Construction Method of Three-Stage Vacuum Preloading Drainage System for Ecological Dredging of River, Lake and Reservoir

Abstract

This invention discloses a construction method for a three-stage vacuum preloading drainage system for ecological dredging of river, lake, and reservoir sediments, comprising the following steps: S1, removing debris; S2, constructing sealing trenches around the soft soil foundation to be reinforced; S3, laying a working cushion layer on the soft soil foundation to be reinforced; S4, arranging a layered three-stage drainage system; S5, arranging a data acquisition system; S6, sequentially laying woven fabric, geotextile, and sealing membrane on the working cushion layer; S7, connecting the main drainage pipes of each stage of the drainage system to the corresponding vacuum negative pressure equipment or vacuum negative pressure station; S8, performing vacuum preloading reinforcement of the soft soil foundation using a stepped loading mode; S9, unloading after passing inspection. The technical solution of this invention essentially eliminates the uneven soil texture characterized by "hard top and soft bottom," while also shortening the construction period and reducing project costs.

Description

Technical Field

[0001] This invention belongs to the field of soft soil solidification technology, and in particular relates to a construction method for a three-stage vacuum preloading drainage system for ecological dredging sediment in rivers, lakes and reservoirs. Background Technology

[0002] River, lake, and reservoir dredged sediment is characterized by high water content, high compressibility, low shear strength, poor permeability, and virtually no bearing capacity. Therefore, soft soil foundation reinforcement treatment is necessary before engineering construction or resource utilization. Common methods can be broadly categorized into physical treatment and chemical solidification treatment, including vacuum preloading, heat treatment, dewatering, sedimentation and drying, sludge disposal, and chemical solidification agent treatment. Among these, vacuum preloading is the most traditional and widely used method due to its advantages of low cost, simple construction, and no pollution.

[0003] Vacuum preloading is a method of reinforcing soft soil foundations by creating negative excess pore water pressure in the soil while keeping the total stress essentially constant, thereby increasing the effective stress. Specifically, vertical drainage boards are inserted into the soft soil. The vacuum pressure forces water and air out of the soil through the drainage boards, reducing pore water pressure while increasing effective stress, thus significantly improving the bearing capacity of the soft soil foundation. The air extraction and drainage process in vacuum preloading is essentially the dissipation of excess pore water pressure, consisting of two parts: first, the direct transfer of vacuum causing a decrease in pore water pressure; and second, the drop in water level caused by vacuum extraction, leading to the dissipation of pore water pressure.

[0004] Through investigation of existing technologies, the inventors discovered that the following existing technologies employ a combination of strengths and weaknesses to address the problems of long curing cycles, unsatisfactory curing effects, and the tendency for "hard top and soft bottom" in traditional soft soil foundation solidification treatment. For example, the existing technologies disclose a closed direct extraction segmented vacuum preloading foundation treatment method, with publication number CN102733371B, and a construction process for a compound pressurized vacuum preloading soft soil foundation with drainage boards of different lengths, with publication number CN109295969A.

[0005] The specific technical analysis is as follows: An existing technology discloses a closed-loop, segmented vacuum preloading foundation treatment method, with publication number CN102733371B. This existing technology involves a vertical plastic drainage board comprising two parts: an insert portion into the soil and a portion flat against the soil surface. The drainage system on the soil surface consists of the plastic drainage board flat against the soil surface, a sealing joint, an airtight sealed water pipe, and an airtight sealed main pipe. After the geomembrane is sealed, it is connected to a vacuum pump for closed-loop direct extraction. When a vacuum preloading foundation treatment project requires the combined application of long and short boards for pretreatment cushion layer construction, after the short board construction completes the pretreatment cushion layer construction, when the long board is installed for deep foundation treatment, the filter cloth in the shallow soil section of the long board's insert portion is surface-sealed or directly replaced with a sealed water pipe. This transforms the long vertical plastic drainage board into a three-section system with an airtight middle section for segmented direct extraction.

[0006] Analysis reveals the following technical deficiencies in the existing technology: Firstly, the existing technology uses short drainage boards for shallow pretreatment and long drainage boards for deep foundation treatment, requiring two separate installations of both short and long drainage boards and the construction of two sealing systems. In contrast, the drainage board installation and sealing system construction in this application are completed in a single step. Compared to this application, the existing technology involves more complex procedures, significantly longer construction time, and increased material consumption, leading to higher project costs. Secondly, the vacuum negative pressure of each level of the drainage system in this application is determined based on the depth of the drainage boards, with different vacuum negative pressures set for each level instead of a uniform maximum negative pressure of 85 kPa. This increases energy consumption compared to this application. Thirdly, except for the primary drainage system where the drainage board unit is connected to the drainage branch pipe via a top connection, the secondary and tertiary systems in this application use a bottom connection. This results in a certain difference in treatment effectiveness compared to this application. Finally, to prevent repeated consumption of vacuum in shallow soil sections and increase the efficiency of vacuum transfer to deeper layers… The previous technology required on-site application of quick-setting gelling water or factory prefabrication for the sealing treatment of filter cloth in shallow soil sections of long plates. However, this application cleverly sets the drainage system into three levels, with each level having a different function. This not only reduces energy consumption and saves materials, but also better solves the problem of "hard on top and soft on the bottom" after the soft soil foundation has been solidified.

[0007] The prior art discloses a construction process for a double-pressure vacuum preloading soft soil foundation with drainage boards of different lengths, with publication number CN109295969A. This invention discloses a construction process for a double-pressure vacuum preloading soft soil foundation with drainage boards of different lengths, characterized by the following steps: (1) First, insert short plastic drainage boards into the upper layer of blown silt, lay a horizontal pipe network, and perform short-term vacuum treatment; (2) Use mechanical insertion to drive long plastic drainage boards, lay a horizontal pipe network, and perform graded vacuum treatment on the long drainage boards; (3) Perform intermittent vacuuming and air-pressurization alternating treatment on the long drainage boards to accelerate the drainage of water in the soft soil, while the short boards continuously perform vacuum reinforcement. The construction period using this method is shortened by more than 20% compared to the conventional vacuum preloading method, with high consolidation, small post-construction settlement, high safety, and low price.

[0008] Analysis reveals the following technical defects in the existing technology: Similar to CN102733371B, this technology adds a third stage to the existing long and short plastic boards, namely, an alternating stage of intermittent vacuuming and pressurization. Compared with this application, the process is more complex and the construction period is longer. The overlapping part of the long and short boards used in this process is too long, which significantly increases material consumption. In addition, the drainage system of this application is set with different vacuum negative pressures at each level, which reduces energy consumption and improves the effect after the soft foundation is cured. The phenomenon of "hard on top and soft on the bottom" is greatly improved.

[0009] In summary, the applicant argues that in existing vacuum preloading foundation treatment projects requiring the combined application of long and short plates for pre-treatment subgrade construction, the current vacuum preloading technology first reinforces the shallow soil by inserting short plates to form a hard shell layer, thus meeting the bearing capacity requirements for mechanical entry. Then, long plates are installed to reinforce the deeper soil. However, the installed long plates still perform vacuum reinforcement on the shallow soil within the height range of the previously installed short plates (vacuum is transferred to the shallow soil, resulting in vacuum loss). Since the shallow soil has already met the treatment requirements through short plate reinforcement, and due to subsequent foundation cap construction, a portion of the shallow soil will be excavated, resulting in significant waste during the long plate construction process. If the vacuum along the length range of the long plate could be transferred to the deeper soil instead of being wasted on the shallow soil, it would not only save a significant amount of energy but also improve the treatment effect on the deeper soil.

[0010] Furthermore, a tiered vacuum drainage consolidation method for ultra-soft soil foundations is disclosed in the prior art, with publication number CN102776877B. Specifically, a medium-coarse sand cushion layer is laid on the ultra-soft soil foundation to be reinforced. Drainage boards are installed at equal intervals on the foundation, with pore water pressure probes and settlement markers between the drainage boards. A sealing membrane and a vacuum jet pump are placed on top of the sand cushion layer. Tiered vacuum preloading is applied, increasing in pressure level. After the pore water pressure and settlement stabilize, the next level of load is applied, and so on, until all loads are applied, completing the tiered vacuum drainage consolidation construction of the ultra-soft soil foundation. This invention effectively overcomes the problem of drainage board clogging and improves the reinforcement effect of ultra-soft soil foundations. Compared with existing ultra-soft soil foundation drainage consolidation reinforcement methods, it has lower engineering costs, simpler operation, and solves the problem of frequent failures in vacuum preloading reinforcement of ultra-soft soil foundations with high clay content and high organic matter content.

[0011] The "step-by-step" concept of this technology is not based on the same principle as the "step-by-step" concept in this application. This technology is actually a slow vacuum negative pressure loading process, applying pressure in stages, i.e., 10 kPa, 20 kPa, 40 kPa, 60 kPa, and 80 kPa. In contrast, this application classifies the drainage system into stages, loading it in steps according to different vacuum negative pressure design standards based on the depth of the drainage board. The design standards are that the vacuum negative pressure of the first-stage drainage system must reach 50-60 kPa, the vacuum negative pressure of the second-stage drainage system must reach 65-75 kPa, and the vacuum negative pressure of the third-stage drainage system must reach 80-90 kPa. The two are fundamentally different, and the treatment effect after the soft foundation is cured is also significantly different.

[0012] Furthermore, existing technology also discloses a novel vacuum preloading process for treating soft soil foundations, with the publication number: This invention relates to a novel method for vacuum preloading treatment of soft soil foundations. This technology includes the following: a shallow vertical drainage board, a deep vertical drainage board, a transverse drainage branch pipe connected to the shallow vertical drainage board, a transverse drainage main pipe connected to the deep vertical drainage board, a sealing system, and a vacuum pumping device. This invention achieves a novel insertion of the drainage board. Through this novel insertion, the soil can be divided into two layers for separate treatment. That is, the vacuum level can be directly transmitted to the deep vertical drainage board through the vertical air supply pipe, avoiding the damping effect experienced in the shallow soil layer, thus enabling better reinforcement of the deep soil layer.

[0013] In summary, the applicant inventors have discovered at least the following technical problems with the aforementioned prior art:

[0014] 1. Vacuum is transmitted to the soil along the drainage board, but a large number of engineering practices show that the vacuum decreases with depth. The soil strength varies significantly at different depths, resulting in a "hard on top and soft on the bottom" phenomenon after treatment, and the deep reinforcement effect is not good.

[0015] 2. The drainage boards are installed along their entire length, but the drainage effect of the drainage boards in deep soil is not obvious. Therefore, the drainage effect of the deep drainage boards is not fully utilized. In addition, the deep drainage boards are prone to bending under soil stress, which hinders the vacuum and has a significant impact on the treatment effect.

[0016] 3. Conventional vacuum preloading has a very long construction period, typically 120-180 days, which is difficult to meet the time requirements of many projects.

[0017] Therefore, based on the above technical problems, a stepped pressure air extraction and drainage system for vacuum preloading is proposed on the basis of conventional vacuum preloading technology. This system can basically solve the problem of "hard on top and soft on the bottom" after reinforcement, effectively improve the uniformity of the soft foundation after reinforcement, significantly shorten the construction period, and reduce the cost of construction materials. Summary of the Invention

[0018] To address the problems existing in the prior art, this invention provides a construction method for a three-stage vacuum preloading drainage system for ecological dredging of river, lake, and reservoir sediments, which essentially eliminates the uneven soil texture of "hard on top and soft on the bottom" and improves the treatment cycle of soft soil foundations.

[0019] This invention is implemented as follows: a construction method for a three-stage vacuum preloading drainage system for ecological dredging of river, lake, and reservoir sediments, comprising the following steps:

[0020] S1. Remove debris;

[0021] S2. Create a sealing trench around the soft foundation to be reinforced;

[0022] S3. Lay a working pad layer on the soft foundation to be reinforced;

[0023] S4. Drainage system arrangement: The drainage system is a three-level drainage system, namely a primary drainage system, a secondary drainage system and a tertiary drainage system; each level of drainage system includes several vertically downward drainage board units arranged along the transverse and longitudinal directions of the soft foundation, and the drainage board units of the same level of drainage system have the same depth;

[0024] Above the tertiary drainage system is the secondary drainage system, with individual drainage boards of the secondary drainage system located between the individual drainage boards of the tertiary drainage system, and the lower end of the individual drainage boards of the secondary drainage system overlapping the upper end of the individual drainage boards of the tertiary drainage system by a certain distance; above the secondary drainage system is the primary drainage system, with individual drainage boards of the primary drainage system located between the individual drainage boards of the secondary drainage system, and the lower end of the individual drainage boards of the primary drainage system overlapping the upper end of the individual drainage boards of the secondary drainage system by a certain distance.

[0025] The upper end of each drainage board unit in the primary drainage system is connected to the primary water vapor separator via a connector and a primary drainage branch pipe;

[0026] The upper end of each drainage board unit in the secondary drainage system is connected to a secondary water vapor separator via a joint and a secondary drainage branch pipe;

[0027] The upper end of each drainage board unit in the three-stage drainage system is connected to the secondary water vapor separator via a joint and a tertiary drainage branch pipe.

[0028] The drain outlets of the aforementioned primary, secondary, and tertiary water vapor separators are connected to the main drain pipe or drainage ditch via drain pipes; the suction ports of the aforementioned primary, secondary, and tertiary water vapor separators are connected to independently controlled vacuum negative pressure equipment or vacuum negative pressure stations via suction main pipes.

[0029] The specific layout method for the three-stage drainage system is as follows:

[0030] 1) Determine the installation depth of each drainage board system and the length of each drainage board unit in each drainage system based on the depth of the soft soil foundation.

[0031] 2) First, install the individual drainage boards of the deepest tertiary drainage system, then install the secondary and primary drainage systems in sequence.

[0032] When installing a three-stage drainage system, the lower end of the pre-prepared drainage unit of the three-stage drainage system is sealed and connected to the three-stage drainage branch pipe with a sealing clamp, with the end with the three-stage drainage branch pipe facing down; the drainage unit of the three-stage drainage system is installed one by one according to the horizontal and vertical spacing and the layout diagram of the drainage unit.

[0033] When installing a secondary drainage system, the lower end of the pre-prepared secondary drainage unit is sealed and connected to the secondary drainage branch pipe using a sealing clamp, with the end with the secondary drainage branch pipe facing downwards. The secondary drainage unit is located between the secondary drainage units of the tertiary drainage system. During installation, the secondary drainage units are installed one by one according to the horizontal and vertical spacing and the layout diagram of the drainage units. The installation depth of the secondary drainage units overlaps with the upper end of the tertiary drainage units by a certain distance.

[0034] When installing the primary drainage system, the upper end of the pre-prepared primary drainage unit is sealed and connected to the primary drainage branch pipe, with the end with the primary drainage branch pipe facing upwards. The primary drainage unit is located between the secondary drainage units. During installation, the primary drainage units are installed one by one according to the horizontal and vertical spacing and the layout diagram of the drainage units. The installation depth of the primary drainage units overlaps with the upper end of the secondary drainage units by a certain distance.

[0035] 3) Connect the drainage branch pipe of each drainage system to the corresponding water vapor separator bottle. Connect the water vapor separator bottle of each stage to the corresponding vacuum negative pressure equipment or vacuum negative pressure station through the drainage main pipe. At the same time, connect the drain outlet of each water vapor separator bottle to the main drainage pipe or drainage ditch through the drain pipe.

[0036] S5. Deploy a data acquisition system: The data acquisition system includes a pressure acquisition device for acquiring vacuum pressure, a water level acquisition device for acquiring water level, a surface settlement acquisition device for acquiring surface settlement, and a soft soil pore water pressure acquisition device for acquiring soft soil pore water pressure.

[0037] S6. Lay woven fabric, geotextile and sealing membrane in sequence on the working pad layer. The sealing membrane extends to the sealing trench around its perimeter. Backfill the sealing trench with sealing soil.

[0038] S7. Connect the main drain pipe of each drainage system to the corresponding vacuum negative pressure device or vacuum negative pressure station, turn on the vacuum negative pressure device, and test the vacuum negative pressure device to check for air leakage. If there is air leakage, seal and repair it.

[0039] S8. When vacuum preloading is used to reinforce soft soil, a stepped loading mode is adopted.

[0040] More preferably, the spacing between individual drainage boards in the three-stage drainage system is 0.5~1.0m.

[0041] In a further preferred embodiment, the drainage boards of adjacent drainage systems overlap by 0.2~0.8m.

[0042] More preferably, the length of the drainage board is 4 to 8 meters.

[0043] More preferably, one end of each drainage board unit in the primary, secondary, and tertiary drainage systems is equipped with a connector, and the side wall of the connector is provided with a drainage branch pipe connector.

[0044] Further preferably, the lower part of the connector of the drainage board unit connecting the secondary and tertiary drainage systems is a wedge-shaped structure.

[0045] Further preferred, the tiered loading mode adopted in step 8 is as follows: In the initial stage, the vacuum equipment at each level is loaded slowly at the same time to ensure that the pressure at each level reaches the vacuum negative pressure design standard, that is, the vacuum negative pressure of the first-level drainage system must reach 50-60 kPa, the vacuum negative pressure of the second-level drainage system must reach 65-75 kPa, and the vacuum negative pressure of the third-level drainage system must reach 80-90 kPa. The initial loading is completed within 5-7 days, and the settlement rate at this stage is greater than 50 mm / d.

[0046] The mid-term period begins when the vacuum negative pressure of the drainage system at all levels reaches the design standard. During this stage, the settlement rate is between 10 and 50 mm / d and tends to gradually decrease. The mid-term loading is completed in 30 to 45 days. During the process, the vacuum negative pressure should be closely monitored. If there is any leakage, it should be repaired in time to ensure that the vacuum negative pressure continues to act on the soft soil foundation.

[0047] Later, when the settlement rate is less than 10 mm / d, it can be considered that the loading has entered the later stage, and the later loading is completed in 7-10 days.

[0048] The advantages and technical effects of this invention are as follows:

[0049] The system described in this invention has made significant improvements to the commonly used vacuum preloading and decompression drainage systems in current engineering projects. It has a clear structure, a well-defined principle, obvious treatment effects, a significantly shortened construction period, simple operation, safe use, and material savings. Its feasibility has been verified through engineering tests, and it has achieved the expected results. This invention is particularly effective in treating deep soft soil foundations, and it basically eliminates the uneven soil texture of "hard on top and soft on the bottom".

[0050] In addition, based on the cascade pressure air extraction and drainage system, it can be combined with new dehydration technologies such as electroosmosis, heating, and pressurization to achieve significant progress in soft soil foundation reinforcement. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the drainage system in this invention;

[0052] Figure 2 This is a schematic diagram of the planar structure of the drainage system in this invention;

[0053] Figure 3 A schematic diagram showing the connection between the primary drainage board and the top plate pipe joint of the drainage system in this invention.

[0054] Figure 4 A schematic diagram of the connection between the secondary (tertiary) drainage board and the bottom plate pipe joint in the drainage system of this invention;

[0055] Figure 5 This is a schematic cross-sectional view of the sealing clip structure in this invention.

[0056] In the diagram: 1. Working pad layer; 2. Sealing membrane; 3. Sealing trench; 4. Primary drainage system; 5. Top plate pipe joint; 6. Primary drainage branch pipe; 7-1. Primary water vapor separator bottle; 7-2. Secondary water vapor separator bottle; 7-3. Tertiary water vapor separator bottle; 8. Primary extraction main pipe; 9. Primary one-way valve; 10. Primary pressure control chamber; 11. Secondary drainage system; 12. Bottom plate pipe joint; 13. Secondary drainage branch pipe; 14. Secondary extraction main pipe; 15. Secondary one-way valve; 16. Secondary pressure control chamber; 17. Tertiary drainage system; 18. Tertiary drainage branch pipe; 19. Tertiary extraction main pipe; 20. Tertiary one-way valve; 21. Tertiary pressure control chamber; 22. Sealing clamp. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0058] Please see Figure 1 , one The construction method for a three-stage vacuum preloading drainage system for ecological dredging of sediment in rivers, lakes, and reservoirs includes the following steps:

[0059] S1. Debris Removal: Clean and dispose of stagnant water, aquatic plants, roots, and other debris at the project site. Utilize a rapid, harmless fermentation fertilizer production system to quickly and harmlessly process waste such as weeds, reeds, lotus leaves, and water hyacinths. Through scientific formulation and process control, produce organic fertilizer and various substrates. After site clearing, construct basic infrastructure such as roads, office areas, temporary facilities, temporary power supply, and temporary water supply.

[0060] S2. A sealing trench 3 is dug around the soft foundation to be reinforced. It mainly plays a role in perimeter sealing during the drainage and consolidation of the bottom mud. The sealing trench is dug manually or mechanically. After laying the sealing membrane, the edge of the sealing membrane is buried in the sealing trench. The depth is not less than 1.0m. The edge of the membrane is inserted vertically into the bottom mud, and water is covered in the trench to ensure the sealing effect of the sealing system.

[0061] S3. Lay a working cushion layer 1 on the soft foundation to be reinforced. The working cushion layer is a necessary measure for construction safety. First, lay a 150g / m³ layer on the mud pit after clearing the surface. 2 Woven fabric, then lay 1-3 layers of brambles, and then lay a layer of 150g / m² fabric on top of the brambles. 2 Woven fabric;

[0062] S4. Drainage system arrangement: The drainage system is a three-level drainage system, namely a primary drainage system 4, a secondary drainage system 11 and a tertiary drainage system 17; each level of drainage system includes several vertically downward drainage board units arranged along the transverse and longitudinal directions of the soft foundation, and the drainage board units of the same level of drainage system have the same depth.

[0063] Above the tertiary drainage system is the secondary drainage system, with individual drainage boards of the secondary drainage system located between the individual drainage boards of the tertiary drainage system, and the lower end of the individual drainage boards of the secondary drainage system overlapping the upper end of the individual drainage boards of the tertiary drainage system by a certain distance; above the secondary drainage system is the primary drainage system, with individual drainage boards of the primary drainage system located between the individual drainage boards of the secondary drainage system, and the lower end of the individual drainage boards of the primary drainage system overlapping the upper end of the individual drainage boards of the secondary drainage system by a certain distance.

[0064] The upper end of each drainage board unit in the primary drainage system is connected to the primary water vapor separator bottle 7-1 via a joint and a primary drainage branch pipe 6;

[0065] The upper end of each drainage board unit in the secondary drainage system is connected to the secondary water vapor separator bottle 7-2 via a joint and a secondary drainage branch pipe 13;

[0066] The upper end of each drainage board unit in the three-stage drainage system is connected to the secondary water vapor separator 7-3 via a joint and a tertiary drainage branch pipe;

[0067] The aforementioned primary, secondary, and tertiary water vapor separators are existing finished products. For example, a vacuum pre-compression self-standing water collection device produced by Jiangsu Xintai Geotechnical Technology Co., Ltd. can be used, which has high air extraction and drainage efficiency and saves energy.

[0068] The drain outlets of the aforementioned primary, secondary, and tertiary water vapor separators are connected to the main drain pipe or drainage ditch via drain pipes. The suction ports of the aforementioned primary, secondary, and tertiary water vapor separators are connected to independently controlled vacuum negative pressure equipment or vacuum negative pressure stations via primary suction main pipe 8, secondary suction main pipe 14, and tertiary suction main pipe 19. Vacuum pressure gauges are installed in each pressure chamber to control the working response of the suction and drainage system under the cascade pressure. Furthermore, primary one-way valve 9, secondary one-way valve 15, and tertiary one-way valve 20 are respectively installed on primary suction main pipe 8, secondary suction main pipe 14, and tertiary suction main pipe 19. The one-way valves are designed to prevent the cascade negative pressure in the site from dropping too quickly due to sudden situations such as power outages or mechanical failures, which could affect the treatment effect and construction period.

[0069] The specific drainage system layout method is as follows:

[0070] 1) Determine the installation depth of the drainage board in each level of the drainage system and the length of the individual drainage board in each level of the drainage system based on the depth of the soft soil foundation. For example, if the depth of the soft soil foundation is 20m, the length of the individual drainage board in each level of the drainage system can be determined to be 7m, and the length of the drainage board in the overlapping part of the adjacent level of the drainage system can be determined to be 0.5m.

[0071] 2) First, install the drainage board units of the deepest tertiary drainage system, then install the secondary and primary drainage systems in sequence. The installation order of drainage board units for each level of drainage system should be row by row or start from the middle and proceed to both sides or the perimeter to avoid the impact of siltation.

[0072] When installing the three-stage drainage system, the lower end of the pre-prepared drainage unit of the three-stage drainage system is sealed and connected to the three-stage drainage branch pipe 18 through the sealing clamp 22, with the end with the three-stage drainage branch pipe facing down; the drainage unit of the three-stage drainage system is installed one by one according to the horizontal and vertical spacing and the drainage unit layout diagram.

[0073] When installing the secondary drainage system, the lower end of the pre-prepared secondary drainage unit is sealed and connected to the secondary drainage branch pipe 13 with a sealing clamp, with the end with the secondary drainage branch pipe facing downwards. The secondary drainage unit is located between the tertiary drainage unit and the designed primary drainage unit. During installation, the secondary drainage units are installed one by one according to the horizontal and vertical spacing and the layout diagram of the drainage units. In order to ensure the effect of soft soil treatment and take into account the project cost, the installation depth of the secondary drainage unit should overlap the upper end of the tertiary drainage unit by a certain length, preferably 0.5m.

[0074] When constructing the primary drainage system, the upper end of the pre-prepared primary drainage unit is sealed and connected to the primary drainage branch pipe 6, with the end with the primary drainage branch pipe facing upwards. The primary drainage unit is located between the secondary and tertiary drainage units. During construction, the primary drainage units are constructed one by one according to the horizontal and vertical spacing and the layout diagram of the drainage units. In order to ensure the effect of soft soil treatment and take into account the project cost, the construction depth of the primary drainage unit should overlap with the upper end of the secondary drainage unit by a certain length, preferably 0.5m.

[0075] 3) Connect the drain branch pipe of each stage of the drainage system to the corresponding water vapor separator. Each water vapor separator is connected to the corresponding vacuum negative pressure equipment or vacuum negative pressure station via the main drain pipe. The vacuum negative pressure station has three independent pressure control chambers: a primary pressure control chamber 10, a secondary pressure control chamber 16, and a tertiary pressure control chamber 21. Simultaneously, connect the drain outlet of each water vapor separator to the main drain pipe or drainage ditch via a drain pipe.

[0076] Each drainage system consists of several drainage board units arranged along the transverse and longitudinal directions of the soft foundation, and the drainage board units are installed at the same depth.

[0077] A lower-level drainage system should be constructed between the upper-level drainage systems, and the upper end of the lower-level drainage system should overlap with the lower end of the upper-level drainage system by a certain distance.

[0078] The primary drainage system is located in the shallow layer of soft soil. The upper end of each drainage board unit of the primary drainage system is connected to the primary water vapor separator via a joint and a primary drainage branch pipe.

[0079] The suction port of the first-stage water vapor separator is connected to the first-stage vacuum negative pressure device through the first-stage suction main pipe, and the discharge port of the first-stage water vapor separator is connected to the main drainage pipe or drainage ditch through the drainage pipe.

[0080] In addition to the upper end of the drainage board unit of the first-level drainage system being connected to the first-level water vapor separator via a connector and a first-level drainage branch pipe, the lower end of the drainage unit of the other drainage systems is connected to the corresponding water vapor separator via a connector and an independent corresponding-level drainage branch pipe. The air extraction port of each water vapor separator is connected to the corresponding level vacuum negative pressure device through the corresponding level's main air extraction pipe, and the drain port of each water vapor separator is connected to the main drainage pipe or drainage ditch through a connecting drain pipe.

[0081] Preferably, the spacing between individual drainage boards in the same level of drainage system is 1.0m.

[0082] S5. Deploy a data acquisition system: The data acquisition system includes a pressure acquisition device for acquiring vacuum pressure, a water level acquisition device for acquiring water level, a surface settlement acquisition device for acquiring surface settlement, and a soft soil pore water pressure acquisition device for acquiring soft soil pore water pressure.

[0083] The aforementioned pressure acquisition device, water level acquisition device, surface settlement acquisition device, and pore pressure acquisition device are mature technologies in the field of soft soil solidification treatment. The pressure acquisition device involves wrapping one end of a PU high-pressure hose with gauze and burying it near the individual drainage boards in each level of the drainage system, with the other end connected to an integrated data acquisition unit. The pore water pressure acquisition device involves burying a vibrating wire pore water pressure gauge near the individual drainage boards in each level of the drainage system, with the other end also connected to the integrated data acquisition unit. Water level and surface settlement acquisition also utilize mature technologies and are connected to the integrated data acquisition unit. Finally, the integrated data acquisition unit is connected to an external server via a data cable and a data transmitting antenna, thereby enabling remote real-time data acquisition, reading, analysis, and judgment.

[0084] S6. Lay woven fabric, geotextile and sealing membrane in sequence on the working pad layer. The sealing membrane extends to the sealing trench around its perimeter. Backfill the sealing trench with sealing soil.

[0085] S7. Connect the main drain pipe of each drainage system to the corresponding vacuum negative pressure equipment or vacuum negative pressure station pressure control room, and connect the first-level pressure control room 10, the second-level pressure control room 16 and the third-level pressure control room 21 respectively. Turn on the vacuum negative pressure equipment, and test the vacuum negative pressure equipment to check for air leakage. If there is air leakage, perform sealing and repair.

[0086] S8. When vacuum preloading is used to reinforce soft soil, a stepped loading mode is adopted, specifically:

[0087] Initially, all levels of negative pressure vacuum equipment are loaded slowly to ensure that the pressure at each level reaches the vacuum negative pressure design standard. That is, the vacuum negative pressure of the first-level drainage system must reach 50-60 kPa, the vacuum negative pressure of the second-level drainage system must reach 65-75 kPa, and the vacuum negative pressure of the third-level drainage system must reach 80-90 kPa. The initial loading is completed within 5-7 days, and the settlement rate during this stage is greater than 50 mm / d.

[0088] The mid-term period begins when the vacuum negative pressure of the drainage system at all levels reaches the design standard. During this stage, the settlement rate is between 10 and 50 mm / d and tends to gradually decrease. The mid-term loading is completed in 30 to 45 days. During the process, the vacuum negative pressure should be closely monitored. If there is any leakage, it should be repaired in time to ensure that the vacuum negative pressure continues to act on the soft soil foundation.

[0089] Later, when the settlement rate is less than 10 mm / d, it can be considered that the loading has entered the later stage, and the later loading is completed in 7-10 days. Generally, if the average daily settlement is less than or equal to 10 mm / d for 7 consecutive days, the unloading requirements can be met. Alternatively, the unloading standard can be determined according to the design documents of the actual project.

[0090] The "step-by-step" concept of this technology is not based on the same principle as the "step-by-step" concept in this application. This technology is actually a slow vacuum negative pressure loading process, applying pressure in stages, i.e., 10kPa, 20kPa, 40kPa, 60kPa, and 80kPa. In contrast, this application classifies the drainage system into stages, applying step-by-step loading according to different vacuum negative pressure design standards based on the depth of the drainage board. The design standards are that the vacuum negative pressure of the first-stage drainage system must reach 50-60kPa, the vacuum negative pressure of the second-stage drainage system must reach 65-75kPa, and the vacuum negative pressure of the third-stage drainage system must reach 80-90kPa. The two are fundamentally different, and the treatment effect after the soft foundation is cured is also significantly different.

[0091] Preferably, the spacing between individual drainage boards in a three-stage drainage system is 0.5~1.0m. The optimal spacing is 0.5m.

[0092] Preferably, the overlap of individual drainage boards in adjacent drainage systems is 0.2~0.8m. The optimal overlap is 0.5m.

[0093] Preferably, the length of the drainage board is 4 to 8 meters, and the optimal length is 5 meters. In order to reduce the difficulty of construction, the length of the drainage board in each stage of the drainage system should be the same.

[0094] Preferably, one end of each drainage board unit in the primary, secondary, and tertiary drainage systems is equipped with a connector, and the side wall of the connector is provided with a drainage branch pipe connector to improve the installation efficiency of the drainage riser.

[0095] Preferably, the lower part of the connector of the drainage board unit connecting the secondary and tertiary drainage systems is a wedge-shaped structure, which facilitates the installation of the drainage board.

[0096] In summary, each level of the drainage system is independently connected to its own vacuum negative pressure equipment. Therefore, each level can be configured with a more reasonable vacuum negative pressure. This design maximizes energy efficiency, avoids energy waste, and reduces project costs. Each level of the drainage system can specifically consolidate and dry soil layers at different depths in soft soil foundations. Furthermore, the drainage boards in the secondary and tertiary drainage systems use a bottom-connected design, preventing pressure loss during transmission and effectively solving the "hard on top, soft on the bottom" phenomenon after solidification. This results in more uniform soil texture and better performance. Generally, the vacuum negative pressure of the deepest drainage system can be set at around 85 kPa, gradually decreasing from bottom to top. The vacuum negative pressure of the shallow drainage system can be set at 50 kPa or even lower. During the process, the vacuum negative pressure of each level of the drainage system is adjusted continuously based on the observed water flow and settlement. The process continues until settlement stabilizes. Generally, a daily settlement of less than or equal to 20 mm / d is sufficient to meet the unloading requirements.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method for a three-stage vacuum preloading drainage system for ecological dredging of river, lake, and reservoir sediments, characterized in that: Includes the following steps: S1. Remove debris; S2. Create a sealing trench around the soft foundation to be reinforced; S3. Lay a working pad layer on the soft foundation to be reinforced; S4. Drainage system arrangement: The drainage system is a three-level drainage system, namely a primary drainage system, a secondary drainage system and a tertiary drainage system; each level of drainage system includes several vertically downward drainage board units arranged along the transverse and longitudinal directions of the soft foundation, and the drainage board units of the same level of drainage system have the same depth; Above the tertiary drainage system is the secondary drainage system, with individual drainage boards of the secondary drainage system located between the individual drainage boards of the tertiary drainage system, and the lower end of the individual drainage boards of the secondary drainage system overlapping the upper end of the individual drainage boards of the tertiary drainage system by a certain distance; above the secondary drainage system is the primary drainage system, with individual drainage boards of the primary drainage system located between the individual drainage boards of the secondary drainage system, and the lower end of the individual drainage boards of the primary drainage system overlapping the upper end of the individual drainage boards of the secondary drainage system by a certain distance. The upper end of each drainage board unit in the primary drainage system is connected to the primary water vapor separator via a connector and a primary drainage branch pipe; The upper end of each drainage board unit in the secondary drainage system is connected to a secondary water vapor separator via a joint and a secondary drainage branch pipe; The upper end of each drainage board unit in the three-stage drainage system is connected to the secondary water vapor separator via a joint and a tertiary drainage branch pipe. The drain outlets of the aforementioned primary, secondary, and tertiary water vapor separators are connected to the main drain pipe or drainage ditch via drain pipes; the suction ports of the aforementioned primary, secondary, and tertiary water vapor separators are connected to independently controlled vacuum negative pressure equipment or vacuum negative pressure stations via suction main pipes. The specific layout method for the three-stage drainage system is as follows: 1) Determine the installation depth of each drainage board system and the length of each drainage board unit in each drainage system based on the depth of the soft soil foundation. 2) First, install the individual drainage boards of the deepest tertiary drainage system, then install the secondary and primary drainage systems in sequence. When installing a three-stage drainage system, the lower end of the pre-prepared drainage unit of the three-stage drainage system is sealed and connected to the three-stage drainage branch pipe with a sealing clamp, with the end with the three-stage drainage branch pipe facing down; the drainage unit of the three-stage drainage system is installed one by one according to the horizontal and vertical spacing and the layout diagram of the drainage unit. When installing a secondary drainage system, the lower end of the pre-prepared secondary drainage unit is sealed and connected to the secondary drainage branch pipe using a sealing clamp, with the end with the secondary drainage branch pipe facing downwards. The secondary drainage unit is located between the secondary drainage units of the tertiary drainage system. During installation, the secondary drainage units are installed one by one according to the horizontal and vertical spacing and the layout diagram of the drainage units. The installation depth of the secondary drainage units overlaps with the upper end of the tertiary drainage units by a certain distance. When installing the primary drainage system, the upper end of the pre-prepared primary drainage unit is sealed and connected to the primary drainage branch pipe, with the end with the primary drainage branch pipe facing upwards. The primary drainage unit is located between the secondary drainage units. During installation, the primary drainage units are installed one by one according to the horizontal and vertical spacing and the layout diagram of the drainage units. The installation depth of the primary drainage units overlaps with the upper end of the secondary drainage units by a certain distance. 3) Connect the drainage branch pipe of each drainage system to the corresponding water vapor separator bottle. Connect the water vapor separator bottle of each stage to the corresponding vacuum negative pressure equipment or vacuum negative pressure station through the drainage main pipe. At the same time, connect the drain outlet of each water vapor separator bottle to the main drainage pipe or drainage ditch through the drain pipe. S5. Deploy a data acquisition system, which includes a pressure acquisition device for acquiring vacuum pressure, a water level acquisition device for acquiring water level, a surface settlement acquisition device for acquiring surface settlement, and a soft soil pore water pressure acquisition device for acquiring soft soil pore water pressure. S6. Lay woven fabric, geotextile and sealing membrane in sequence on the working pad layer. The sealing membrane extends to the sealing trench around its perimeter. Backfill the sealing trench with sealing soil. S7. Connect the main drain pipe of each drainage system to the corresponding vacuum negative pressure device or vacuum negative pressure station, turn on the vacuum negative pressure device, and test the vacuum negative pressure device to check for air leakage. If there is air leakage, seal and repair it. S8. When vacuum preloading reinforces soft soil, a stepped loading mode is adopted. The stepped loading mode is as follows: In the initial stage, the vacuum equipment at each level is loaded slowly at the same time to ensure that the pressure at each level reaches the vacuum negative pressure design standard. That is, the vacuum negative pressure of the first-level drainage system must reach 50-60 kPa, the vacuum negative pressure of the second-level drainage system must reach 65-75 kPa, and the vacuum negative pressure of the third-level drainage system must reach 80-90 kPa. The initial loading is completed within 5-7 days, and the settlement rate during this stage is greater than 50 mm / d. The mid-term period begins when the vacuum negative pressure of the drainage system at all levels reaches the design standard. During this stage, the settlement rate is between 10 and 50 mm / d and tends to gradually decrease. The mid-term loading is completed in 30 to 45 days. During the process, the vacuum negative pressure should be closely monitored. If there is any leakage, it should be repaired in time to ensure that the vacuum negative pressure continues to act on the soft soil foundation. Later, when the settlement rate is less than 10 mm / d, it can be considered that the loading has entered the later stage, and the later loading is completed in 7-10 days.

2. The construction method of the three-stage vacuum preloading drainage system for ecological dredging of river, lake and reservoir sediments according to claim 1, characterized in that: The spacing between individual drainage boards in a tertiary drainage system is 0.5~1.0m.

3. The construction method of the three-stage vacuum preloading drainage system for ecological dredging of river, lake and reservoir sediments according to claim 1, characterized in that: The individual drainage boards of adjacent drainage systems overlap by 0.2~0.8m.

4. The construction method of the three-stage vacuum preloading drainage system for ecological dredging of river, lake and reservoir sediments according to claim 1, characterized in that: The length of the drainage board is 4-8m.

5. The construction method of the three-stage vacuum preloading drainage system for ecological dredging of river, lake and reservoir sediments according to claim 1, characterized in that: One end of each drainage board unit in the primary, secondary, and tertiary drainage systems is equipped with a connector, and the side wall of the connector is provided with a drainage branch pipe connector.

6. The construction method of the three-stage vacuum preloading drainage system for ecological dredging of river, lake and reservoir sediments according to claim 1, characterized in that: The lower part of the connector of the drainage board unit connecting the secondary and tertiary drainage systems has a wedge-shaped structure.

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