A method for improving saline-alkali soil in coastal areas

Abstract

This invention discloses a method for improving saline-alkali soil in coastal areas. The top of the saline-alkali soil is set as a leveling layer. Above the leveling layer, a working cushion layer, a drainage sand cushion layer, a composite fabric membrane layer, an upper cushion layer, and a backfill layer are placed above the composite fabric membrane layer. A pressure trench is set on one side of the working cushion layer. This invention, through the setting of the leveling layer, ensures the flatness requirements of the soil bottom while incorporating multiple design elements for stress and drainage. The sealing membrane edge setting facilitates vacuum drainage and ensures the accuracy of upper filling and loading. The working cushion layer and drainage sand cushion layer greatly provide a working surface for the construction of the superstructure. By dividing the foundation treatment into zones, construction can be carried out according to their functions, and different loading conditions can be controlled to achieve their intended use, greatly improving work efficiency and reducing costs.

Description

Technical Field

[0001] This invention relates to the field of soil improvement construction for saline-alkali land, and particularly to a method for applying soil improvement to saline-alkali land in coastal areas. Background Technology

[0002] Construction in coastal areas, in particular, requires the treatment of unfavorable saline-alkali soil geology to achieve suitable construction conditions. During the construction of large-scale themed buildings, newly filled soil, if untreated, exhibits low overall strength and high unevenness; the underlying silty soil is characterized by high water content, low strength, and high compressibility. Without foundation treatment, significant post-construction settlement will occur, generating negative skin friction on the pile foundations or creating large unsupported areas under the pile caps. This can lead to uneven settlement in non-building areas (roads, landscaping), causing problems such as road cracking and landscape tilting. Therefore, targeted treatment of both existing saline-alkali soil layers and newly filled soil layers is necessary, and the degree and indicators of this treatment must be more precisely controlled according to different application environments. Summary of the Invention

[0003] This invention provides a method for improving saline-alkali soil in coastal areas, which solves the technical problems of soil improvement methods such as drainage, preloading, and replacement within different geological zones of large coastal stadiums.

[0004] The specific technical solution is as follows:

[0005] A method for improving saline-alkali soil in coastal areas includes a leveling layer on top of the saline-alkali soil, a working cushion layer on top of the leveling layer, a drainage sand cushion layer on top of the working cushion layer, a sealing system on top of the drainage sand cushion layer, an upper cushion layer and a backfill layer on top of the sealing system; a membrane trench on one side of the working cushion layer, an impermeable layer below the membrane trench, a sealing membrane at the bottom of the membrane trench, and backfill soil filling the inside of the membrane trench;

[0006] The sealing membrane edge is integrally connected with the geotextile in the flat layer and the sealing membrane in the sealing system. The three are arranged in an F-shape, and the sealing membrane edge is set along the slope and the membrane connection.

[0007] The specific steps of the method for improving saline-alkali land in coastal areas are as follows:

[0008] Step 1: Based on the distribution of treatment areas, current elevation, and geological conditions, the foundation treatment area for building applications is divided into four zones: tropical rainforest greenhouse area, water quality pavilion area, entrance pavilion area, and water limit pavilion area.

[0009] Step 2: First, drain the surface water from the site and level the site. Set up a leveling layer according to the site conditions. The leveling layer consists of one layer of woven fabric, two layers of brambles, and one layer of geotextile. When laying the geotextile, mechanical sewing is required, and the overlap width of the joints should not be less than 10cm. The overlap width of the bramble joints should not be less than 20cm.

[0010] Step 3: Lay a working layer made of gravel and a drainage sand cushion layer made of medium and coarse sand on the geotextile. During construction, the elevation and flatness of the top and bottom surfaces of the drainage sand cushion layer should be strictly controlled.

[0011] Step 4: Before reinforcing and installing the plastic drainage boards, conduct drilling and soil sampling tests and vane shear tests. After reinforcing and installing the plastic drainage boards, conduct instrument monitoring. Install the plastic drainage boards according to the design requirements. The plastic drainage boards should be exposed at least 0.2m above the surface of the drainage sand cushion layer. The last plastic drainage board should be installed no more than 0.45m from the boundary of the reinforced area.

[0012] Step 5: Lay the filter pipe, and then lay the sealing system on top of the filter pipe; connect one end of the membrane outlet bend to the filter pipe and lay the sealing membrane, then connect the other end to the jet pump and connect to the vacuum equipment; the sealing system uses one layer of geotextile and two layers of sealing membrane; the sealing membrane is set at the sealing trench with sealing membrane edge and is fixed by compacting the backfill soil in the trench;

[0013] Step 6: Set up surface settlement rods, install observation instruments, and connect vacuum equipment; when starting the pump, start it in batches and evenly to test the air pumping; check; after reaching the design requirements and stabilizing the air pumping for 72 hours, start formal air pumping; start timing.

[0014] Step 7: After 15 days of vacuum preloading and degassing, lay a layer of geotextile on the membrane before loading, then load the cushion layer, followed by layered backfilling of crushed stone and compaction. The height of each backfill layer should not exceed 0.5m. Settlement markers are placed on the surface of the protective layer, and then the crushed stone and soil are compacted. The compacted soil density should be no less than 18kN / m³. 3 The backfill compaction height of the tropical rainforest greenhouse area is 0.45m, with one layer of loading; the backfill compaction height of the entrance venue area is 1.45m, with three layers of loading; the backfill compaction height of the water quality pavilion area is 2.15m, with four layers of loading; and the backfill compaction height of the water limit pavilion area is 1.25m, with three layers of loading.

[0015] Step 8: After the surcharge time meets the design requirements and reaches the unloading standard, stop the pump and drain the water; after the vacuum zone preload is unloaded, replace the membrane trench with improved soil, and require layered backfilling and compaction with a compaction coefficient of not less than 95%. The improved soil gradation is sand:soil = 1:1; after the membrane trench is replaced, compact it with a compaction degree of not less than 95%; after reinforcement, conduct on-site testing, including drilling soil sampling tests and vane shear tests.

[0016] Furthermore, the drainage sand cushion layer should be laid with a thickness of not less than 0.5m in both dry and water-covered areas. The mud content of the drainage sand cushion layer should not exceed 5%, the dry density should be greater than 1.5t / m3, and the permeability coefficient should be greater than 1×10⁻⁶. -2 cm / s.

[0017] Furthermore, the plastic drainage boards should be arranged in a square pattern with a spacing of 0.9m; the distance between the plastic drainage boards and the boundary of the reinforced area should be ≤0.45m; when installing the plastic drainage boards, the length of the back strip should be less than 30cm, and the number of back strips should not exceed 5% of the total number installed.

[0018] The filter tube is made of a soft plastic tube with a diameter of φ63mm and is perforated. The perforations are arranged in a triangular pattern along the tube body, with a filter hole diameter of 6mm and a spacing of 5cm.

[0019] Furthermore, the permeable layer is cut off at the bottom of the membrane trench, and the shallowest point extends 500mm below the top surface of the impermeable layer. The bottom width of the membrane trench is not less than 1.3m, and the slope of the membrane trench is 2:1.

[0020] Furthermore, when digging the membrane trench, the plastic drainage board inside the trench should be retained. The plastic drainage board should be inserted upwards into the drainage sand cushion layer along the edge of the trench, and the insertion depth should be greater than 0.2m.

[0021] Furthermore, after laying the sealing membrane, backfilling is carried out using trench backfill soil. The trench backfill soil is plain clay, and a water-covered embankment is constructed and compacted in layers to prevent air leakage from the sealing membrane. The thickness of the trench bedding layer on the sealing membrane at the membrane pressing trench shall not be less than 1m.

[0022] Furthermore, the sealing membrane edge is set at least at the bottom and on the slope adjacent to the improved soil in the pressure trench, and the sealing membrane edge is fixed and sealed with woven fabric or geotextile in the leveling layer at the side, and extends upward to be integrated with the sealing membrane in the sealing system.

[0023] Furthermore, the sealing membrane extends above the sealing system and is installed on one side of the slope of the upper cushion layer and backfill layer, limiting the slope of the upper cushion layer and backfill layer and reinforcing each soil layer.

[0024] Furthermore, the standard control indicators for vacuum pre-compression pump shutdown and unloading are: consolidation degree ≥90%; and the measured average settlement rate over 5 to 10 consecutive days not exceeding 2 mm / d.

[0025] The beneficial effects of this invention are reflected in:

[0026] 1) The present invention, through the setting of a leveling layer, is different from the leveling obtained on the original soil layer. By setting up a woven fabric, two layers of brambles and one layer of geotextile, it not only ensures the flatness requirements of the bottom of the soil layer, but also combines its stress and drainage with multiple settings.

[0027] 2) The present invention uses a sealing film to seal the edges, which on the one hand facilitates the formation of a vacuum to facilitate drainage, and on the other hand helps to ensure the accuracy of the upper filling and stacking;

[0028] 3) This invention, through the working cushion layer and the drainage sand cushion layer, can greatly provide an operating surface for the construction of the superstructure, ensuring construction efficiency and quality;

[0029] 4) This invention, by dividing the foundation treatment of buildings into zones, allows for separate construction based on their functions and control through different surcharge conditions to achieve their intended use, thereby greatly improving work efficiency and reducing costs.

[0030] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention; the main objects and other advantages of the invention may be realized and obtained by means of the methods particularly pointed out in the description. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the construction structure for applying methods to improve the soil quality of saline-alkali land in coastal areas.

[0032] Figure 2 This is a schematic diagram of the pressure trench and its connection structure.

[0033] Attached reference numerals: 1-Soil, 2-Plastic drainage board, 3-Film trench, 4-Leveling layer, 5-Working cushion layer, 6-Drainage sand cushion layer, 7-Sealing system, 8-Upper cushion layer, 9-Backfill layer, 10-Imperible layer, 11-Sealing membrane edge trim, 12-Trench backfill soil, 13-Trench cushion layer. Detailed Implementation

[0034] Taking a university theme park as an example, located in a coastal area, the project covers an area of ​​approximately 1,400 acres, with the core area occupying 400 acres. The foundation treatment scope only includes the tropical rainforest greenhouse, water quality pavilion, entrance pavilion, and water limit pavilion. It requires that the foundation bearing capacity at the handover elevation be no less than 100 kPa, the design load be 35 kPa, the average degree of consolidation of the soil within the treatment depth should not be less than 90%, and the post-construction settlement below the handover elevation should not exceed 30 mm; the foundation treatment scope extends 3 meters outward from the treatment outline provided by the architectural design.

[0035] like Figure 1 and Figure 2As shown, the top of the saline-alkali soil 1 is set as a leveling layer 4, a working cushion layer 5 is set above the leveling layer 4, a drainage sand cushion layer 6 is set above the working cushion layer 5, a sealing system 7 is set above the drainage sand cushion layer 6, an upper cushion layer 8 and a backfill layer 9 are set above the sealing system 7; a membrane trench 3 is set on one side of the working cushion layer 5, an impermeable layer 10 is set below the membrane trench 3, a sealing membrane edge 11 is set on the bottom surface of the membrane trench 3, and the inside of the membrane trench 3 is filled with trench backfill soil 12;

[0036] The sealing membrane edge 11 is integrally connected with the geotextile in the leveling layer 4 and the sealing membrane in the sealing system 7. The three are arranged in an F-shape, and the sealing membrane edge 11 is set along the slope and the pressure trench 3.

[0037] Combination Figure 1 and Figure 2 The following are the specific steps for further explaining the application methods of soil improvement in saline-alkali land in coastal areas:

[0038] Step 1: Based on the distribution of treatment areas, current elevation, and geological conditions, the foundation treatment area for building applications is divided into four zones: tropical rainforest greenhouse area, water quality pavilion area, entrance pavilion area, and water limit pavilion area.

[0039] Step 2: First, drain the surface water from the site and level the site. Set up leveling layer 4 according to the site conditions. Leveling layer 4 consists of one layer of woven fabric, two layers of brambles, and one layer of geotextile. When laying the geotextile, mechanical sewing is required, and the overlap width of the joints should not be less than 10cm. The overlap width of the bramble joints should not be less than 20cm.

[0040] Step 3: Lay a working cushion layer 5 made of gravel and a drainage sand cushion layer 6 made of medium and coarse sand on the geotextile. During construction, the elevation and flatness of the top and bottom surfaces of the drainage sand cushion layer 6 should be strictly controlled.

[0041] Among them, the thickness of the drainage sand cushion layer 6 in both the dry and loose areas and the water-covered areas shall not be less than 0.5m, the mud content of the drainage sand cushion layer 6 shall not be greater than 5%, the dry density shall be greater than 1.5t / m3, and the permeability coefficient shall be greater than 1x10-2cm / s.

[0042] Step 4: Before installing the plastic drainage board 2, conduct drilling and soil sampling tests and vane shear tests. After installing the plastic drainage board 2, conduct instrument monitoring. Install the plastic drainage board 2 according to the design requirements. The plastic drainage board 2 should be exposed on the surface of the drainage sand cushion layer 6 for no less than 0.2m. The last plastic drainage board 2 should be installed no more than 0.45m away from the boundary of the reinforced area.

[0043] The plastic drainage boards 2 are arranged in a square with a spacing of 0.9m; the distance between the plastic drainage boards 2 and the boundary of the reinforced area should be ≤0.45m; when installing the plastic drainage boards 2, the length of the back strip should be less than 30cm, and the number of back strips should not exceed 5% of the total number installed.

[0044] Step 5: Lay the filter pipe, and then lay the sealing system 7 on top of the filter pipe; connect one end of the membrane outlet bend to the filter pipe and lay the sealing membrane, and then connect the other end to the jet pump and the vacuum equipment; the sealing system 7 uses one layer of geotextile and two layers of sealing membrane; the sealing membrane is provided with sealing membrane edge 11 at the membrane pressing trench 3 and is compacted and fixed by the trench backfill soil 12 in the trench.

[0045] The filter tube is made of a soft plastic tube with a diameter of φ63mm and is perforated. The perforations are arranged in a triangular pattern along the tube body, with a filter hole diameter of 6mm and a spacing of 5cm.

[0046] In this embodiment, the bottom of the membrane trench 3 cuts through the permeable layer, extending at least 500mm below the top surface of the impermeable layer 10. The bottom width of the membrane trench 3 is not less than 1.3m, and the slope of the membrane trench 3 is 2:1. When excavating the membrane trench 3, the plastic drainage board 2 inside the trench is retained. The plastic drainage board 2 is inserted upwards along the trench edge into the drainage sand cushion layer 6, with an insertion depth greater than 0.2m. After laying the sealing membrane, backfill soil 12 is used for backfilling. The backfill soil 12 is plain clay, and a water-covered embankment is constructed, compacted in layers to prevent air leakage from the sealing membrane. The thickness of the trench cushion layer 13 on the sealing membrane at the membrane trench 3 must not be less than 1m.

[0047] In this embodiment, the sealing membrane edge 11 is provided at least at the bottom and on the slope adjacent to the improved soil 1 in the pressure trench 3. The sealing membrane edge 11 is fixedly and sealed to the leveling layer 4 with woven fabric or geotextile at the side, and extends upward to be integrally provided with the sealing membrane in the sealing system 7. The sealing membrane edge 11 also extends above the sealing system 7 to one side of the slope of the upper cushion layer 8 and the backfill layer 9, limiting the slope of the upper cushion layer 8 and the backfill layer 9 and reinforcing each soil layer.

[0048] Step 6: Set up surface settlement rods, install observation instruments, and connect vacuum equipment; when starting the pump, start it in batches and evenly to test the air pumping; check; after reaching the design requirements and stabilizing the air pumping for 72 hours, start formal air pumping; start timing.

[0049] Step 7: After vacuum preloading and degassing for 15 days, lay a layer of geotextile on the membrane before loading, then load the cushion layer 8, followed by layered backfilling of crushed stone and compaction. The height of each backfill layer should not exceed 0.5m. Settlement markers are placed on the surface of the protective layer, and then crushed stone and soil compaction is carried out. The compacted soil density should not be less than 18kN / m³. 3The backfill compaction height of the tropical rainforest greenhouse area is about 0.45m, and it is loaded in one layer; the backfill compaction height of the entrance venue area is about 1.45m, and it is loaded in three layers; the backfill compaction height of the water quality pavilion area is about 2.15m, and it is loaded in four layers; and the backfill compaction height of the water limit pavilion area is about 1.25m, and it is loaded in three layers.

[0050] Step 8: After the surcharge time meets the design requirements and reaches the unloading standard, stop the pump and drain the water; after the vacuum zone preload is unloaded, replace the membrane trench 3 with improved soil, and require layered backfilling and compaction with a compaction coefficient of not less than 95%. The improved soil gradation is sand:soil = 1:1; after the membrane trench 3 is replaced, it is compacted with a compaction degree of not less than 95%; after reinforcement, conduct on-site testing, including drilling soil sampling tests and vane shear tests.

[0051] In this embodiment, the standard control index for vacuum pre-compression pump shutdown and unloading is a consolidation degree ≥90% and a measured average settlement rate of no more than 2 mm / d over 5 to 10 consecutive days.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving saline-alkali soil in coastal areas, characterized in that, The top of the saline-alkali soil (1) is set as a leveling layer (4), a working cushion layer (5) is set above the leveling layer (4), a drainage sand cushion layer (6) is set above the working cushion layer (5), a sealing system (7) is set above the drainage sand cushion layer (6), an upper cushion layer (8) and a backfill layer (9) are set above the sealing system (7); a membrane trench (3) is set on one side of the working cushion layer (5), an impermeable layer (10) is set below the membrane trench (3), a sealing membrane edge (11) is set on the bottom surface of the membrane trench (3), and the trench backfill soil (12) is filled inside the membrane trench (3); The sealing membrane edge (11) is integrally connected with the geotextile in the flat layer (4) and the sealing membrane in the sealing system (7), and the three are arranged in an F-shape. The sealing membrane edge (11) is set along the slope and the pressure trench (3) for the entire length. The specific steps of the method for improving saline-alkali land in coastal areas are as follows: Step 1: Based on the distribution of treatment areas, current elevation, and geological conditions, the foundation treatment area for building applications is divided into four zones: tropical rainforest greenhouse area, water quality pavilion area, entrance pavilion area, and water limit pavilion area. Step 2: First, drain the surface water from the site and level the site. Set up a leveling layer (4) according to the site conditions. The leveling layer (4) consists of a layer of woven fabric, two layers of brambles and a layer of geotextile. When laying the geotextile, mechanical sewing is required, and the overlap width of the joints should not be less than 10cm. The overlap width of the bramble joints should not be less than 20cm. Step 3: Lay a working cushion layer (5) made of gravel and a drainage sand cushion layer (6) made of medium and coarse sand on the geotextile. During construction, the elevation and flatness of the top and bottom surfaces of the drainage sand cushion layer (6) should be strictly controlled. Step 4: Before reinforcing and installing the plastic drainage board (2), conduct drilling and soil sampling tests and vane shear tests. After reinforcing and installing the plastic drainage board (2), conduct instrument monitoring. Install the plastic drainage board (2) according to the design requirements. The plastic drainage board (2) should be exposed on the surface of the drainage sand cushion layer (6) by no less than 0.2m. The last plastic drainage board (2) should be installed no more than 0.45m away from the boundary of the reinforced area. Step 5: Lay the filter pipe, and then lay the sealing system (7) on top of the filter pipe; connect one end of the membrane outlet bend to the filter pipe and lay the sealing membrane, and then connect the other end to the jet pump and the vacuum equipment; the sealing system (7) uses one layer of geotextile and two layers of sealing membrane; the sealing membrane is provided with sealing membrane edge (11) at the membrane pressing trench (3) and is compacted and fixed by the backfill soil (12) in the trench; Step 6: Set up surface settlement rods, install observation instruments, and connect vacuum equipment; start the pump in batches and evenly for trial pumping; check; after reaching the design requirements and stabilizing pumping for 72 hours, begin formal pumping; start timing. Step 7: After vacuum preloading and degassing for 15 days, lay a layer of geotextile on the membrane before loading, then load the cushion layer (8), and then fill and compact the crushed stone soil in layers. The height of each layer should not exceed 0.5m; the compacted density of the soil should not be less than 18kN / m³. 3 The backfill compaction height of the tropical rainforest greenhouse area is 0.45m, with one layer of loading; the backfill compaction height of the entrance venue area is 1.45m, with three layers of loading; the backfill compaction height of the water quality pavilion area is 2.15m, with four layers of loading; and the backfill compaction height of the water limit pavilion area is 1.25m, with three layers of loading. Step 8: After the surcharge time meets the design requirements and reaches the unloading standard, stop the pump and drain the water; after the vacuum zone preload is unloaded, replace the membrane trench (3) with improved soil, and require layered backfilling and compaction with a compaction coefficient of not less than 95%. The improved soil gradation is sand:soil = 1:1; after the membrane trench (3) is replaced, compact it with a compaction degree of not less than 95%; after reinforcement, conduct on-site testing, and carry out drilling soil sampling test and vane shear test.

2. The method for improving saline-alkali soil in coastal areas as described in claim 1, characterized in that, The drainage sand cushion layer (6) shall be laid with a thickness of not less than 0.5m in both the dry and water-covered areas. The mud content of the drainage sand cushion layer (6) shall not exceed 5%, the dry density shall be greater than 1.5t / m3, and the permeability coefficient shall be greater than 1×10. -2 cm / s.

3. The method for improving saline-alkali soil in coastal areas as described in claim 1, characterized in that, The plastic drainage boards (2) are arranged in a square with a spacing of 0.9m; the distance between the plastic drainage boards (2) and the boundary of the reinforced area should be ≤0.45m; when the plastic drainage boards (2) are installed, the length of the back strip should be less than 30cm, and the number of back strips should not exceed 5% of the total number of boards installed; The filter tube is made of a soft plastic tube with a diameter of φ63mm and is perforated. The perforations are arranged in a triangular pattern along the tube body, with a filter hole diameter of 6mm and a spacing of 5cm.

4. The method for improving saline-alkali soil in coastal areas as described in claim 1, characterized in that, The bottom of the membrane trench (3) is cut off from the permeable layer, and the shallowest part enters 500mm below the top surface of the impermeable layer (10). The bottom width of the membrane trench (3) is not less than 1.3m, and the slope of the membrane trench (3) is 2:

1.

5. The method for improving saline-alkali soil in coastal areas as described in claim 1, characterized in that, When digging the trench (3), the plastic drainage board (2) inside the trench should be retained. The plastic drainage board (2) should be inserted into the drainage sand cushion layer (6) along the edge of the trench, and the insertion depth should be greater than 0.2m.

6. The method for improving saline-alkali soil in coastal areas as described in claim 1, characterized in that, After the sealing membrane is laid, the trench backfill soil (12) is used for backfilling. The trench backfill soil (12) is plain clay. The water-covered embankment is filled and compacted in layers to prevent the sealing membrane from leaking air.

7. The method for improving saline-alkali soil in coastal areas as described in claim 1, characterized in that, The sealing membrane edge (11) is set at least at the bottom and on the slope of the adjacent improved soil (1) in the pressure trench (3), and the sealing membrane edge (11) is fixed and sealed with the leveling layer (4) by woven fabric or geotextile at the side, and extends upward to be integrated with the sealing membrane in the sealing system (7).

8. The method for improving saline-alkali soil in coastal areas as described in claim 1, characterized in that, The sealing membrane edge (11) extends above the sealing system (7) and is set on one side of the slope of the upper cushion layer (8) and the backfill layer (9), limiting the slope of the upper cushion layer (8) and the backfill layer (9) and reinforcing each soil layer.

9. The method for improving saline-alkali soil in coastal areas as described in claim 1, characterized in that, The standard control indicators for vacuum pre-compression pump shutdown and unloading are: consolidation degree ≥90%; and the measured average settlement rate over 5 to 10 consecutive days not exceeding 2 mm / d.

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