Cofferdam structure suitable for large-particle-size pebble river bed and construction method

Abstract

The invention discloses a cofferdam structure suitable for a large-particle-size pebble river bed and a construction method. The cofferdam structure comprises a pebble cofferdam, cohesive soil and steel sheet piles, wherein the pebble cofferdam is formed by direct filling of a pebble stratum in a riverbed, the cohesive soil is backfilled in the middle of the pebble cofferdam after a steel casing is lengthened through a guide hole, and the steel sheet piles are inserted and driven in the cohesive soil to form an enclosure system and an anti-seepage system. Wherein the pebble cofferdam forms an anti-scouring protective structure layer and an inverted filter layer and serves as a construction platform at the same time; the steel casing is formed by rolling a steel plate, and a spiral band made of steel bars is arranged in the steel casing and used for assisting sinking of the steel casing and sinking compaction of the cohesive soil. The construction method comprises the steps of filling the pebble cofferdam, sinking the guide hole of the steel casing, backfilling and tamping the cohesive soil, inserting and driving the steel sheet piles and caulking the locking opening, and forming the stable cofferdam structure with good anti-seepage performance. According to the construction method, local materials are used for filling the cofferdam, the cohesive soil is used for backfilling and preventing seepage, later-stage dismantling is facilitated, the cost is reduced, and the construction efficiency and quality are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge construction, and more specifically, relates to a cofferdam structure and a construction method suitable for a riverbed of large-diameter pebbles. Background Art

[0002] There are often large-diameter pebble strata in riverbeds and floodplains. When constructing cross-river bridges, the construction of pile foundations and piers in the riverbed usually requires the construction of cofferdams first, followed by pumping, foundation pit excavation and support, and finally structural construction. However, when constructing cofferdams in large-diameter pebble riverbeds, the large-diameter pebble layer is a typical mechanically unstable stratum, which makes cofferdam construction difficult, the stability of the retaining structure is difficult to ensure, and the anti-seepage effect is poor, which can easily cause a significant adverse impact on construction operations.

[0003] In traditional technology, steel cofferdam structures such as steel pipe piles and steel sheet piles are usually used as the retaining system, but the construction technology of steel pipe pile and steel sheet pile cofferdam is mainly suitable for soft geological layers such as silty clay and sand. If you encounter a construction area with hard geological conditions such as a large-diameter pebble layer, you usually face the following problems: First, it is extremely difficult to drive steel pipe piles and steel sheet piles, the construction efficiency is low, and they are very easy to damage; second, when driving steel pipe piles and steel sheet piles in the riverbed, it is necessary to set up an operating platform, the process is cumbersome and the cost is high; at the same time, the retaining structure located in the loose pebble layer is easily affected by the impact of water flow, and it is difficult to ensure anti-seepage and sealing; finally, the internal support structure of the traditional steel sheet pile cofferdam is complex, and the internal working space is very limited. In response to the above problems, some new technologies have been proposed in recent years, such as the patent document with authorization number CN111549806B. This invention patent discloses a cofferdam construction method for flowing water system sand and gravel strata, including: the first step, filling sand and gravel in flowing water until the filling is above the water surface. The pre-pressed container bag is buried while the sand and gravel cofferdam is built; the second step, longitudinally drilling holes in the sand and gravel cofferdam and lowering the steel conduit at the same time, and after the drilling is completed, the PVC conduit is lowered to the bottom of the hole in the steel conduit; the third step, using a high-pressure pump to spray cement slurry through a nozzle into the PVC conduit at high speed to form a cylindrical high-pressure jet pile with a certain strength; the fourth step, repeating the second and third steps. This invention solves the problems of high cost and long time consumption when three or more cofferdam structures are combined in the prior art, and effectively improves the stability of the cofferdam. However, the invention patent uses high-pressure jet cement slurry for construction, which has high construction costs; and the high-pressure jet cement slurry is difficult to dismantle after hardening and forming, which affects the construction efficiency and also affects the river and waterway. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a cofferdam structure and a construction method suitable for a large-diameter pebble riverbed. The pebble cofferdam is built by directly taking materials from the pebble stratum in the riverbed, backfilling with clay in the middle and inserting steel sheet piles to form a containment system and an anti-seepage system, thereby reducing construction costs and improving construction efficiency.

[0005] In order to achieve the above-mentioned object, according to one aspect of the present invention, there is provided a cofferdam structure suitable for use in a riverbed with large-diameter pebbles, characterized in that it comprises a pebble cofferdam formed by directly filling the pebble stratum in the riverbed, clay soil backfilled in the middle of the pebble cofferdam after connecting a steel casing through a lead hole, and steel sheet piles driven into the clay soil, wherein the steel casing is formed by rolling a steel plate, and a spiral belt made of steel bars is arranged inside the steel casing to assist the sinking of the steel casing and the sinking and compaction of the clay soil;

[0006] The pebble cofferdam and the steel sheet piles together form a containment system that provides structural stability and protection; the clay soil and the steel sheet piles together form an anti-seepage system that prevents moisture from penetrating into the construction area.

[0007] Furthermore, the pebble cofferdam forms an anti-scour protection structural layer, which protects the clay and the steel sheet piles inside the cofferdam from direct impact of water flow in the water, and supports and protects the steel sheet piles.

[0008] Furthermore, the pebble cofferdam is filled with large-diameter pebbles to form an inverted filter layer to protect the clay in the middle and ensure the stability of the middle anti-seepage system.

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

[0010] Furthermore, the steel sheet piles are Larsen steel sheet piles, which are connected by locking joints to form a steel sheet pile cofferdam that is overall strong and has high anti-seepage performance.

[0011] According to another aspect of the present invention, the present invention provides a construction method for a cofferdam in a riverbed with large particle size pebbles, forming the above-mentioned cofferdam structure suitable for a riverbed with large particle size pebbles, characterized in that it comprises the following steps:

[0012] S100: According to the design width and height requirements of the cofferdam, the pebble cofferdam is formed by layering and compacting the cofferdam with local materials in the riverbed pebble stratum by using an excavator;

[0013] S200: Using the filled pebble cofferdam as a construction platform, using a crane to lift the steel casing to the jaws of the pipe rolling machine, clamping it and adjusting the vertical accuracy of the steel casing to meet the construction technical standards, and then using a rotary drilling rig to perform rotary drilling and hole digging;

[0014] S300: After the rotary drilling and leading hole is completed, the steel casing is extended, and then the pipe rolling machine power head is used to pressurize the pipe rolling and sinking the steel casing. During the process, every time the drilling advances about 40cm, the grab device is started to cooperate in taking soil from the casing in time, and the soil is taken out from the steel casing and the bucket is opened to unload the soil until the steel casing reaches the designed depth, and then the soil taking device is removed;

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

[0016] S500: After the clay backfill is completed, the steel sheet pile is inserted into the backfill hole. When inserting and driving, the steel sheet pile is first lifted by a crane, and the lifted steel sheet pile is in a vertical state. A 90-type vibrating hammer is used to complete the pile insertion in sequence along the locking mouth of the previous steel sheet pile;

[0017] S600: Use caulking material to fill the gap in the locking mouth of the steel sheet pile;

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

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

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

[0021] Furthermore, when the guide hole is drilled in step S200, the gap between two adjacent pile holes is 10 to 15 cm.

[0022] Furthermore, in step S500, the bidirectional verticality of the steel sheet pile is ensured to be controlled within 5‰, and if the verticality requirement is not met, the pile is reinserted until it meets the requirements.

[0023] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0024] 1. The cofferdam structure suitable for a riverbed with large grain sizes of pebbles of the present invention is constructed into a pebble cofferdam by using local materials and utilizing the large grain sizes of pebbles in the riverbed to form an anti-scouring protective structural layer, thereby effectively protecting the internal structure of the cofferdam from direct impact of the water flow. A mechanical hole is drilled in the middle of the pebble cofferdam to backfill with clay and steel sheet piles are inserted to form a key anti-seepage layer, thereby further forming a containment system and an anti-seepage system, thereby solving the problems that the construction of traditional steel pipe piles and steel sheet pile cofferdams in riverbeds with large grain sizes of pebbles is difficult, the traditional cofferdam structure is easily affected by the impact of the water flow, and the stability and anti-seepage performance are difficult to ensure, thereby improving the stability and safety, overall sealing and anti-seepage performance of the cofferdam, ensuring a dry construction environment, and promoting efficient construction.

[0025] 2. The anti-seepage system of the cofferdam structure suitable for a riverbed with large-diameter pebbles of the present invention adopts clay soil backfilling, which is convenient for later demolition, improves construction efficiency, and reduces the impact on the river channel and waterway.

[0026] 3. The pebble cofferdam of the present invention, which is suitable for the cofferdam structure in the riverbed with large particle size pebbles, not only serves as a retaining structure layer, but also serves as a working platform, which solves the problem that the traditional method requires additional materials and costs to build a large equipment working platform in the riverbed, and the construction is complicated and inefficient. The use of the pebble cofferdam not only reduces the material cost, but also provides a sufficient working area and carrying capacity as a working platform, which is convenient for the operation of construction equipment and the stacking of materials. The working platform can be adjusted according to the changes in the riverbed terrain, which improves the construction flexibility and efficiency.

[0027] 4. The cofferdam structure of the present invention, which is suitable for use in a riverbed with large-diameter pebbles, utilizes the pebbles existing in the riverbed to form a pebble cofferdam as a pebble filter layer, thereby preventing the middle key anti-seepage layer composed of clay and steel sheet piles in the middle of the cofferdam from being loosened or collapsed by direct water flow impact, thereby protecting the stability and integrity of the anti-seepage layer and extending the service life of the cofferdam.

[0028] 5. The cofferdam structure suitable for use in a riverbed with large-diameter pebbles of the present invention utilizes an outer pebble layer to support and enclose steel sheet piles, thereby solving the problem that a traditional cofferdam structure requires a complex supporting structure to ensure its stability, thereby limiting the working space. The supporting and enclosing 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 suitable for a riverbed with large grain size pebbles is provided with a spiral belt inside, and the design of the spiral belt reduces the resistance of the steel casing to sink, thus facilitating its smooth installation. At the same time, when the back-rubbing pipe rotates, the action of the spiral belt makes the clay soil sink and compact more tightly, thus improving the strength and stability of the backfill soil and further enhancing the anti-seepage performance of the cofferdam. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic cross-sectional structure diagram of a cofferdam structure suitable for use in a riverbed with large-diameter pebbles according to an embodiment of the present invention;

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

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

[0033] Figure 4 This is a schematic diagram of clay soil backfilling in an embodiment of the present invention;

[0034] Figure 5 This is a plan view of a cofferdam in a large-grained pebble formation 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 The present invention is a schematic flow chart of a construction method for a cofferdam in a riverbed with large-diameter pebbles according to an embodiment of the present invention.

[0037] In all the drawings, the same reference numerals represent the same technical features, specifically: 1- riverbed; 2- pebble cofferdam; 3- steel casing; 4- clay soil; 5- steel sheet piles; 6- spiral belt. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present 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 indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0040] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0041] In this patent, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "includes..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0042] like Figure 1 As shown, an embodiment of the present invention provides a cofferdam structure suitable for a riverbed with large-diameter pebbles, comprising a pebble cofferdam 2, a clay 4 backfilled in the middle of the pebble cofferdam 2, and a steel sheet pile 5 driven into the clay 4, wherein:

[0043] The pebble cofferdam 2 is a cofferdam filled with large-size pebbles in the riverbed, and the steel sheet piles 5 are arranged in the middle. The steel sheet piles 5 are connected by locks to ensure the firmness of the overall steel sheet pile cofferdam. The pebble cofferdam 2 and the steel sheet piles 5 together form a containment system, thereby protecting the construction area. On the pebble cofferdam platform, the clay 4 is backfilled after the steel casing 3 is extended by mechanical holes, and the steel sheet piles 5 are inserted as the key anti-seepage layer. The steel sheet piles 5 are connected by locks to ensure sealing, and together with the backfilled clay 4, an anti-seepage system is formed, thereby enhancing the anti-seepage effect. The stability and anti-seepage of the cofferdam structure in the large-size pebble riverbed are achieved by combining the containment system and the anti-seepage system.

[0044] like Figure 1 and Figure 5As shown, the containment system includes a pebble cofferdam 2 and steel sheet piles 5, which provide structural stability and protect the internal structure. The pebble cofferdam 2 is the main component of the cofferdam structure. It uses machinery such as excavators to obtain local materials from the riverbed pebble stratum in the riverbed 1, and uses large-diameter pebbles to fill the pebble cofferdam 2 with a designed height above the water surface to ensure the flood control capacity of the cofferdam. The slope ratio of the two sides of the pebble cofferdam 2 is set to 1:1.5~1:2 according to the construction conditions, which not only ensures the stability of the structure, but also facilitates the construction operation. The pebbles of the pebble cofferdam 2 come from the existing riverbed, which are easy to obtain and have low cost. It mainly plays the following roles:

[0045] (1) The pebble cofferdam 2 is constructed by filling the existing riverbed with pebbles as an anti-scour protection structure layer, which effectively protects the clay 4 and the steel sheet piles 5 inside the cofferdam from direct impact of the water flow, reduces the influence of water pressure on the internal structure, and ensures the stability and safety of the structure.

[0046] (2) The pebble cofferdam 2 is mainly a cofferdam filled with large-size pebbles, thereby forming an anti-filtration layer. As an anti-filtration layer of the intermediate clay layer, it can prevent the clay 4 from being directly washed away by water flow, thereby protecting the backfill clay 4, enhancing the anti-seepage sealing of the structure, and ensuring the internal stability of the cofferdam.

[0047] (3) The pebble cofferdam 2 can be used as a construction access road for the entire enclosure structure construction, providing a working platform for the construction of the inner area of ​​the cofferdam. It has a good bearing capacity and can bear 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, clay backfilling, and steel sheet pile insertion. The working platform can be adjusted according to changes in the riverbed terrain to ensure that a flat construction platform can be formed on irregular ground.

[0048] like Figure 6 As shown, the steel sheet pile 5 is a Larsen steel sheet pile, which is arranged in the middle of the pebble cofferdam 2. They are connected by a lock to form an integrally firm steel sheet pile cofferdam, thereby improving the overall stability of the cofferdam. At the same time, the pebble cofferdam 2 supports and protects the steel sheet pile 5, freeing up more working space and solving the problem of complex internal supporting structure of the steel sheet pile and limited working space.

[0049] like Figure 1 , Figure 4 and Figure 5As shown, the anti-seepage system includes clay 4 and steel sheet piles 5, which are used to ensure that water outside the cofferdam will not easily penetrate in. On the working platform formed by the pebble cofferdam 2, a mechanical hole is used to cooperate with a pipe rolling machine to press down the steel casing 3 to rotate and cut the riverbed, and the clay 4 is backfilled after taking soil with a grab bucket. Finally, the steel sheet piles 5 are inserted into the clay 4 to form a key anti-seepage layer to ensure that the inside of the cofferdam is not affected by water penetration.

[0050] like Figure 2 As shown, the steel casing 3 is rolled from a 12mm thick steel plate, with a length of 6m and a diameter of 0.8m. When in use, multiple sections of the steel casing 3 are connected and used as a guide device during the rotary excavation of the riverbed to ensure that the drill bit can accurately penetrate the riverbed stratum along the predetermined path. At the same time, it also plays a role in protecting the borehole to prevent the hole wall from collapsing due to external pressure or changes in geological conditions during the rotary excavation process. A spiral belt 6 made of a 5cm wide steel bar is arranged inside the steel casing 3, which helps the steel casing 3 to cut into the riverbed stratum when rotating in the forward direction, and reduces resistance by cutting the soil during the sinking process, thereby promoting the smooth installation of the steel casing 3; and when the steel casing 3 is pulled up by reverse rotation, it can help the soil sink, and effectively help compact the soil, thereby improving the strength of the clay 4 in the hole.

[0051] The clay soil 4 has good anti-seepage performance to ensure the sealing of the cofferdam structure and prevent water penetration. The clay soil 4 is backfilled into the steel casing 3 in layers and compacted in layers using a punching device to enhance the sealing performance.

[0052] like Figure 6 As shown, the steel sheet piles 5 are Larsen steel sheet piles, and the steel sheet piles are connected by locks, thereby ensuring the integrity and sealing of the steel sheet pile cofferdam and improving the anti-seepage effect.

[0053] The cofferdam structure of the invention utilizes large-size pebbles in the riverbed 1 to build a pebble cofferdam 2 above the water surface, forming a stable retaining structure to resist the impact of water flow and provide a solid construction platform. Mechanical drilling operations are carried out on the pebble cofferdam platform, and a steel casing 3 with a spiral belt 6 is used as a guide device to rotate and press down deep into the riverbed stratum. Then, clay with good anti-seepage performance is backfilled and compacted in layers. Finally, steel sheet piles 5 are inserted to ensure that they are closely combined with the clay to form an efficient anti-seepage layer. At the same time, the stability of the retaining system is further enhanced, providing a safe and reliable working environment for subsequent underwater projects such as pile foundations and piers.

[0054] Embodiment 2:

[0055] like Figure 7 As shown, the embodiment of the present invention provides a construction method for a cofferdam in a riverbed with large-diameter pebbles, and the specific steps are as follows:

[0056] Step 1: Prefabrication of steel casing and installation of spiral belt: Use high-quality steel plates with a thickness of 12mm to ensure that the steel casing 3 has sufficient strength and durability. The steel plates need to undergo strict quality inspection to ensure their performance in complex construction environments. Use a professional plate rolling machine to accurately roll the steel plates into a cylindrical steel casing with a length of 6m and a diameter of 0.8m. Ensure dimensional accuracy during the rolling process to prevent deformation or dimensional errors. The rolled steel casing is firmly welded to ensure that there are no gaps at each joint. Use 5cm wide high-strength steel bars to evenly weld and arrange the spiral belt on the inner wall of the steel casing. The spacing and angle of the spiral belt are precisely adjusted according to the design requirements to optimize the auxiliary effect during the sinking and earth extraction process.

[0057] Step 2: Pebble cofferdam filling: First, conduct a detailed geological survey and assessment of the pebble resources in the riverbed strata to ensure that the selected materials meet the project requirements. Prepare large machinery such as excavators and loaders to efficiently transport and fill the pebbles.

[0058] According to the design width and height requirements of the cofferdam, the cofferdam is formed by filling with large-diameter pebbles from the riverbed pebble stratum. During construction, attention should be paid to layered filling and layered compaction to ensure that each layer of pebbles reaches the optimal density, thereby improving the overall stability and bearing capacity of the cofferdam.

[0059] Step 3: Drilling construction: In order to ensure the construction accuracy of the steel casing, a rotary drilling rig with a 0.6m diameter drill bit is used to drill the hole when the first section of the steel casing is buried. The filled pebble cofferdam is used as a construction platform, and the steel casing 3 is vertically lifted into the jaws of the pipe rolling machine by a crane and clamped. Then, the pipe rolling machine is adjusted to make the vertical accuracy of the steel casing meet the construction technical standards before the rotary drilling rig is used to drill the drill hole.

[0060] When using a rotary drilling rig for rotary drilling and boring, the bite distance between two adjacent pile holes is 10-15cm, and the boring depth is 4-5m. A high-performance rotary drilling rig equipped with a 0.6m diameter drill bit is selected to ensure that the drill bit can effectively penetrate the complex pebble layer and maintain good boring quality. The drilling speed and depth are strictly controlled according to the design parameters, and the bite distance between adjacent pile holes is set to 10-15cm to ensure that the inserted steel sheet piles form a continuous and solid overall structure underground, while avoiding excessive interference with the surrounding stratum structure. During the entire boring process, a professional monitoring system is equipped to monitor the drilling situation in real time, adjust the drilling parameters in time, and ensure construction safety and quality.

[0061] Step 4: Casing sinking and synchronous soil extraction: After the rotary drilling and leading hole is completed, the steel casing is extended. The steel casing 3 is pressed down by the forward and reverse rotation of the pipe rolling machine power head and the pressure cylinder. The spiral belt 7 of the steel casing 3 cuts the soil under the forward rotation to help the steel casing enter the clay layer more smoothly, so that the steel casing 3 cuts into the clay layer of the riverbed stratum. During the process, every time the drilling depth is about 40cm, the grab device is started to cooperate with the soil extraction from the casing in time to reduce the sinking resistance of the steel casing 3. The soil cut by the grab bucket teeth is contained in the bucket body, and then it is lifted out of the steel casing 3 and the bucket is opened to unload the soil. When encountering obstacles in the underground hole, it is necessary to use a rotary drilling rig to assist in clearing the obstacles. When the steel casing 3 reaches the designed depth, the soil extraction device is removed. Environmental protection requirements must be paid attention to during the process to ensure that the abandoned soil is reasonably stacked and does not cause environmental pollution.

[0062] Step 5: Backfill and compaction of clay soil in casing: Select appropriate clay soil according to engineering requirements, and ensure that its key performance indicators such as plasticity index, liquid limit, and plastic limit meet the standards to achieve an ideal anti-seepage effect. Use an excavator to fill the pre-prepared clay soil into the steel casing 3, and backfill the clay soil every time the steel casing is lifted by 50cm in the reverse rotation to better control the backfill quality and progress. During the backfilling process, it is carried out in layers, and the backfilled clay soil is compacted by stamping equipment to ensure that each layer of soil can achieve the best density. During the compaction process, attention should be paid to uniform force to avoid local overpressure or underpressure. When the clay soil is backfilled to the top of the cofferdam, the steel casing 3 is twisted upward and smoothly removed using a pipe twisting machine. When the steel casing is lifted by reverse rotation, the internal spiral belt 6 helps to make the soil sink more tightly, thereby improving the compaction and stability of the backfill soil in 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 can be rubbed left and right to make the soil sink, and a series of physical and chemical reactions will occur between the cement and the soil to harden the soft soil and increase the density of the backfill soil in the hole.

[0064] Step 6: Steel sheet pile insertion: After the clay soil 4 is backfilled, the steel sheet pile 5 is inserted into the backfill hole. When inserting and driving, the steel sheet pile 5 is first lifted by a crane and arranged in strict accordance with the design requirements. During the lifting process, special attention should be paid to maintaining the verticality of the steel sheet pile to prevent the difficulty of insertion and driving or affect the quality of the project due to tilt. When the steel sheet pile 5 is lifted in a vertical state, a 90-type vibrating hammer is used to insert a new pile along the lock of the previous steel sheet pile 5 to ensure that the bidirectional verticality of the steel sheet pile 5 is controlled within 5‰. For steel sheet piles that do not meet the verticality requirements, the insertion and driving must be stopped immediately and the position must be readjusted until it is qualified. After the insertion and driving is completed, carefully check the lock connection between the steel sheet piles to ensure that it is airtight and leak-free to enhance the water-stopping effect of the entire cofferdam structure.

[0065] Step 7: Locking caulking and overall sealing: Select slats, cotton wool and other materials with good elasticity and weather resistance as caulking materials, wedge them into the locking mouth of the steel sheet pile to fill any gaps.

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

[0067] After pumping water from the cofferdam to form a dry working platform and completing the construction of pile foundations, piers, etc., the cofferdam is dismantled in accordance with the principles of environmental protection, safety and efficiency. Special equipment such as vibrating hammers and hydraulic pile pullers are used to pull steel sheet piles out of the clay soil, and the pebbles and clay soil backfill in the cofferdam are cleaned. The recyclable pebbles are used for riverbed leveling or other projects.

[0068] As described in the above embodiments, the construction of cofferdams under different pebble riverbed conditions can be achieved, the flexibility, adaptability and efficiency of the construction can be improved, and the safety and quality of the construction process can be ensured.

[0069] It will be easily understood by those skilled in the art that the above description is only 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 in the protection scope of the present invention.

Claims

1. A cofferdam structure suitable for use in a riverbed with large-diameter pebbles, characterized in that: The invention comprises a pebble cofferdam (2) formed by directly filling the pebble stratum in the riverbed, a clay soil (4) backfilled in the middle of the pebble cofferdam (2) after a steel casing (3) is connected through a lead hole, and a steel sheet pile (5) is inserted into the clay soil (4); the steel casing (3) is formed by rolling a steel plate, and a spiral belt (6) made of steel strips is arranged inside the steel casing to assist the sinking of the steel casing (3) and the sinking and compaction of the clay soil (4); The pebble cofferdam (2) and the steel sheet piles (5) together form a containment system that provides structural stability and protection; the clay soil (4) and the steel sheet piles (5) together form an anti-seepage system that prevents moisture from penetrating into the construction area.

2. The cofferdam structure suitable for use in a riverbed with large-diameter pebbles according to claim 1 is characterized in that: The pebble cofferdam (2) forms an anti-scour protection structural layer, protecting the clay (4) and the steel sheet piles (5) inside the cofferdam from direct impact by water flow in the water, and supporting and protecting the steel sheet piles (5).

3. A cofferdam structure suitable for use in a riverbed with large-diameter pebbles according to claim 2, characterized in that: The pebble cofferdam (2) is filled with large-diameter pebbles to form an inverted filter layer, which protects the clay soil (4) in the middle and ensures the stability of the middle anti-seepage system.

4. A cofferdam structure suitable for use in a riverbed with large-diameter pebbles according to claim 3, characterized in that: The pebble cofferdam (2) forms an operating platform for the construction of the entire enclosure structure and the inner area of ​​the cofferdam, and the operating platform can be adjusted according to changes in the riverbed topography.

5. A cofferdam structure suitable for use in a riverbed with large-diameter pebbles according to any one of claims 1 to 4, characterized in that: The steel sheet piles (5) are Larsen steel sheet piles, which are connected by locking joints to form a steel sheet pile cofferdam that is overall strong and has high anti-seepage performance.

6. A method for constructing a cofferdam in a riverbed with large pebble grains, forming a cofferdam structure suitable for a riverbed with large pebble grains as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: S100: According to the design width and height requirements of the cofferdam, the pebble cofferdam is formed by layering and compacting the cofferdam with local materials in the riverbed pebble stratum by using an excavator; S200: Using the filled pebble cofferdam as a construction platform, using a crane to lift the steel casing to the jaws of the pipe rolling machine, clamping it and adjusting the vertical accuracy of the steel casing to meet the construction technical standards, and then using a rotary drilling rig to perform rotary drilling and hole digging; S300: After the rotary drilling and leading hole is completed, the steel casing is extended, and then the pipe rolling machine power head is used to pressurize the pipe rolling and sinking the steel casing. During the process, every time the drilling advances about 40cm, the grab device is started to cooperate in taking soil from the casing in time, and the soil is taken out from the steel casing and the bucket is opened to unload the soil until the steel casing reaches the designed depth, and then the soil taking device is removed; S400: The pipe rolling machine rotates in the opposite direction to lift the steel casing. Every time 50 cm is pulled out, the clay soil is backfilled with an excavator and compacted with a stamping device until the clay soil is backfilled to the top of the pebble cofferdam; S500: After the clay backfill is completed, the steel sheet pile is inserted into the backfill hole. When inserting and driving, the steel sheet pile is first lifted by a crane, and the lifted steel sheet pile is in a vertical state. A 90-type vibrating hammer is used to complete the pile insertion in sequence along the locking mouth of the previous steel sheet pile; S600: Use caulking material to fill the gap in the locking mouth of the steel sheet pile; S700: Repeat the above steps to complete the closing of the pebble steel sheet pile cofferdam, conduct a comprehensive quality inspection to ensure the safety and stability of the structure, and complete the construction of the cofferdam in the large-diameter pebble riverbed.

7. A method for constructing a cofferdam in a riverbed of large-diameter pebbles according to claim 6, characterized in that: Before step S100, it also includes selecting high-quality steel plates and using a professional plate rolling machine to accurately roll the steel plates into cylindrical steel casings, and using 5 cm wide high-strength steel strips to evenly arrange spiral strips on the inner wall of the steel casing.

8. A method for constructing a cofferdam in a riverbed of large-diameter pebbles according to claim 6, characterized in that: The pebble cofferdam slope constructed in step S100 forms a slope ratio of 1:1.5 to 1:

2.

9. A method for constructing a cofferdam in a riverbed of large-diameter pebbles according to claim 6, characterized in that: When the guide hole is drilled in step S200, the gap between two adjacent pile holes is 10 to 15 cm.

10. A method for constructing a cofferdam in a riverbed of large-diameter pebbles according to claim 6, characterized in that: In step S500, the bidirectional verticality of the steel sheet pile is ensured to be controlled within 5‰. If the verticality requirement is not met, the pile is reinserted until it meets the requirements.

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