Bearing platform steel sheet pile cofferdam construction method and cofferdam structure

Abstract

The invention provides a pile cap steel sheet pile cofferdam construction method and a cofferdam structure. The pile cap steel sheet pile cofferdam construction method comprises the following steps that S1, a construction area is measured and marked; s2, steel sheet pile construction is conducted, and a cofferdam is formed; pumping water; s3, the inner side of the cofferdam is excavated to the designed elevation, and a support is installed; s4, continuously excavating, and repeating the step S3 until the designed pit bottom is excavated; s5, an inner surrounding plate is constructed, an inner ring is formed, and a water tank is formed between the inner ring and the cofferdam; and S6, subsequent bearing platform construction is completed. Water seepage can be reduced, meanwhile, the water tank and the inner ring are matched for use, water seepage can be collected and discharged in time, gap water seepage of the steel sheet piles can be effectively controlled without pouring of the double-layer steel sheet piles and concrete, and the construction environment of the bearing platform is guaranteed; working procedures such as double-layer steel sheet pile driving, concrete pouring and solidification are reduced, the construction process is simplified, and the overall construction period is shortened compared with a traditional scheme; and bonding of concrete and the steel sheet piles is avoided, the support and the steel sheet piles can be quickly dismounted after bearing platform construction is completed, and the dismounting time is shortened.

Description

Technical Field

[0001] This invention relates to the field of steel sheet pile cofferdam technology, specifically to a construction method and structure for a steel sheet pile cofferdam. Background Technology

[0002] In the field of civil engineering bridge construction, pier cap construction is a crucial step. Steel sheet pile cofferdams, as a commonly used support structure, are widely used in the foundation construction of various bridges. Specifically, pier cap steel sheet pile cofferdams are temporary water-retaining / soil-retaining support structures used in bridge, wharf and other projects for the construction of pier caps (especially underwater pier caps), and are a common technology in the field of foundation engineering.

[0003] Specifically, the construction process begins by driving in sheet piles to form a closed enclosure structure, which encloses the construction space. After the water is pumped out, the pile foundation, reinforcement binding, and concrete pouring of the pier can be carried out in a dry environment. This method is suitable for pier construction in shallow water, soft soil layers, or aquatic environments.

[0004] In actual construction, gaps inevitably exist between steel sheet piles. Therefore, a small amount of liquid often seeps in through the gaps during actual use. To solve this problem, at present, the common practice is to drive double-layer steel sheet piles and then pour concrete between the two layers of steel sheet piles to seal the cofferdam. However, in actual construction, this method requires multiple layers of sheet piles, which increases the construction period. After driving two layers of sheet piles, concrete needs to be poured and allowed to solidify, further increasing the construction period. After the foundation construction is completed, the demolition is hampered by the concrete, which also affects the construction period. Summary of the Invention

[0005] The main objective of this invention is to provide a construction method and structure for a steel sheet pile cofferdam, which solves the problems of inconvenient operation and long construction period of existing methods.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for constructing a steel sheet pile cofferdam includes the following steps: S1. Measure and mark the construction area; S2. Sheet pile construction to form a cofferdam; dewatering; S3. Excavate the inner side of the cofferdam to the design elevation and install the support frame; S4. Continue excavating, repeating S3, until the bottom of the designed pit is reached; S5. Construction of the inner enclosure panel to form an inner ring, with a water channel formed between the inner ring and the cofferdam; S6. Complete the subsequent foundation construction.

[0007] In the preferred embodiment, S5 includes: S51. A water collection channel is formed by excavating the edge of the pit bottom; S52. A water collection pit is formed by excavating the lowest point of the water collection channel; S53. The inner circumference panel is constructed along the water collection channel to complete the inner ring construction. After construction, the water collection channel and the cofferdam will form a U-shaped structure; a water channel will be formed between the inner ring and the cofferdam. S54. A water pumping device is installed in the water tank; it is used to pump water out after the water level in the water tank reaches the design water level. S55. Monitoring equipment is installed on the cofferdam to monitor the water level in the tank. The top view of the water collection tank is U-shaped, and the depth of the water collection tank near the opening end is less than the depth of the other end.

[0008] In the preferred design, the height of the inner ring is lower than the height of the cofferdam. The top surface of the inner ring is adapted to the bottom support; Several perforated plates are installed between the top surface of the inner ring and the bottommost support; these are used to prevent workers from stepping into empty spaces and do not obstruct underwater drainage. The perforated plate located below the monitoring equipment has detection holes; the perforated plate located at the pumping equipment has pumping holes. The monitoring equipment and pumping equipment are connected to external control equipment and power supply, with preset water level values. When the detected water level reaches the preset water level, the pumping equipment starts to work.

[0009] In the preferred embodiment, the bracket is fixed to the inner sheet piles; A support frame is installed between the support frame and the outer sheet piles. The support frame abuts against the outer sheet piles to increase the stability of the connection between the sheet piles.

[0010] A cofferdam structure for a construction method of steel sheet pile cofferdam for pier cap includes several steel sheet piles that make up the cofferdam; the steel sheet piles are staggered and connected one inside and one outside to form the cofferdam. An excavation pit is formed on the inner side of the cofferdam, and an inner ring is set inside the excavation pit; The foundation for construction is located on the inner side of the inner ring; A water channel is formed between the inner circle and the cofferdam.

[0011] In the preferred embodiment, a support frame is provided on the inner side of the cofferdam to support the sheet piles; The support system includes several purlins, which are installed close to the sheet piles; The purlin is fixedly connected to the inner sheet pile; Several purlins are arranged in a square shape, with diagonal bracing between the two purlins at the corners; The purlin has several through holes; Several support rods are provided between the purlins on opposite sides.

[0012] In the preferred embodiment, the purlin is provided with several supports, which support the outer sheet piles. The outer sheet piles are subjected to the outward force of the support frame, while the inner sheet piles are subjected to the tension of the purlin, resulting in a relative force at the connection between the inner and outer sheet piles, ensuring the seal at the connection. The support frame includes a fixed base placed on top of the purlin; The top of the mounting base is provided with a limiting hole, which is a polygonal hole; A limit block is provided inside the limit hole; The bottom of the limit block is provided with a threaded post, which passes through the fixed seat and the through hole; The threaded post is connected to a nut, which is located at the bottom of the purlin. The top of the mounting base has two fixing blocks; Both fixed blocks are rotatably connected to shafts; one end of the top rod is connected between the two shafts, and the other end of the top rod abuts against the steel sheet pile.

[0013] In a preferred embodiment, the push rod includes a movable rod connected to the rotating shaft; The section of the movable rod furthest from the fixed base is equipped with two fixed shafts, which are located on both sides of the movable rod. The fixed shaft is equipped with rollers; A suspension rope is provided at the bottom of the section of the movable rod near the roller, and a counterweight is provided at the bottom of the suspension rope.

[0014] In a preferred embodiment, the push rod includes a sleeve rod connected to the rotating shaft; A sliding rod is slidably connected inside the sleeve rod, and the sliding rod extends out of the sleeve rod from the side of the sleeve rod away from the fixed seat; The end of the sliding rod is equipped with a top block, which abuts against the steel sheet pile; The sliding rod is a square rod; An operating hole is provided on the side of the sleeve near the fixed base; The sleeve has a rotating block inside, and the sleeve has a rotating hole that matches the rotating block. The rotating block can only rotate within the rotating hole. The rotating block has an internal hexagonal hole on the side near the operating hole, and it communicates with the operating hole; The other side of the rotating block is provided with a threaded rod, and the sliding rod is provided with a threaded hole. The threaded rod extends into the threaded hole and is threadedly connected to the threaded hole.

[0015] In the preferred embodiment, the inner ring includes several inner plates and corner plates; the corner plates are L-shaped, and the inner plates and corner plates are combined to form a square shape; Both the inner panel and the corner panel have connecting buckles along their edges; Two adjacent fasteners are close together; The side of the connector buckle is provided with a sealing groove. When two connector buckles are combined, the sealing grooves on their sides combine to form a sealing hole, which is filled with concrete or sealant. The bottom of the water tank is lower than the bottom of the foundation pit, and the bottom of the water tank is set at an angle; The pumping equipment is located at the lowest point of the water tank; A water level sensor is installed inside the cofferdam, and the water level sensor is aligned with the water tank to detect the water level in the tank.

[0016] This invention provides a construction method and structure for a steel sheet pile cofferdam with a foundation. By adopting the above solution, the following beneficial effects are achieved: By using a support frame to create relative pressure at the connection between the inner and outer sheet piles, seepage can be reduced. In addition, the use of a water trough and inner ring can collect and drain seepage water in a timely manner. This effectively controls seepage between sheet piles without the need for double-layer sheet piles and concrete pouring, thus ensuring a safe construction environment for the foundation.

[0017] The process of driving double-layer steel sheet piles, pouring concrete, and solidifying is reduced, simplifying the construction process and shortening the overall construction period compared to traditional methods. Furthermore, the modular installation of the supports and braces makes operation convenient and further improves construction efficiency.

[0018] Without the bonding between concrete and sheet piles, the supports and sheet piles can be quickly removed after the foundation construction is completed, shortening the removal time; moreover, the sheet piles can be reused, reducing construction costs. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the structure after the construction of this invention; Figure 2 This is a schematic diagram of the structure of the present invention; Figure 3 yes Figure 2 The main view; Figure 4 yes Figure 2 Side view; Figure 5 This is a schematic diagram of the inner ring structure; Figure 6 This is a structural diagram of the support frame. Figure 1 ; Figure 7 This is a sectional view of the support structure. Figure 1 ; Figure 8 This is a structural diagram of the support frame. Figure 2 ; Figure 9 This is a sectional view of the support structure. Figure 2 .

[0020] In the picture: 1. Foundation pit; 2. Sheet pile; 3. Support; 4. Purlin; 5. Through hole; 6. Diagonal brace; 7. Foundation; 8. Support frame; 9. Fixed seat; 10. Limiting hole; 11. Limiting block; 12. Threaded column; 13. Nut; 14. Fixed block; 15. Rotating shaft; 16. Movable rod; 17. Lifting rope; 18. Counterweight; 19. Roller; 10. Fixed shaft; 11. Sleeve rod; 12. Sliding rod; 13. Top block; 14. Operating hole; 15. Threaded hole; 16. Threaded rod; 17. Rotating block; 18. Inner ring; 19. Inner plate; 10. Angle plate; 10. Connecting buckle; 11. Sealing groove; 12. Water tank; 13. Water level sensor; 14. Detailed Implementation

[0021] Example 1: A method for constructing a steel sheet pile cofferdam includes the following steps: S1: Survey and mark the construction area: Before construction, existing technology was used to accurately measure the construction area of ​​the pier cap, determine the plane position, outline dimensions and driving points of the steel sheet piles of the cofferdam, and mark them with lime or laser lights.

[0022] S2: Sheet pile construction to form a cofferdam; dewatering: Based on the marked locations, a number of sheet piles 2 are driven into the ground one by one using a vibratory pile driver (preferably model DZ60) or an impact pile driver. Adjacent sheet piles 2 are connected by their own interlocking joints, and are staggered to form a closed cofferdam. The planar dimensions of the cofferdam are determined according to the design dimensions of the pier cap, preferably 2-2.5m larger than the outer contour of the pier cap, to reserve space for construction operations. During the driving of the sheet piles, the verticality is controlled by a theodolite to ensure the overall stability of the cofferdam. After the cofferdam is formed, a centrifugal water pump of model 150WQ150-15-11 is used to pump out the water accumulated inside the cofferdam. During the pumping process, the settlement and displacement of the cofferdam are monitored.

[0023] S3: Excavate the inner side of the cofferdam to the design elevation, and install the support frame. After dewatering is completed, the soil inside the cofferdam is excavated in layers, with each layer having an excavation depth of ≤1.5m to avoid instability of the cofferdam due to excessive excavation at once. After excavation reaches the first layer design elevation (preferably 2-3m below ground level), excavation is stopped and the support 3 is installed. The support 3 is fixed to the inner sheet piles 2 by welding or bolts. At the same time, a bracing 5 is installed between the support 3 and the outer sheet piles 2. The bracing 5 abuts against the outer sheet piles 2. Through the interaction of the inner tension and the outer thrust, the sealing performance of the sheet pile connection is ensured, reducing water seepage.

[0024] S4: Continue excavating, repeating S3, until the designed pit bottom is reached: After the first layer of support is installed, the soil is excavated in layers, with each layer excavated to a depth of 1.5m. The support installation steps of S3 are repeated until the design bottom elevation of the pit is reached. During the excavation process, water and loose soil at the bottom of the pit are cleaned up in a timely manner to ensure that the bottom of the pit is flat. At the same time, the excavation depth is monitored in real time using a level instrument of model DS05 to ensure that the bottom elevation of the pit meets the design requirements.

[0025] S5: Construction of the inner enclosure panel to form an inner ring, with a water channel formed between the inner ring and the cofferdam. S51: At the edge of the pit bottom, a small excavator is used to excavate to form a water collection trough. The width of the water collection trough is preferably 500-1000mm, the depth is preferably 100-500mm, and the top view is U-shaped. The depth of the water collection trough near the opening end is less than the depth of the other end, forming an inclined slope of 10%-15%, which facilitates the collection of water. S52: At the lowest point of the water collection channel, a water collection pit is further excavated to form a water collection pit. Pumping equipment is installed at the water collection pit to pump out the water in the water collection pit. S53: The inner plate 601 and corner plate 602 of the inner enclosure are spliced ​​along the edge of the water collection trough to form a U-shaped inner ring 6. The planar dimensions of the inner ring 6 are larger than the design dimensions of the foundation, and the interval is not less than 50cm. The area between the inner ring 6 and the cofferdam forms a water trough 7. The water collection trough and the cofferdam together form a U-shaped drainage structure. The height of the inner ring 6 is lower than the height of the cofferdam. The top surface of the inner ring is adapted to the bottom support 3. Several perforated plates are laid between the two. The perforated plates are used to prevent workers from stepping into the gap, and at the same time, they do not affect the seepage of water at the joint of the steel sheet pile 2 into the water trough 7. S54: Install a submersible water pump in the sump pit. The pumping equipment extends to the outside of the cofferdam through a pipeline and is used to automatically pump water when the water level in the water tank 7 reaches the design water level. S55: A water level sensor 8 is installed on the support 3 inside the cofferdam. The water level sensor 8 is preferably an infrared liquid level sensor. The detection end of the water level sensor 8 is aligned with the water tank 7 to monitor the water level in the water tank 7 in real time. Both the monitoring equipment and the pumping equipment are connected to an external PLC control device and a backup power supply. A preset water level threshold is set. When the water level is detected to reach the preset value, the control device automatically starts the pumping equipment to drain water. The pumping equipment automatically stops when the water level drops to a safe value, thus realizing automatic water level control.

[0026] S6: Complete the subsequent construction of foundation 4: After the inner ring 6 and water trough 7 are completed, the subsequent construction of the foundation 4 will proceed: First, a 100mm thick C15 concrete pad layer will be laid at the bottom of the pit. After the pad layer reaches 70% of the design strength, the foundation reinforcement will be tied and the embedded parts will be installed. After the reinforcement is tied, the formwork will be installed, and finally, C30-C40 foundation concrete will be poured. During the pouring process, the concrete will be vibrated to ensure its strength. After the foundation concrete has cured, the formwork and support 3 will be removed, and finally the steel sheet piles 2 will be removed to complete the foundation construction.

[0027] The entire process is simple to operate, more efficient, and shortens the construction period.

[0028] The term "foundation 4" in this application refers to the foundation structure that needs to be constructed.

[0029] Example 2: like Figure 1-5 As shown, a cofferdam structure for a steel sheet pile cofferdam construction method for a foundation includes several interconnected steel sheet piles 2. The steel sheet piles 2 are staggered and connected one inside and one outside to form a closed cofferdam. A foundation pit 1 is formed on the inner side of the cofferdam. A U-shaped inner ring 6 is provided in the foundation pit 1. The foundation 4 designed and constructed is located inside the inner ring 6. A water trough 7 is formed between the inner ring 6 and the cofferdam. The water trough 7 is used to collect seepage water at the connection of the steel sheet piles 2 so that it can be discharged by pumping equipment, avoiding adverse effects of seepage water on the foundation construction environment and ensuring the foundation construction environment.

[0030] A water collection trough is provided inside the foundation pit 1. The water collection trough is close to the inner ring 6. The slope of the water collection trough is the same as that of the water trough 7. It is used to collect the water accumulated in the foundation pit 1.

[0031] A support 3 is installed on the inner side of the cofferdam to support the steel sheet piles 2 and prevent them from deforming during the excavation process; Specifically, the support 3 includes several purlins 301, which are preferably Q355B I-beams. The purlins 301 are set close to the inner side of the sheet pile 2 and are fixedly connected to the inner side of the sheet pile 2 by M24 high-strength bolts, or the purlins 301 are connected and fixed to the sheet pile 2 by welding. The purlins 301 are arranged in a U-shape. At the corners, two purlins 301 are welded together with diagonal braces 303, which are preferably Q355B channel steel, to enhance the overall stability of the support. Furthermore, several support rods are provided between the purlins 301 on opposite sides. The support rods are preferably Q355B round steel, and the two ends of the support rods are connected to the purlins 301 by bolts to further improve the load-bearing capacity of the support.

[0032] The web of the purlin 301 is provided with several through holes 302 evenly distributed.

[0033] The purlin 301 is provided with several supports 5. The supports 5 press against the outer steel sheet piles 2, so that the outer steel sheet piles 2 are subjected to an outward pushing force, and the inner steel sheet piles 2 are subjected to the tension of the purlin 301. The connection between the inner and outer steel sheet piles 2 generates a relative clamping force, thereby ensuring the sealing performance of the connection and reducing water seepage.

[0034] The support frame 5 includes a fixing seat 501 placed on top of the purlin 301. The fixing seat 501 is preferably a welded part of Q235 steel. The top is provided with a limiting hole 502, which is preferably a regular hexagonal hole. A matching limiting block 503 is provided in the limiting hole 502. The limiting block 503 is preferably a regular hexagonal structure that matches the limiting hole 502. A threaded post 504 is welded to the bottom of the limiting block 503. The threaded post 504 passes through the fixing seat 501 and the through hole 302 of the purlin 301. A nut 505 is threadedly connected to the bottom. The fixing seat 501 is fixed to the purlin 301 by tightening the nut 505.

[0035] Two fixing blocks 506 are welded to the top of the fixing base 501. Each fixing block 506 is rotatably connected to a rotating shaft 507 through a bearing. One end of the top rod is connected between the two rotating shafts 507, and the other end of the top rod abuts against the outer steel sheet pile 2.

[0036] In one embodiment, such as Figure 6 and 7 As shown, the push rod adopts the first embodiment: the push rod includes a movable rod 581 welded to the rotating shaft 507. Two fixed shafts 585 are welded to the section of the movable rod 581 away from the fixed seat 501. The two fixed shafts 585 are symmetrically arranged on both sides of the movable rod 581. Rollers 584 are rotatably connected to the fixed shafts 585 through bearings. The rollers 584 are preferably made of nylon. The rollers 584 contact the steel sheet pile 2 to reduce the friction between the push rod and the steel sheet pile. A suspension rope 582, preferably a steel wire rope, is tied to the bottom of the section of the movable rod 581 near the rollers 584. A counterweight 583 is suspended at the bottom of the suspension rope 582. The weight of the counterweight 583 keeps the rollers 584 in close contact with the steel sheet pile 2, maintaining a stable jacking force.

[0037] In another embodiment, such as Figure 8 and 9As shown, the top rod adopts the second implementation method: the top rod includes a sleeve rod 591 welded to the rotating shaft 507, and a sliding rod 592 is slidably connected inside the sleeve rod 591. The sliding rod 592 is preferably Q355B square steel, and the sliding rod 592 extends out of the sleeve rod 591 from the side away from the fixed seat 501; a top block 593 is welded to the end of the sliding rod 592, and a rubber pad is pasted on the side of the top block 593 to avoid damaging the sheet pile 2 and to increase friction; an operating hole 594 is opened on the side of the sleeve rod 591 near the fixed seat 501; a rotating block 597 is rotatably connected inside the sleeve rod 591 through a bearing, and the sleeve rod 591 is provided with a connection to the rotating block 597. The rotating block 597 can only rotate within the rotating hole and cannot move axially. The rotating block 597 has an internal hexagonal hole on the side near the operating hole 594, which communicates with the operating hole 594 for easy operation with an internal hexagonal wrench. A threaded rod 596 is welded to the other side of the rotating block 597. A threaded hole 595 is provided inside the sliding rod 592, and the threaded rod 596 extends into the threaded hole 595 and is threadedly connected to it. Rotating the rotating block 597 with an internal hexagonal wrench causes the threaded rod 596 to rotate, which in turn drives the sliding rod 592 to slide along the sleeve rod 591, adjusting the jacking force of the top block 593 on the sheet pile 2 to adapt to different distances and support requirements.

[0038] Furthermore, the inner ring 6 includes several inner plates 601 and corner plates 602. The inner plates 601 are preferably Q235 steel plates, and the corner plates 602 are preferably L-shaped Q235 steel plates. The inner plates 601 and corner plates 602 are combined into a U-shape by connecting buckles 603. The connecting buckles 603 are preferably Q235 steel stampings, welded to the edges of the inner plates 601 and corner plates 602, with two adjacent connecting buckles 603 closely fitted together. A sealing groove 604 is provided on the side of the connecting buckle 603. After two connecting buckles 603 are combined, the sealing groove 604 on its side forms a sealing hole. Waterproof sealant or fine stone concrete is filled into the sealing hole to ensure the sealing performance of the inner ring 6.

[0039] The bottom of the water tank 7 is 300-1000mm lower than the bottom of the foundation pit 1. The bottom of the water tank 7 is inclined along the direction of the sump pit with a slope of 10%-15%, which facilitates the flow of accumulated water to the sump pit. The pumping equipment is located at the lowest point of the water tank 7. A water level sensor 8 is installed on the support inside the cofferdam. The detection end of the water level sensor 8 is aligned with the water tank 7 to detect the water level in the water tank in real time and realize automatic drainage.

[0040] Throughout the construction of the pier cap and cofferdam, this method can not only address the seepage at the connection of the sheet piles, but also shorten the construction period, thus facilitating the construction of the pier cap and its cofferdam.

[0041] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for constructing a steel sheet pile cofferdam with a foundation, characterized in that: Includes the following steps: S1. Measure and mark the construction area; S2. Sheet pile construction to form a cofferdam; dewatering; S3. Excavate the inner side of the cofferdam to the design elevation and install the support frame; S4. Continue excavating, repeating S3, until the bottom of the designed pit is reached; S5. Construction of the inner enclosure panel to form an inner ring, with a water channel formed between the inner ring and the cofferdam; S6. Complete the subsequent foundation construction.

2. The construction method of a steel sheet pile cofferdam for a pier cap according to claim 1, characterized in that: S5 includes: S51. A water collection channel is formed by excavating the edge of the pit bottom; S52. A water collection pit is formed by excavating the lowest point of the water collection channel; S53. The inner circumference panel is constructed along the water collection channel to complete the inner ring construction. After construction, the water collection channel and the cofferdam will form a U-shaped structure; a water channel will be formed between the inner ring and the cofferdam. S54. A water pumping device is installed in the water tank; it is used to pump water out after the water level in the water tank reaches the design water level. S55. Monitoring equipment is installed on the cofferdam to monitor the water level in the tank. The top view of the water collection tank is U-shaped, and the depth of the water collection tank near the opening end is less than the depth of the other end.

3. The construction method of a steel sheet pile cofferdam for a pier cap according to claim 2, characterized in that: The height of the inner ring is lower than the height of the cofferdam; The top surface of the inner ring is adapted to the bottom support; Several perforated plates are installed between the top surface of the inner ring and the bottommost support; these are used to prevent workers from stepping into empty spaces and do not obstruct underwater drainage. The perforated plate located below the monitoring equipment has detection holes; the perforated plate located at the pumping equipment has pumping holes. The monitoring equipment and pumping equipment are connected to external control equipment and power supply, with preset water level values. When the detected water level reaches the preset water level, the pumping equipment starts to work.

4. The construction method of a steel sheet pile cofferdam for a pier cap according to claim 1, characterized in that: The bracket is fixed to the inner steel sheet piles; A support frame is installed between the support frame and the outer sheet piles. The support frame abuts against the outer sheet piles to increase the stability of the connection between the sheet piles.

5. A cofferdam structure for use in the construction method of the steel sheet pile cofferdam of any one of claims 1-4, characterized in that: Includes several sheet piles (2) that make up the cofferdam; the sheet piles (2) are connected in an alternating pattern to form the cofferdam; An excavation pit (1) is formed on the inner side of the cofferdam, and an inner ring (6) is provided inside the excavation pit (1). The designed and constructed foundation (4) is located inside the inner ring (6); A water channel (7) is formed between the inner circle (6) and the cofferdam.

6. The cofferdam structure for the construction method of sheet pile cofferdam for pier caps according to claim 5, characterized in that: A support frame (3) is provided on the inner side of the cofferdam to support the sheet piles (2); The support (3) includes several purlins (301), which are set close to the sheet pile (2); The purlin (301) is fixedly connected to the inner sheet pile (2); Several purlins (301) are arranged in a square shape, and a diagonal brace (303) is provided between two purlins (301) at the corner. The purlin (301) has several through holes (302); Several support rods are provided between the purlins (301) on opposite sides.

7. The cofferdam structure for the construction method of sheet pile cofferdam for pier caps according to claim 6, characterized in that: The purlin (301) is provided with several supports (5), which support the outer steel sheet pile (2). The outer sheet pile (2) is subjected to the outward force of the support frame (5), and the inner sheet pile (2) is subjected to the tension of the purlin (301), so that the connection between the inner and outer sheet piles (2) generates a relative force to ensure the seal of the connection. The support (5) includes a fixing seat (501) placed on top of the purlin (301); The top of the fixing base (501) is provided with a limiting hole (502), and the limiting hole (502) is a polygonal hole; A limiting block (503) is provided inside the limiting hole (502); The bottom of the limiting block (503) is provided with a threaded post (504), which passes through the fixed seat (501) and the through hole (302). The threaded column (504) is threaded with a nut (505), which is located at the bottom of the purlin (301); The top of the fixing base (501) is provided with two fixing blocks (506); Two fixed blocks (506) are rotatably connected to a rotating shaft (507); one end of the top rod is connected between the two rotating shafts (507), and the other end of the top rod abuts against the steel sheet pile (2).

8. The cofferdam structure for the construction method of steel sheet pile cofferdam for pier cap as described in claim 7, characterized in that: the top rod includes a movable rod (581) connected to the rotating shaft (507). The movable rod (581) is provided with two fixed shafts (585) on the section away from the fixed base (501), and the two fixed shafts (585) are located on both sides of the movable rod (581); The fixed shaft (585) is equipped with a roller (584); The bottom of the movable rod (581) near the roller (584) is provided with a suspension rope (582), and the bottom of the suspension rope (582) is provided with a counterweight (583).

9. The cofferdam structure for the construction method of steel sheet pile cofferdam for pier cap as described in claim 7, characterized in that: the top rod includes a sleeve rod (591) connected to the rotating shaft (507). A sliding rod (592) is slidably connected inside the sleeve rod (591). The sliding rod (592) extends out of the sleeve rod (591) from the side of the sleeve rod (591) away from the fixed seat (501). The end of the sliding rod (592) is provided with a top block (593), which abuts against the steel sheet pile (2); The sliding rod (592) is a square rod; The sleeve (591) has an operating hole (594) on the side near the fixed base (501). The sleeve (591) is provided with a rotating block (597), and the sleeve (591) is provided with a rotating hole that matches the rotating block (597). The rotating block (597) can only rotate within the rotating hole. The rotating block (597) has an internal hexagonal hole on the side near the operating hole (594) and communicates with the operating hole (594); The other side of the rotating block (597) is provided with a threaded rod (596), and the sliding rod (592) is provided with a threaded hole (595). The threaded rod (596) extends into the threaded hole (595) and is threadedly connected to the threaded hole (595).

10. The cofferdam structure for the construction method of sheet pile cofferdam for pier caps according to claim 5, characterized in that: The inner ring (6) includes several inner plates (601) and corner plates (602); the corner plates (602) are L-shaped, and the inner plates (601) and corner plates (602) are combined to form a square shape; Both the inner panel (601) and the corner panel (602) are provided with connecting buckles (603) at their edges; Two adjacent connecting buckles (603) are close together; The connecting buckle (603) has a sealing groove (604) on its side. After the two connecting buckles (603) are combined, the sealing groove (604) on their side is combined to form a sealing hole, which is filled with concrete or sealant. The bottom surface of the water tank (7) is lower than the bottom surface of the foundation pit (1), and the bottom surface of the water tank (7) is set at an angle; The pumping equipment is located at the lowest point of the water tank (7); A water level sensor (8) is installed on the inner side of the cofferdam. The water level sensor (8) is aligned with the water tank (7) to detect the water level in the water tank (7).

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