Segmental interlocking combined steel sheet pile cofferdam construction method

Abstract

The present application relates to the cofferdam construction technical field, especially segmental interlocking combined steel sheet pile cofferdam construction method, including the steps of clearing obstacles, measuring and lofting, earth filling conical operation platform, inserting and driving steel sheet pile, soil reinforcement, auxiliary engineering, cofferdam building, cofferdam removal, which is used for the flat terrain in southeast region, grade II and III inland waterway, can quickly form a barrier to the river, and has short construction period.

Description

Technical Field

[0001] This invention relates to the field of cofferdam construction technology, and in particular to a construction method for segmented interlocking combined steel sheet pile cofferdams. Background Technology

[0002] Cofferdams are common temporary engineering works used in river management and pumping station projects to create dry construction conditions. Traditional earthen cofferdams have large cross-sections and occupy a large area, requiring a large amount of soil to be extracted and piled up in the early stage, and a large amount of surplus soil to be disposed of in the later stage. The load changes significantly before and after construction, so their application is limited when there are important buildings nearby and the soil source is limited. Steel sheet pile cofferdams are more commonly used in Shanghai due to their simple structure, small cross-section, and small footprint.

[0003] The piles of steel sheet pile cofferdams are generally U-shaped Larssen steel sheet piles, which include a U-shaped main body and interlocking joints integrally formed on both sides of the main body. Two adjacent Larssen steel sheet piles are positioned and connected through the interlocking joints, and at the same time, the interlocking joints are used to block water and mud.

[0004] To ensure the construction quality of sheet pile cofferdams, technicians in this field have developed a construction method for sheet pile cofferdams, which mainly includes the following steps: Step 1, clearing obstacles: remove stones and bricks from the sheet pile construction area and place them outside the construction area; Step 2, surveying and setting out: use a total station to survey and set out the outer edge line of the sheet pile cofferdam; Step 3, constructing a work platform: construct a work platform according to the work location. The work platform can be a masonry platform or a mobile platform such as a vehicle or boat; Step 4, driving sheet piles: drive sheet piles along the surveyed edge line to obtain the main body of the cofferdam; Step 5, dewatering and reinforcement: pump out the water from the main body of the cofferdam and install corbels, walers, and steel tie rods to reinforce the sheet piles; Step 6, construction within the cofferdam: clean the sludge at the bottom of the cofferdam and construct buildings within the main body of the cofferdam; Step 7, dismantling the cofferdam: pour water into the foundation pit, then dismantle the reinforcement structure and pull out the sheet piles.

[0005] In step four, when the cofferdam is a single row of sheet piles, the sheet piles are continuously driven in, and after closure, water is pumped out for reinforcement. Then, the main structure is constructed inside the cofferdam. After the construction is completed, the cofferdam is dismantled. This method is mainly used for the construction of independent structures in water, such as bridge piers. When the cofferdam is a double row of sheet piles, a segmented cofferdam is adopted. The first segment of double-row sheet piles is constructed first, and then soil is filled to form a temporary work platform. The second segment of double-row sheet piles is constructed on the temporary work platform. This cycle continues until the main body of the cofferdam is completed. The foundation pit is excavated inside the main body of the cofferdam, and then the main structure is constructed. This method is mainly used for the construction of water conservancy projects such as sluice gates.

[0006] During the construction of a double-row sheet pile cofferdam, transverse sheet piles are installed between two rows of longitudinal sheet piles to form multiple partitioned cofferdam grids. Soil is then filled into the cofferdam grids, and roads and operating platforms are constructed. This method ensures that the cofferdam can be advanced step by step. The disadvantage is that the construction speed is slow and the cofferdam partitions cannot be formed quickly. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a construction method for segmented interlocking combined steel sheet pile cofferdams.

[0008] This invention is achieved through the following technical solution: a construction method for segmented interlocking combined steel sheet pile cofferdams, comprising the following steps:

[0009] Step 1: Clear obstacles. Remove stones and bricks from the cofferdam construction area and move them outside the construction area.

[0010] Step 2: Measurement and layout. Set up control measurement points on the riverbank land upstream and downstream of the cofferdam that are not affected by construction, and use a total station to measure and lay out the outer edges of the inner and outer rows of combined steel sheet piles.

[0011] Step 3: Fill the cone-shaped working platform with soil. Fill the cone-shaped working platform with soil at the junction of the cofferdam and the riverbank. When filling the soil, advance from the riverbank along the central axis of the composite steel sheet piles towards the center of the river. When filling, make sure that the composite steel sheet piles are smoothly connected to the riverbank.

[0012] Step 4: Drive sheet piles. Larssen sheet piles are used. The sheet piles have interlocking joints on the sides, forming outer and inner sheet piles. The outer and inner sheet piles are distributed alternately. Construction proceeds from one side of the riverbank to the opposite bank piece by piece. After the initial section is completed, steel slabs are fully laid on top of the initial section of sheet piles. The pile driver moves to the top of the sheet piles and proceeds to the opposite bank. At least two rows of sheet piles are constructed, with steel slabs laid between the upper ends of each row of sheet piles.

[0013] Step 5: Backfilling and reinforcement. Starting from the initial section, remove the steel sheet piles section by section, and then backfill with soil. During the backfilling process, drain water from the composite steel sheet piles on the opposite bank until the water level inside the composite steel sheet piles drops by 100cm to prevent the water level inside the composite steel sheet piles from rising during the backfilling process. At the same time, control the pressure of the composite steel sheet piles. When the backfill of this section is higher than the water surface, continue backfilling and compacting to obtain the first plain soil layer. The height of the first plain soil layer is the same as the water level outside the composite steel sheet piles. Backfill and compact the first plain soil layer in 30cm increments. Pre-drill holes for tie rods on the upper side of the steel sheet piles. When the backfill is 5cm away from the holes, install the walers and tie rods in 2m increments. Then, pass the tie rods through the extension arm and the holes on the steel sheet piles, adjust the position, and tighten the nuts to complete the tie rod installation. After the tie rods are installed, continue backfilling and compacting the soil in 30cm increments until the predetermined height is reached to obtain the second plain soil layer.

[0014] Step 6, Ancillary works: The steel slabs are completely removed, a hardened road surface is constructed on the surface of the second subgrade, a wave-breaking plate is constructed on the water-facing side of the hardened road surface, and guardrails are constructed on both sides of the hardened road surface to obtain composite steel sheet piles.

[0015] Step 7: Construction within the cofferdam. Combined steel sheet piles are used to cut off the river channel. When there is a sluice gate upstream of the river, the combined steel sheet piles only need to be constructed downstream of the cofferdam to prevent backflow of downstream river water. When there is no sluice gate upstream of the river, combined steel sheet piles are constructed both upstream and downstream of the cofferdam. After the combined steel sheet piles are constructed, the cofferdam is drained to expose the riverbed. The foundation pit is excavated at the predetermined location, and retaining piles are constructed outside the foundation pit to prevent silt from the riverbed from entering the foundation pit. The foundation is constructed inside the foundation pit, and the functional buildings are constructed on the foundation.

[0016] Step 8: Demolish the combined sheet piles, fill the cofferdam with water to balance the pressure inside and outside the cofferdam, remove the hardened road surface, wave barriers, and guardrails, then lay steel slabs, excavate the second layer of subgrade, remove the tie rods, and then excavate the first layer of subgrade. After all excavation is completed, remove the extension arms and bracket steel plates section by section, and pull out the sheet piles. During construction, first use a pile driver to clamp the head of the sheet pile and vibrate it for 1-2 minutes to loosen the soil around the sheet pile and reduce the soil resistance to the sheet pile, and then slowly vibrate it upwards.

[0017] Furthermore, in step three, the elevation difference between the conical working platform and the top elevation of the cofferdam is within 10cm, allowing the piling machinery to travel from the riverbank to the conical working platform for operation.

[0018] Furthermore, in step four, a mixture of grease is applied to the interlock before driving the sheet piles.

[0019] Furthermore, the initial construction includes the following steps:

[0020] A. First, mark the pile positions on the ground, and then park the pile driver on the conical work platform to drive the piles.

[0021] B. Based on the position of the first side pile, direct the pile driver to move. After positioning, once the first sheet pile is driven into place, control the center line of the subsequent piles to coincide with the center of the first sheet pile.

[0022] C. The robotic arm picks up the steel sheet pile, and the pile-holding worker aligns the pile with the pile position and completes the pile insertion in a vertical state. After the pile is stable, the position and bidirectional verticality of the steel sheet pile are re-measured. If it does not meet the requirements, the pile needs to be re-inserted until it is qualified.

[0023] D. After the first pile is driven into the ground and stabilized, the vibration function of the robotic arm is turned on intermittently to drive the first sheet pile with a small displacement, and the verticality of the pile is tracked and checked until the pile sinks into the ground for more than 3m. Then, it is continuously driven to the set elevation of the pile top + 3.0m.

[0024] E. For subsequent sheet pile driving, insert the sheet pile along the axis of the combined sheet pile and the interlock of the previous sheet pile. After the pile is in place, start the vibration function and drive it to the design elevation in stages.

[0025] Furthermore, positioning piles are constructed before the first sheet pile is driven, and guide supports are installed. There are two positioning piles, and the line connecting the two positioning piles is on the straight line where the sheet piles are located. After the two positioning piles are driven, guide supports are installed between the upper ends of the two positioning piles. The guide supports include an outer guide arm and an inner guide arm, both of which are made of I-beams or channel steel. The outer guide arm and the inner guide arm are parallel. The bottom of the outer sheet pile mates with the outer guide arm, and the bottom of the inner sheet pile mates with the inner guide arm, thereby making the sheet piles in the same row straight. Adjusting pads are installed between the outer guide arm and the positioning pile. The outer guide arm, adjusting pads, inner guide arm and positioning pile are fixed with long bolts. During driving, the back of the sheet pile is close to the guide frame and gradually sinks.

[0026] Furthermore, the construction of the sheet piles in the advance section includes the following steps:

[0027] a. After the pile driver completes the pile construction within the arm span of the conical working platform, a steel slab is fully laid on top of the two rows of steel sheet piles as a temporary working platform. The pile driver then moves to the temporary working platform to carry out pile driving construction.

[0028] b. After the sheet piles within the arm span are completed, continue to lay steel slabs on top of the two rows of completed sheet piles, and construct the next section of sheet piles. Continue to advance towards the opposite bank for construction until all sheet piles are constructed.

[0029] Furthermore, the inner sheet piles are connected with reinforcing structures.

[0030] Furthermore, the reinforcing structure includes an H-beam welded to the inside of the inner sheet pile, and a slot that mates with the H-beam is installed on the inner sheet pile.

[0031] Furthermore, the reinforcing structure includes a curved steel plate with an S-shaped cross-section, one side of which is welded and fixed to the inner middle position of the inner steel sheet pile.

[0032] The beneficial effects of this invention are as follows:

[0033] 1. Applicable to the flat southeastern region, Class II and Class III inland waterways, it can quickly create river barriers with a short construction period.

[0034] 2. The bottom of the outer sheet pile mates with the outer guide arm, and the bottom of the inner sheet pile mates with the inner guide arm, thus making the sheet piles in the same row straight. To control the distance between the outer guide arm and the inner guide arm, an adjustment pad is installed between the outer guide arm and the positioning pile. The adjustment pad is a steel plate, and the thickness value is selected as needed. The outer guide arm, adjustment pad, inner guide arm and positioning pile are fixed with long bolts. When driving, the back of the sheet pile is close to the guide frame and sinks gradually.

[0035] 3. The first soil layer has more contact with water and has poorer compaction. The second soil layer does not contact water and is easier to compact. Furthermore, the construction method of filling and compacting soil layer by layer results in higher resistance to settlement and deformation, thus avoiding cracking of the hardened pavement.

[0036] 4. The thickness of the H-beam is the same as the width of the inner sheet pile, thus forming a triangular pile body. This compensates for the insufficient stiffness of a single sheet pile cofferdam in soft soil layers, strengthens the supporting force of the sheet pile, ensures the stability and safety of the structure, and creates favorable conditions for the subsequent excavation of the foundation pit inside the cofferdam.

[0037] 5. A positioning block is installed on the outer extension arm. The positioning block is a U-shaped block. The waist of the U-shaped block is fixed to the extension arm. When the inner steel sheet pile is driven, the bottom inner side of the inner steel sheet pile fits with the two wing ends of the U-shaped block, thus forming a guide and providing support for the inner steel sheet pile from the outside. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the distribution of composite steel sheet piles;

[0039] Figure 2 A top view of the connection between the positioning pile structure and the guide arm;

[0040] Figure 3 This is a schematic diagram showing the connection between the positioning pile structure and the guide arm;

[0041] Figure 4 This is a schematic diagram of the initial stage of driving steel sheet piles.

[0042] Figure 5 This is a schematic diagram of a steel slab structure.

[0043] Figure 6 This is a schematic diagram of the connecting arm structure;

[0044] Figure 7 This is a schematic diagram of the sheet pile structure after the sheet piles have been driven in.

[0045] Figure 8 This is a top view diagram showing the completed installation of sheet piles.

[0046] Figure 9 This is a schematic diagram of the sheet pile structure after backfilling.

[0047] Figure 10 This is a schematic diagram of the tie rod distribution;

[0048] Figure 11 This is a schematic diagram showing the connection between sheet piles and H-beams;

[0049] Figure 12 This is a schematic diagram of the curved steel plate structure in Example 2.

[0050] The components include: 1. Riverbed; 2. Bank revetment; 3. Foundation pit; 4. Retaining piles.

[0051] 5. Combined sheet piles; 501. Positioning piles; 502. Adjusting pads; 503. Outer guide arm; 504. Inner guide arm; 505. Sheet piles; 506. Fixing bolts; 507. Connecting plates; 508. Locking joints; 509. Extension arms; 510. Steel slabs; 511. Conical work platform; 512. Stop blocks; 513. Positioning blocks; 514. Hardened road surface; 515. First subsoil layer; 516. Second subsoil layer; 517. Tie rods; 518. Angle steel; 519. H-beams; 520. Curved steel plates. Detailed Implementation

[0052] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In the following embodiments,

[0055] The sheet pile 505 is a Larssen sheet pile. The sheet pile 505 has a locking lug 508 on its side. In the same row, two adjacent sheet piles 505 are connected by the locking lug 508 to form an interlock and strengthen the seal.

[0056] The sheet piles 505 consist of two rows, spaced 400-500 cm apart, suitable for Class II and Class III inland waterways. When a steel slab 510 is laid between the upper ends of the two rows of sheet piles 505, the wheels of engineering vehicles can approach and be supported by the sheet piles 505, reducing deformation of the slab 510 and ensuring safety. Downward-facing stops 512 are fixed to both ends of the slab 510, engaging with the outer side of the sheet piles 505 to prevent slippage of the slab 510.

[0057] In the same row, sheet piles 505 form outer sheet piles and inner sheet piles, which are distributed alternately.

[0058] Example 1

[0059] like Figure 1-11 As shown, a construction method for a segmented interlocking composite steel sheet pile cofferdam includes the following steps:

[0060] Step 1, Clearing Obstacles: Remove stones and bricks from the construction area of ​​sheet pile 505 and pile them outside the construction area to prevent the sheet pile 505 from encountering obstacles and being unable to sink when it is being lowered.

[0061] Step 2, Measurement and Layout: Select control measurement points on the riverbank land upstream and downstream of the cofferdam, unaffected by construction, and use a total station to measure and lay out the outer edges of the inner and outer rows of sheet piles 505 of the combined sheet pile 5. During the sinking of the sheet piles 505, two theodolites are used to control the verticality of the sheet piles 505 using the forward intersection method.

[0062] Step 3: Constructing the Conical Working Platform 511 by piling soil at the junction of the composite sheet pile 5 and the riverbank. During soil piling, advance from the riverbank along the central axis of the composite sheet pile 5 towards the center of the river. The elevation difference between the conical working platform 511 and the top elevation of the cofferdam should be within 10cm. The filling length should ensure a smooth connection between the composite sheet pile 5 and the existing riverbank, allowing the piling machinery to travel from the riverbank to the conical working platform 511. The conical working platform 511 should be compacted and stable to meet the bearing capacity requirements of the piling equipment.

[0063] Step 4, driving sheet piles 505: To reduce friction between the interlocks 508 during driving and to reduce leakage in the cofferdam, a mixture of grease and grease is applied to the inside of the interlocks 508 before driving the sheet piles 505. Construction proceeds from one side of the riverbank towards the opposite bank, dividing the combined sheet piles 5 into two sections according to the pile driver's operating position. The section closest to the riverbank (5-8m) is designated as the starting section. The pile driver is positioned on the filled conical operating platform 511, driving each sheet pile individually. After the starting section is completed, a steel slab 510 is fully laid on top of the sheet piles 505 in the starting section. The pile driver then moves to the top of the sheet piles 505 and continues construction towards the opposite bank.

[0064] In this step, the initial section construction includes the following steps:

[0065] A. First, mark the pile positions on the ground, and then park the pile driver on the conical work platform 511 to drive the piles.

[0066] B. Based on the position of the first side pile, direct the pile driver to move. After positioning, once the first pile is driven into place, ensure that the center line of subsequent piles coincides with the center of the first pile;

[0067] C. The robotic arm picks up the steel sheet pile 505, and the pile-holding worker aligns the pile with the pile position, completing the pile insertion in a vertical state. After the pile is stable, the position and bidirectional verticality of the pile are re-measured. If it does not meet the requirements, the pile needs to be re-inserted until it is qualified.

[0068] D. After the first pile is driven into the ground and stabilized, the vibration function of the manipulator is turned on intermittently to drive the first pile with a small displacement and to track and check the verticality of the pile until the pile sinks into the ground for more than 3m. Only then can it be continuously driven to the set elevation of the pile top + 3.0m.

[0069] E. The subsequent sheet piles 505 are driven in sequence along the axis of the combined sheet pile 5 and the interlocking joint 508 of the previous sheet pile 505. After the piles are in place, the vibration function is activated and the piles are driven to the design elevation in stages.

[0070] To ensure the straightness of the sheet piles 505, positioning piles 501 are constructed before the first sheet pile 505 is installed, along with guide supports. Specifically, there are two positioning piles 501, and the line connecting the two positioning piles 501 lies on the straight line of the row of sheet piles 505. After the two positioning piles 501 are driven in, guide supports are installed between their upper ends. The guide supports include an outer guide arm 503 and an inner guide arm 504, both made of I-beams or channel steel, and are parallel to each other. The bottom of the outer sheet pile mates with the outer guide arm 503, and the bottom of the inner sheet pile mates with the inner guide arm 504, thus ensuring the straightness of the sheet piles 505 in the same row. To control the distance between the outer guide arm 503 and the inner guide arm 504, an adjusting shim 502 is installed between the outer guide arm 503 and the positioning pile 501. The adjusting shim 502 is made of steel plate, and the thickness is selected as needed. The outer guide arm 503, adjusting shim 502, inner guide arm 504, and positioning pile 501 are fixed with long bolts. During driving, the back of the sheet pile 505 is close to the guide frame and gradually sinks. At this time, theodolites are used to observe in two mutually perpendicular directions to ensure that the sheet pile 505 is inserted straight and upright.

[0071] The construction of the 505 sheet piles in the advance section includes the following steps:

[0072] a. After the pile driver completes the pile construction within the arm extension range on the conical working platform 511, a steel slab 510 is fully laid on top of the two rows of steel sheet piles 505 as a temporary working platform. The pile driver then moves to the temporary working platform to carry out pile driving construction.

[0073] b. After the sheet piles 505 within the arm's span are completed, continue laying steel slabs 510 on top of the two completed rows of sheet piles 505, and then construct the next section of sheet piles 505. This process is repeated until all sheet piles 505 are completed. During the driving of the sheet piles 505, a total station is used for tracking and measurement to check the deviation of the sheet piles 505 at any time. When a sheet pile 505 deviates, it is corrected promptly using a chain hoist. When a sheet pile 505 deviates, it is pulled upwards by 1.0-2.0m and then driven downwards, repeating this up-and-down motion several times to correct its position. If the deviation is too large to be corrected with a chain hoist, it is pulled out and re-inserted. During this process, the inner guide arm 504 and the outer guide arm 503 are connected to an extension arm 509 on the same straight line, which guides the sheet piles 505. After the sheet pile 505 is inserted, the extension arm 509 is fixed to the sheet pile 505 by fixing bolt 506, and then the next extension arm 509 is connected until the sheet pile 505 is driven in.

[0074] Step 5, Soil Filling and Reinforcement: Excavators are used to excavate and load soil, and 5-ton dump trucks transport the soil to the construction site. During underwater soil filling, construction proceeds from the initial section towards the opposite bank. After each layer of soil is laid on the composite sheet piles 5, it is compacted to prevent leakage and enhance the overall integrity of the dam. Areas that cannot be compacted by rolling are tamped using electric rammers or manually. During the filling process, water is drained from inside the composite sheet piles 5 on the opposite bank until the water level inside the composite sheet piles 5 drops by 100cm. Starting from the initial section, the steel sheet piles 510 are removed section by section, and then soil is filled to prevent the water level inside the composite sheet piles 5 from rising during the filling process, while controlling the pressure of the composite sheet piles 5. When the fill in this section is above the water surface, filling and compaction continue to obtain the first plain soil layer 515. The height of the first plain soil layer 515 is the same as the water level outside the composite sheet piles 5. On the first plain soil layer 515, soil is filled and compacted in 30cm layers. Pre-drill holes for tie rods 517 on the upper side of the sheet piles 505. When the backfill is 5cm from the hole, install the walers and tie rods 517 in 2m increments. In this embodiment, the extension arm 509 forms the walers, connecting the two rows of sheet piles 505 to form a whole. The tie rods 517 are made of Φ42mm round steel, and each end of each tie rod 517 is anchored with two high-strength nuts. A 20mm thick Q235 trapezoidal bracket steel plate (not shown in the figure) is installed on the lower edge of the extension arm 509. The bracket steel plate is welded to the sheet piles 505, and the weld thickness is not less than 8mm. Mark the installation position of the trapezoidal bracket steel plate vertically downwards 110mm from the center of the hole. Then, check whether the positions of each hole and the installation position of the trapezoidal bracket steel plate are on the same baseline by pulling a line. Adjust any that do not meet the requirements to ensure that the axial deviation is controlled within 10mm. Weld the cut trapezoidal bracket steel plates to the marked installation positions. Before welding, thoroughly clean the welding area of ​​rust, oil, and other debris. The welded trapezoidal bracket steel plates must be inspected on-site by the quality inspector according to the "Code for Acceptance of Construction Quality of Steel Structures" GB50205-2020, and there should be no twisting, incomplete welding, or other defects. Use a crane to lift the extension arm 509 onto the installed trapezoidal bracket steel plate. Then, pass the tie rod 517 through the openings on the extension arm 509 and the sheet pile 505, adjust the position, and tighten the nut to complete the installation of the tie rod 517.

[0075] After installing tie rod 517, continue filling soil in 30cm layers, compacting it until the predetermined height is reached, resulting in the second subgrade layer 516. The first subgrade layer 515 has more contact with water and thus lower density; the second subgrade layer 516 does not contact water and is easier to compact. This layer-by-layer filling and compaction method results in higher resistance to settlement and deformation, thereby preventing cracking of the hardened pavement 514.

[0076] For the conical slopes at both ends of the composite sheet pile 5, an excavator is used to spread the soil and shape it, followed by manual cleaning and leveling of the dam slope to ensure that the straightness, slope, and flatness of the slope meet the requirements. When the compaction of a local slope does not meet the design requirements, manual tamping should be used. After tamping, a geomembrane is laid on top, ensuring it is laid tightly against the dam slope, maintaining a natural flatness and moderate tightness. The geomembrane joints are overlapped, with an overlap width of at least 30 cm. The overlap joints should be longitudinal joints along the slope direction; horizontal joints are prohibited. The geomembrane should extend at least 1 m into the dam body. Laying personnel should wear soft-soled shoes to avoid damaging the geomembrane. After laying, a layer of concrete is poured to prevent water erosion of the dam foundation soil, thereby avoiding affecting the stability of the composite sheet pile 5. Backfilling is carried out section by section. After the previous section is backfilled, steel slabs 510 are laid before proceeding to the next section of backfilling.

[0077] Step Six, Ancillary Works: The steel slab 510 is completely dismantled, and a hardened road surface 514 is constructed on the upper surface of the second subgrade soil layer 516 to allow engineering vehicles to pass through during construction within the cofferdam. Wave-breaking slabs are constructed on the water-facing side of the hardened road surface 514, and guardrails are constructed on both sides of the hardened road surface 514 to obtain the composite steel sheet piles 5.

[0078] Step 7, Construction within the Cofferdam: Combined sheet piles 5 will cut off the river channel. When there is a sluice gate upstream, the combined sheet piles 5 only need to be constructed downstream of the cofferdam to prevent backflow of downstream river water. When there is no sluice gate upstream, combined sheet piles 5 will be constructed both upstream and downstream of the cofferdam. After the combined sheet piles 5 are completed, the cofferdam will be drained, exposing the riverbed 1. A foundation pit 3 will be excavated at the predetermined location, and a retaining cofferdam will be constructed outside the foundation pit 3. Retaining piles 4 will prevent silt from the riverbed 1 from entering the foundation pit 3. The foundation will be constructed within the foundation pit 3, and functional structures such as pump gates will be built on the foundation.

[0079] Step 8, Cofferdam Removal: Water is pumped into the cofferdam to balance the pressure inside and outside. The hardened road surface 514, wave barriers, guardrails, and other ancillary structures are removed, and then steel slabs 510 are laid. The second subgrade layer 516 is excavated, tie rods 517 are removed, and then the first subgrade layer 515 is excavated. After all excavation is completed, the extension arm 509 and bracket steel plates are removed section by section, and the sheet piles 505 are pulled out. During construction, the sheet pile head is first clamped with a pile driver and vibrated for 1-2 minutes to loosen the soil around the sheet pile 505, causing "liquefaction" and reducing the soil resistance to the sheet pile 505. Then, it is slowly pulled upwards. When pulling the pile, attention is paid to the load on the pile driver. If it is difficult to pull upwards or cannot be pulled out, the pulling should be stopped, paused for 1-2 minutes, then the pile is driven down 10-20cm, and then pulled upwards again to extract the pile.

[0080] The construction method of the segmented interlocked combined steel sheet pile cofferdam provided in this embodiment is particularly applicable to the river channels in the southeastern region with gentle terrain. Since the elevation difference between the upstream and downstream of the cofferdam is small, when the upstream sluice is closed, the water level drop at the cofferdam is also small. Constructing the combined steel sheet pile 5 downstream of the cofferdam can prevent the backflow of the downstream river water. Due to the gentle terrain of the riverbed 1 and the deep silt layer of the riverbed 1, the steel sheet pile 505 is prone to tilt. In this embodiment, the inner steel sheet pile is connected with a reinforcement structure, and the reinforcement structure includes the H-shaped steel 519 welded on the inner side of the inner steel sheet pile. A card slot matching with the H-shaped steel 519 is installed on the inner steel sheet pile. Two angle steels 518 are welded on the inner side of the inner steel sheet pile. The angle steels 518 are distributed close to the edge of the inner steel sheet pile, and a card slot is formed between the two angle steels 518. After the card slot is installed, the weld is polished and then an anti-rust layer is coated. An H-shaped steel 519 with a length of about 2m is used as a standard block. The standard block is inserted into the card slot, and then the H-shaped steel 519 is pulled by a winch to move horizontally in the card slot, from the end of the card slot to the tail of the card slot. If it passes smoothly without jamming, the card slot is qualified. The card slot extends upward to the upper end of the inner steel sheet pile, and the ratio of the length value of the card slot to the length value of the steel sheet pile 505 is 1:1-3, so as to guide the H-shaped steel 519 in the initial stage. During the pile insertion process, part of the card slot is inserted into the soil layer.

[0081] During the test, an attempt was made to directly weld and fix the reinforcement structure to the inner steel sheet pile to shorten the pile insertion cycle. It was found during the test that when the reinforcement structure was pre-fixed to the inner steel sheet pile, the pile insertion resistance increased, and the inner steel sheet pile was no longer flat. The vibration also weakened the effect of pile insertion, resulting in the inner steel sheet pile being unable to sink stably to the predetermined elevation. Later, the card slot form was adopted. During the pile insertion process, the inner steel sheet pile was first sunk to the predetermined elevation, and then the H-shaped steel 519 was inserted. Since the nearby soil layer was loosened by vibration during the sinking process of the inner steel sheet pile, the resistance of the H-shaped steel 519 during the sinking process decreased. In this embodiment, the thickness value of the H-shaped steel 519 is the same as the width value of the inner steel sheet pile, so as to form a triangular pile body, compensating for the problem of insufficient stiffness of a single steel sheet pile cofferdam in soft soil layers, strengthening the supporting force of the steel sheet pile 505, ensuring the stability and safety of the structure, and creating favorable conditions for the subsequent excavation of the foundation pit 3 inside the cofferdam.

[0082] The angle steels 518 are located on both sides of the inner steel sheet pile, which can avoid interference when the manipulator grabs the steel sheet pile 505.

[0083] Due to the introduction of the reinforcement structure, the inner steel sheet pile cannot fit with the extension arm 509 during the pile driving process. To ensure the guiding effect on the inner steel sheet pile, a positioning block 513 is installed on the outer extension arm 509. In this embodiment, the positioning block 513 is a U-shaped block, and the waist of the U-shaped block is fixed to the extension arm 509. When driving the inner steel sheet pile, the inner side of the bottom of the inner steel sheet pile fits with the two wing ends of the U-shaped block, thus forming a guide and providing support for the inner steel sheet pile from the outside.

[0084] The segmented interlocking combined steel sheet pile cofferdam construction method provided in this embodiment is applicable to the flat terrain of the southeast region and Class II and Class III inland waterways. It can quickly form a river barrier with a short construction period.

[0085] Example 2

[0086] like Figure 12 As shown, a segmented interlocking composite sheet pile cofferdam construction method differs from Example 1 in that, during testing, a curved steel plate 520 with an S-shaped cross-section was also attempted as a reinforcing structure. One side of the curved steel plate 520 was welded and fixed to the inner middle of the inner sheet pile. Due to the elastic deformation of the curved steel plate 520 itself, during pile insertion and extraction, the curved steel plate 520 transmitted vibrations to the soil layer, thus preventing a significant increase in resistance during pile insertion and extraction. During use, the curved steel plate 520 extends into the backfill layer, reinforcing the support force of the inner sheet pile and buffering shear forces from the side. The disadvantage is that the connection between the curved steel plate 520 and the inner sheet pile is relatively weak.

[0087] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method for segmented interlocking composite steel sheet pile cofferdams, characterized in that, Includes the following steps, Step 1: Clear obstacles. Remove stones and bricks from the cofferdam construction area and move them outside the construction area. Step 2: Measurement and layout. Set up control measurement points on the riverbank land upstream and downstream of the cofferdam that are not affected by construction, and use a total station to measure and lay out the outer edges of the inner and outer rows of combined steel sheet piles. Step 3: Fill the cone-shaped working platform with soil. Fill the cone-shaped working platform with soil at the junction of the combined steel sheet pile and the riverbank. When filling the soil, move from the riverbank along the central axis of the combined steel sheet pile towards the center of the river. When filling, make sure that the combined steel sheet pile and the riverbank are smoothly connected. Step 4: Drive sheet piles. Larssen sheet piles are selected. The sheet piles have interlocking joints on the sides, forming outer and inner sheet piles, which are distributed alternately. Before the first sheet pile is constructed, positioning piles are constructed and guide supports are installed. The guide supports include outer and inner guide arms, which are connected to an extension arm in a straight line. The extension arm guides the sheet piles. Construction proceeds from one side of the riverbank to the opposite bank piece by piece. After the initial section is completed, steel slabs are fully laid on top of the initial section of sheet piles. The pile driver moves to the top of the sheet piles and proceeds to the opposite bank. At least two rows of sheet piles are constructed, with steel slabs laid between the upper ends of each row of sheet piles. Step 5: Backfilling and reinforcement. Starting from the initial section, remove the steel sheet piles section by section, and then backfill with soil. During the backfilling process, drain water from the composite steel sheet piles on the opposite bank until the water level inside the composite steel sheet piles drops by 100cm to prevent the water level inside the composite steel sheet piles from rising during the backfilling process. At the same time, control the pressure of the composite steel sheet piles. When the backfill of this section is higher than the water surface, continue backfilling and compacting to obtain the first plain soil layer. The height of the first plain soil layer is the same as the water level outside the composite steel sheet piles. Backfill and compact the first plain soil layer in 30cm increments. Pre-drill holes for tie rods on the upper side of the steel sheet piles. When the backfill is 5cm away from the holes, install the walers and tie rods in 2m increments. Then, pass the tie rods through the extension arm and the holes on the steel sheet piles, adjust the position, and tighten the nuts to complete the tie rod installation. After the tie rods are installed, continue backfilling and compacting the soil in 30cm increments until the predetermined height is reached to obtain the second plain soil layer. Step 6, Ancillary works: The steel slabs are completely removed, a hardened road surface is constructed on the surface of the second subgrade, a wave-breaking plate is constructed on the water-facing side of the hardened road surface, and guardrails are constructed on both sides of the hardened road surface to obtain composite steel sheet piles. Step 7: Construction within the cofferdam. Combined steel sheet piles are used to cut off the river channel. After the combined steel sheet piles are completed, the cofferdam is drained to expose the riverbed. A foundation pit is excavated at the preset location, and the foundation is constructed in the foundation pit. Functional buildings are then constructed on the foundation. Step 8: Remove the combined steel sheet piles, pour water into the cofferdam to balance the pressure inside and outside the cofferdam, remove the hardened road surface, wave shield, and guardrail, then lay the steel slab, excavate the second plain soil layer, remove the tie rods, then excavate the first plain soil layer. After all excavation is completed, remove the extension arm section by section and pull out the steel sheet piles.

2. The construction method for segmented interlocking combined steel sheet pile cofferdams according to claim 1, characterized in that, In step three, the elevation difference between the conical working platform and the top elevation of the cofferdam is within 10cm, allowing the piling machinery to travel from the riverbank to the conical working platform for operation. In step seven, when there is a sluice gate upstream of the river, the composite sheet piles only need to be constructed downstream of the cofferdam to prevent backflow of downstream river water. When there is no sluice gate upstream of the river, composite sheet piles are constructed both upstream and downstream of the cofferdam, and retaining piles are constructed outside the foundation pit to prevent silt from the riverbed from entering the foundation pit. In step eight, during construction, the head of the sheet pile is first clamped with a pile driver and vibrated for 1-2 minutes to loosen the soil around the sheet pile and reduce the resistance of the soil to the sheet pile. Then, it is slowly vibrated upwards.

3. The construction method for segmented interlocking combined steel sheet pile cofferdams according to claim 1, characterized in that, In step four, before driving the sheet piles, apply a mixture of grease and grease to the interlock.

4. The construction method for segmented interlocking combined steel sheet pile cofferdams according to claim 1, characterized in that, The initial construction includes the following steps: A. First, mark the pile positions on the ground, and then park the pile driver on the conical work platform to drive the piles. B. Based on the position of the first side pile, direct the pile driver to move. After positioning, once the first sheet pile is driven into place, control the center line of the subsequent piles to coincide with the center of the first sheet pile. C. The robotic arm picks up the steel sheet pile, and the pile-holding worker aligns the pile with the pile position and completes the pile insertion in a vertical state. After the pile is stable, the position and bidirectional verticality of the steel sheet pile are re-measured. If it does not meet the requirements, the pile needs to be re-inserted until it is qualified. D. After the first pile is driven into the ground and stabilized, the vibration function of the robotic arm is turned on intermittently to drive the first sheet pile with a small displacement, and the verticality of the pile is tracked and checked until the pile sinks into the ground for more than 3m. Then, it is continuously driven to the set elevation of the pile top + 3.0m. E. For subsequent sheet pile driving, insert the sheet pile along the axis of the combined sheet pile and the interlock of the previous sheet pile. After the pile is in place, start the vibration function and drive it to the design elevation in stages.

5. The construction method for segmented interlocking combined steel sheet pile cofferdams according to claim 4, characterized in that, There are two positioning piles, and the line connecting the two positioning piles is on the straight line where the sheet piles are located. After the two positioning piles are driven in, a guide bracket is installed between the upper ends of the two positioning piles. The outer guide arm and the inner guide arm are both made of I-beams or channel steel. The outer guide arm and the inner guide arm are parallel. The bottom of the outer sheet pile mates with the outer guide arm, and the bottom of the inner sheet pile mates with the inner guide arm, thereby making the sheet piles in the same row straight. An adjusting pad is installed between the outer guide arm and the positioning pile. The outer guide arm, the adjusting pad, the inner guide arm and the positioning pile are fixed with long bolts. During driving, the back of the sheet pile is close to the guide frame and gradually sinks.

6. The construction method for segmented interlocking combined steel sheet pile cofferdams according to claim 1, characterized in that, The construction of the steel sheet piles in the advance section includes the following steps: a. After the pile driver completes the pile construction within the arm span of the conical working platform, a steel slab is fully laid on top of the two rows of steel sheet piles as a temporary working platform. The pile driver then moves to the temporary working platform to carry out pile driving construction. b. After the sheet piles within the arm span are completed, continue to lay steel slabs on top of the two rows of completed sheet piles, and construct the next section of sheet piles. Continue to advance towards the opposite bank for construction until all sheet piles are constructed.

7. The construction method for segmented interlocking combined steel sheet pile cofferdams according to claim 1, characterized in that, The inner sheet piles are connected with a reinforcing structure.

8. The construction method for segmented interlocking combined steel sheet pile cofferdams according to claim 7, characterized in that, The reinforcing structure includes an H-beam welded to the inside of the inner sheet pile, and a slot that mates with the H-beam is installed on the inner sheet pile.

9. The construction method for segmented interlocking combined steel sheet pile cofferdams according to claim 7, characterized in that, The reinforcing structure includes a curved steel plate with an S-shaped cross-section, one side of which is welded and fixed to the middle of the inner side of the inner sheet pile.

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