing process, the sampling ring, with its thin-walled, bladed structure, minimizes disturbance to the structural soft soil. At the same time, the one-way exhaust valve is open to expel excess gas from the sampling ring, ensuring that the structural soft soil can smoothly enter the sampling ring. S2: Lifting and pulling large-volume structural soft soil samples; when the sampling ring tube is filled with structural soft soil, the cutting edge of the pre-installed lifting plate is inserted into the bottom of the sampling ring tube, completely covering the bottom of the sampling ring tube. Then, the sampling ring tube is lifted out using lifting machinery and placed on the permeable stone on site. The lifting plate is then removed, and the permeable stone supports and covers the lower opening of the sampling ring tube, forming a drainage channel at the bottom of the sampling ring tube. The permeability of the permeable stone is selected based on the permeability characteristics of the underlying soil layer of the actual structural soft soil stratum, choosing the permeable stone that best approximates the actual drainage conditions. The lifting plate is then removed from between the soil sample and the permeable stone, and a seal is set between the sampling ring tube and the permeable stone. S3: Drainage board and monitoring device installation; Remove the upper sealing cover and use a cutting tool to install the drainage board and monitoring device inside the structural soft soil; S4: Repeat S1-S3 to prepare multiple samples for comparative experiments; S5： When using only the vacuum pre-pressure mode: reseal the upper sealing cover and connect the one-way exhaust valve, connecting hose, and vacuum pump in sequence to form an upper drainage channel and provide vacuum negative pressure; When using surcharge preloading or vacuum-surcharge combined preloading: wrap the connecting hose inside the flexible sealing membrane, and place the surcharge weight on the flexible sealing membrane at the same time; S6: According to the designed vacuum preloading reinforcement scheme, start the vacuum pump, set up the load in stages, and simultaneously start the monitoring device to record the vacuum preloading process data until the design requirements are met. S7: Take samples and conduct laboratory tests on the reinforced structural soft soil to verify and compare the reinforcement effect, so as to select the most economical and reasonable reinforcement scheme that meets the foundation design requirements; The structural soft soil vacuum preloading field model test device includes a sampling ring cutter cylinder, a cutting lifting plate, permeable stones, a drainage board, a vacuum pump, and a monitoring device, as well as a sealing unit. The sampling ring cutter cylinder is a thin-walled annular structure with an open lower end and a thin-walled, sharpened edge. The drainage board and monitoring unit are axially arranged inside the sampling ring cutter cylinder, with the drainage board connected to the vacuum pump located outside the sampling ring cutter cylinder via a connecting hose. The cutting lifting plate and permeable stones alternately cover and support the lower opening of the sampling ring cutter cylinder according to the test progress. The sealing unit seals the top opening of the sampling ring cutter cylinder. The sealing unit includes an upper sealing cover used in vacuum pre-compression experiments, and a flexible sealing membrane and a load used in surcharge pre-compression or vacuum-surcharge combined pre-compression experiments. The upper sealing cover is a rigid structure and is threadedly connected to the outer wall of the top opening of the sampling ring knife cylinder. A one-way exhaust valve is provided in the middle of the upper sealing cover. The flexible sealing membrane is a flexible structure that seals and covers the top opening of the sampling ring cutter tube. A load is placed on the flexible sealing membrane to provide experimental load for the soil inside the sampling ring cutter tube.

2. The testing method for a field model test device for vacuum preloading of structural soft soil according to claim 1, characterized in that: The one-way exhaust valve connects from the inside of the sampling ring cutter cylinder to the outside and shuts off in the reverse direction.

3. The testing method for a field model test device for vacuum preloading of structural soft soil according to claim 1, characterized in that: The drainage board is a porous, interconnected plastic structure. After the structural soft soil sample is prepared, the drainage board is placed inside the structural soft soil using a cutting tool. The number, diameter, and spacing of the drainage boards need to be configured according to the test plan.

4. The testing method for a field model test device for vacuum preloading of structural soft soil according to claim 1, characterized in that: The vacuum pump is equipped with a water vapor separation device, which can apply vacuum negative pressure to the surface of structural soft soil while collecting moisture.

5. The testing method for a field model test device for vacuum preloading of structural soft soil according to claim 1, characterized in that: The monitoring device includes a pore water pressure gauge, a stratified settlement gauge, and a water level sensor. According to the experimental design, after the large-volume structural soft soil sample is prepared, the monitoring device is placed in the structural soft soil using a cutting tool. The data generated by the monitoring device is used to evaluate the vacuum preloading effect.

6. The testing method for a field model test device for vacuum preloading of structural soft soil according to claim 1, characterized in that: The cutting lifting plate is a plate-shaped structure. One side of the cutting lifting plate is provided with a cutting edge for cutting, and the perimeter of the cutting lifting plate is provided with lifting holes.

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