Construction method of auxiliary scouring prevention wall of river filling platform mixing pile

Abstract

The application relates to the riverway protection field and discloses a construction method of a riverway filling platform mixing pile auxiliary anti-scouring wall forming and grooving. The method comprises the following steps: firstly, carrying out riverbed rechecking, obstacle cleaning and construction lofting; then, carrying out zoned filling and earth cofferdam operation, so that a water-preventing area, a wall forming pre-control area and an equipment bearing area are formed; subsequently, carrying out layered compaction, anti-seepage surface protection, drainage structure and load diffusion treatment on the cofferdam body, and identifying defect positions through core drilling sampling, settlement observation, appearance inspection and seepage inspection; carrying out cement soil pre-solidification on the defect positions to form a front-groove composite closed belt; then, installing a detachable guiding and limiting structure, injecting wall protection mud, and sequentially grooving to form a groove through a hole cleaning, a lower steel reinforcement cage and a concrete pouring guide pipe, and pouring mud to form a continuous anti-seepage wall. The application can close potential seepage channels before grooving and improve the stability of the soil body around the groove wall, and reduce the risks of mud leakage, hole collapse and wall discontinuity.

Description

Technical Field

[0001] This invention relates to the field of river protection, and in particular to a construction method for a river fill platform with mixing piles to assist in trenching and scour prevention walls. Background Technology

[0002] In river management, sluice gate reinforcement, dike seepage prevention, and riverbed erosion control projects, it is often necessary to construct temporary earthen cofferdams within existing river channels, and then build anti-seepage walls using these cofferdams or their top construction platforms. These anti-seepage walls are typically formed using techniques such as mud-wall grab bucket trenching, lowering steel cages, and pouring concrete under the mud. This creates a continuous seepage interception structure in the riverbed or downstream sluice gate scour area, thereby improving the seepage resistance, erosion resistance, and overall stability of the river structure foundations and the downstream riverbed.

[0003] In actual construction, riverbed cofferdams are not simply water-retaining structures; they also need to simultaneously fulfill multiple functions, including construction diversion, load-bearing for heavy trenching equipment, trench opening stability control, slurry circulation, and subsequent cofferdam dismantling and reuse. Especially when the riverbed surface contains silt, fine sand, silty loam, sandy loam, or localized riprap, the interior of the cofferdam fill is prone to forming loose interlayers, voids, fissures, or water-softened areas. When trenching equipment repeatedly moves across the top surface of the cofferdam and uses grab buckets for trenching, localized wheel pressure or track pressure can further amplify the risk of uneven settlement and lateral deformation of the cofferdam body, thereby inducing problems such as trench opening deformation, trench wall spalling, slurry leakage, hole collapse, and unstable wall joint quality.

[0004] Current methods for constructing river anti-seepage walls typically treat earthen cofferdam construction, anti-seepage facing, equipment platforms, guide wall installation, slurry wall protection, and trenching as independent construction phases. While these methods can accomplish conventional construction, their technical control focuses primarily on filling and compaction, guide wall positioning, or slurry index control, lacking proactive identification and localization of the relationship between internal defects in the earthen cofferdam and trenching disturbances. In other words, only after slurry leakage, hole collapse, platform settlement, or trench wall instability occur during trenching are measures taken, such as grouting, backfilling, plugging leaks, or local reinforcement. This reactive approach makes it difficult to establish stable seepage-blocking bearing conditions before trenching and is insufficiently adaptable to weak interlayers, seepage channels, and disturbances from heavy equipment within the river channel.

[0005] Therefore, it is necessary to provide a construction method for a riverbed fill platform with mixing piles to assist in trenching and scour prevention walls. This method allows the earthen cofferdam to form clearly defined seepage prevention, wall formation, and load-bearing functional zones during the filling stage. Before trenching, the pre-controlled area for wall formation and the equipment disturbance area can be pre-consolidated and pre-sealed based on the quality verification results of the cofferdam body. This simplifies the construction control chain and improves the trenching stability, wall continuity, and cofferdam construction safety of the seepage prevention wall under riverbed earthen cofferdam conditions. Summary of the Invention

[0006] To address the technical problems in existing river cofferdam anti-seepage wall construction, where the processes of cofferdam filling, anti-seepage facing, trenching platform, guide wall installation, mud wall protection, and concrete pouring are fragmented and make it difficult to pre-control internal defects, seepage channels, and disturbances caused by trenching equipment before trenching, leading to issues such as grout leakage, hole collapse, trench deformation, uneven platform settlement, and unstable wall joint quality, this invention provides a construction method for a river cofferdam anti-scour wall assisted by mixing piles on a river filling platform.

[0007] This invention is achieved using the following technical solution: a construction method for a riverbed filling platform assisted trenching anti-scour wall using mixing piles, comprising the following steps: S1. Based on the axis of the proposed anti-seepage wall, conduct riverbed verification, obstacle clearing, and construction control layout, and construct an earthen cofferdam along the axis of the anti-seepage wall. The earthen cofferdam is divided into a water-adjacent anti-seepage zone, a wall pre-control zone, and an equipment bearing zone in a direction perpendicular to the axis of the anti-seepage wall, so as to undertake the functions of water-adjacent anti-seepage, trench control, and equipment bearing, respectively.

[0008] S2. The earthen cofferdam construction body is layered, leveled and compacted. A flexible seepage-proof protective face is set in the water-adjacent seepage-proof area, and a drainage cross slope and seepage-proof drainage structure are set in the equipment bearing area, so that the earthen cofferdam construction body can also serve as a temporary water-retaining body and a seepage-proof wall construction platform.

[0009] S3. Conduct quality verification of the cofferdam body in the pre-construction control area and on both sides. Based on the verification results, identify loose interlayers, holes, cracks, softened layers or weak bearing parts in the earth cofferdam body, and construct cement-soil pre-consolidated bodies in the corresponding parts so that the cement-soil pre-consolidated bodies and the earth cofferdam body together form a composite closed zone in front of the trench.

[0010] S4. Install a detachable guide and limiting structure in the composite closed zone in front of the trench, inject wall protection mud into the area to be trenched, and perform grab trenching in a sequential jumping manner; during the trenching process, adjust the performance of the wall protection mud, trenching progress or local reinforcement measures according to the displacement, settlement, leakage and stability of the soil cofferdam working body.

[0011] S5. After the trench is inspected and accepted, a steel cage and concrete pouring pipe are installed. Concrete is poured under the condition of mud wall protection to form a continuous anti-seepage wall. After the continuous anti-seepage wall is inspected and accepted, the earthen cofferdam is dismantled in the direction of retreat and the reusable soil is recycled.

[0012] As a further improvement to the above scheme, in step S1, the earthen cofferdam construction body is constructed in a phased manner. First, the first phase of the construction body is formed by filling from one bank of the river to the middle of the river and constructing the first phase of the anti-seepage wall section. Then, the second phase of the construction body is formed by filling from the other bank of the river to the completed wall section, so that the second phase of the anti-seepage wall section and the first phase of the anti-seepage wall section form an overlapping and closed relationship at the end.

[0013] As a further improvement to the above scheme, in step S2, the flexible seepage-proof protective surface includes a geomembrane laid on the slope of the water-adjacent seepage-proof area and a bagged sand and gravel protective layer pressed on the outside of the geomembrane; the top surface of the equipment bearing area forms a transverse slope to both sides with the pre-controlled wall area as the high point, and seepage-proof drainage ditches are set on both sides of the transverse slope.

[0014] As a further improvement to the above scheme, in step S3, the quality verification of the cofferdam body includes at least two of the following: core sampling, settlement observation, visual inspection, and surface seepage inspection; when the verification results show that there are discontinuous compacted sections in the earth cofferdam working body, cement-soil mixing piles are continuously constructed at the corresponding locations, and cement-soil mixing piles are densely arranged below the walking path of the trenching equipment.

[0015] As a further improvement to the above scheme, in step S4, the detachable guide and limiting structure includes two rows of inverted L-shaped steel guide wall units arranged opposite to each other, forming a grab bucket entry guide space between the two rows of inverted L-shaped steel guide wall units, and the inverted L-shaped steel guide wall units can be disassembled and transferred for reuse after the construction of the corresponding trench section is completed.

[0016] As a further improvement to the above scheme, in step S4, the sequential trenching method includes first constructing the first-phase trench section and then constructing the second-phase trench section; in each trench section, first excavate the two main holes at both ends, then excavate the secondary hole in the middle, and trim the trench wall along the length of the trench section; after the first-phase trench section is completed, a joint pipe is installed on the side to be connected, and the joint hole wall is cleaned before the second-phase trench section is constructed to ensure that the joint between adjacent trench sections is continuous and tight.

[0017] As a further improvement to the above scheme, in step S5, the hole is cleaned for the first time before the steel cage is lowered, and the hole is cleaned for the second time after the steel cage is lowered; after the second hole cleaning is qualified, the concrete is poured with mud, and the lower end of the concrete pouring guide pipe is kept embedded in the poured concrete.

[0018] As a further improvement to the above scheme, during steps S4 to S5, the horizontal displacement, vertical settlement, deformation rate, slope seepage and trench stability of the earthen cofferdam are monitored. When the monitoring results reach the warning conditions, trenching or pouring operations are suspended, and measures such as widening the cofferdam, counter-pressure at the slope toe, grouting in the trench, local backfilling, cement-soil reinforcement or drainage are taken.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This application divides the earth cofferdam construction body into a water-proof and seepage-proof zone, a wall-forming pre-control zone, and an equipment-bearing zone, so that water-blocking and seepage prevention, trench positioning, and equipment bearing are formed collaboratively within the same cofferdam system, reducing the problems of repeated processing and insufficient stability caused by the decentralized control of each link in traditional construction.

[0020] 2. Before trenching, this application conducts a quality review of the pre-controlled area of ​​the wall and the equipment disturbance area, and constructs a cement-soil pre-consolidated body based on the review results, so that it and the soil cofferdam work body together form a composite closed zone in front of the trench, thereby pre-sealing potential seepage channels and improving the stability of the soil around the trench wall, reducing the risk of trenching leakage, hole collapse and wall discontinuity.

[0021] 3. This application combines a detachable guide and limit structure, sequential trenching, and construction monitoring feedback control to enable the positioning of the guide wall, the connection of trench sections, and the parameters of mud wall protection to be adjusted according to the state of the cofferdam, thereby improving the adaptability of the anti-seepage wall construction and the stability of the wall quality under the conditions of river earth cofferdam. Attached Figure Description

[0022] Figure 1 A flowchart illustrating a construction method for a riverbed filling platform with mixing piles to assist in trenching and scour prevention walls; Figure 2 This is a schematic diagram of the overall construction process; Figure 3 Schematic diagram of cross-sectional zoning of earthen cofferdam; Figure 4 This is a schematic diagram of the grooving and guiding / limiting structure; Figure 5 This is a schematic diagram of the construction of a seepage-proof wall.

[0023] Explanation of key symbols: 1. River channel; 2. Earth cofferdam construction body; 21. Water-adjacent seepage prevention zone; 22. Pre-construction control zone; 23. Equipment bearing zone; 3. Flexible seepage prevention facing; 31. Geomembrane; 32. Bagged sand and gravel protective layer; 4. Seepage prevention drainage ditch; 5. Load diffusion plate; 6. Composite sealing strip in front of the trench; 61. Cement-soil pre-consolidated body; 7. Demountable guide and limiting structure; 71. Inverted L-shaped steel guide wall unit; 8. Wall protection mud; 9. Trench; 10. Reinforcing cage; 11. Concrete pouring guide pipe; 12. Continuous seepage prevention wall; 13. Joint pipe. Detailed Implementation

[0024] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0025] For ease of explanation, in this embodiment, the river channel refers to an existing river channel requiring seepage prevention or erosion control reinforcement; the seepage barrier wall is a continuous wall installed within the riverbed or downstream of a hydraulic structure. In the accompanying drawings, the river channel can be marked as 1, the earthen cofferdam as 2, the water-adjacent seepage prevention zone as 21, the pre-controlled wall zone as 22, the equipment bearing zone as 23, the flexible seepage barrier face as 3, the geomembrane as 31, the bagged sand and gravel protective layer as 32, the seepage prevention drainage ditch as 4, the load diffusion plate as 5, the composite sealing strip in front of the trench as 6, the cement-soil pre-consolidated body as 61, the detachable guide and limiting structure as 7, the inverted L-shaped steel guide wall unit as 71, the wall protection slurry as 8, the trench hole as 9, the reinforcing cage as 10, the concrete pouring duct as 11, the continuous seepage barrier wall as 12, and the joint pipe as 13.

[0026] Example 1: This example provides a construction method for a riverbed filling platform with mixing piles to assist in trenching and scour prevention. It is applicable to water conservancy projects where the riverbed surface contains silt, fine sand, silty loam, sandy loam, or locally riprap, and where temporary earthen cofferdams are needed for mud slurry wall trenching construction.

[0027] Before construction, the design axis of the cutoff wall is checked. The check includes the cutoff wall axis location, the current riverbed elevation, the construction water level, the existing distribution of riprap or boulders, the route for the trenching equipment, and temporary diversion conditions. For boulders, isolated rocks, or other hard obstacles located on both sides of the cutoff wall axis, amphibious excavators, grab buckets, or impact crushers are used to clear them to a position that will not affect trenching. After clearing, total stations, GNSS receivers, or levels are used to set up axis control stakes and elevation control stakes. These control stakes are spaced along the cutoff wall axis and serve as control benchmarks for earth cofferdam filling, guide wall installation, and trench segment division.

[0028] Subsequently, an earthen cofferdam 2 was constructed within the river channel 1 along the axis of the anti-seepage wall. The earthen cofferdam 2 was divided into three sections perpendicular to the axis of the anti-seepage wall: a water-adjacent anti-seepage zone 21, a wall-forming pre-control zone 22, and an equipment-bearing zone 23. The water-adjacent anti-seepage zone 21 was located near the incoming water or normal water level to withstand water flow erosion and form an anti-seepage interface on the water-adjacent side. The wall-forming pre-control zone 22 was located near the axis of the proposed anti-seepage wall and was used to arrange the trenching area, guiding and limiting structures, and the composite sealing zone in front of the trench. The equipment-bearing zone 23 was located on the backwater side of the wall-forming pre-control zone 22 or on the main travel side of the construction equipment and was used to support the trenching machine, lifting equipment, concrete pouring equipment, and mud circulation equipment.

[0029] The earthen cofferdam 2 can be constructed using the advance method. The preferred filling material is silty loam, heavy silty loam, or a blended cohesive soil with low permeability and good compactability. During construction, the underwater portion can be advanced and filled using excavators and dump trucks. The portion above the water surface should be laid in layers of 30cm to 50cm thickness. After leveling with a bulldozer, a vibratory roller or other compaction equipment should be used to repeatedly compact the material along the axis of the anti-seepage wall, with adjacent wheel tracks overlapping. For the trenching area of ​​the anti-seepage wall and the path of the trenching equipment, the leveling accuracy should be improved and localized overloading avoided, ensuring that the earthen cofferdam 2, while forming a temporary water barrier, also has the stable capacity to support the trenching equipment.

[0030] After the earthen cofferdam 2 is filled to the design top elevation, the slope of the water-adjacent seepage prevention zone 21 is trimmed to form a continuous slope, sharp stones, debris, and local protrusions are removed, and then the geomembrane 31 is laid. The overlapping parts of the geomembrane 31 are treated by welding, hot-melt connection, or compression sealing, and the overlap width is determined according to the site water level and slope conditions. A bagged sand and gravel protective layer 32 is pressed on the outside of the geomembrane 31, covering the water-adjacent slope and extending to the toe of the water-adjacent slope to prevent damage to the geomembrane 31 caused by water flow erosion, wind and waves, or construction disturbance. For the back slope, plastic film, rainproof cloth, geotextile, or other covering materials can be used to reduce the risk of rainwater erosion and slope softening.

[0031] The top surface of the equipment bearing area 23 forms a transverse slope to both sides with the pre-construction control area 22 as the relative high point. The transverse slope can be 1.5% to 3%. Anti-seepage drainage ditches 4 are respectively installed on the upstream and downstream sides of the equipment bearing area 23. The anti-seepage drainage ditches 4 can be constructed using a geomembrane lining, mortar plastering, precast troughs, or steel plate troughs. The anti-seepage drainage ditches 4 are used to collect and discharge rainwater, flushing water, or overflow water from the mud system from the platform surface, preventing water from seeping down the softened soil cofferdam 2 along the drainage ditches.

[0032] Load diffusion plates 5 are laid on the travel path of the trenching equipment in the pre-construction control zone 22 and the equipment bearing zone 23. The load diffusion plates 5 can be made of steel plates, composite steel sections, or modular roadbed boxes, and their laying direction is consistent with the axis of the anti-seepage wall or the travel direction of the trenching equipment tracks. The load diffusion plates 5 are used to diffuse the pressure of the trenching equipment tracks or wheels, reducing the shear disturbance of local loads on the soil near the trench opening. For locations with insufficient local bearing capacity, a crushed stone cushion layer, a graded sand and gravel cushion layer, or a geogrid reinforcement layer can be laid under the load diffusion plates 5.

[0033] After the earthen cofferdam 2 is formed, the quality of the cofferdam body in the pre-controlled area 22 and its two sides is checked. The quality check includes at least two of the following: core sampling, settlement observation, visual inspection, and surface seepage inspection. During core sampling, sampling points are set up along the axis of the anti-seepage wall or on both sides, with a sampling depth at least covering the depth affected by trenching disturbance. By observing the integrity, water content, compactness, interlayer distribution, and pore condition of the core samples, it is determined whether there are discontinuous compacted sections within the earthen cofferdam 2. Settlement observation and visual inspection are used to determine whether there are localized settlements, cracks, heaves, slope slippage, or seepage points on the platform.

[0034] When the quality verification of the cofferdam body shows the presence of loose interlayers, pores, fissures, water-bearing softened layers, or weak bearing areas within the pre-control zone 22, a cement-soil pre-consolidated body 61 is constructed at the corresponding location. The cement-soil pre-consolidated body 61 is preferably a cement-soil mixing pile. The cement-soil mixing piles can be continuously arranged along both sides of the anti-seepage wall axis, or densely arranged below defective sections, seepage sections, and the path of the trenching equipment. The pile diameter can be 500mm to 700mm, preferably 600mm; the pile length is determined based on the depth of the defective layer and the depth of trenching disturbance, preferably penetrating the loose interlayer or softened layer and entering a relatively stable soil layer. Ordinary Portland cement can be used, and the cement content is determined based on the soil quality and strength requirements. Adjacent cement-soil mixing piles can overlap, be tangential, or be continuously arranged at small intervals, so that the cement-soil pre-consolidated body 61 and the soil cofferdam working body 2 together form a composite closed zone 6 in front of the trench.

[0035] The composite sealing strip 6 in front of the trench is not simply a foundation reinforcement structure. Its location corresponds to the outer side of the trench outline of the anti-seepage wall and the area affected by disturbance from the trenching equipment. Its function is to pre-close the potential seepage channels within the soil cofferdam working body 2 before trenching with the grab bucket, and to pre-consolidate the soil on the outer side of the trench wall, so that the mud pressure can act more stably on the trench wall during trenching, reducing the risk of grout leakage, hole collapse, and trench opening deformation.

[0036] After the pre-trench composite sealing strip 6 meets the construction requirements, a detachable guide and limiting structure 7 is installed within the pre-construction control zone 22. The detachable guide and limiting structure 7 includes two rows of oppositely arranged inverted L-shaped steel guide wall units 71. Each row of inverted L-shaped steel guide wall units 71 includes horizontal and vertical members. The horizontal members are embedded within the earthen cofferdam working body 2 and compacted with the backfill soil. The vertical members extend upwards and limit the entry position of the grab bucket into the trench. The net distance between the two rows of vertical members is greater than the design thickness of the anti-seepage wall. For example, when the design thickness of the anti-seepage wall is 600mm, the net distance between the two rows of vertical members can be set to approximately 700mm to provide guidance margin for the trenching equipment. Adjacent inverted L-shaped steel guide wall units 71 are connected by bolts, connecting plates, pins, or welded temporary connectors, allowing them to be disassembled and transferred to the next construction section for reuse after the corresponding trench section is completed.

[0037] After the detachable guide and limiting structure 7 is installed, its axial position, top surface elevation, inner clearance, and straightness should be checked. If the deviation of the guide wall axis or the top surface elevation exceeds the allowable range for construction, the position of the inverted L-shaped steel guide wall unit 71 should be adjusted first, and then backfilling and compaction should be carried out. After the guide wall is installed, the wall-protecting mud 8 is injected into the area to be trenched. The wall-protecting mud 8 can be bentonite mud. Before trenching, the mud specific gravity, viscosity, and sand content should be tested. Under normal conditions, the mud specific gravity can be controlled at 1.03 g / cm³. 3 Up to 1.08 g / cm 3 The viscosity can be controlled between 32s and 50s, and the sand content should not exceed 6%. When the formation has high permeability or slight leakage occurs, the mud specific gravity or mud level can be appropriately increased.

[0038] The trenching construction adopts a sequential, skip-trenching method. Specifically, the first-stage trench section is constructed first, followed by the second-stage trench section. Within each trench section, a grab bucket is used for trenching. First, the main holes at both ends of the trench section are excavated, then the secondary holes between the two main holes are excavated. Finally, the trench wall is trimmed along the length of the trench section, ensuring that the trench holes 9 form a continuous and straight trench profile. This method allows the grab bucket to experience relatively balanced force during the construction of the main holes, and eliminates local unevenness in the trench wall through the secondary holes and the trimming with the grab bucket, thereby improving the verticality of the trench holes 9 and the straightness of the trench section.

[0039] After the first-stage trench section is completed, a joint pipe 13 is installed on the side to be connected to the second-stage trench section. The joint pipe 13 is installed vertically and close to the end of the trench section. After the initial setting of the first-stage trench section concrete, the joint pipe 13 is pulled out, and mud is added to the joint hole during the pulling process to prevent the joint hole from collapsing. Before the construction of the second-stage trench section, the wall of the joint hole is cleaned to remove mud and loose attachments, ensuring that the concrete of the second-stage trench section can form a dense and continuous joint with the end of the first-stage trench section.

[0040] During trenching, the horizontal displacement, vertical settlement, deformation rate, slope seepage, and trench opening stability of the earthen cofferdam 2 are monitored. Horizontal displacement can be observed using a total station, inclinometer, or displacement observation points; vertical settlement can be observed using a level; slope seepage can be assessed by inspecting the wet patches around the water-adjacent seepage prevention zone 21, drainage ditch, and pre-construction control zone 22. If grout leakage, wall spalling, increased horizontal displacement, or increased settlement rate of the earthen cofferdam 2 are detected, appropriate measures should be taken based on the severity of the anomaly. For minor grout leakage, increase the level or specific gravity of the wall-protecting slurry 8 and add bentonite slurry; for moderate grout leakage, add clay balls, bentonite lumps, sawdust, fiber materials, or graded plugging material into the trench; for severe grout leakage, local hole collapse, or significant platform deformation, trenching should be suspended, and the abnormal areas should be locally backfilled, reinforced with cement and soil, reinforced with slope toe counterweight, or widened. Trenching should resume after the monitoring results stabilize.

[0041] After the trench 9 reaches the designed depth, trench completion acceptance is conducted. Acceptance includes checking the trench depth, trench thickness, trench wall verticality, bottom sediment thickness, mud parameters, and trench section planar position. After successful acceptance, a first cleaning is performed to remove bottom sediment and replace substandard mud. Subsequently, the reinforcing cage 10 is lowered. When lowering the reinforcing cage 10, it should be aligned with the centerline of trench 9 and lowered slowly to avoid collision with the trench wall or guide wall. After the reinforcing cage 10 is lowered, a second cleaning is performed to ensure that the bottom sediment thickness, mud specific gravity, viscosity, and sand content meet the pouring requirements.

[0042] After the second cleaning of the borehole is deemed satisfactory, a concrete pouring guide pipe 11 is installed. The bottom of the concrete pouring guide pipe 11 is maintained at an appropriate distance from the bottom of the trench. During pouring, isolation plugs, isolation balls, or other isolation materials are used to separate the concrete from the slurry inside the pipe, ensuring the first batch of concrete can seal the bottom. During pouring, the concrete surface rises continuously, and the lower end of the concrete pouring guide pipe 11 remains embedded in the already poured concrete to prevent slurry from being trapped in the concrete wall. When multiple concrete pouring guide pipes 11 are used simultaneously, the height difference of the concrete surface within the control range of adjacent pipes should be controlled to ensure a uniform rise of the concrete within the trench section. After pouring is completed, a continuous seepage barrier wall 12 is formed.

[0043] After the continuous anti-seepage wall 12 meets the acceptance criteria, the earthen cofferdam 2 is dismantled in the retreat direction. During dismantling, the earthen cofferdam 2 above the water surface is dismantled first to reduce the amount of underwater dismantling work; then, the underwater cofferdam soil is dredged and dismantled. The reusable soil obtained from the dismantling can be used for subsequent cofferdam filling, riverbank backfilling, or site restoration; soil unsuitable for reuse is transported to a designated area for disposal. Thus, the earthen cofferdam filling, phased wall construction, and cofferdam dismantling and reuse form a closed construction chain.

[0044] The construction method of this embodiment divides the earthen cofferdam 2 into a water-proof and seepage-proof zone 21, a wall pre-control zone 22, and an equipment-bearing zone 23 at the initial stage of construction. Before trenching, a composite closed zone 6 is formed in front of the trench using a cement-soil pre-consolidation body 61, so that the water-blocking, seepage-proof, load-bearing, and trenching functions of the earthen cofferdam are achieved synergistically within the same system. Compared with the traditional construction method of first filling the platform and then passively dealing with grout leakage or hole collapse, this embodiment can complete defect identification and localized pre-treatment before trenching, resulting in better construction stability and quality control.

[0045] Example 2: This example, based on Example 1, further illustrates the methods for phased construction and handling abnormal working conditions; When the river channel cross-section is wide or a portion of the flow passage needs to be maintained during construction, the earthen cofferdam construction body 2 adopts a phased construction method. In the first phase, construction begins from the first bank of the river towards the middle of the channel to form the first-phase construction body, and a first-phase anti-seepage wall section is constructed on top of this body. After the first-phase anti-seepage wall section reaches the required strength or meets acceptance criteria, some soil material from the first-phase construction body is removed to create a temporary flow passage or to provide soil for the second-phase construction. In the second phase, construction begins from the second bank of the river towards the first-phase anti-seepage wall section to form the second-phase construction body, and a second-phase anti-seepage wall section is constructed on top of this body, allowing the second-phase anti-seepage wall section to overlap and close with the first-phase anti-seepage wall section at the ends.

[0046] In phased construction, the overlapping ends of the first-phase and second-phase anti-seepage wall sections are key areas for quality control. During overlapping construction, space is reserved at the ends of the already constructed trench sections for joint pipe drilling or joint hole wall treatment; before the trench section to be constructed, the joint hole walls are cleaned to remove mud, sediment, and loose concrete. This ensures that the concrete can penetrate the joint hole walls and form a continuous joint with the already constructed wall sections during subsequent concrete pouring.

[0047] When core sampling reveals cavities, loose interlayers, or water-bearing softened layers near the pre-construction control zone 22 of the earthen cofferdam, instead of large-scale reinforcement of the entire cofferdam section, continuous cement-soil mixing piles are constructed along both sides of the anti-seepage wall axis based on the location and depth of the defects. For the equipment load-bearing zone 23, where the trenching equipment frequently moves, cement-soil mixing piles can be densely arranged below the track centerline or wheel track centerline to form a seepage-resistant and load-bearing composite section. This seepage-resistant and load-bearing composite section simultaneously serves to seal seepage channels and reduce equipment load disturbance, avoiding the inability to address deep loose interlayers by simply relying on steel plate pressure distribution.

[0048] If slight grout leakage occurs during trenching but the earthen cofferdam 2 does not experience significant displacement, first maintain the grout level in the trench above the groundwater level or river level, and increase the specific gravity of the wall-protecting grout 8. Simultaneously, add sealing material to the leaking section, allowing it to enter the seepage channel with the grout and form a temporary seal. If the grout leakage continues to increase or localized rockfalls occur on the trench wall, suspend the grab excavation, backfill the abnormal section locally, and resume trenching once the grout levels recover and the trench wall stabilizes. If monitoring shows continuous settlement or increased horizontal displacement of the earthen cofferdam 2, stop the trenching equipment from moving in the abnormal area and use methods such as slope toe counterpressure, cofferdam widening, cement-soil reinforcement, or drainage to address the issue until the deformation rate meets the conditions for continued construction.

[0049] This embodiment transforms the construction of riverbed cofferdams from traditional experience-based process control to cofferdam state-driven construction control through a construction logic of "verification and identification—localized pre-consolidation—monitoring feedback—anomaly handling." Its innovation lies not in the individual use of geomembranes, steel guide walls, mud slurry walls, or cement-soil mixing piles, but in the coupled configuration of these measures according to three functional zones: water-adjacent seepage prevention, wall pre-construction control, and equipment load-bearing capacity. Furthermore, it forms a composite sealing zone in front of the trench before trenching, thereby improving trenching stability and wall continuity under complex riverbed geological conditions.

[0050] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A construction method for a riverbed fill platform assisted by mixing piles to form a trench for erosion control wall, characterized in that, Includes the following steps: S1. Based on the axis of the proposed anti-seepage wall, conduct riverbed verification, obstacle clearing and construction control layout. In the river channel, construct earthen cofferdams in sections along the axis of the anti-seepage wall. The earthen cofferdams form water-adjacent anti-seepage zone, wall pre-control zone and equipment bearing zone in sequence along the direction perpendicular to the axis of the anti-seepage wall. S2. The earthen cofferdam working body is layered, leveled and compacted, and a flexible seepage-proof protective surface is formed in the water-adjacent seepage-proof area, and a drainage cross slope and seepage-proof drainage structure are formed in the equipment bearing area, so that the earthen cofferdam working body can serve as a temporary water-retaining body and a seepage-proof wall construction bearing platform. S3. Conduct quality verification of the cofferdam body in the pre-construction control area and on both sides. Based on the verification results, identify loose interlayers, holes, cracks, softened layers or weak bearing parts, and construct cement-soil pre-consolidated bodies in the corresponding parts so that the cement-soil pre-consolidated bodies and the soil cofferdam construction body together form a composite closed zone in front of the trench. S4. Install a detachable guide and limiting structure in the composite closed zone in front of the trench, inject wall protection mud into the area to be trenched, and perform grab trenching in a sequential jumping method; during the trenching process, adjust the performance of the wall protection mud, trenching progress or reinforcement measures according to the displacement, settlement, leakage and stability of the soil cofferdam working body. S5. After the trench is accepted, a steel cage and concrete pouring pipe are installed. Concrete is poured under the condition of mud wall protection to form a continuous anti-seepage wall. After the continuous anti-seepage wall is accepted, the earthen cofferdam is dismantled in the direction of retreat. The composite sealing strip in front of the trench is located on the outside of the trench outline of the anti-seepage wall. It is used to pre-close and pre-consolidate the seepage channels and equipment disturbance areas of the earth cofferdam before trenching, so as to reduce the risks of trench collapse, cofferdam leakage and uneven settlement of the construction platform.

2. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, In step S1, the earthen cofferdam construction is carried out in stages. First, the first phase of the construction is formed by advancing from one bank of the river to the middle of the river and constructing the first phase of the anti-seepage wall section. Then, the soil material of the first phase of the construction is removed or nearby soil material is used to advance from the other bank of the river to the wall section to form the second phase of the construction, so that the second phase of the anti-seepage wall section and the first phase of the anti-seepage wall section form an overlapping and closed relationship at the end.

3. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, In step S2, a geomembrane is laid on the slope of the water-adjacent seepage prevention zone, and a bagged sand and gravel protective layer is pressed on the outside of the geomembrane, extending to the toe of the water-adjacent slope; the top surface of the equipment bearing area forms a transverse slope on both sides with the pre-controlled wall area as the high point, and seepage prevention drainage ditches are set on the downstream and upstream sides of the transverse slope to drain the water from the platform surface and block the water in the drainage ditch from seeping into the earthen cofferdam working body.

4. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, In step S2, the filling layer of the earth cofferdam working body above the water surface is laid in layers of predetermined thickness, and the compaction equipment rolls along the axis of the anti-seepage wall and overlaps the adjacent wheel tracks; load diffusion plates are laid on the walking path of the trenching equipment in the wall pre-control zone and the equipment bearing zone. The load diffusion plates are used to reduce the local wheel pressure or track pressure of the trenching equipment on the earth cofferdam working body.

5. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, In step S3, the quality verification of the cofferdam body includes at least two of the following: core sampling, settlement observation, visual inspection, and surface seepage inspection. When the core sample or on-site verification results show that there is a discontinuous compacted section in the soil cofferdam body, cement-soil mixing piles are continuously constructed on both sides of the pre-control zone corresponding to the discontinuous compacted section, and cement-soil mixing piles are densely arranged below the walking path of the trenching equipment to form a seepage-resistant bearing composite section extending along the axis of the anti-seepage wall.

6. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, In step S4, the detachable guide and limiting structure includes two rows of inverted L-shaped steel guide wall units arranged opposite to each other, with the net distance between the two rows of inverted L-shaped steel guide wall units being greater than the design thickness of the anti-seepage wall; the horizontal limbs of the inverted L-shaped steel guide wall units are embedded in the earth cofferdam working body, and the vertical limbs are used to limit the position of the grab bucket entering the trench. Adjacent inverted L-shaped steel guide wall units are connected by detachable connectors, so that the inverted L-shaped steel guide wall units can be transferred and reused after the construction of the corresponding trench section is completed.

7. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, In step S4, bentonite slurry is used for wall protection. Before trenching, the specific gravity, viscosity and sand content of the wall protection slurry are tested and controlled. When leakage of slurry in the trench, falling of the trench wall, increase of horizontal displacement of the earthen cofferdam or increase of settlement rate occur during the trenching process, the level or specific gravity of the wall protection slurry is increased, and sealing material is added to the trench or the trenching is suspended and the abnormal parts are reinforced.

8. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, In step S4, the sequential trenching method includes constructing the first-phase trench section first and then the second-phase trench section; within each trench section, the main holes at both ends of the trench section are excavated first, and then the secondary holes between the two main holes are excavated, and the trench wall is trimmed along the length of the trench section; after the first-phase trench section is completed, a joint pipe is installed on the side to be joined; after the concrete of the first-phase trench section has initially set, the joint pipe is pulled out and mud is added to the joint hole; before the construction of the second-phase trench section, the joint hole wall is cleaned to form a dense and continuous joint between adjacent trench sections.

9. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, In step S5, the hole is cleaned for the first time before the steel cage is lowered, and the hole is cleaned for the second time after the steel cage is lowered. After the second hole cleaning is qualified, the concrete pouring pipe is lowered and the concrete is poured with mud. During the pouring process, the concrete surface rises continuously and the lower end of the concrete pouring pipe is kept embedded in the poured concrete to form a continuous and closed seepage-proof wall.

10. The construction method for a riverbed fill platform assisted trenching anti-scouring wall using mixing piles as described in claim 1, characterized in that, During steps S4 to S5, the horizontal displacement, vertical settlement, deformation rate, slope seepage, and trench stability of the earthen cofferdam are monitored. When any monitoring result reaches the warning condition, trenching or pouring operations are suspended, and measures such as widening the cofferdam, counter-pressure at the slope toe, grouting in the trench, local backfilling, cement-soil reinforcement, or drainage are taken. After the continuous anti-seepage wall is accepted, the earthen cofferdam above the water surface is first demolished, and then the underwater cofferdam soil is dredged and demolished. The soil can be reused for subsequent cofferdam filling or riverbank backfilling.

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