Anti-seepage cofferdam and construction method thereof

Abstract

The present invention provides an anti-seepage cofferdam and a construction method thereof, comprising high-pressure rotary jet grouting pile foundations located on the waterfront and waterfront sides and a steel pipe pile foundation located in between; a crushed stone cushion layer and a core stone are sequentially arranged above the high-pressure rotary jet grouting pile foundations; natural soil is provided between the steel pipe piles of the steel pipe pile foundations; a crushed stone cushion layer and backfilled medium-coarse sand are sequentially arranged above the natural soil; two stone cushion layers and a mortar block stone face protection are sequentially arranged above the core stone on the waterfront side, and a bottom protection block stone is also arranged at the front end of the waterfront side; two stone cushion layers, a mixed filter layer, a geotextile filter layer, and bagged sand are sequentially arranged above the core stone on the waterfront side; and a concrete wave retaining wall is further arranged above the two stone cushion layers above the core stone on the waterfront side and near the steel pipe pile foundation. The present invention can enhance the stability of the offshore anti-seepage cofferdam, prevent seawater backflow and infiltration, and facilitate construction.

Description

Technical Field

[0001] The invention belongs to the technical field of cofferdams, and in particular relates to an anti-seepage cofferdam and a construction method thereof. Background Art

[0002] When constructing water conservancy projects, drainage is necessary to maintain the working environment of long-term water conservancy equipment. Therefore, the construction of temporary water retaining structures is particularly important. Most water conservancy projects use cofferdams as temporary water retaining structures. The function of a cofferdam is to prevent silt and water from entering the construction equipment, facilitating the drainage of internal water and thus facilitating construction. Its stability is crucial to the success of the entire project.

[0003] In recent years, with the rapid development of my country's economy, a large amount of infrastructure has been built in coastal areas, necessitating the construction of cofferdams. However, due to the presence of wave loads in coastal areas, conventional cofferdams are often unstable and subject to significant deformation under the impact of waves, resulting in seawater leakage and even cofferdam collapse, posing a significant safety hazard to cofferdam construction.

[0004] Chinese invention patent application CN201911367123 provides a water-stopping cofferdam structure and construction method for underwater crossbeam construction. This structure, used for enclosing and stopping water between two piers in shallow water, comprises a horizontal support structure, a vertical support structure, and a footing structure. The horizontal support structure comprises a purlin and steel pipe brace. The vertical support structure comprises two interlocking steel pipe pile curtains, longitudinal beams, and auxiliary piles. The two interlocking steel pipe pile curtains are welded and fixed to the outside of a purlin, and the interlocking steel pipe piles are inserted deep into the soft foundation. The longitudinal beams are longitudinally connected between the two purlins by connectors and are located below the plane of the horizontal support structure. Multiple auxiliary piles are fixed below the longitudinal beams and penetrate deep into the soft foundation. The footing structure comprises a filling layer and high-pressure jet grouting piles. The water-stopping cofferdam structure for underwater crossbeam construction provided by this invention is modular, has good water-stopping effects, can withstand strong water flow and wave forces, is simple and quick to manufacture, transport, and install, can save costs, accelerate construction progress, and has excellent engineering utilization value.

[0005] Chinese invention patent CN201910357095 provides a method for reinforcing an unstable steel sheet pile cofferdam in an offshore soft soil foundation. The method includes first removing part of the purlins in the collapsed area, pulling out the deformed steel sheet piles, and backfilling the collapsed area with stone slabs. The steel sheet piles are then re-driven, and stones are thrown outside the newly driven steel sheet piles and steel pipe piles are driven inside. After the water level in the cofferdam meets the construction requirements, the purlins and internal supports are installed, and the bottom purlins are firmly welded to the top of the steel pipe piles. Finally, after desilting the bottom of the cofferdam, steel sections and steel mesh are laid, and the steel sections are welded to the steel pipe piles. The bottom concrete is poured in layers. After pouring, a circle of brick retaining walls is installed on the top surface of the bottom concrete, and side ditches and water collection wells are set inside the brick retaining walls. This invention not only improves the safety and stability of the steel sheet pile cofferdam, but also speeds up the construction progress and effectively solves the sudden instability of the steel sheet pile cofferdam.

[0006] However, none of the above inventions discloses a complete marine anti-seepage cofferdam and a construction method thereof. Summary of the Invention

[0007] In order to design an offshore anti-seepage cofferdam that is convenient to construct, highly stable, and economically reasonable, the present invention provides an anti-seepage cofferdam and a construction method thereof. The structure can effectively improve the stability of the cofferdam and is easy to construct at sea, and can be used in related projects of offshore cofferdams.

[0008] In order to solve the above problems, the technical solution proposed by the present invention is:

[0009] The present invention first provides an anti-seepage cofferdam, which includes a high-pressure rotary jet grouting pile foundation located on the water-facing side and the water-receiving side and a steel pipe pile foundation located in the middle, wherein the steel pipe pile foundation includes a row of steel pipe piles close to the water-facing side and a row of steel pipe piles close to the water-receiving side; a crushed stone cushion layer and a core stone are sequentially arranged above the high-pressure rotary jet grouting pile foundations on the water-facing side and the water-receiving side, natural soil is provided between the steel pipe piles of the steel pipe pile foundation, and a crushed stone cushion layer and a backfill are sequentially arranged above the natural soil of the steel pipe pile foundation. For medium-coarse sand, two stone cushion layers and mortared block stone facing are arranged in sequence above the core stone of the embankment on the water-facing side, and a bottom protection block stone covering part of the steel pipe pile foundation, part of the crushed stone cushion layer and part of the embankment core stone is also arranged at the front end of the water-facing side; two stone cushion layers, a mixed filter layer, a geotextile filter layer and bagged sand are arranged in sequence above the core stone of the embankment on the backwater side, and a concrete wave-breaking wall is also arranged above the two stone cushion layers above the core stone of the embankment on the backwater side and close to the steel pipe pile foundation.

[0010] In the present invention, the medium-coarse sand in the backfill medium-coarse sand 12 does not come from the ocean, and the natural soil 13 itself is the ocean foundation material.

[0011] In a specific embodiment, the core stone (3) is filled with a single block of stone with a weight of 0 to 100 kg, preferably a single block of 10 to 100 kg; the bottom block stone (4) is filled with a single block of stone with a weight of 100 to 200 kg; the two-piece stone cushion layer (6) is made of two pieces of unweathered hard granite with good gradation and a particle size of 80 to 150 mm; the mortar block stone protection surface (7) is made of a material comprising stone and cement mortar, and the stone in the mortar block stone protection surface is a block of stone with a regular shape and uniform size, preferably The invention relates to a method for preparing a 30-50cm side-length regular hexagonal block stone with a thickness of 5-15cm; the mixed filter layer (8) adopts a well-graded mixed stone material with a particle size of 5-80mm, specifically slag or sandy gravel; the geotextile filter layer (9) comprises one or more layers of woven geotextile; the bagged sand (10) and the backfill medium-coarse sand (12) both use medium sand with an average particle size of 0.35-0.5mm and / or coarse sand with an average particle size of more than 0.5mm; the crushed stone cushion layer (11) adopts crushed stone with an average particle size of 10-40mm.

[0012] In a specific embodiment, the uniaxial saturated ultimate compressive strength of the stone used in the mortar block stone facing (7) after soaking is not less than 50 MPa, the strength grade of the cement mortar used is not less than M15, and the strength grade of the grouting cement mortar used is not less than M20.

[0013] In a specific embodiment, the slope of the core stone (3), i.e., the ratio of the height to the width of the slope formed by the core stone, is 1:1-2, and the slope of the bottom protection block stone (4), i.e., the ratio of the height to the width of the slope formed by the bottom protection block stone, is 1:2-2.5.

[0014] In a specific embodiment, the wave-breaking wall (5) is constructed using C40 high-strength concrete, and has a wall height of 0.3 to 0.8 m, preferably 0.45 m, a wall bottom width of 0.3 to 0.6 m, preferably 0.4 m, and a wall top width, i.e., a wall thickness of 0.1 to 0.3 m, preferably 0.15 m.

[0015] In a specific embodiment, the pile diameter of the high-pressure rotary jet pile (1) is 0.7-1.0m, the pile center spacing is 0.6-0.9m, and the pile diameter is greater than the pile center spacing, and the foundation replacement rate is 85-95%; preferably, the pile diameter of the high-pressure rotary jet pile (1) is 0.8m, the pile center spacing is 0.75m, and the foundation replacement rate is 89%; the diameter of the steel pipe pile (2) is 1.2-1.8m, and the pile spacing between two adjacent steel pipe piles in the same row, that is, the center distance between them, is 1.4-2m, and the pile spacing is greater than the diameter of the steel pipe pile; preferably, the diameter of the steel pipe pile (2) is 1.4-1.5m, and the pile spacing between two adjacent steel pipe piles in the same row is 1.6m.

[0016] In a specific embodiment, the anti-seepage cofferdam located above the gravel cushion layer (11) has a trapezoidal structure as a whole.

[0017] In a specific embodiment, the geotextile filter layer (9) has a unit area mass of 300 to 500 g / m 3 The filament woven geotextile is made of 70-90g / m 2 The woven bag, wherein the sand in the bagged sand (10) has a mud content of ≤5% and a permeability coefficient of ≥5×10 -3 cm / s medium-coarse sand, and the compaction degree of the crushed stone cushion layer (11) is not less than 96%.

[0018] In a specific embodiment, a twisted king-shaped block (14) made of concrete is further provided on the side of the concrete wave-blocking wall (5) close to the waterfront side, and the width of the twisted king-shaped block (14) is 1.2 to 1.8 m.

[0019] The present invention also provides a construction method of an anti-seepage cofferdam, wherein the structure of the anti-seepage cofferdam is the anti-seepage cofferdam described above, and the method comprises the following steps:

[0020] Step 1, according to the design requirements, the rotary jet piles and the steel pipe piles are constructed within the design range. When constructing the rotary jet piles, the cement slurry is rotary jetted while drilling. The steel pipe piles are constructed including the steps of drilling and piling. The distance between two adjacent steel pipe piles in the two rows of steel pipe piles is 3 to 8 meters, preferably 5 to 6 meters. After construction, the top height of the steel pipe pile is 1.5 to 5 meters higher than the top height of the rotary jet pile, preferably 2 to 3 meters higher.

[0021] Step 2: Laying a 30-80 cm thick gravel cushion layer (11) on the treated foundation;

[0022] Step 3: Dumping and filling the embankment core stone (3);

[0023] Step 4: dumping the bottom protection block stone (4) and the two stone cushion layers (6), and using the mortar block stone protection (7) to promptly cover the two stone cushion layers (6) on the waterside;

[0024] Step 5: Laying a mixed filter layer (8), a geotextile filter layer (9) and bagged sand (10) on the backwater side;

[0025] Step 6: Backfill medium-coarse sand (12) above the gravel cushion (11) at the steel pipe pile foundation (2);

[0026] Step 7: pouring concrete wave-blocking wall (5).

[0027] In the present invention, in step one, the drill rod length should be measured and marked to ensure accurate drilling depth and re-injection depth, ensuring design compliance. Double- and triple-tube grouting methods should be used. In step two, the content of slender and flat particles in the gravel cushion layer should be less than 20% by weight, and the gravel should not contain impurities such as clay lumps and plants. Bulk and bagged gravel should be prepared for settlement after disposal. In step three, the order of layered and segmented construction of the core stone filling should be determined based on design requirements, construction capacity, and consideration of tide levels and wave effects. In step 4, the ratio of the maximum side length to the minimum side length of the bottom protection block should not be greater than 1.52. When dumping the bottom protection block, the influence of the drift caused by the block should be considered according to natural conditions such as water depth, water flow and waves. The content of slender and flat particles in the second stone cushion layer should be less than 20wt%. After the second stone is laid, the water-facing side should be promptly covered with mortar block protection to prevent damage from wind, waves and water flow. If there is damage, it should be repaired. In step 5, the mixed filter layer should be constructed in sections and layers, and each layer should be staggered a sufficient distance. The length of the geotextile filter layer should be increased by a certain amount based on the designed slope length. The strength of the nylon line for laying the block splices shall not be less than 150N. After laying, the protective layer construction and upper backfill should be carried out in a timely manner, and should be carried out from the foot of the slope to the top of the slope. The bagged sand should be dumped in a timely manner after the geotextile filter layer is laid. In step 6, the coarse sand in the backfill should be compacted using the two-point resonance compaction method. In step seven, the concrete wave-breaking wall is made by cast-in-place method, and the wave action during the construction period should be taken into consideration.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) The anti-seepage cofferdam described in the present invention adopts a specifically arranged and combined high-pressure rotary jet cast-in-place pile foundation and a steel pipe pile foundation, which significantly improves the stability of the cofferdam, reduces the difficulty of offshore construction, and saves construction costs; the present invention uses a composite water-blocking structure of two stone cushion layers, a mixed filter layer, a geotextile filter layer, and bagged sand to effectively prevent seawater infiltration and increase the stability of the cofferdam; the present invention also sets a concrete wave-breaking wall on the core stone of the embankment on the backwater side, which can effectively prevent the problem of seawater backflow caused by waves.

[0030] 2) The construction method adopted by the cofferdam structure of the present invention can adapt to the wind and wave environment at sea, increase the accuracy of construction, achieve better compaction, and effectively connect the selection of various anti-seepage materials, so that the cofferdam is more integrated and the anti-seepage ability of the cofferdam structure is stronger, thereby making the performance of the cofferdam more stable.

[0031] In general, the present invention can enhance the stability of offshore anti-seepage cofferdams, prevent seawater backflow and infiltration, and facilitate construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 It is a cross-sectional view of the anti-seepage cofferdam of the present invention.

[0034] Figure 2 This is a large-scale plan layout drawing of high-pressure rotary jet grouting piles.

[0035] Among them: 1. High-pressure rotary jet pile foundation; 2. Steel pipe pile foundation; 3. Embankment core stone; 4. Bottom protection block stone; 5. Concrete wave retaining wall; 6. Two-piece stone cushion layer; 7. Mortared block stone facing; 8. Mixed inverted filter layer; 9. Geotextile filter layer; 10. Bag sand; 11. Gravel cushion layer; 12. Backfill medium and coarse sand; 13. Natural soil; 14. Twisted King-shaped block. DETAILED DESCRIPTION

[0036] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0037] Example 1

[0038] The anti-seepage cofferdam structure in this example includes a high-pressure jet grouting pile foundation 1 and a steel pipe pile foundation 2, as well as a core stone 3 set along the water-facing side and the back-facing side and a bottom protection block 4 set along the water-facing side. The core stone is filled on the high-pressure jet grouting pile foundation 1, and backfill sand 12 is filled between the core stones 3 on the water-facing side and the back-facing side. Under the backfill sand, a steel pipe pile foundation 2 is used to reinforce the foundation. Natural soil 13 is placed between the steel pipe piles, and above the core stone 3 on the back-facing side A concrete wave-breaking wall 5 is provided, and a crushed stone cushion layer 11 is provided under the core stone 3, the bottom protection block stone 4, and the backfill sand 12. Two stone cushion layers 6 are provided on the water-facing side and the water-receiving side of the core stone. The core stone 3 on the water-facing side is further provided with a mortar block stone protective surface 7 on the two stone cushion layers 6, and the core stone 3 on the water-receiving side is further provided with a mixed inverted filter layer 8, a geotextile filter layer 9, and bagged sand 10 in sequence on the two stone cushion layers 6; the cofferdam has a trapezoidal structure as a whole.

[0039] That is to say, the present invention provides an anti-seepage cofferdam, comprising high-pressure rotary jet pile foundations located on the waterfront side and the water-receiving side and a steel pipe pile foundation located in the middle; a crushed stone cushion layer and a core stone are sequentially arranged above the high-pressure rotary jet pile foundation, natural soil is located between the steel pipe piles of the steel pipe pile foundation, a crushed stone cushion layer and backfill medium-coarse sand are sequentially arranged above the natural soil, two stone cushion layers and a mortar block stone face protection are sequentially arranged above the core stone of the waterfront side, and a bottom protection block stone is also arranged at the front end position of the waterfront side; two stone cushion layers, a mixed filter layer, a geotextile filter layer and bagged sand are sequentially arranged above the core stone of the water-receiving side, and a concrete wave-breaking wall is also arranged above the two stone cushion layers above the core stone of the water-receiving side and close to the steel pipe pile foundation.

[0040] The cofferdam foundation in this example utilizes high-pressure jet grouting and steel pipe piles, effectively improving its stability and reducing construction difficulty. Furthermore, a composite water-blocking structure consisting of two stone cushions, a mixed filter layer, a geotextile filter layer, and bagged sand significantly enhances the cofferdam's anti-seepage performance. A wave barrier constructed on the core stone effectively prevents seawater backflow.

[0041] In this example, the core stone 3 has a slope of 1:1.5 and uses 0-100kg boulders; the bottom protection boulders 4 have a slope of 1:2 and both use 100-200kg boulders. In this example, the wave barrier 5 is constructed of C40 high-strength concrete, with a height of 0.45m, a width of 0.4m, and a thickness of 0.15m. In this example, the two-piece stone cushion 6 on the upstream and downstream sides of the core stone 3 is constructed of well-graded, unweathered, hard granite with a particle size of 80-150mm. In this example, medium-coarse sand 12 is backfilled between the core stones 4 on the upstream and downstream sides, using medium sand or higher. In this example, the high-pressure jet grouting piles 1 have a diameter of 0.8m, a center-to-center spacing of 0.75m, and a foundation replacement rate of 89%. The steel pipe piles 2 have a diameter of 1.5m and a spacing of 1.6m. In this example, the mortar block stone face 7 set on the two stone cushion layers 6 on the waterside has a uniaxial saturated ultimate compressive strength of 50 MPa after saturation, the strength grade of the cement mortar used is M15, and the strength grade of the grouting cement mortar used is M20. In this example, the mixed filter layer 8 set on the two stone cushion layers 6 on the backwater side uses a well-graded mixed stone. In this example, the geotextile filter layer 9 set on the mixed filter layer 8 uses a unit area mass of 400 g / m 3 In this example, the woven bag used for the bagged sand 10 provided on the geotextile filter layer 9 is 80g / m 2 Woven bags, the sand used is mud content ≤ 5%, permeability coefficient ≥ 5×10 -3 In this example, the crushed stone cushion layer 11 provided under the cofferdam body is compacted layer by layer using a light roller and its compaction degree is not less than 96%.

[0042] Example 2

[0043] The construction method of the stable anti-seepage cofferdam structure in Example 2 comprises the following steps:

[0044] Step 1: Drive rotary jet piles 1 and steel pipe piles 2 within the design range according to the design requirements. It is necessary to measure the length of the drill rod and mark it to understand the drilling depth and re-jet depth of the drill rod.

[0045] Step 2: Lay a 50cm thick gravel cushion layer 11 on the treated foundation. After the gravel and bagged gravel are thrown, the average contour line of the embankment section shall not be less than the designed section, and the average thickness shall not be less than the designed thickness, and allowance shall be made for settlement.

[0046] Step 3: Dump and fill 10-100kg core stones from 3 to 2.4m, that is, the height of the entire core stone layer is 2.4m. The order of layered and segmented construction of dumped stones shall be determined according to the specific design requirements, construction capacity, tide level and wave influence.

[0047] Step 4: Throw and fill the outer side of the embankment with bottom protection blocks 4, considering the influence of natural conditions such as water depth, water flow and waves on the drift of blocks, then lay two pieces of stones 6 and cover the water-facing side with mortared block stone protection 7 in time to prevent damage from wind, waves and water flow. If there is any damage, it should be repaired.

[0048] Step 5: Lay the mixed filter layer 8 in layers, staggering each layer sufficiently. After the geotextile filter layer 9 is laid, the protective layer and upper backfill should be constructed promptly. Bag sand 10 should be dumped promptly after the geotextile filter layer is laid. The total height of the mixed filter layer 8, geotextile filter layer 9, and bag sand 10 is 2.4 meters.

[0049] Step 6: Backfill medium-coarse sand 12 to the top elevation of the preloading top and compact it using the two-point resonance compaction method.

[0050] Step 7: Concrete wave-blocking wall 5 is poured, and wave action during construction is considered. Finally, a twisting king block (14) made of concrete is set.

[0051] The above content is a further detailed description of the present invention in conjunction with specific embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions and substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. An anti-seepage cofferdam, characterized in that: The anti-seepage cofferdam comprises a high-pressure jet grouting pile foundation (1) located on the upstream side and the downstream side and a steel pipe pile foundation (2) located in the middle, wherein the steel pipe pile foundation (2) comprises a row of steel pipe piles close to the upstream side and a row of steel pipe piles close to the downstream side; a crushed stone cushion layer (11) and a core stone (3) are sequentially arranged above the high-pressure jet grouting pile foundation (1) on the upstream side and the downstream side, natural soil (13) is provided between the steel pipe piles of the steel pipe pile foundation (2), a crushed stone cushion layer (11) and backfill medium-coarse sand (12) are sequentially arranged above the natural soil (13) of the steel pipe pile foundation (2), and a crushed stone cushion layer (11) and backfill medium-coarse sand (12) are sequentially arranged above the natural soil (13) of the steel pipe pile foundation (2). Two stone cushion layers (6) and mortar block stone facing (7) are sequentially arranged above the core stone (3), and a bottom protection block stone (4) covering part of the high-pressure jet grouting pile foundation (1), part of the crushed stone cushion layer (11) and part of the embankment core stone (3) is also arranged at the front end position of the water-facing side; two stone cushion layers (6), a mixed filter layer (8), a geotextile filter layer (9) and bagged sand (10) are sequentially arranged above the embankment core stone (3) on the backwater side, and a concrete wave-blocking wall (5) is also arranged above the two stone cushion layers (6) on the backwater side and near the steel pipe pile foundation (2); The diameter of the high-pressure rotary jet pile is 0.7~1.0m, the pile center distance is 0.6~0.9m, and the pile diameter is larger than the pile center distance; the diameter of the steel pipe pile is 1.2~1.8m, and the pile distance between two adjacent steel pipe piles in the same row, that is, the center distance between them, is 1.4~2m, and the pile distance is larger than the diameter of the steel pipe pile; the pile distance between two adjacent steel pipe piles in two rows is 3~8m, and after construction, the top height of the steel pipe pile is 1.5~5m higher than the top height of the rotary jet pile; the embankment core stone (3) is filled with a single block of stone weighing 10~100kg; the bottom protection block stone (4) is filled with a single block of stone weighing 100~200kg; the two-piece stone cushion layer (6) is made of well-graded and particle size between 80~150m m of unweathered hard granite; the mortar block stone face (7) is constructed by laying materials comprising stone and cement mortar, and the stone in the mortar block stone face is a block stone of regular shape and uniform size; the mixed filter layer (8) is a mixed stone with good gradation, and the particle size of the mixed stone is 5-80 mm; the geotextile filter layer (9) includes one or more layers of woven geotextile; the bagged sand (10) and the backfill medium and coarse sand (12) are both made of medium sand with an average particle size of 0.35-0.5 mm and / or coarse sand with an average particle size of 0.5 mm or more; the crushed stone cushion layer (11) is made of crushed stone with an average particle size of 10-40 mm, and the thickness of the crushed stone cushion layer (11) is 30-80 cm.

2. The anti-seepage cofferdam according to claim 1, characterized in that: The stone materials in the mortar-laid block stone protection surface (7) are regular hexagonal blocks with a side length of 30 to 50 cm and a thickness of 5 to 15 cm; the mixed filter layer (8) is made of slag or sand and gravel.

3. The anti-seepage cofferdam according to claim 2, characterized in that: The uniaxial saturated ultimate compressive strength of the stone used in the mortar block stone protection (7) after being soaked is not less than 50 MPa, the strength grade of the cement mortar used is not less than M15, and the strength grade of the grouting cement mortar used is not less than M20.

4. The anti-seepage cofferdam according to claim 1, characterized in that: The slope of the core stone (3), i.e., the ratio of the height to the width of the slope formed by the core stone, is 1:1-2, and the slope of the bottom protection block stone (4), i.e., the ratio of the height to the width of the slope formed by the bottom protection block stone, is 1:2-2.

5.

5. The anti-seepage cofferdam according to claim 1, characterized in that: The concrete wave-blocking wall (5) is constructed using C40 high-strength concrete, and has a wall height of 0.3-0.8 m, a wall bottom width of 0.3-0.6 m, and a wall top width, i.e., a wall thickness of 0.1-0.3 m.

6. The anti-seepage cofferdam according to claim 1, characterized in that: The foundation replacement rate of the high-pressure rotary jet grouting piles is 85-95%. The diameter of the steel pipe piles is 1.4-1.5m, and the distance between two adjacent steel pipe piles in the same row is 1.6m.

7. The anti-seepage cofferdam according to claim 1, characterized in that: The anti-seepage cofferdam is located above the gravel cushion layer (11) and has an overall trapezoidal structure.

8. The anti-seepage cofferdam according to claim 1, characterized in that: The geotextile filter layer (9) has a unit area mass of 300-500 g / m 3 The filament woven geotextile is made of 70-90g / m 2 woven bag, wherein the sand in the bagged sand (10) has a mud content of ≤5% and a permeability coefficient of ≥5×10 -3 cm / s medium-coarse sand, and the compaction degree of the crushed stone cushion layer (11) is not less than 96%.

9. The anti-seepage cofferdam according to claim 1, characterized in that: A twisted king-shaped block (14) made of concrete is further provided on the side of the concrete wave-blocking wall (5) close to the waterfront side, and the width of the twisted king-shaped block (14) is 1.2-1.8 m.

10. A construction method for an anti-seepage cofferdam, characterized in that: The structure of the anti-seepage cofferdam is the anti-seepage cofferdam according to any one of claims 1 to 9, and the method comprises the following steps: Step 1: Driving rotary jet piles and steel pipe piles within the design range according to design requirements. When driving the rotary jet piles, rotary jet cement slurry is sprayed while drilling. Driving the steel pipe piles includes drilling and piling steps. The distance between two adjacent steel pipe piles in the two rows of steel pipe piles is 5-6m. After construction, the top height of the steel pipe pile is 2-3m higher than the top height of the rotary jet pile. Step 2: Lay a crushed stone cushion layer (11) on the treated foundation; Step 3: Dumping and filling the embankment core stone (3); Step 4: dumping the bottom protection block stone (4) and the two stone cushion layers (6), and using the mortar block stone protection (7) to promptly cover the two stone cushion layers (6) on the waterside; Step 5: Lay the mixed filter layer (8), geotextile filter layer (9) and bagged sand (10) on the backwater side; Step 6: Backfill medium-coarse sand (12) above the gravel cushion (11) at the steel pipe pile foundation (2); Step 7: Casting concrete wave-breaking wall (5).

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