Positioning and supporting device for steel sheet pile construction and steel sheet pile cofferdam construction method adopting same

Abstract

The invention discloses a positioning and supporting device for steel sheet pile construction. The positioning and supporting device comprises an enclosing purlin and a plurality of supporting assemblies. The enclosing purlin is of a rigid plane structure defined by a plurality of purlins. One side of the supporting assembly is fixed to the purlin, and the other side of the supporting assembly extends in a surrounding area of the surrounding purlin to form an attachment end. When the attachment end of the supporting assembly is fixedly connected with an existing steel casing on the seabed, the supporting assembly and the steel casing form a stable triangular support structure in the vertical plane. The enclosing purlins are indirectly fixed to the periphery of the steel casing so as to position and support installation of the steel sheet piles. The device further comprises a positioning plate which is used for positioning the steel sheet pile during inserting and driving. The invention further discloses a construction method of the steel sheet pile cofferdam, the positioning and supporting device for steel sheet pile construction is adopted, integrated construction of positioning and supporting is achieved from the structure and the working procedure, the construction efficiency is improved, the construction cost is saved, and the construction safety and the construction quality of underwater operation are improved.

Description

Technical Field

[0001] The invention relates to the technical field of steel sheet pile cofferdam construction, and in particular to a positioning support device for steel sheet pile construction and a steel sheet pile cofferdam construction method using the device. Background Art

[0002] Before constructing the foundation of a bridge project in shallow sea water, a steel sheet pile cofferdam is often used as a temporary retaining structure to prevent water and soil from invading the construction site, so that after draining the seawater in the cofferdam, the foundation pit can be excavated and the foundation can be built. In the traditional steel sheet pile cofferdam construction method, it is usually necessary to install a guide frame first, and then insert and drive the steel sheet piles along the position of the guide frame. When constructing a rectangular steel sheet pile cofferdam, it is necessary to first install four guide frames along the four sides. After the steel sheet piles are inserted and the lock is closed, the guide frame is removed, and then four purlins are installed in sequence along the inner side of the steel sheet piles. Finally, the purlin angle braces, intermediate supports and other supporting structures are installed to complete the construction of the steel sheet pile cofferdam.

[0003] The above-mentioned traditional construction methods have the following disadvantages and shortcomings: (1) The overall construction efficiency of the steel sheet pile cofferdam is low. Usually, the guide frame and the purlin are two different structures used to provide different functions. The traditional construction method is to install the guide frame and the purlin in stages, which is not only labor-intensive but also time-consuming and labor-intensive; (2) There is a high safety risk in constructing a steel sheet pile cofferdam at sea. Due to the phased construction problem mentioned in (1), the workers need to work on the water many times, and there is no reliable and safe platform, which poses a high risk of safe construction; (3) The cost of tooling equipment is high and the economy is poor. During construction, the construction team needs to process the guide frame and the purlin structure separately. The two structures are used separately, resulting in a large amount of steel, which is not economical in construction. Summary of the invention

[0004] The main technical problem to be solved by the present invention is to provide a construction device and a construction method for a steel sheet pile cofferdam, so as to realize the integrated construction of positioning and supporting from the perspectives of structure and process, so as to improve the construction efficiency.

[0005] In order to solve the above technical problems, the present invention provides a positioning support device for steel sheet pile construction, comprising a perimeter purlin and a plurality of support components;

[0006] The surrounding purlin is a rigid plane structure formed by a number of purlins;

[0007] One side of the support assembly is fixed to the purlin; the other side of the support assembly extends within the enclosed area of ​​the surrounding purlin to form an attachment end;

[0008] When the attachment end of the support assembly is fixedly connected to the existing steel casing on the seabed: the support assembly and the steel casing form a rigid structure in a vertical plane; the perimeter purlin is indirectly fixed to the periphery of the steel casing to position and support the installation of the steel sheet piles;

[0009] The positioning support device also includes a positioning plate for positioning the steel sheet pile during driving construction.

[0010] In a preferred embodiment, the steel sheet pile is provided with locking openings on both sides;

[0011] The positioning plate is limitedly matched with the purlin along the width direction of the purlin; the positioning plate is provided with a first notch on the side close to the steel sheet pile, and the first notch is equal to the distance from the locking mouth to the purlin so as to be nested in the outer periphery of the locking mouth.

[0012] In a preferred embodiment, the support assembly is a triangular support structure, including a first support rod and a second support rod; at least one of the first support rod and the second support rod is fixed to the purlin;

[0013] When the support assembly is fixedly connected to the steel casing, the first support rod, the second support rod and the steel casing form a triangular structure in a vertical plane.

[0014] In a preferred embodiment, the first support rod is a horizontal support rod, and the second support rod is an oblique support rod; one end of the horizontal support rod is fixed to the side of the purlin, and one end of the oblique support rod is fixed in the length direction of the first support rod; the ends of the horizontal support rod and the oblique support rod away from the purlin extend on the inner side of the surrounding purlin and are located on the same vertical line.

[0015] In a preferred embodiment, the enclosure purlin is a rectangular structure; the enclosure purlin is provided with angle braces at the corners; the two ends of the angle braces are respectively rigidly connected or hinged to two adjacent purlins to jointly construct a triangular structure.

[0016] In a preferred embodiment, it further includes a plurality of corbels; when the steel sheet piles are installed, the roots of the corbels are welded, riveted or bolted to the steel sheet piles, and the tops support the surrounding purlins.

[0017] The present invention also provides a method for constructing a steel sheet pile cofferdam, which uses the positioning support device for steel sheet pile construction described above;

[0018] The construction method comprises the following steps:

[0019] Step 1: driving the steel casing into the seabed and mapping the relative position and actual size of the steel casing;

[0020] Step 2: Locate and draw the relative position and size of the steel casing measured in step 1 on the processing site; use the drawn steel casing as a positioning reference, and lay out the axis of the purlin, angle brace and horizontal support rod on the processing site according to the design drawings;

[0021] Step 3: Select the steel structure used for processing the positioning support device, and cut and trim the steel structure according to the design drawings;

[0022] Step 4: According to the design drawings, the purlins, angle braces, horizontal support rods and diagonal support rods are connected as a whole;

[0023] Step 5: Mark the welding positions of the attachment ends of the horizontal support rod and the oblique support rod and the steel casing on the surface of the steel casing;

[0024] Step 6: hoist the positioning support device to the periphery of the steel casing and adjust it to the installation position described in step 5, and then weld the attachment ends of the horizontal support rod and the oblique support rod to the steel casing;

[0025] Step 7: Using the surrounding purlin as a guide mechanism, the steel sheet piles are inserted and driven.

[0026] In a preferred embodiment, the following steps are further performed after step 7:

[0027] Step 8: The root of the corbel is welded or bolted to the first steel sheet pile, and the top is abutted against the bottom of the purlin, or welded or bolted to the purlin from the bottom of the purlin;

[0028] Step 9: During low tide, the oblique support rods and the horizontal support rods are cut off, and the steel casing is removed.

[0029] In a preferred embodiment, the step 4 comprises the following steps:

[0030] Step 41: hoisting the purlins in sequence and placing them at the layout position; connecting the plurality of purlins according to the design drawings to form the enclosure purlin;

[0031] Step 42: hoisting the angle brace and placing it at the lofted position; then connecting the angle brace to the purlin;

[0032] Step 43: hoisting the horizontal support rod and placing it at the lofting position; then connecting the horizontal support rod with the purlin;

[0033] Step 44: Locate the position of the oblique support rod above or below the horizontal support rod; then hoist the oblique support rod to the lofted position and connect it to the horizontal support rod.

[0034] In a preferred embodiment, the steel sheet pile includes a first steel sheet pile and a second steel sheet pile, and the first steel sheet pile and the second steel sheet pile are centrally symmetrically connected through the locking opening;

[0035] The step 7 comprises the following steps:

[0036] Step 71: using a pile driver to clamp the first steel sheet pile to the outside of the enclosure purlin, so that the first steel sheet pile is in close contact with the enclosure purlin;

[0037] Step 72: inserting the first steel sheet pile and controlling the penetration and verticality of the first steel sheet pile;

[0038] Step 73: the positioning plate is arranged on the purlin; the second steel sheet pile is clamped by a pile driver, and one side locking opening of the second steel sheet pile is locked with the adjacent first steel sheet pile locking opening, and the other side locking opening is embedded in the first notch of the positioning plate; the second steel sheet pile is driven in the manner of step 72;

[0039] Step 74: Clamp another piece of the first steel sheet pile to be closely attached to the outer side of the purlin, and lock one side locking opening of the first steel sheet pile with the locking opening of the second steel sheet pile; and drive the first steel sheet pile in the manner of step 72;

[0040] Step 75: Repeat steps 73 to 74 until the steel sheet piles are closed on the outside of the purlin.

[0041] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0042] The positioning and supporting device adopted in the construction method provided by the present invention has the functions of a traditional guide frame and a surrounding purlin at the same time, and realizes integrated construction of positioning and supporting from the perspectives of structure and process, which not only improves construction efficiency and saves construction costs, but also reduces the number of times workers work on water, thereby improving construction safety and quality.

[0043] The construction method provided by the present invention adopts the positioning plate to assist in positioning the steel sheet piles, thereby improving the insertion accuracy of the steel sheet piles under seawater conditions.

[0044] The positioning support device provided by the present invention has a simple structure and reliable connection, and can be hoisted into the water after the overall production of the water working platform is completed, thereby ensuring the construction quality and greatly reducing the construction difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a three-dimensional schematic diagram of the positioning support device in Embodiment 1 and Embodiment 2 of the present invention when it cooperates with the steel casing and the steel sheet pile for construction;

[0046] Figure 2 It is a top view of the positioning support device described in Embodiment 1 and Embodiment 2 of the present invention when it cooperates with the steel casing and the steel sheet pile for construction;

[0047] Figure 3 It is a cross-sectional view of the positioning support device in Embodiment 1 and Embodiment 2 of the present invention when it cooperates with the steel casing and the steel sheet pile for construction;

[0048] Figure 4 It is a three-dimensional schematic diagram of the positioning support device described in Embodiment 1 and Embodiment 2 of the present invention;

[0049] Figure 5 It is a three-dimensional schematic diagram of the positioning plate in the first embodiment and the second embodiment of the present invention when working;

[0050] Figure 6 This is a top view of the positioning plate described in Embodiment 1 and Embodiment 2 of the present invention when in operation.

[0051] Markings in the figure are: 1-positioning support device for steel sheet pile construction, 11-purlin, 111-purlin, 12-support assembly, 121-horizontal support rod, 122-oblique support rod, 13-angle brace, 14-corbel, 15-positioning plate, 151-first notch, 152-second notch, 2-steel casing, 3-steel sheet pile, 30-lock, 31-first steel sheet pile, 32-second steel sheet pile, 4-seabed. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0053] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0054] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "provided with", "installed / connected", "connected", etc. should be understood in a broad sense. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium. It can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0055] Embodiment 1

[0056] like Figure 1 to Figure 6 As shown, an embodiment of the present invention provides a positioning support device 1 for steel sheet pile construction, which uses the existing steel casing 2 on the seabed 4 as a positioning reference to position and support the construction of the steel sheet pile cofferdam. The positioning support device 1 includes a purlin 11, a plurality of support components 12, a corbel 14 and a positioning plate 15. The plurality of support components 12 fix the purlin 11 to the periphery of the steel casing 2 so that the purlin 11 can position the insertion of the steel sheet pile 3. When the steel sheet pile 3 is inserted and closed, the purlin 11 is fixed to the inner side of the steel sheet pile 3 through the corbel 14 to provide lateral support for the steel sheet pile 3. The specific structure and connection relationship of the above components are further explained below in conjunction with the illustrations.

[0057] The purlin 11 is welded by at least four purlins 111, and the whole is a rigid rectangular structure. In order to improve the in-plane rigidity, the purlin 11 is provided with a corner brace 13 at the corner. The two ends of the corner brace 13 are respectively rigidly connected or hinged to the two adjacent purlins 111 to jointly construct a triangular structure, thereby improving the deformation resistance of the purlin 11 in the horizontal direction. For the convenience of description, the side of the purlin 11 facing the rectangular area is defined as the inner side, and the side away from the rectangular area is defined as the outer side.

[0058] like Figure 3-4As shown, similar to the common air conditioner outdoor unit support frame, the support assembly 12 is a triangular support structure, including a first support rod and a second support rod. In this embodiment, the first support rod is a horizontal support rod 121, and the second support rod is an oblique support rod 122. The horizontal support rod 121 is vertically welded to the inner side of the purlin 111 and extends inward along the plane direction of the surrounding purlin 11. The oblique support rod 122 is welded to the length direction of the horizontal support rod 121 and is in the same vertical plane as the horizontal support rod 121. For the convenience of description, the ends of the horizontal support rod 121 and the oblique support rod 122 away from the purlin 111 are defined as attachment ends. As shown in the figure, the attachment ends of the horizontal support rod 121 and the oblique support rod 122 are on the same vertical line. When the positioning support device 1 is installed on the steel casing 2, the attachment ends of the horizontal support rod 121 and the oblique support rod 122 are welded to the outer wall of the steel casing 2 at different heights, and the extension direction of the horizontal support rod 121 passes through the center of the steel casing 2 to ensure that the support assembly 12 is stable under force. In order to improve the lateral stability of the support assembly 12 and the surrounding purlin 11, an arc plate can be welded to the attachment ends of the horizontal support rod 121 and the oblique support rod 122, and the arc plate matches the curvature of the outer wall of the steel casing 2 to increase the connection area with the steel casing 2. It should be understood that as long as the same technical effect can be achieved, the connection method of the horizontal support rod 121 and the purlin 111 should not be limited. In other implementations, the horizontal support rod 121 can be bolted or riveted to the inner side of the purlin 111.

[0059] like Figure 1 , Figure 3 and Figure 4 As shown, at least one corbel 14 is welded below the purlin 111. The corbel 14 is flush with the purlin 111 on the outside so as not to affect the steel sheet pile 3 being inserted and driven in by being attached to the outside of the purlin 111. After the steel sheet pile 3 is inserted and driven with the surrounding purlin 11 as a guide mechanism, the root of the corbel 14 facing the outside is welded or bolted to the steel sheet pile 3. In this way, even if the support assembly 12 is removed due to construction needs, the surrounding purlin 11 can be stably fixed to the inner side of the steel sheet pile 3 by the corbel 14, providing lateral support to the steel sheet pile 3. It can be understood that in other embodiments, the corbel 14 can be separated from the purlin 111. When the corbel 14 is fixed to the inner wall of the steel sheet pile 3, the top abuts against the purlin 111 or is bolted to the purlin 111, so as to support the purlin 111.

[0060] like Figure 6As shown, the steel sheet piles 3 in this embodiment are Larsen steel sheet piles, with a "J"-shaped cross section and locks 30 on both sides. As shown in the figure, when the steel sheet piles 3 are inserted into the seabed 4 close to the purlin 11, two adjacent steel sheet piles 3 are staggered and connected in a centrally symmetrical manner through the locks 30. Therefore, when one of the steel sheet piles 3 is close to the purlin 11, any adjacent steel sheet pile 3 is separated from the purlin 11, lacking reliable positioning when inserted. For the convenience of the following description, the steel sheet piles 3 inserted close to the purlin 11 are defined as first steel sheet piles 31, and the steel sheet piles 3 separated from the purlin 11 are defined as second steel sheet piles 32.

[0061] To solve this problem, the positioning support device 1 is also provided with a positioning plate 15. Figure 5-6 As shown, the positioning plate 15 adopts a T-shaped cross-section, which is formed by vertically welding the wing plate at the top and the web plate at the bottom. The web plate is provided with two second notches 152 at intervals along the length direction, and the distance between the two second notches 152 is equal to the width of the purlin 111, so that the positioning plate 15 can be nested on the purlin 111. In this way, the positioning plate 15 can slide along the extension direction of the purlin 111, and limit the purlin 111 along the width direction of the purlin 111. The positioning plate 15 extends a certain length along the outer side direction of the purlin 111. The web plate is provided with two opposite first notches 151 in the outer side direction of the purlin 111, and the distance from the first notch 151 to the outer edge of the purlin 111 is equal to the cross-sectional height of the steel sheet pile 3. In other words, the first notch 151 is equal to the distance from the locking opening 30 of the first steel sheet pile 31 to the outer edge of the purlin 111. When the second steel sheet pile 32 needs to be driven into the seabed 4, the locking opening 30 on one side can be connected to the locking opening 30 of the second steel sheet pile 32, and the locking opening 30 on the other side can be embedded in the first notch 151, so as to ensure that there is no deviation when the pile is driven, thereby improving the driving accuracy of the steel sheet pile 3 in seawater conditions.

[0062] Embodiment 2

[0063] like Figure 1 to Figure 6 As shown, an embodiment of the present invention provides a construction method of a steel sheet pile cofferdam, which adopts a positioning support device 1 for steel sheet pile construction described in Example 1. The construction method includes the following steps:

[0064] Step 1: The steel casing 2 is driven into the seabed 4 by a vibratory hammer, and the relative position and actual size of the steel casing 2 are measured.

[0065] Step 2: Clear a steel structure processing site on the offshore platform. Layout and draw the relative position and size of the steel casing 2 measured in step 1 on the processing site. Using the drawn steel casing 2 as the positioning reference, layout the axis of the purlin 11, corner brace 13 and horizontal support rod 121 on the processing site according to the design drawings, and make positioning marks.

[0066] Step 3: Select the steel structure used for processing the positioning support device 1, and cut and trim the steel structure according to the lengths of the purlins 111, the angle braces 13, the horizontal support rods 121 and the oblique support rods 122 on the design drawings, as well as the welding angles of the ends of each rod. If the above-mentioned rods are combined in cross section using double-jointed steel structures, the steel structures that need to be double-joined should be welded after cutting to form a whole.

[0067] Step 4: According to the design drawings, the purlin 111, the angle brace 13, the horizontal support rod 121 and the oblique support rod 122 are welded into a whole. The specific steps are as follows:

[0068] Step 41: hoist the purlins 111 in sequence and place them in place according to the layout positions on the processing site, so that the purlins 111 enclose a closed frame. Weld the ends of the purlins 111, requiring the weld thickness to meet the design requirements, the weld to be full, without holes and slag inclusions;

[0069] Step 42: hoist the angle brace 13, place it in place according to the layout position on the processing site and perform on-site welding;

[0070] Step 43: hoisting the horizontal support rod 121, placing it in place according to the layout position on the processing site and welding it on site;

[0071] Step 44: Locate the position of the oblique support rod 122 on the horizontal support rod 121, then hoist the oblique support rod 122 to the lofted position, and then weld it to the horizontal support rod 121;

[0072] Step 45: Welding lifting ears at the mid-span positions of the four sides of the plurality of purlins 111 to facilitate construction workers to lift the positioning support device 1.

[0073] Step 5: Mark the installation position of the positioning support device 1 on the surface of the steel casing 2 on the seabed 4, specifically the welding position of the attachment ends of the horizontal support rod 121 and the oblique support rod 122 and the steel casing 2.

[0074] Step 6: Use the sling to hoist the positioning support device 1 to the periphery of the steel casing 2, and slowly adjust it to the installation position described in step 5. After checking, weld the attachment ends of the horizontal support rod 121 and the oblique support rod 122 to the steel casing 2. If there is a gap between the attachment end of the support assembly 12 and the surface of the steel casing 2, a gusset plate can be used for welding to fill it.

[0075] Step 7: Use the purlin 11 as a guide mechanism to drive the steel sheet piles 3. In this embodiment, the steel sheet piles 3 are Larsen steel sheet piles. The specific driving and driving construction can be divided into the following steps:

[0076] Step 71: using a pile driver to clamp the first steel sheet pile 31 to the outside of the surrounding purlin 11, so that the first steel sheet pile 31 is in close contact with the surrounding purlin 11;

[0077] Step 72: inserting and driving the first steel sheet pile 31. During the inserting and driving process, the penetration and elevation of the first steel sheet pile 31 need to be well controlled, and in order to ensure the verticality of the steel sheet pile 3, two theodolites are used to monitor and control in different directions;

[0078] Step 73: Install the positioning plate 15 described in the first embodiment on the purlin 111. Then use a pile driver to clamp the second steel sheet pile 32 to the piling position. To prevent displacement, the locking opening 30 on one side of the second steel sheet pile 32 is locked with the locking opening 30 of the adjacent first steel sheet pile 31, and the locking opening 30 on the other side is embedded in the first notch 151 of the positioning plate 15. The second steel sheet pile 32 is driven in according to the method in step 72. After the driving is completed, the positioning plate 15 is removed;

[0079] Step 74: Clamp another first steel sheet pile 31 to be closely attached to the outer side of the purlin 11, and lock one side locking opening 30 with the locking opening 30 of the second steel sheet pile 32, and drive the first steel sheet pile 31 in the manner of step 72;

[0080] Step 75: Repeat steps 73 to 74 until the steel sheet piles 3 are closed on the outside of the purlin 11 .

[0081] Step 8: A corbel 14 is arranged at a position 1 / 4 of the length from the end of the purlin 111. Specifically, the base of the corbel 14 is welded to the first steel sheet pile 31, and the top thereof abuts against the bottom of the purlin 111, or is welded or bolted to the purlin 111 from the bottom of the purlin 111.

[0082] Step 9: During the ebb tide, check whether the components of the positioning support device 1 are correctly installed and reliably connected. After ensuring that they are correct, cut off the oblique support rods 122 and the horizontal support rods 121, and remove the steel casing 2. At this time, the purlin 11 is completely supported by the corbels 14. Furthermore, according to actual needs, other support rods can be added in the plane of the purlin 11 to reinforce the plane rigidity of the purlin 11.

[0083] Step 10: Set up observation equipment and observation points to observe the deformation of the steel sheet pile cofferdam to ensure stability and reliability.

[0084] It is understandable that, in other embodiments, the rods of the positioning support device 1 may also be connected by bolt connection, rivet connection, etc., without affecting the technical effects of the embodiments of the present invention.

[0085] The above description is only a preferred specific implementation mode of the present invention, and does not limit the patent scope of the present invention. Any technical equivalent changes made using the contents of the present invention specification shall fall within the protection scope of the present invention.

Claims

1. A positioning support device for steel sheet pile construction, characterized in that: It includes a purlin and several supporting components; The surrounding purlin is a rigid plane structure formed by a number of purlins; One side of the support assembly is fixed on the purlin; The other side of the support assembly extends within the enclosed area of ​​the purlin to form an attachment end; When the attachment end of the support assembly is fixedly connected to the existing steel casing on the seabed: the support assembly and the steel casing form a rigid structure in a vertical plane; the perimeter purlin is indirectly fixed to the periphery of the steel casing to position and support the installation of the steel sheet piles; The positioning support device also includes a positioning plate for positioning the steel sheet pile during driving construction.

2. A positioning support device for steel sheet pile construction according to claim 1, characterized in that: The steel sheet pile is provided with locking openings on both sides; The positioning plate is limitedly matched with the purlin along the width direction of the purlin; the positioning plate is provided with a first notch on the side close to the steel sheet pile, and the first notch is equal to the distance from the locking mouth to the purlin so as to be nested in the outer periphery of the locking mouth.

3. A positioning support device for steel sheet pile construction according to claim 1, characterized in that: The support assembly is a triangular support structure, including a first support rod and a second support rod; at least one of the first support rod and the second support rod is fixed to the purlin; When the support assembly is fixedly connected to the steel casing, the first support rod, the second support rod and the steel casing form a triangular structure in a vertical plane.

4. A positioning support device for steel sheet pile construction according to claim 3, characterized in that: The first support rod is a horizontal support rod, and the second support rod is an oblique support rod; one end of the horizontal support rod is fixed to the side of the purlin, and one end of the oblique support rod is fixed in the length direction of the first support rod; the ends of the horizontal support rod and the oblique support rod away from the purlin extend on the inner side of the surrounding purlin and are located on the same vertical line.

5. A positioning support device for steel sheet pile construction according to claim 1, characterized in that: The surrounding purlin is a rectangular structure; the surrounding purlin is provided with angle braces at the corners; the two ends of the angle braces are respectively rigidly connected or hinged to two adjacent purlins to jointly construct a triangular structure.

6. A positioning support device for steel sheet pile construction according to claim 1, characterized in that: It also includes a plurality of corbels; when the steel sheet piles are installed, the roots of the corbels are welded, riveted or bolted to the steel sheet piles, and the tops support the surrounding purlins.

7. A construction method for a steel sheet pile cofferdam, characterized in that: A positioning support device for steel sheet pile construction as described in claims 1 to 6 is used; The construction method comprises the following steps: Step 1: driving the steel casing into the seabed and mapping the relative position and actual size of the steel casing; Step 2: Locate and draw the relative position and size of the steel casing measured in step 1 on the processing site; use the drawn steel casing as a positioning reference, and lay out the axis of the purlin, angle brace and horizontal support rod on the processing site according to the design drawings; Step 3: Select the steel structure used for processing the positioning support device, and cut and trim the steel structure according to the design drawings; Step 4: According to the design drawings, the purlins, angle braces, horizontal support rods and diagonal support rods are connected as a whole; Step 5: Mark the welding positions of the attachment ends of the horizontal support rod and the oblique support rod and the steel casing on the surface of the steel casing; Step 6: hoist the positioning support device to the periphery of the steel casing and adjust it to the installation position described in step 5, and then weld the attachment ends of the horizontal support rod and the oblique support rod to the steel casing; Step 7: Using the surrounding purlin as a guide mechanism, the steel sheet piles are inserted and driven.

8. The construction method of a steel sheet pile cofferdam according to claim 7, characterized in that: After step 7, there are the following steps: Step 8: The root of the corbel is welded or bolted to the first steel sheet pile, and the top is abutted against the bottom of the purlin, or welded or bolted to the purlin from the bottom of the purlin; Step 9: During low tide, the oblique support rods and the horizontal support rods are cut off, and the steel casing is removed.

9. The construction method of a steel sheet pile cofferdam according to claim 7, characterized in that: The step 4 comprises the following steps: Step 41: hoisting the purlins in sequence and placing them at the layout position; connecting the plurality of purlins according to the design drawings to form the enclosure purlin; Step 42: hoisting the angle brace and placing it at the lofted position; then connecting the angle brace to the purlin; Step 43: hoisting the horizontal support rod and placing it at the lofting position; then connecting the horizontal support rod with the purlin; Step 44: Locate the position of the oblique support rod above or below the horizontal support rod; then hoist the oblique support rod to the lofted position and connect it to the horizontal support rod.

10. The construction method of a steel sheet pile cofferdam according to claim 7, characterized in that: The steel sheet piles include a first steel sheet pile and a second steel sheet pile, and the first steel sheet pile and the second steel sheet pile are centrally symmetrically connected through the locking opening; The step 7 comprises the following steps: Step 71: using a pile driver to clamp the first steel sheet pile to the outside of the enclosure purlin, so that the first steel sheet pile is in close contact with the enclosure purlin; Step 72: inserting the first steel sheet pile and controlling the penetration and verticality of the first steel sheet pile; Step 73: the positioning plate is arranged on the purlin; the second steel sheet pile is clamped by a pile driver, and one side locking opening of the second steel sheet pile is locked with the adjacent first steel sheet pile locking opening, and the other side locking opening is embedded in the first notch of the positioning plate; the second steel sheet pile is driven in the manner of step 72; Step 74: Clamp another piece of the first steel sheet pile to be closely attached to the outer side of the purlin, and lock one side locking opening of the first steel sheet pile with the locking opening of the second steel sheet pile; and drive the first steel sheet pile in the manner of step 72; Step 75: Repeat steps 73 to 74 until the steel sheet piles are closed on the outside of the purlin.

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