Construction method for underwater low-pile bearing platform of steel sheet pile cofferdam in shallow sea mud flat area

Abstract

The invention relates to a construction method for an underwater low-pile bearing platform of a steel sheet pile cofferdam in a shallow sea mud flat area. The construction method comprises the following steps that guide piles and steel sheet piles are inserted and driven to form the steel sheet pile cofferdam; steel enclosing purlins and inner supporting systems are installed in the steel sheet pile cofferdam through supporting brackets, a profile steel platform frame and an assembly type hopper are installed on the lower-layer inner supporting system, and an operation platform is installed on the upper-layer inner supporting system; steel sheet pile cofferdam bottom sealing is conducted through the assembly type hopper, an operation platform is dismantled, a steel pile casing is cut off, an exposed pile head is cut off, and a hoop type lifting appliance is arranged in a sleeving mode to lift off the pile head; finishing exposed reinforcing steel bars of the pile body; permeable formwork cloth is laid on the steel formwork through the laying pedestal, the steel formwork is installed on the top of the pile body, and bearing platform concrete is poured. The construction method has the beneficial effects that the inserting and driving efficiency and perpendicularity of the steel sheet pile are improved, meanwhile, effective control over the elevation of the bottom sealing concrete is achieved, the pile head treatment time of the low-pile bearing platform is shortened, and the construction efficiency of the bearing platform steel formwork in the coastal chlorine-rich environment is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of bridge engineering, and particularly relates to a construction method for a low-pile cap in water with a steel sheet pile cofferdam in a shallow beach and tidal flat area. Background Art

[0002] The construction technology of the Larsen steel sheet pile cofferdam is mostly used in the construction of cross-sea bridges. Especially in recent years, with the booming development of China's transportation network, the construction of cross-sea bridges has been increasing, so the construction of pile caps in water has become frequent. And an important factor affecting the success and safety of the pile cap project in water is the design and construction of the temporary protection project for isolating seawater. Due to its own unique advantages, the Larsen steel sheet pile is the first choice for cofferdam construction. However, the construction of the Larsen steel sheet pile cofferdam in the shallow beach and tidal flat area is more difficult than that in general sea areas and inland rivers. Not only is the depth of the bearing stratum limited, but also the influence of periodic tides on the construction needs to be considered.

[0003] Due to the influence of tides, the position of the sea tide is periodically changing, and the highest water level and the lowest water level are constantly changing with the ebb and flow of the tide. This requires higher requirements for the stability, anti-seepage, anti-heave, and anti-overturning capabilities of the overall structure of the cofferdam. The conventional steel sheet pile cofferdam process is difficult to meet the construction requirements of the low-pile cap in water in the shallow beach and tidal flat area, and there is much room for improvement in the overall structural system and the construction efficiency of the pile cap.

[0004] In view of this, there is an urgent need to invent a construction method for a low-pile cap in water with a steel sheet pile cofferdam in a shallow beach and tidal flat area, which has a fast cofferdam forming speed, high pile cap operation efficiency, simple construction operation, and prominent economic and technical benefits. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a construction method for a low-pile cap in water with a steel sheet pile cofferdam in a shallow beach and tidal flat area.

[0006] This construction method for a low-pile cap in water with a steel sheet pile cofferdam in a shallow beach and tidal flat area includes the following steps:

[0007] Step 1: Driving guide piles and steel sheet piles, and forming a steel sheet pile cofferdam after closing.

[0008] Step 2: Installing a layer of steel waling and an internal support system at two different heights inside the steel sheet pile cofferdam through support brackets. First, install the lower internal support system, then install a steel platform frame and a prefabricated hopper on the lower internal support system, and then construct the upper internal support system, and install an operation platform on the upper internal support system.

[0009] Step 3: Sealing the bottom of the steel sheet pile cofferdam through the prefabricated hopper, removing the operation platform and cutting the steel casing, cutting off the exposed pile head, and sleeving a hoop-type lifting tool to lift off the pile head; trimming the exposed steel bars of the pile body.

[0010] Step 4: Lay the permeable formwork fabric on the steel formwork through the laying pedestal, install the steel formwork at the top of the pile body, and pour the cap concrete.

[0011] Preferably, in Step 1, fitting grooves in the shape of coupled steel sheet piles are provided on both sides of the guide piles, and vertical T-shaped embedded sliding grooves are provided inside the guide piles. A connecting slider and a supporting slider are vertically inserted into the vertical T-shaped embedded sliding grooves of the guide piles, and the connecting slider and the supporting slider have the same shape; several supporting sliders are provided between two vertically adjacent connecting sliders, and the installation quantity of the supporting sliders is adjusted according to the spacing of the internal support system. The connecting slider is fixedly connected with a supporting corbel, and the internal support system is fixed on the supporting corbel.

[0012] Preferably, in Step 2, bolt holes are arranged at equal intervals on the surface of the connecting slider. The supporting corbel and the connecting slider are fixed by connecting bolts. A lifting ring is arranged at the top of the supporting corbel, and bolt holes are arranged at equal intervals on the connecting surface between the supporting corbel and the guide pile. The size and spacing of the bolt holes are the same as those on the surface of the connecting slider.

[0013] Preferably, in Step 2, a groove is provided above the supporting corbel, and a steel waling is installed in the groove. The internal support system is fixedly connected with the steel waling. The steel platform frame is a symmetrically arranged Π-shaped double-beam support. The end of the Π-shaped double-beam support and the steel waling are connected by high-strength bolts. The Π-shaped double-beam support is evenly distributed with conduit limiting cylinders. A limiting wing plate is arranged at the top of the conduit limiting cylinder, and a prefabricated hopper is arranged on the limiting wing plate. The bottom of the conduit limiting cylinder is connected with a hanging conduit.

[0014] Preferably, in Step 2, the operating platform includes a central operating platform and an end operating platform. Hoop brackets are fixed on the steel casing. Both the central operating platform and the end operating platform are connected and fixed to the hoop brackets welded on the steel casing by high-strength bolts.

[0015] Preferably, in Step 3, a reinforced concrete pile is poured in the steel casing. After the steel casing is cut off, expansion holes are arranged on the exposed pile head of the reinforced concrete pile for preliminary expansion and detachment. Electric control tooth bars are symmetrically arranged on both sides of the hoop-type lifting tool. Limiting ring plates are evenly distributed circumferentially on the hollow inner wall. Anti-slip sleeves are arranged on the surface of the limiting ring plates. The limiting ring plates are fastened to the pile head through the cooperation of the electric control tooth bars and the limiting ring plates, and the pile head is lifted and removed.

[0016] Preferably, a reinforced concrete pile is poured in the steel casing, and a super-cast section of the pile foundation main reinforcement is provided at the top of the reinforced concrete pile. Composite sleeves are arranged on the pile foundation main reinforcement in the super-cast section.

[0017] Preferably, in step 4, the paving pedestal includes an upper tension wheel shaft rod, an adjusting support, a lower tension wheel shaft rod, a main adjusting rod and an auxiliary adjusting rod. Upper tension wheels and lower tension wheels are arranged at both the front and rear ends of the paving pedestal. The upper tension wheel shaft rod is fixed in the adjusting support. The lower tension wheel shaft rod is connected to the auxiliary adjusting rod. A support cross beam is arranged between the front and rear adjusting supports. A sliding support is arranged on the support cross beam. A paving wheel is arranged between the sliding supports on both left and right sides. The paving wheel is controlled by the main adjusting rod. The paving pedestal is hoisted with a bearing platform steel formwork. The permeable formwork cloth is passed through the upper tension wheel and the lower tension wheel from one side and stretched into the upper tension wheel and the lower tension wheel on the other side. After tightening the auxiliary adjusting rod, the main adjusting rod is lowered so that the paving wheel abuts against the steel formwork. Subsequently, the paving wheel is slid from one end to the other end through the sliding support to complete the paving. After cutting, the main adjusting rod and the auxiliary adjusting rod are loosened, and the steel formwork is removed.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1) The present invention develops a guiding pile-assisted internal support installation technology. By setting guiding piles and optimizing the guiding pile body structure, the driving efficiency and verticality of steel sheet piles are effectively improved, and the installation difficulty of the collar support corbel in the traditional process is solved through the slider structure.

[0020] 2) The present invention develops a concrete sealing technology for a steel platform conduit group. By setting a steel platform frame with a conduit limiting cylinder, the effective control of the elevation of the sealing concrete is realized, and the sealing quality is improved.

[0021] 3) The present invention develops a composite casing isolation steel bar hoop pile head lifting and removing technology. By presetting a composite casing on the over-poured section of the main reinforcement of the pile foundation reinforcement cage, the bond force between the concrete and the steel bars is eliminated, and the pile head can be quickly chiseled with a hoop-type lifting tool, shortening the treatment time of the pile head of the low-pile cap.

[0022] 4) The present invention develops an automatic paving technology for permeable formwork cloth on a steel formwork. Through the paving pedestal structure, the automatic tensioning and paving of the permeable formwork cloth on the steel formwork are realized, improving the construction efficiency of the bearing platform steel formwork in the coastal chlorine-rich environment. Description of the Drawings

[0023] Figure 1 is a schematic diagram of the operation platform structure in the present invention;

[0024] Figure 2 is Figure 1 the enlarged view of point A in

[0025] Figure 3 is a schematic diagram of the guiding pile structure in the present invention;

[0026] Figure 4 is a schematic diagram of the installation of the support corbel in the present invention;

[0027] Figure 5It is a schematic diagram of the installation of the medium - sized steel platform frame in the present invention;

[0028] Figure 6 It is a schematic diagram of the structure of the conduit limiting cylinder in the present invention;

[0029] Figure 7 It is a schematic diagram of the setting of the splitting holes in the present invention;

[0030] Figure 8 It is a schematic diagram of the operation of the hoop - type fixture in the present invention;

[0031] Figure 9 It is a plan view of the structure of the hoop - type fixture in the present invention;

[0032] Figure 10 It is a sectional view of the structure of the paving pedestal in the present invention;

[0033] Figure 11 It is a top view of the paving pedestal in the present invention.

[0034] Explanation of reference numerals: 1 - steel sheet pile; 2 - steel waling; 3 - guide pile; 4 - end operation platform; 5 - corner brace; 6 - high - strength bolt; 7 - steel casing; 8 - traction equipment; 9 - casing bracket; 10 - central operation platform; 11 - chute; 12 - steel sheet pile fitting groove; 13 - connecting slider; 14 - bolt hole; 15 - supporting slider; 16 - conduit limiting cylinder; 17 - medium - sized steel platform frame; 18 - limiting wing plate; 19 - assembled hopper; 20 - bottom - sealed concrete; 21 - connecting bolt; 22 - lifting ring; 23 - supporting bracket; 24 - pile head; 25 - splitting hole; 26 - pile body; 27 - lifting rope; 28 - electric control tooth bar; 29 - composite casing; 30 - main reinforcement of pile foundation; 31 - limiting ring plate; 32 - hoop - type lifting device; 33 - anti - slip sleeve; 34 - support cross beam; 35 - steel formwork; 36 - permeable formwork cloth; 37 - sliding support; 38 - main adjusting rod; 39 - adjusting support; 40 - auxiliary adjusting rod; 41 - upper tensioning wheel; 42 - lower tensioning wheel; 43 - paving wheel; 44 - hose of concrete pump truck; 45 - lower - hanging conduit. Specific embodiments

[0035] The following describes the present invention in further detail with reference to the embodiments. The description of the following embodiments is only for helping to understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0036] Embodiment 1

[0037] As an embodiment, a construction method for a low - pile cap in water with a steel sheet pile cofferdam in a shallow beach area is proposed, including the following steps:

[0038] Step 1: Drive the guide piles 3 and the steel sheet piles 1, and form a steel sheet pile cofferdam after closure; as Figure 1 shown, a traction device 8 is connected to the end operation platform 4, and the corner braces 5 are connected to the four corners of the steel waling 2; the operation platform includes a central operation platform 10 and an end operation platform 4, and a casing bracket 9 is fixed on the steel casing 7. Both the central operation platform 10 and the end operation platform 4 are connected and fixed by high-strength bolts 6 and the casing brackets 9 welded on the steel casing 7; as Figure 2 shown, steel sheet pile fitting grooves 12 in the shape of the coupled steel sheet pile 1 are arranged on both sides of the guide pile 3, and a vertical T-shaped embedded sliding groove 11 is arranged inside the guide pile 3. A connecting slider 13 and a supporting slider 15 are vertically inserted into the vertical T-shaped embedded sliding groove 11 of the guide pile 3, and the connecting slider 13 and the supporting slider 15 have the same shape; several supporting sliders 15 are arranged between two adjacent connecting sliders 13 in the vertical direction, and the installation quantity of the supporting sliders 15 is adjusted according to the spacing of the internal support system. The connecting slider 13 is fixedly connected with a supporting bracket 23, and the internal support system is fixed on the supporting bracket 23.

[0039] Step 2: Install a layer of steel waling 2 and an internal support system at two different heights inside the steel sheet pile cofferdam through the supporting brackets 23 respectively. First, install the lower-layer internal support system, then install the profiled steel platform frame 17 and the assembled hopper 19 on the lower-layer internal support system, then construct the upper-layer internal support system, and install the operation platform on the upper-layer internal support system;

[0040] Step 3: Seal the bottom of the steel sheet pile cofferdam through the assembled hopper 19, remove the operation platform and cut off the steel casing 7, cut off the exposed pile head 24, and hoist the pile head 24 by sleeving a hoop-type lifting tool 32; trim the exposed steel bars of the pile body 26;

[0041] Step 4: Lay the permeable formwork cloth 36 on the steel formwork 35 through the paving pedestal, install the steel formwork 35 on the top of the pile body 26, and pour the cap concrete.

[0042] Embodiment 2

[0043] As another embodiment, this Embodiment 2 is proposed on the basis of Embodiment 1. A more specific construction method for a low-pile cap in water with a steel sheet pile cofferdam in a shallow beach area includes the following steps:

[0044] Step 1: Drive the guide piles and the steel sheet piles, and form a steel sheet pile cofferdam after closure;

[0045] Step 2: Install a layer of steel waling 2 and an internal support system at two different heights inside the steel sheet pile cofferdam through the supporting brackets 23 respectively. First, install the lower-layer internal support system, then install the profiled steel platform frame 17 and the assembled hopper 19 on the lower-layer internal support system, then construct the upper-layer internal support system, and install the operation platform on the upper-layer internal support system; as Figure 4As shown in the figure, bolt holes 14 are equidistantly arranged on the surface of the connecting slider 13. The supporting bracket 23 and the connecting slider 13 are fixed by connecting bolts 21. A lifting ring 22 is arranged at the top of the supporting bracket 23. Bolt holes 14 are equidistantly arranged on the connecting surface between the supporting bracket 23 and the guide pile 3. The size and spacing of the bolt holes 14 are the same as those on the surface of the connecting slider 13; As Figure 4 and Figure 5 shown in the figure, a groove is provided above the supporting bracket 23. A steel waling 2 is installed in the groove. The internal support system is fixedly connected to the steel waling 2. The profiled steel platform frame 17 is a symmetrically arranged Π-shaped double-beam bracket. The end of the Π-shaped double-beam bracket and the steel waling 2 are connected by high-strength bolts 6. Pipe limiting cylinders 16 are evenly distributed on the Π-shaped double-beam bracket; As Figure 6 shown in the figure, a limiting wing plate 18 is arranged at the top of the pipe limiting cylinder 16. An assembled hopper 19 is arranged on the limiting wing plate 18. The bottom of the pipe limiting cylinder 16 is connected to a hanging conduit 45. After dredging to the design elevation, the blinding concrete 20 is connected into all the assembled hoppers 19 through the hose 44 of the truck pump, and then the concrete is synchronously poured through the hanging conduit 45 inside the pipe limiting cylinder 16;

[0046] Step 3: Seal the bottom of the steel sheet pile cofferdam through the assembled hopper 19, remove the operation platform and cut off the steel casing 7, cut off the exposed pile head 24, and set a hoop-type lifting tool 32 to lift off the pile head 24; Trim the exposed steel bars of the pile body 26;

[0047] Step 4: Lay the permeable formwork cloth 36 on the steel formwork 35 through the laying platform, install the steel formwork 35 on the top of the pile body 26, and pour the cap concrete.

[0048] It should be noted that the same or similar parts in this embodiment and Embodiment 1 can be referred to each other and will not be described in detail in this application.

[0049] Embodiment 3

[0050] As another embodiment, this Embodiment 3 is proposed on the basis of Embodiment 2. A more specific construction method for a low-pile cap in water with a steel sheet pile cofferdam in a shallow beach area includes the following steps:

[0051] Step 1: Drive the guide piles and steel sheet piles, and form a steel sheet pile cofferdam after closing;

[0052] Step 2: Install a layer of steel waling 2 and an internal support system at two different heights inside the steel sheet pile cofferdam through the supporting brackets 23 respectively. First, install the lower internal support system, then install the profiled steel platform frame 17 and the assembled hopper 19 on the lower internal support system, then construct the upper internal support system, and install the operation platform on the upper internal support system;

[0053] Step 3: Use the prefabricated hopper 19 to seal the bottom of the steel sheet pile cofferdam. Demolish the operation platform and cut off the steel casing 7. Cut off the exposed pile head 24, and set a hoop-type lifting tool 32 to lift off the pile head 24; trim the exposed steel bars of the pile body 26; as Figure 7 and Figure 8 shown, a reinforced concrete pile is cast in the steel casing 7. After cutting off the steel casing 7, set a splitting hole 25 on the exposed pile head 24 of the reinforced concrete pile for preliminary splitting and detachment. Electric control tooth bars 28 are symmetrically arranged on both sides of the hoop-type lifting tool 32, and limiting ring plates 31 are evenly distributed circumferentially on the hollow inner wall. Anti-slip sleeves 33 are arranged on the surface of the limiting ring plates 31. The limiting ring plates 31 are fastened to the pile head 24 through the cooperation of the electric control tooth bars 28 and the limiting ring plates 31, and the pile head 24 is lifted off; a reinforced concrete pile is cast in the steel casing 7. The top of the reinforced concrete pile is provided with a super-cast section of the pile foundation main reinforcement 30, and a composite casing 29 is arranged on the pile foundation main reinforcement 30 in the super-cast section.

[0054] Step 4: Lay the permeable formwork cloth 36 on the steel formwork 35 through the laying pedestal, install the steel formwork 35 on the top of the pile body 26, and pour the bearing platform concrete.

[0055] It should be noted that the same or similar parts in this embodiment and Embodiment 2 can be referred to each other and will not be elaborated in this application.

[0056] Embodiment 4

[0057] As another embodiment, this Embodiment 4 is proposed on the basis of Embodiment 3. A more specific construction method for a low-pile bearing platform in water in a shallow beach and shoal area by using a steel sheet pile cofferdam includes the following steps:

[0058] Step 1: Drive the guide piles and steel sheet piles, and form a steel sheet pile cofferdam after closure;

[0059] Step 2: Install a layer of steel waling 2 and an internal support system at two different heights inside the steel sheet pile cofferdam through the support brackets 23 respectively. First install the lower internal support system, then install the steel platform frame 17 and the prefabricated hopper 19 on the lower internal support system, then construct the upper internal support system, and install the operation platform on the upper internal support system;

[0060] Step 3: Use the prefabricated hopper 19 to seal the bottom of the steel sheet pile cofferdam. Demolish the operation platform and cut off the steel casing 7. Cut off the exposed pile head 24, and set a hoop-type lifting tool 32 to lift off the pile head 24; trim the exposed steel bars of the pile body 26;

[0061] Step 4: Lay the permeable formwork cloth 36 on the steel formwork 35 through the laying pedestal, install the steel formwork 35 on the top of the pile body 26, and pour the bearing platform concrete; as Figure 10 and Figure 11As shown, the paving pedestal includes the upper tension pulley 41 shaft rod, the adjusting support 39, the lower tension pulley 42 shaft rod, the main adjusting rod 38 and the auxiliary adjusting rod 40. The upper tension pulley 41 and the lower tension pulley 42 are arranged at both the front and rear ends of the paving pedestal. The upper tension pulley 41 shaft rod is fixed in the adjusting support 39. The lower tension pulley 42 shaft rod is connected to the auxiliary adjusting rod 40. A support cross beam 34 is arranged between the front and rear adjusting supports 39. A sliding support 37 is arranged on the support cross beam 34. A paving wheel 43 is arranged between the left and right sliding supports 37. The paving wheel 43 is controlled by the main adjusting rod 38. The paving pedestal is hoisted with a bearing platform steel formwork 35. The permeable formwork cloth 36 is passed through the upper tension pulley 41 and the lower tension pulley 42 from one side and then stretched into the upper tension pulley 41 and the lower tension pulley 42 on the other side. After the auxiliary adjusting rod 40 is tightened, the main adjusting rod 38 is lowered so that the paving wheel 43 abuts against the steel formwork 35. Then the paving wheel 43 is slid from one end to the other end through the sliding support 37 to complete the paving. After cutting, the main adjusting rod 38 and the auxiliary adjusting rod 40 are loosened, and the steel formwork 35 is removed.

[0062] It should be noted that the parts that are the same or similar to those in Embodiment 3 in this embodiment can be referred to each other and will not be elaborated in this application.

[0063] In this specification, the various embodiments are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

Claims

1. A method for constructing a low pile cap in water of a steel sheet pile cofferdam in a shallow sea beach area, characterized in that: The following steps are involved: Step 1: insert guide piles and steel sheet piles, and close them together to form a steel sheet pile cofferdam; Step 2: Install a layer of steel purlin and internal support system at two different heights in the steel sheet pile cofferdam through supporting corbels. First install the lower internal support system, then install the steel platform frame and assembled hopper on the lower internal support system, then construct the upper internal support system, and install the operating platform on the upper internal support system. Step 3: Use the assembled hopper to seal the bottom of the steel sheet pile cofferdam, dismantle the operating platform and cut off the steel casing, cut off the exposed pile head, and use a hoop-type lifting device to lift the pile head; trim the exposed steel bars on the pile body; Step 4: Lay the permeable formwork cloth on the steel formwork by laying the pedestal, install the steel formwork on the top of the pile body, and pour the cap concrete.

2. The method for constructing a low pile cap in water of a steel sheet pile cofferdam in a shallow sea beach area according to claim 1, characterized in that: In step one, coupling grooves in the shape of coupled steel sheet piles are provided on both sides of the guide pile, and a vertical T-shaped embedded groove is provided on the inner side of the guide pile. A connecting slider and a supporting slider are vertically inserted into the vertical T-shaped embedded groove of the guide pile, and the connecting slider and the supporting slider have the same shape; several supporting sliders are provided between two vertically adjacent connecting sliders, and the number of supporting sliders installed is adjusted according to the spacing of the internal support system, the connecting slider is fixedly connected to the supporting corbel, and the internal support system is fixed on the supporting corbel.

3. The method for constructing a low pile cap in water of a steel sheet pile cofferdam in a shallow sea beach area according to claim 1, characterized in that: In step 2, bolt holes are arranged at equal intervals on the surface of the connecting slider, the supporting corbel and the connecting slider are fixed by connecting bolts, a lifting ring is arranged on the top of the supporting corbel, and bolt holes are arranged at equal intervals on the connecting surface of the supporting corbel and the guide pile, and the size and spacing of the bolt holes are the same as those on the surface of the connecting slider.

4. The method for constructing a low pile cap in water of a steel sheet pile cofferdam in a shallow sea beach area according to claim 2, characterized in that: In step two, a groove is provided above the supporting corbel, a steel purlin is installed in the groove, the internal support system and the steel purlin are fixedly connected, the steel platform frame is a symmetrically arranged Π-shaped double-beam bracket, the end of the Π-shaped double-beam bracket and the steel purlin are connected by high-strength bolts, and conduit limiting cylinders are evenly distributed on the Π-shaped double-beam bracket. A limiting wing plate is provided on the top of the conduit limiting cylinder, an assembled hopper is provided on the limiting wing plate, and a hanging conduit is connected to the bottom of the conduit limiting cylinder.

5. The method for constructing a low pile cap in water of a steel sheet pile cofferdam in a shallow sea beach area according to claim 1, characterized in that: In step 2, the operating platform includes a central working platform and a terminal working platform, casing bull legs are fixed on the steel casing, and the central working platform and the terminal working platform are connected and fixed by high-strength bolts and casing bull legs welded on the steel casing.

6. The method for constructing a low pile cap in water of a steel sheet pile cofferdam in a shallow sea beach area according to claim 1, characterized in that: In step three, reinforced concrete piles are cast in the steel casing. After the steel casing is cut off, expansion holes are set on the exposed reinforced concrete pile heads for preliminary expansion and separation. Electric-controlled gear rods are symmetrically arranged on both sides of the hoop-type lifting device, and limiting ring plates are evenly distributed in the circumferential direction of the hollow inner wall. Anti-slip sleeves are arranged on the surface of the limiting ring plates. The limiting ring plates are fastened to the pile head through the electric-controlled gear rods and the limiting ring plates, and the pile head is lifted and removed.

7. The method for constructing a low pile cap in water of a steel sheet pile cofferdam in a shallow sea beach area according to claim 1, characterized in that: Reinforced concrete piles are cast in the steel casing, a pile foundation main reinforcement over-filling section is provided on the top of the reinforced concrete pile, and a composite casing is provided on the pile foundation main reinforcement in the over-filling section.

8. The method for constructing a low pile cap in water of a steel sheet pile cofferdam in a shallow sea beach area according to claim 1, characterized in that: In step 4, the paving platform includes an upper tensioning wheel shaft, an adjusting support, a lower tensioning wheel shaft, a main adjusting rod and an auxiliary adjusting rod. Upper and lower tensioning wheels are arranged at the front and rear ends of the paving platform, the upper tensioning wheel shaft is fixed in the adjusting support, the lower tensioning wheel shaft and the auxiliary adjusting rod are connected, a support crossbeam is arranged between the front and rear adjusting supports, a sliding support is arranged on the support crossbeam, a paving wheel is arranged between the left and right sliding supports, and the paving wheels are controlled by the main adjusting rod; the paving platform is hoisted with a foundation steel formwork, the permeable formwork cloth is passed through the upper tensioning wheel and the lower tensioning wheel from one side and then stretched to the upper tensioning wheel and the lower tensioning wheel on the other side, after tightening the auxiliary adjusting rod, the main adjusting rod is lowered to make the paving wheel abut against the steel formwork, and then the paving wheel is slid from one end to the other end through the sliding support to complete the paving, and the main adjusting rod and the auxiliary adjusting rod are released after cutting, and the steel formwork is transported away.

9. Low pile cap in water for steel sheet pile cofferdam in shallow sea beach area, characterized by: Obtained by the method according to any one of claims 1 to 8.

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