Cofferdam structure suitable for large particle size cobble riverbed and construction method

Abstract

The application discloses a cofferdam structure suitable for a large-grain pebble riverbed and a construction method. The cofferdam structure comprises a pebble cofferdam formed by directly filling a pebble stratum in the riverbed, viscous soil backfilled in the middle of the pebble cofferdam through hole extension and lengthening of a steel casing and steel sheet piles inserted into the viscous soil, forming a support system and an anti-seepage system. The pebble cofferdam forms a scour-resistant protective structure layer and a filter layer, and simultaneously serves as a construction platform. The steel casing is made of a steel sheet, and a spiral belt made of a steel strip is arranged in the steel casing, which is used for assisting sinking of the steel casing and sinking and compaction of the viscous soil. The construction method comprises pebble cofferdam filling, steel casing hole extension and sinking, viscous soil backfilling and tamping, steel sheet pile insertion and locking and joint sealing, forming a stable cofferdam structure with good anti-seepage performance. The application fills the cofferdam by using local materials and adopts viscous soil backfilling for anti-seepage, is convenient for later removal, reduces cost, and improves construction efficiency and quality.

Description

Technical Field

[0001] This invention belongs to the field of bridge construction technology, and more specifically, relates to a cofferdam structure and construction method suitable for riverbeds with large-diameter pebbles. Background Technology

[0002] Riverbeds and floodplains often contain strata of large-diameter pebbles. During the construction of bridges spanning rivers, the construction of pile foundations and piers in the riverbed typically requires the construction of cofferdams first, followed by dewatering, excavation and support of the foundation pit, and finally, structural construction. However, when constructing cofferdams in riverbeds with large-diameter pebbles, the pebble layer, being a typical mechanically unstable stratum, presents significant challenges. These challenges include difficulties in cofferdam construction, challenges in ensuring the stability of the retaining structure, and poor seepage prevention, which can have a substantial negative impact on construction operations.

[0003] Traditional techniques typically employ steel cofferdam structures, such as driven steel pipe piles and sheet piles, as the retaining system. However, the construction technology of steel pipe pile and sheet pile cofferdams is mainly suitable for soft geological layers such as silty clay and sand. When encountering construction areas with hard geological conditions such as large-diameter pebble layers, the following problems are usually faced: First, driving steel pipe piles and sheet piles is extremely difficult, inefficient, and very easy to damage; second, driving steel pipe piles and sheet piles in riverbeds requires the construction of working platforms, which is cumbersome and costly; at the same time, the retaining structure located in loose pebble layers is easily affected by water flow, making it difficult to guarantee seepage prevention and sealing; finally, the internal support structure of traditional steel sheet pile cofferdams is complex, and the internal working space is very limited. To address the above problems, some new technologies have been proposed in recent years, such as patent document CN111549806B, which discloses a method for constructing cofferdams in sandy and gravelly strata of flowing water systems. The method includes: first, filling sand and gravel into flowing water until it reaches a predetermined height above the water surface, simultaneously filling and burying pre-compressed container bags while constructing the sand and gravel cofferdam; second, drilling longitudinal holes within the sand and gravel cofferdam while simultaneously lowering steel guide pipes, and after drilling, lowering PVC guide pipes into the bottom of the holes within the steel guide pipes; third, using a high-pressure pump to inject cement slurry at high speed through nozzles into the PVC guide pipes to form cylindrical high-pressure jet grouting piles with a certain strength; fourth, repeating steps two and three. This invention solves the problems of high cost and long construction time when combining three or more cofferdam structures in existing technologies, effectively improving the stability of the cofferdam. However, the high cost of using high-pressure jet grouting cement slurry in this invention patent is high; and the difficulty of dismantling the hardened high-pressure jet grouting cement slurry affects construction efficiency and can also impact river channels and waterways. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a cofferdam structure and construction method suitable for riverbeds with large-diameter pebbles. By directly sourcing pebbles from the pebble strata in the riverbed to construct the cofferdam, backfilling with cohesive soil in the middle and driving steel sheet piles, a retaining system and an anti-seepage system are formed, reducing construction costs and improving construction efficiency.

[0005] To achieve the above objectives, according to one aspect of the present invention, the present invention provides a cofferdam structure suitable for large-diameter pebble riverbeds, characterized in that it comprises a pebble cofferdam directly constructed by filling the pebble strata in the riverbed, cohesive soil backfilled in the middle of the pebble cofferdam after extending the steel casing through a pilot hole, and steel sheet piles driven into the cohesive soil. The steel casing is made of rolled steel plates and has a spiral band made of steel bars inside to assist the sinking of the steel casing and the sinking and compaction of the cohesive soil.

[0006] The pebble cofferdam and the sheet piles together form a retaining system that provides structural stability and protection; the cohesive soil and the sheet piles together form a seepage prevention system that prevents water from seeping into the construction area.

[0007] Furthermore, the pebble cofferdam forms an anti-erosion protective structural layer, protecting the cohesive soil and sheet piles inside the cofferdam from the direct impact of the water flow, and providing support and protection for the sheet piles.

[0008] Furthermore, the cofferdam is constructed using large-diameter pebbles to form a filter layer, which protects the intermediate cohesive soil and ensures the stability of the intermediate seepage prevention system.

[0009] Furthermore, the pebble cofferdam forms a working platform for the construction of the entire retaining structure and the internal area of ​​the cofferdam, and the working platform can be adjusted according to changes in the riverbed topography.

[0010] Furthermore, the sheet piles are Larssen sheet piles, which are connected by interlocking joints to form a solid sheet pile cofferdam with high seepage prevention performance.

[0011] According to another aspect of the present invention, the present invention provides a construction method for a cofferdam suitable for riverbeds with large-diameter pebbles, forming the aforementioned cofferdam structure suitable for riverbeds with large-diameter pebbles, characterized by comprising the following steps:

[0012] S100: In accordance with the design width and height requirements of the cofferdam, a cofferdam is formed by using an excavator to fill and compact the cofferdam in layers in the pebble stratum of the riverbed.

[0013] S200: Using the already filled cofferdam as a construction platform, a crane is used to lift the steel casing into the jaws of the pipe rolling machine and clamp it. The vertical accuracy of the steel casing is then adjusted to meet the construction technical standards. Then, a rotary drilling rig is used to drill the pilot hole.

[0014] S300: After the rotary drilling pilot hole is completed, the steel casing is extended. Then, the power head of the pipe rolling machine is used to pressurize and roll the pipe to sink the steel casing. During the process, every time the drilling is about 40cm, the grab bucket device is activated to promptly remove soil from the casing. After the casing is pulled out, the bucket is opened to unload the soil until the steel casing reaches the designed depth. After that, the soil removal device is removed.

[0015] S400: The pipe-rolling machine rotates in the opposite direction to lift the steel casing. Every 50cm of the casing is pulled out, an excavator is used to backfill with cohesive soil, and a stamping device is used to compact it until the cohesive soil is backfilled to the top of the pebble cofferdam.

[0016] S500: After the cohesive soil backfill is completed, steel sheet piles are driven into the backfill hole. When driving, the steel sheet piles are first lifted by a crane. When the steel sheet piles are lifted vertically, a 90-type vibratory hammer is used to drive the piles in sequence through the interlock of the previous steel sheet pile.

[0017] S600: Use caulking material to fill the gaps in the interlocking joints of steel sheet piles;

[0018] S700: Repeat the above steps to complete the closure of the cofferdam made of pebble sheet piles, conduct a comprehensive quality inspection to ensure the structural safety and stability, and complete the construction of the cofferdam in the large-diameter pebble riverbed.

[0019] Furthermore, before step S100, the process includes selecting high-quality steel plates and using a professional plate rolling machine to precisely roll the steel plates into cylindrical steel casings, and using 5cm wide high-strength steel strips to evenly arrange spiral strips on the inner wall of the steel casing.

[0020] Furthermore, the slope of the cofferdam filled in step S100 forms a slope ratio of 1:1.5 to 1:2.

[0021] Furthermore, during the rotary drilling of the pilot hole in step S200, the boreholes between two adjacent pile holes are interlocked by 10-15 cm.

[0022] Furthermore, in step S500, the bidirectional verticality of the sheet piles is controlled within 5‰. If the verticality requirement is not met, the piles are re-inserted until they meet the requirements.

[0023] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0024] 1. The cofferdam structure of this invention, applicable to riverbeds with large-diameter pebbles, utilizes locally sourced materials, employing large-diameter pebbles from the riverbed to construct a pebble cofferdam, forming an anti-scour protective structural layer. This effectively protects the internal structure of the cofferdam from direct water flow impact. Mechanically drilled holes are used in the middle of the pebble cofferdam for backfilling with cohesive soil and driving steel sheet piles to form a critical seepage-proof layer, further forming the retaining system and seepage-proof system. This solves the problems of high construction difficulty of traditional steel pipe pile and steel sheet pile cofferdams in riverbeds with large-diameter pebbles, the susceptibility of traditional cofferdam structures to water flow impact, and the difficulty in guaranteeing stability and seepage prevention. It improves the stability and safety of the cofferdam, its overall sealing and seepage prevention capabilities, ensures a dry construction environment, and promotes efficient construction.

[0025] 2. The cofferdam seepage prevention system of the present invention, applicable to riverbeds with large-diameter pebbles, uses cohesive soil backfill, which facilitates later dismantling, improves construction efficiency, and reduces the impact on river channels and waterways.

[0026] 3. The pebble cofferdam structure of the present invention, applicable to cofferdam structures in large-diameter pebble riverbeds, not only serves as a retaining structure layer but also as a working platform. It solves the problems of traditional methods that require additional materials and costs to build large equipment working platforms in the riverbed, resulting in complex construction and low efficiency. The use of pebble cofferdams not only reduces material costs but also provides sufficient working area and load-bearing capacity as a working platform, facilitating the operation of construction equipment and the stacking of materials. Furthermore, the working platform can be adjusted according to changes in riverbed topography, improving construction flexibility and efficiency.

[0027] 4. The cofferdam structure of the present invention, applicable to riverbeds with large-diameter pebbles, utilizes the pebbles present in the riverbed to form a pebble cofferdam as a pebble filter layer. This prevents the intermediate key anti-seepage layer composed of cohesive soil and sheet piles in the middle of the cofferdam from being loosened or collapsed by direct water flow, thus protecting the stability and integrity of the anti-seepage layer and extending the service life of the cofferdam.

[0028] 5. The cofferdam structure of the present invention, applicable to riverbeds with large-diameter pebbles, utilizes an outer pebble layer to support and protect steel sheet piles. This solves the problem that traditional cofferdam structures require complex support structures to ensure their stability, thus limiting the working space. The supporting and protecting effect of the pebble layer releases more working space, facilitates the operation of construction equipment and the stacking of materials, and improves construction efficiency.

[0029] 6. The steel casing of the cofferdam structure of this invention, applicable to cofferdams in large-diameter pebble riverbeds, is equipped with a spiral band inside. The spiral band design reduces the resistance to the sinking of the steel casing, facilitating its smooth installation. At the same time, the spiral band's effect during the rotation of the backfill pipe causes the cohesive soil to sink and compact more tightly, improving the strength and stability of the backfill soil and further enhancing the seepage prevention performance of the cofferdam. Attached Figure Description

[0030] Figure 1 This is a cross-sectional structural diagram of a cofferdam structure suitable for large-diameter pebble riverbeds according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic elevation view of the steel casing according to an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the steel casing pipe sinking according to an embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram of cohesive soil backfilling according to an embodiment of the present invention;

[0034] Figure 5 This is a plan view of the cofferdam for large-diameter pebble strata according to an embodiment of the present invention;

[0035] Figure 6 This is a schematic diagram of a partial steel sheet pile cofferdam structure according to an embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram of a construction method for a cofferdam suitable for riverbeds with large-diameter pebbles, according to an embodiment of the present invention.

[0037] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1-riverbed; 2-pebble cofferdam; 3-steel casing; 4-cohesive soil; 5-steel sheet pile; 6-spiral belt. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0040] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0041] In this patent, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0042] like Figure 1 As shown, this embodiment of the invention provides a cofferdam structure suitable for riverbeds with large-diameter pebbles, including a pebble cofferdam 2, cohesive soil 4 backfilled in the middle of the pebble cofferdam 2, and sheet piles 5 driven into the cohesive soil 4, wherein...

[0043] The pebble cofferdam 2 is a cofferdam constructed by filling the riverbed with large-diameter pebbles. Steel sheet piles 5 are installed in the middle, and the steel sheet piles 5 are connected by interlocking joints to ensure the overall stability of the cofferdam. The pebble cofferdam 2 and the steel sheet piles 5 together form a retaining system to protect the construction area. On the pebble cofferdam platform, after mechanically extending the steel casing 3, the cohesive soil 4 is backfilled, and the steel sheet piles 5 are driven in as a key seepage barrier layer. The steel sheet piles 5 are connected by interlocking joints to ensure sealing, and together with the backfilled cohesive soil 4, they form a seepage barrier system, thereby enhancing the seepage prevention effect. The stability and seepage prevention of the cofferdam structure in the large-diameter pebble riverbed are achieved through the combination of the retaining system and the seepage barrier system.

[0044] like Figure 1 and Figure 5As shown, the retaining system includes a pebble cofferdam 2 and sheet piles 5, providing structural stability and protecting the internal structure. The pebble cofferdam 2 is the main component of the cofferdam structure. Using excavators and other machinery, pebble materials are sourced locally from the riverbed pebble strata in the riverbed 1. Large-diameter pebbles are used to construct the pebble cofferdam 2, which is designed to be above the water surface, ensuring the cofferdam's flood control capacity. The slope ratio of the two sides of the pebble cofferdam 2 is set to 1:1.5 to 1:2 according to construction conditions, ensuring both structural stability and ease of construction. The pebbles in the pebble cofferdam 2 are sourced from the existing riverbed, making them readily available and inexpensive. They primarily serve the following functions:

[0045] (1) The cofferdam 2 is constructed by filling with pebbles that exist in the existing riverbed. As an anti-scouring protective structure layer, it effectively protects the cohesive soil 4 and the steel sheet piles 5 inside the cofferdam from the direct impact of water flow, reduces the impact of water pressure on the internal structure, and ensures the stability and safety of the structure.

[0046] (2) The cofferdam 2 is mainly a cofferdam filled with large-diameter pebbles, thus forming a filter layer. As a filter layer of the intermediate clay layer, it can prevent the cohesive soil 4 from being directly washed away by the water flow, thus protecting the backfilled cohesive soil 4, enhancing the seepage prevention and sealing of the structure, and ensuring the internal stability of the cofferdam.

[0047] (3) The pebble cofferdam 2 can serve as a construction access road for the entire retaining structure, providing a working platform for construction within the cofferdam area. It has good load-bearing capacity and can withstand the weight of heavy machinery and materials, providing a solid and stable working surface for construction operations, facilitating subsequent construction operations such as steel casing sinking, cohesive soil backfilling, and sheet pile driving. Furthermore, the working platform can be adjusted according to changes in the riverbed topography, ensuring that a flat construction platform can be formed even on irregular ground.

[0048] like Figure 6 As shown, the sheet piles 5 are Larssen sheet piles, installed in the middle of the pebble cofferdam 2. They are connected by interlocking joints to form a solid sheet pile cofferdam, improving the overall stability of the cofferdam. Simultaneously, the pebble cofferdam 2 provides support and protection for the sheet piles 5, freeing up more working space and solving the problem of complex internal support structures and limited working space associated with sheet piles.

[0049] like Figure 1 , Figure 4 and Figure 5As shown, the seepage prevention system includes cohesive soil 4 and steel sheet piles 5, which are used to ensure that water outside the cofferdam will not easily seep in. On the working platform formed by the pebble cofferdam 2, mechanical drilling is used in conjunction with a pipe rolling machine to press down the steel casing 3 to rotate and cut the riverbed. After the soil is removed by grab bucket, the cohesive soil 4 is backfilled. Finally, the steel sheet piles 5 are driven into the cohesive soil 4 to form a key seepage prevention layer, ensuring that the inside of the cofferdam is not affected by water seepage.

[0050] like Figure 2 As shown, the steel casing 3 is made of 12mm thick steel plate, with a length of 6m and a diameter of 0.8m. Multiple sections of the steel casing 3 are connected together during use as a guiding device in the rotary drilling process, ensuring the drill bit accurately penetrates the riverbed strata along the predetermined path. Simultaneously, it protects the borehole, preventing borehole wall collapse due to external pressure or changes in geological conditions during rotary drilling. Inside the steel casing 3 is a spiral band 6 made of 5cm wide steel bars. During forward rotation, this helps the steel casing 3 cut into the riverbed strata and reduces resistance by cutting the soil during descent, facilitating smooth installation. Conversely, when the steel casing 3 is rotated in the reverse direction to pull it up, it helps the soil settle and effectively compacts the soil, increasing the strength of the cohesive soil 4 inside the borehole.

[0051] The cohesive soil 4 has good seepage prevention performance to ensure the sealing of the cofferdam structure and prevent water infiltration. It is backfilled into the steel casing 3 in layers and compacted in layers using a stamping device to enhance the sealing performance.

[0052] like Figure 6 As shown, the sheet pile 5 is a Larssen sheet pile, and the sheet piles are connected by interlocking joints, thereby ensuring the integrity and sealing of the sheet pile cofferdam and improving the seepage prevention effect.

[0053] The cofferdam structure of this invention utilizes large-diameter pebbles from the riverbed 1 to construct a pebble cofferdam 2 that rises above the water surface, forming a stable retaining structure to resist the impact of water flow and provide a robust construction platform. Mechanical drilling operations are carried out on the pebble cofferdam platform, using a steel casing 3 with a spiral belt 6 as a guiding device to rotate and press deep into the riverbed strata. Then, cohesive soil with good seepage prevention properties is backfilled and compacted in layers. Finally, steel sheet piles 5 are driven to ensure that they are tightly bonded to the cohesive soil, forming a highly efficient seepage prevention layer, while further enhancing the stability of the retaining system and providing a safe and reliable working environment for subsequent underwater engineering such as pile foundations and piers.

[0054] Example 2:

[0055] like Figure 7 As shown in the figure, this embodiment of the invention provides a construction method for cofferdams suitable for riverbeds with large-diameter pebbles. The specific steps are as follows:

[0056] Step 1: Steel Casing Prefabrication and Spiral Strip Installation: High-quality steel plates with a thickness of 12mm are selected to ensure sufficient strength and durability of the steel casing. The steel plates undergo rigorous quality testing to guarantee their performance in complex construction environments. A professional plate rolling machine is used to precisely roll the steel plates into cylindrical steel casings with a length of 6m and a diameter of 0.8m. Dimensional accuracy must be ensured during the rolling process to prevent deformation or dimensional errors. The rolled steel casings are then firmly welded to ensure seamless joints. Spiral strips, using 5cm wide high-strength steel bars, are evenly welded onto the inner wall of the steel casing. The spacing and angle of the spiral strips are precisely adjusted according to design requirements to optimize the auxiliary effect during sinking and soil removal processes.

[0057] Step 2: Cofferdam Construction: First, conduct a detailed geological survey and assessment of the cobblestone resources in the riverbed strata to ensure that the selected materials meet the project requirements. Prepare large machinery such as excavators and loaders for efficient transportation and cobblestone filling.

[0058] In accordance with the design width and height requirements of the cofferdam, large-diameter pebbles from the riverbed pebble strata were used to construct the pebble cofferdam. During construction, attention should be paid to layered filling and compaction to ensure that each layer of pebbles achieves optimal density, thereby improving the overall stability and load-bearing capacity of the cofferdam.

[0059] Step 3: Pre-drilling construction: To ensure the construction accuracy of the steel casing, a rotary drilling rig with a 0.6m diameter drill bit is used for pre-drilling when the first section of the steel casing is buried. The already filled cofferdam is used as the construction platform. The steel casing 3 is vertically lifted into the jaws of the pipe rolling machine and clamped. Then, by adjusting the pipe rolling machine, the vertical accuracy of the steel casing is made to meet the construction technical standards before the rotary drilling rig is used for rotary drilling pre-drilling.

[0060] When using a rotary drilling rig for pilot drilling, the interlocking distance between adjacent pile holes should be 10-15 cm, and the pilot drilling depth should be 4-5 m. A high-performance rotary drilling rig equipped with a 0.6 m diameter drill bit should be selected to ensure that the drill bit can effectively penetrate complex gravel layers and maintain good pilot drilling quality. Drilling speed and depth should be strictly controlled according to design parameters, and the interlocking distance between adjacent pile holes should be set at 10-15 cm to ensure that the inserted sheet piles form a continuous and robust monolithic structure underground, while avoiding excessive interference with the surrounding strata. Throughout the pilot drilling process, a professional monitoring system should be used to monitor the drilling progress in real time and adjust drilling parameters promptly to ensure construction safety and quality.

[0061] Step 4: Casing Demolition and Synchronous Soil Removal: After the rotary drilling pilot hole is completed, the steel casing is extended. The casing 3 is lowered using the forward and reverse rotation of the casing chuck's power head and the pressure of the hydraulic cylinder. The spiral band 7 of the casing 3 cuts through the soil during forward rotation, helping the casing enter the clay layer more smoothly, allowing it to penetrate into the clay layer of the riverbed strata. During this process, every approximately 40cm of drilling, the grab bucket device is activated to remove soil from inside the casing, reducing the resistance to the casing 3's descent. The soil cut by the grab bucket teeth is collected inside the bucket and then pulled out of the casing 3, and the bucket is opened to unload the soil. When obstacles are encountered in the underground borehole, the rotary drilling rig is used to assist in clearing them. Once the casing 3 reaches the designed depth, the soil removal device is removed. Environmental protection requirements must be observed throughout the process to ensure proper disposal of excavated soil and to prevent environmental pollution.

[0062] Step 5: Backfilling and Compacting of Cohesive Soil Inside the Casing: Select suitable cohesive soil according to project requirements, ensuring that its key performance indicators such as plasticity index, liquid limit, and plastic limit meet the standards to achieve the ideal seepage prevention effect. Use an excavator to fill the pre-prepared cohesive soil into the steel casing 3. Backfill with cohesive soil every time the steel casing is rotated in the opposite direction and lifted 50cm, to better control the backfilling quality and progress. During the backfilling process, it is carried out in layers, and the backfilled cohesive soil is compacted using a tamping machine to ensure that each layer of soil achieves optimal density. During compaction, attention should be paid to uniform force application to avoid local over- or under-compaction. After the cohesive soil is backfilled to the top of the cofferdam, use a pipe-rolling machine to twist the steel casing 3 upwards and move it out smoothly. When the steel casing is rotated in the opposite direction and lifted, the internal spiral band 6 helps the soil settle more compactly, improving the compaction and stability of the backfill soil inside the hole.

[0063] When there is too much water in the hole and the loess cannot be compacted, some cement (about 15%) can be added to the loess. At the same time, the casing is rubbed from side to side to make the soil sink and cause a series of physical and chemical reactions between the cement and the soil, which hardens the soft soil and improves the compaction of the backfill soil in the hole.

[0064] Step 6: Sheet Pile Driving: After the cohesive soil 4 is backfilled, steel sheet piles 5 are driven into the backfill holes. During driving, a crane is used to lift the sheet piles 5, arranging them strictly according to design requirements. Special attention must be paid to maintaining the verticality of the sheet piles during lifting to prevent tilting, which could lead to driving difficulties or affect project quality. With the sheet piles 5 lifted vertically, a 90-type vibratory hammer is used to insert the new pile along the interlock of the previous sheet pile 5, ensuring the bidirectional verticality of the sheet piles 5 is controlled within 5‰. For sheet piles that do not meet the verticality requirements, driving must be stopped immediately, and the position readjusted until it meets the requirements. After driving, carefully check the interlock connections between the sheet piles to ensure they are sealed and leak-free, thereby enhancing the water-stopping effect of the entire cofferdam structure.

[0065] Step 7: Sealing and overall sealing of the interlock: Select materials with good elasticity and weather resistance, such as strips or cotton wool, as sealing materials, wedge them into the interlock of the steel sheet pile, and fill any gaps that may exist.

[0066] Step 8: Repeat the above steps to complete the closure of the cofferdam, conduct a comprehensive quality inspection to ensure the structural safety and stability, and complete the construction of the cofferdam in the large-diameter pebble riverbed.

[0067] After pumping water out of the cofferdam to create a dry working platform for the construction of pile foundations and piers, the cofferdam is dismantled in accordance with the principles of environmental protection, safety, and efficiency. Specialized equipment such as vibratory hammers and hydraulic pile extractors are used to pull the sheet piles out of the cohesive soil. The pebbles and cohesive backfill material inside the cofferdam are then cleared. Recyclable pebbles are used for riverbed leveling or other projects.

[0068] As described in the above embodiments, cofferdam construction can be realized under different pebble riverbed conditions, improving the flexibility, adaptability and efficiency of construction, and ensuring the safety and quality of the construction process.

[0069] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cofferdam structure suitable for riverbeds with large-diameter pebbles, characterized in that, The cofferdam (2) is constructed by directly filling the cobblestone strata in the riverbed, cohesive soil (4) is backfilled in the middle of the cofferdam (2) after the steel casing (3) is extended through the guide hole, and steel sheet piles (5) are driven into the cohesive soil (4); the steel casing (3) is made of rolled steel plate and has a spiral strip (6) made of steel strip inside, which is used to assist the sinking of the steel casing (3) and the sinking and compaction of the cohesive soil (4); The cobblestone cofferdam (2) and the sheet piles (5) together form a retaining system that provides structural stability and protection; the cohesive soil (4) and the sheet piles (5) together form a seepage prevention system that prevents water from seeping into the construction area; The pebble cofferdam (2) forms an anti-erosion protective structure layer, which protects the cohesive soil (4) and the sheet piles (5) inside the cofferdam from the direct impact of the water flow, and provides support and protection for the sheet piles (5). The cofferdam (2) is constructed by filling with large-diameter pebbles to form a filter layer, which protects the cohesive soil (4) in the middle and ensures the stability of the intermediate seepage prevention system. The pebble cofferdam (2) forms a working platform for the construction of the entire retaining structure and the internal area of ​​the cofferdam, and the working platform can be adjusted according to the changes in the riverbed topography.

2. The cofferdam structure suitable for riverbeds with large-diameter pebbles according to claim 1, characterized in that, The sheet piles (5) are Larssen sheet piles, which are connected by interlocking joints to form a solid sheet pile cofferdam with high seepage prevention performance.

3. A construction method for a cofferdam suitable for riverbeds with large-diameter pebbles, forming a cofferdam structure as described in claim 1 or 2, characterized in that... Includes the following steps: S100: In accordance with the design width and height requirements of the cofferdam, a cofferdam is formed by using an excavator to fill and compact the cofferdam in layers in the pebble stratum of the riverbed. S200: Using the already filled cofferdam as a construction platform, a crane is used to lift the steel casing into the jaws of the pipe rolling machine and clamp it. The vertical accuracy of the steel casing is then adjusted to meet the construction technical standards. Then, a rotary drilling rig is used to drill the pilot hole. S300: After the rotary drilling pilot hole is completed, the steel casing is extended. Then, the power head of the pipe rolling machine is used to pressurize and roll the pipe to sink the steel casing. During the process, every 40cm of drilling, the grab bucket device is activated to promptly remove soil from the casing. After the casing is pulled out, the bucket is opened to unload the soil until the steel casing reaches the designed depth. Then the soil removal device is removed. S400: The pipe rolling machine rotates in the opposite direction to lift the steel casing. Every 50cm of the casing is pulled out, an excavator is used to backfill with cohesive soil, and a stamping device is used to compact it until the cohesive soil is backfilled to the top of the pebble cofferdam. S500: After the cohesive soil backfill is completed, steel sheet piles are driven into the backfill hole. When driving, the steel sheet piles are first lifted by a crane. When the steel sheet piles are lifted vertically, a 90-type vibratory hammer is used to drive the piles in sequence through the interlock of the previous steel sheet pile. S600: Use caulking material to fill the gaps in the interlocking joints of steel sheet piles; S700: Repeat the above steps to complete the closure of the cofferdam made of pebble sheet piles, conduct a comprehensive quality inspection to ensure the structural safety and stability, and complete the construction of the cofferdam in the large-diameter pebble riverbed.

4. The construction method of a cofferdam suitable for riverbeds with large-diameter pebbles according to claim 3, characterized in that, Before step S100, the process also includes selecting high-quality steel plates and using a professional plate rolling machine to precisely roll the steel plates into cylindrical steel casings, and using 5cm wide high-strength steel strips to evenly arrange spiral strips on the inner wall of the steel casing.

5. A construction method for a cofferdam suitable for riverbeds with large-diameter pebbles according to claim 3, characterized in that, The cofferdam slope filled in step S100 has a slope ratio of 1:1.5 to 1:

2.

6. A construction method for a cofferdam suitable for riverbeds with large-diameter pebbles according to claim 3, characterized in that, In step S200, when rotary drilling is performed, the gaps between two adjacent pile holes are 10-15 cm.

7. A construction method for a cofferdam suitable for riverbeds with large-diameter pebbles according to claim 3, characterized in that, In step S500, the bidirectional verticality of the sheet piles is controlled within 5‰. If the verticality requirement is not met, the piles are re-inserted until they are qualified.

Images