A method for improving soft soil foundation by using a range-extending vacuum preloading device

Abstract

This invention relates to the field of soft soil foundation treatment technology, specifically to a method for efficient treatment of soft soil foundations using extended-range vacuum preloading. The method first selects a test area within the reinforcement zone and determines the average thickness H of the soft soil layer and the vacuum degree decay curve along depth using conventional vacuum preloading tests. The depth at which the vacuum degree decays to half of the vacuum degree under the membrane is scientifically defined as the optimal extended-range depth H1. Subsequently, an extended-range drainage board is customized according to H1, consisting of an upper section of airtight steel wire hose and a lower section of airtight drainage board sealed together by a hand-type joint. In large-scale construction, conventional drainage boards are installed in a square grid, and a customized extended-range drainage board is installed at the center of four adjacent conventional drainage boards, all connected to the vacuum system. This invention effectively eliminates shallow vacuum degree loss, transfers high vacuum degree to deep soil layers, significantly improves the consolidation effect and rate of deep soft soil foundations, and shortens the construction period.

Description

Technical Field

[0001] This invention relates to the field of soft soil foundation treatment technology, and in particular to a method for efficient treatment of soft soil foundations using range-extended vacuum preloading. Background Technology

[0002] Vacuum preloading is a common method for treating soft soil foundations. Its principle is to set up vertical drainage channels (such as plastic drainage boards) in the soil and lay a sealing system on the ground surface. A vacuum pump is used to draw air to create negative pressure in the drainage channels and soil, thereby accelerating the discharge of pore water, promoting soil consolidation, and increasing strength.

[0003] However, traditional vacuum preloading methods face a long-standing technical bottleneck when dealing with deep soft soil foundations: the vacuum level significantly decreases as it is transmitted downwards along the depth of the vertical drainage board. This is mainly due to the resistance inherent in the filter membrane and core of the drainage board itself, as well as the bending and clogging of the drainage board due to soil consolidation during the vacuuming process. In newly filled silt, the vacuum level can decrease at rates exceeding -10 kPa / m. The direct consequences are:

[0004] Limited effective treatment depth: High vacuum only exists in shallow soil, resulting in the formation of only a "hard shell" on the surface, while the consolidation effect in deep soil is very poor due to insufficient vacuum.

[0005] Significant post-construction settlement: If deep soft soil is not effectively reinforced, it will experience significant post-construction settlement under subsequent loads, seriously affecting the safety and use of buildings, roads, storage yards and other facilities.

[0006] Long construction period: In order to achieve the average degree of consolidation required by the design, a longer vacuuming time is needed, which leads to a longer construction period and increased costs.

[0007] Although those skilled in the art have attempted methods such as reducing the spacing between drainage boards and increasing the power of vacuum pumps, these methods have failed to fundamentally solve the essential problem of vacuum intensity decaying with depth, and are also costly. Therefore, there is an urgent need for a method that can effectively improve the efficiency of vacuum intensity transfer to deeper layers and specifically enhance the treatment effect of deep soil. Summary of the Invention

[0008] In view of this, the purpose of this invention is to propose a method for efficient treatment of soft soil foundations using extended-range vacuum preloading, in order to solve the problem of how to scientifically determine the optimal length of the impermeable section in the extended-range drainage board, so as to overcome the problems of poor reinforcement effect, long construction period and material waste in deep soft soil caused by the severe attenuation of vacuum degree along the depth in traditional vacuum preloading.

[0009] To achieve the above objectives, the present invention provides a method for efficient treatment of soft soil foundations using range-extended vacuum preloading, comprising the following steps:

[0010] S1. Conduct conventional vacuum preloading slab insertion operations in the test area of ​​the soft soil foundation to be reinforced, and obtain the average thickness H of the soft soil layer in the test area;

[0011] S2. A vacuum monitoring system is installed in the test area. The vacuum monitoring system includes multiple vacuum gauges arranged along the depth direction of the soil and a vacuum gauge located below the sealing membrane.

[0012] S3. Apply vacuum pre-compression to the test area. After the vacuum level stabilizes, record the vacuum level V0 under the membrane and the vacuum level V(z) at each depth.

[0013] S4. Define the depth that satisfies V(z) = 0.5 × V0 as the optimal range extension depth H1;

[0014] S5. Customize the range-extending drainage board according to the optimal range-extending depth H1. The range-extending drainage board includes an airtight steel wire hose and a drainage board, wherein the length of the airtight steel wire hose is determined based on the optimal range-extending depth H1 and the distance L between the drainage board and the optimal range-extending depth H1.

[0015] S6. During large-scale construction in the reinforced area, drainage boards are arranged in a square grid, and the range-extending drainage board is installed at the center of the area enclosed by four adjacent drainage boards, and connected to a vacuum system for vacuuming operations.

[0016] Preferably, in step S1, the average thickness H of the soft soil layer is obtained by randomly selecting three insertion points in the test area, measuring the insertion depth of the drainage board at each point, and taking the arithmetic mean.

[0017] Preferably, in step S2, the vacuum gauges are arranged as follows: a vacuum gauge is arranged at 1 m intervals along the soil depth direction on the drainage board, with only one vacuum gauge arranged on each drainage board, for a total of H vacuum gauges arranged on H drainage boards, and 1 vacuum gauge is arranged under the membrane, for a total of H+1 vacuum gauges.

[0018] Preferably, the airtight steel wire hose is composed of a spiral steel wire reinforcing layer, a polytetrafluoroethylene inner tube, and a polyvinyl chloride outer protective sleeve, which has high airtightness and can withstand a negative pressure of not less than -80 kPa.

[0019] Preferably, the actual length of the airtight steel wire hose is H1+L / 2, where L is the arrangement spacing of the drainage boards and L / 2 is the length reserved for connecting the vacuum branch pipe.

[0020] Preferably, the length of the drainage section in the extended-range drainage board is H−H1+H4, where H4 is the remaining length of the board body reserved during the installation of the insertion board.

[0021] Preferably, the airtight steel wire hose and the drainage board are sealed together by a hand-shaped connector to form the range-extending drainage board, wherein the drainage board is a standard plastic drainage board.

[0022] The beneficial effects of this invention are as follows:

[0023] I. Significantly improved technical performance

[0024] It fundamentally improves the reinforcement effect of deep soil: through the airless section of the extended drainage board, the loss of shallow vacuum is effectively eliminated, and the high vacuum is directly and efficiently transferred to deep soil (below the optimal extended depth) that cannot be effectively treated by traditional methods, which significantly accelerates the drainage and consolidation of deep soil and greatly reduces post-construction settlement.

[0025] Highly targeted and effective: The "optimal extension depth" is scientifically determined through on-site testing, and extension drainage boards are customized according to this depth. This ensures that the technical solution is perfectly matched with the soil conditions of the specific site, maximizing the elimination of shallow vacuum loss and significantly improving the efficiency of vacuum transfer to deeper soil layers, thereby greatly improving the treatment effect of deep soft soil foundations.

[0026] II. Significant advantages in economic benefits and construction period

[0027] Short construction period and high efficiency: The application of extended-range drainage boards enables deep soil to achieve a high degree of vacuum, which accelerates the overall drainage consolidation rate of the soil. This means that the time required to achieve the same degree of consolidation is shortened, directly reducing labor, equipment and management costs and accelerating project progress.

[0028] Material optimization and conservation were achieved: by determining the "optimal extension depth," "customized" extension drainage boards were made available on demand. This avoided the overuse or underuse of impermeable materials (steel wire hoses), ensuring optimal performance while achieving precise material configuration and cost savings. Simultaneously, the added woven fabric and geotextile layers protected the sealing membrane, improving construction convenience and system sealing.

[0029] Third, it possesses strong adaptability and scientific rigor: This method is not a fixed, empirical solution, but a scientific, tailored solution. Through preliminary small-scale trials, the final solution can be precisely adapted to the specific characteristics of different sites and soil types, maximizing the advantages of the technology and ensuring optimal treatment results and reliability. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is an overall layout diagram of the range-extended vacuum preloading system of the present invention;

[0032] Figure 2 This is a diagram showing the structure and dimensions of the range-extending drainage plate of the present invention;

[0033] Figure 3 This is a plan view of the drainage board and the range extender drainage board of the present invention;

[0034] Figure 4 This is a flowchart of the steps of the present invention.

[0035] In the diagram: 1. Sealing trench; 2. Vacuum pump; 3. Ground surface; 4. Soft soil layer; 5. Sealing membrane; 6. Geotextile; 7. Vacuum pipeline; 8. Drainage board; 9. Extender drainage board; 10. Butterfly joint; 11. Airtight steel wire hose; 12. Hand joint. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0037] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this invention should have the ordinary meaning understood by those skilled in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0038] like Figure 1 The overall layout diagram of the extended-range vacuum preloading system of the present invention includes a vacuum system and a sealing system. The vacuum system mainly includes a vacuum pump 2 and a vacuum pipeline 7; the sealing system mainly includes a sealing membrane 5, a geotextile 6, and a sealing trench 1.

[0039] like Figure 2 As shown in the diagram, the extended-range drainage board 9 of the present invention consists of an upper part of an airtight steel wire hose 11 and a lower part of a drainage board 8. The airtight steel wire hose 11 and the drainage board 8 are connected by a hand-shaped connector 12 in the middle. The airtight steel wire hose 11 arranged in the upper part of the extended-range drainage board 9 can eliminate the loss of shallow vacuum and increase the treatment effect on deep soil foundations.

[0040] like Figure 3 As shown in the diagram, the drainage plate 8 and the extended-range drainage plate 9 of the present invention are arranged in a plan view. The drainage plates 8 are spaced L apart, and the anti-clogging drainage plate 8 and the extended-range drainage plate 9 are arranged in an alternating manner, with the extended-range drainage plate 9 located at the center of adjacent drainage plates 8. The drainage plate 8 and the extended-range drainage plate 9 can be connected to the same vacuum pump 2, or they can be connected to different vacuum pumps 2.

[0041] The main factors affecting the consolidation effect of vacuum preloading in soft soil foundation treatment are the drainage board 8 and the degree of vacuum within the soil. The greater the vacuum degree, the better the soil consolidation effect. To ensure that extended-range vacuum preloading has a better treatment effect on soft soil foundations, the optimal extension depth should be calculated before applying extended-range vacuum preloading technology to treat soft soil foundations in reinforcement areas on a large scale.

[0042] like Figure 4 As shown, a method for efficiently treating soft soil foundations using extended-range vacuum preloading is presented. Its core innovation lies in scientifically determining the "optimal extension depth" through field tests and customizing the crucial "extension drainage board 9" accordingly, ultimately achieving efficient treatment in large-scale construction. The method specifically includes the following steps:

[0043] S1. Conduct conventional vacuum preloading slab insertion operations in the test area of ​​the soft soil foundation to be reinforced, and obtain the average thickness H of the soft soil layer in the test area;

[0044] The vacuum decay rate of drainage board 8 varies in different soil types. To maximize the advantages of range-extended vacuum preloading (REEV) technology in treating soft soil foundations, before applying REEV to large-scale treatment of soft soil foundations in reinforced areas, a small test area is first demarcated from the reinforced area for conventional vacuum preloading board insertion (only drainage boards 8 are installed, without extended drainage boards 9). Three points are randomly selected within the test area for trial insertion of drainage boards 8. The trial insertion is to understand the thickness of the soft soil layer and the insertion depth of drainage boards 8. The average insertion depth of drainage boards 8 at the three points is taken as the insertion depth H of drainage boards 8 in the test area, which is the average thickness H of the soft soil layer in the test area. The insertion depth of drainage boards 8 and the length of drainage boards 8 are different. The insertion depth of drainage boards 8 refers to the length of drainage boards 8 in the soil. The length of drainage boards 8 is equal to the sum of the insertion depth of drainage boards 8 and the length of drainage boards 8 reserved for connection to vacuum branch pipes. Usually, the length of drainage boards 8 reserved for connection to vacuum branch pipes is half of the insertion spacing of drainage boards 8, i.e., L / 2.

[0045] S2. A vacuum monitoring system is installed in the test area. The vacuum monitoring system includes multiple vacuum gauges arranged along the depth direction of the soil and a vacuum gauge located below the sealing membrane.

[0046] After obtaining the insertion depth H of the drainage board 8, a vacuum gauge is placed on the drainage board 8 at 1 m intervals along the soil depth direction. Only one vacuum gauge is placed on each drainage board 8. A total of H vacuum gauges need to be placed on H drainage boards 8. H vacuum gauges are needed on H drainage boards 8. One vacuum gauge is placed under the membrane. A total of H+1 vacuum gauges are needed.

[0047] S3. Apply vacuum pre-compression to the test area. After the vacuum level stabilizes, record the vacuum level V0 under the membrane and the vacuum level V(z) at each depth.

[0048] "Vacuum stability" is an important criterion for judging the state. The standard is that the change in the readings of the vacuum gauges under the membrane and at various depths is less than 5% over a continuous 24-hour period. At this time, the system has reached a dynamic equilibrium state, and the recorded V(z) truly reflects the steady-state decay law of vacuum along the drainage board 8 under the soil conditions of the site.

[0049] S4. Define the depth that satisfies V(z) = 0.5 × V0 as the optimal range extension depth H1;

[0050] Using the depth (H1) where the vacuum level decreases to half of the submembrane vacuum level as the dividing point between "range extension" and "permeability" functions achieves the best balance between technical effectiveness and economy. In areas shallower than H1, the vacuum level decreases drastically, requiring an impermeable section to "escort" the vacuum energy through; in areas deeper than H1, the vacuum level is relatively stable, and drainage can be achieved by the drainage plate 8. Therefore, H1 becomes a scientifically optimal design parameter determined by experimental data for a specific site.

[0051] Within the test area, the construction of materials such as drainage board 8 (including drainage board 8 equipped with a vacuum gauge), vacuum branch pipe, vacuum main pipe, vacuum pump 2, sealing membrane 5, and sealing trench 1 was carried out. After construction was completed, the vacuum pump was turned on to start vacuuming, and the changes in vacuum degree under the membrane and at different depths of drainage board 8 were observed. After the changes in vacuum degree stabilized, the vacuum degree values ​​under the membrane and on drainage board 8 were recorded. The depth H1 at the position where the vacuum degree on drainage board 8 is half that under the membrane was calculated was the optimal extension depth.

[0052] S5. Customize the range extension drainage board 9 according to the optimal range extension depth H1. The range extension drainage board 9 includes an airtight steel wire hose 11 and a drainage board 8, wherein the length of the airtight steel wire hose is determined based on the distance L between the optimal range extension depth H1 and the drainage board 8.

[0053] After determining the optimal depth of elevation extension H1, the elevation extension drainage board 9 is fabricated based on the average thickness H of the soft soil layer and the optimal depth of elevation extension H1. The elevation extension drainage board 9 consists of a drainage board 8, a hand-type connector 12, and an airtight steel wire hose 11, as follows... Figure 2 As shown. The length of the extended-range drainage board 9 is the sum of the insertion depth H of the drainage board 8, the reserved length L / 2 of the vacuum branch pipe, and the reserved length H4 of the drainage board 8 insert plate. The length of the airtight steel wire hose 11 is the sum of the optimal extended-range depth H1 and the reserved length L / 2 of the vacuum branch pipe, i.e., H1+L / 2. The length of the drainage board 8 is H2, which consists of the normal use length H3 and the reserved length H4 of the insert plate. That is, the length of the drainage board segment in the extended-range drainage board 9 is H−H1+H4.

[0054] S6. During large-scale construction in the reinforced area, drainage boards 8 are arranged in a square grid, and the extended-range drainage board 9 is installed at the center of the area enclosed by four adjacent drainage boards 8, and connected to a vacuum system for vacuuming.

[0055] During large-scale construction work in the reinforcement area, woven fabric is first laid on the surface of the soft soil layer 4 to provide a certain bearing capacity. Then, a jackhammer is used to drive drainage boards 8 and extended drainage boards 9 into the soil. The drainage boards 8 are arranged in a square with a spacing of L, and the extended drainage boards 9 are placed in the center of four adjacent drainage boards 8. The drainage boards 8 are connected to the vacuum branch pipe through the butterfly joint 10, the vacuum branch pipe is connected to the vacuum main pipe, and the vacuum main pipe is connected to the vacuum pump 2. The extended drainage boards 9 are connected to the vacuum branch pipe through the tee, the vacuum branch pipe is connected to the vacuum line 7, and the vacuum line 7 is connected to the vacuum pump 2. Next, necessary monitoring instruments, such as vacuum gauges, pore water pressure gauges, and hydrostatic levels, are set up. A sealing trench is excavated, and several layers of geotextile 6 and sealing membrane 5 are laid on the ground surface 3. The geotextile 6 and sealing membrane 5 are then buried in the sealing trench soil around them for sealing. After construction is completed, the vacuum pump is turned on to begin vacuuming.

[0056] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0057] The embodiments of this invention are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for efficient treatment of soft soil foundations using range-extended vacuum preloading, characterized in that, Includes the following steps: S1. Conduct conventional vacuum preloading slab insertion operations in the test area of ​​the soft soil foundation to be reinforced, and obtain the average thickness H of the soft soil layer in the test area; S2. A vacuum monitoring system is installed in the test area. The vacuum monitoring system includes multiple vacuum gauges arranged along the depth direction of the soil and a vacuum gauge located below the sealing membrane. S3. Apply vacuum pre-compression to the test area. After the vacuum level stabilizes, record the vacuum level V0 under the membrane and the vacuum level V(z) at each depth. S4. Define the depth that satisfies V(z) = 0.5 × V0 as the optimal range extension depth H1; S5. Customize the range-extending drainage board according to the optimal range-extending depth H1. The range-extending drainage board includes an airtight steel wire hose and a drainage board, wherein the length of the airtight steel wire hose is determined based on the optimal range-extending depth H1. S6. During large-scale construction in the reinforced area, drainage boards are arranged in a square grid, and the range-extending drainage board is installed at the center of the area enclosed by four adjacent drainage boards, and connected to a vacuum system for vacuuming operations.

2. The method for efficient treatment of soft soil foundation using extended-range vacuum preloading according to claim 1, characterized in that, In step S1, the average thickness H of the soft soil layer is obtained by randomly selecting three insertion points in the test area, measuring the insertion depth of the drainage board at each point, and taking the arithmetic mean.

3. The method for efficient treatment of soft soil foundation using extended-range vacuum preloading according to claim 1, characterized in that, In step S2, the vacuum gauges are arranged as follows: a vacuum gauge is placed at 1 m intervals along the soil depth direction on the drainage board, and only one vacuum gauge is placed on each drainage board. A total of H vacuum gauges are placed on H drainage boards, and 1 vacuum gauge is placed under the membrane, for a total of H+1 vacuum gauges.

4. The method for efficient treatment of soft soil foundation using extended-range vacuum preloading according to claim 1, characterized in that, The airtight steel wire hose is composed of a spiral steel wire reinforcing layer, a polytetrafluoroethylene inner tube, and a polyvinyl chloride outer protective sheath, and has high airtightness and can withstand a negative pressure of not less than -80 kPa.

5. The method for efficient treatment of soft soil foundation using range-extended vacuum preloading according to claim 1, characterized in that, The actual length of the airtight steel wire hose is H1+L / 2, where L is the arrangement spacing of the drainage boards and L / 2 is the length reserved for connecting the vacuum branch pipe.

6. The method for efficient treatment of soft soil foundation using extended-range vacuum preloading according to claim 1, characterized in that, The length of the drainage section in the extended-range drainage board is H−H1+H4, where H4 is the remaining length of the board body reserved during the installation of the insertion board.

7. The method for efficient treatment of soft soil foundation using extended-range vacuum preloading according to claim 1, characterized in that, The airtight steel wire hose and the drainage board are sealed together by a hand-shaped connector to form the range-extending drainage board, wherein the drainage board is a standard plastic drainage board.

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