Mud flat photovoltaic support structure of composite foundation string structure and construction method of mud flat photovoltaic support structure

Abstract

The invention provides a mud flat photovoltaic support structure of a composite foundation string structure and a construction method, the photovoltaic support structure comprises a plurality of photovoltaic support units arranged in parallel, and each photovoltaic support unit at least comprises a span support structure; each span support structure comprises two steel cylinder foundations and a string truss used for installing a photovoltaic panel, the two steel cylinder foundations are inserted into a mud flat foundation, the tops of the two steel cylinder foundations are each provided with a stand column support, and the two ends of the string truss are fixedly connected with the two stand column supports. The steel cylinder is adopted as a supporting foundation for erecting the photovoltaic support in the beach area, the steel pipe piles are driven in a hammering mode, construction is convenient, the bearing capacity is high, the wind and wave resistance is high, and the stable supporting performance of the beach photovoltaic support structure is guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of photovoltaic support construction, and in particular relates to a tidal flat photovoltaic support structure with a composite foundation string structure and a construction method thereof. Background Art

[0002] The tidal flats have the advantages of flat terrain, few obstructions, good lighting conditions, and easy integration with other industries, making them very suitable for the construction of medium-sized or larger photovoltaic power stations. At present, the scale of tidal flat photovoltaic projects under construction or planned in my country continues to grow.

[0003] The foundation soil of the tidal flat is soft and weak in bearing capacity, and the silt layer below is very thick. The PHC pipe piles commonly used at present will produce soil squeezing effect, which is prone to pile displacement and floating. In order to meet the bearing capacity and settlement requirements, it is necessary to drive through the silt layer, the pile length is long, and the construction period is long. In addition, the construction in the tidal flat area is affected by the high and low tides, and the construction window period is short, which greatly reduces the convenience and economy of the tidal flat photovoltaic project construction.

[0004] At the same time, the wind force in coastal tidal flats is stronger than inland areas, and they often face special weather conditions such as typhoons. The flexible cable structures commonly used in open waters such as fish ponds in inland areas will produce large vibration deformations under the action of wind, which has an adverse effect on the safety of photovoltaic structures and cannot be applied to tidal flats. Summary of the invention

[0005] In view of this, the present invention aims to propose a tidal flat photovoltaic support structure with a composite foundation string structure and a construction method thereof, so as to overcome the shortcomings of the existing tidal flat photovoltaic structure and improve the support stability of the tidal flat photovoltaic support.

[0006] First, the contents of the tidal flat photovoltaic support structure of the composite foundation string structure of the present invention are described as follows:

[0007] A tidal flat photovoltaic support structure with a composite foundation string structure, comprising a plurality of photovoltaic support units arranged in parallel, each photovoltaic support unit comprising at least one cross-support structure;

[0008] Each span support structure includes two steel cylinder foundations and a string truss for installing photovoltaic panels. The two steel cylinder foundations are inserted into the tidal flat foundation. A column support is respectively arranged on the top of the two steel cylinder foundations. The two ends of the string truss are connected and fixed to the two column supports.

[0009] Furthermore, the string truss includes two curved beams arranged one in front and one in the back, each of which is arched upwards, the two curved beams are connected to two column supports, and the arch height of the rear curved beam is greater than the arch height of the front curved beam, and a plurality of cross beams are connected between the two curved beams;

[0010] The two column supports are provided with first cables just below the two curved beams, and the two curved beams are respectively connected to the first cables through a plurality of inclined tie rods.

[0011] Furthermore, a second cable is connected between each curved beam near the two end positions and the corresponding column bracket.

[0012] Furthermore, the steel cylinder foundation comprises:

[0013] The steel cylinder is open at the upper and lower ends, and a plurality of auxiliary grids are arranged in the circumferential direction of the upper end of the inner wall of the steel cylinder, and the auxiliary grids are vertically provided with T-shaped grooves, and the upper ends of the T-shaped grooves are open and the lower ends are closed;

[0014] The cap is arranged corresponding to the upper port of the steel cylinder. The cap is a cylindrical structure, and a T-shaped insert plate is arranged in the T-shaped slot of the corresponding auxiliary grid on its side. The T-shaped insert plate is inserted into and fixed in the corresponding T-shaped slot to connect and fix the cap and the steel cylinder.

[0015] Furthermore, the inner wall of the steel cylinder is provided with reinforcing steel plate beams in the vertical and circumferential directions respectively.

[0016] Furthermore, the steel cylinder has a wall thickness of 10-15 mm, a diameter of 2-4 m, and a driving depth of 10-30 m.

[0017] Furthermore, when each photovoltaic support unit is provided with two or more support structures, the adjacent ends of the two adjacent spans of the support share a steel cylinder foundation 1, and the diameter of the shared steel cylinder foundation 1 is larger than the diameter of the steel cylinder foundation 1 at both ends of the photovoltaic support unit.

[0018] The above is a description of the invention content of the tidal flat photovoltaic support structure, and the following is a description of its construction method:

[0019] A method for constructing a tidal flat photovoltaic support structure with a composite foundation string structure comprises the following steps:

[0020] S10: During high tide, use a transport ship to transport the steel cylinder foundation related components to the tidal flat operation area;

[0021] S20. When the water level is low or the tide is low, the steel cylindrical piles are inserted into the set position of the mudflat foundation by their own weight to ensure that the plane position and verticality of the steel cylindrical piles meet the requirements;

[0022] S30: Use a hydraulic vibrating hammer to vibrate and sink the steel cylinder until the depth of the steel cylinder meets the set requirements. During the vibration and sinking process of the steel cylinder, monitor its plane position and verticality. The position deviation is controlled within 15cm and the verticality deviation is ≤0.5‰;

[0023] S40, lift the cap, insert the cap into the upper port of the steel cylinder, insert the T-shaped plug plate of the cap into the T-shaped slot of the steel cylinder sub-grid and fix it, and complete the construction of the steel cylinder foundation;

[0024] S50. Install column brackets on the top of the steel cylinder foundation;

[0025] S60. After each string truss is tensioned, it is hoisted as a whole and connected and fixed to the corresponding column bracket to complete the construction of the tidal flat photovoltaic bracket structure.

[0026] Further, the steel cylinder structure design process includes the following steps:

[0027] a10: Determine the stress condition of the steel cylinder foundation: bear the deadweight of the upper structure, wind load, and current load at high tide;

[0028] The deadweight of the superstructure is the sum of the weight of the column supports, the string truss and the installed photovoltaic panels;

[0029] The wind load is the sum of the wind loads on the windward side of the photovoltaic panel and the windward side of the column above the water surface;

[0030] a20: Calculation of wind load and current load on steel cylinder foundation:

[0031] Calculation of wind loads:

[0032] F 风 =KK2P0A(N)

[0033] Where:

[0034] K- wind load shape factor, which is 0.5 for columns and 1.0 for photovoltaic panels;

[0035] K2-coefficient of variation of wind pressure height at sea;

[0036] P0-basic wind pressure (Pa);

[0037] A-wind-exposed area, the contour projection area perpendicular to the wind direction (m 2 );

[0038] According to this formula, the wind loads on the windward side of the photovoltaic panel and the windward side of the column above the water surface are calculated respectively, and then the two are added together to obtain the wind load size of the steel cylinder foundation.

[0039] The calculation of ocean current load is based on the formula:

[0040]

[0041] Where:

[0042] C D -Drag coefficient 0.6-1.0;

[0043] ρ-seawater density (kg / m 3) ;

[0044] U C - Design current velocity, using the maximum current velocity that may occur during the use of the structure (m / s);

[0045] A-projection area of ​​the component perpendicular to the direction of the ocean current (m 2 );

[0046] a30: Calculate the vertical and horizontal forces on the steel cylinder foundation based on the deadweight of the upper structure of the steel cylinder foundation, the wind load and the current load it bears;

[0047] a40: Initially set the steel cylinder diameter D, side wall thickness t and driving depth L, and calculate its vertical and horizontal bearing limit conditions based on the initial set size of the steel cylinder:

[0048] Among them, the vertical bearing limit of the steel cylinder is:

[0049]

[0050] Where:

[0051] c-soil cohesion (kPa);

[0052] D-diameter of steel cylinder (m);

[0053] L- steel cylinder driving depth (m);

[0054] γ-Heavyness of foundation soil at the bottom of steel cylinder (kN / m 3 );

[0055] γ0-weighted average density of soil above the bottom of the steel cylinder (kN / m 3 );

[0056] N c 、N q 、N r — is a dimensionless constant determined by the friction angle φ in the soil:

[0057]

[0058] Horizontal bearing limit of steel cylinder foundation:

[0059]

[0060] Where:

[0061] c-soil cohesion (kPa);

[0062] D-diameter of steel cylinder (m);

[0063] L- steel cylinder driving depth (m);

[0064] k- rotation angle of steel cylinder under external load (rad);

[0065] m- Proportional coefficient of soil horizontal foundation resistance coefficient with depth growth (kN / m 4 );

[0066] C0-vertical foundation reaction coefficient of soil at the bottom of the cylinder (kN / m 3 );

[0067] t- steel cylinder thickness (m);

[0068] a50: Compare F 竖向 Compared with the vertical force of the steel cylinder foundation obtained in a30, F 水平 and the horizontal force on the steel cylinder foundation obtained in a30, if F 竖向 Greater than the vertical force of the steel cylinder foundation, F 水平 If it is greater than the horizontal force acting on the steel cylinder foundation, it means that the diameter D of the steel cylinder meets the requirements; otherwise, it means that the bearing capacity of the steel cylinder with this diameter is insufficient and the diameter of the steel cylinder needs to be increased until the calculation result meets the requirements.

[0069] Compared with the prior art, the tidal flat photovoltaic support structure of the composite foundation string structure and the construction method thereof described in the present invention have the following advantages:

[0070] In the present invention, a steel cylinder is used as the supporting foundation for erecting a photovoltaic bracket in a tidal flat area, and steel pipe piles are driven by hammering, which is convenient for construction, has high bearing capacity, and high wind and wave resistance, thereby ensuring the stable supporting performance of the tidal flat photovoltaic bracket structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0072] Figure 1 A front view of a tidal flat photovoltaic support structure of a composite foundation string structure according to an embodiment of the present invention;

[0073] Figure 2 A top view of the coated photovoltaic support structure according to an embodiment of the present invention;

[0074] Figure 3 This is a front view of a column support when two adjacent span support structures share a steel cylinder foundation in an embodiment of the present invention;

[0075] Figure 4 It is a top view of a column support when two adjacent span support structures share a steel cylinder foundation in an embodiment of the present invention;

[0076] Figure 5 This is a schematic diagram of the auxiliary grid structure in the steel cylinder of the present invention;

[0077] Figure 6 It is a three-dimensional schematic diagram of a cap in an embodiment of the present invention.

[0078] Description of reference numerals:

[0079] 1-steel cylinder foundation; 11-steel cylinder; 12-cap; 13-sub-grid; 131-T-slot; 14-T-plug plate; 15-reinforced steel plate beam; 2-column bracket; 21-column; 22-connecting beam; 3-chord truss; 31-curved beam; 32-first cable; 33-oblique stay rod; 34-cross beam; 35-second cable. DETAILED DESCRIPTION

[0080] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0081] First, a specific implementation method of a tidal flat photovoltaic support structure with a composite foundation string structure is described as follows:

[0082] like Figure 1 , Figure 2 As shown, a composite foundation string structure for tidal flat photovoltaic support structure includes a plurality of photovoltaic support units arranged in parallel, and each photovoltaic support unit includes at least one span support structure. The truss span is determined based on the project land scale, power generation, photovoltaic module size and other factors, and can be set between 30-80m after the overall structural stability verification. Each span support structure includes two steel cylinder foundations 1 and a string truss 3 for installing photovoltaic panels. The two steel cylinder foundations 1 are inserted into the tidal flat foundation, and a column support 2 is respectively arranged on the top of the two steel cylinder foundations 1. The two ends of the string truss 3 are connected and fixed to the two column supports 2.

[0083] Preferably, the two column brackets 2 in each span have different heights, so that the two ends of the string truss 3 are arranged in a tilted state after installation. This structure can increase the number of photovoltaic panels installed on the string truss 3 and increase the power generation.

[0084] When each photovoltaic support unit is provided with two or more support structures, the adjacent ends of the two adjacent spans of the support share a steel cylinder foundation 1, and the diameter of the shared steel cylinder foundation 1 is larger than the diameter of the steel cylinder foundation 1 at both ends of the photovoltaic support unit.

[0085] Each column bracket 2 is as follows Figure 3 , Figure 4As shown, it includes two columns 21 arranged one after the other on the top of the steel cylinder foundation 1, and a connecting beam 22 connecting the two columns 21. When the adjacent ends of two adjacent spans share a steel cylinder foundation 1, two column brackets 2 are arranged opposite the shared steel cylinder foundation 1, and the two column brackets 2 are of different heights. At this time, the two column brackets 2 include a total of four columns 21, arranged in a square shape, and a connecting beam 22 is provided between each two adjacent columns 21, which improves the support stability of the column brackets 2 as a whole.

[0086] The specific structure of the string truss 3 is as follows: the string truss 3 includes two curved beams 31 arranged one in front of the other and each of which is arched upward, and the arch height of the rear curved beam 31 is greater than the arch height of the front curved beam 31. The front and rear positions of the two curved beams 31 correspond to the positions of the two columns 21 in each column bracket 2, so that the curved beams 31 and the corresponding columns 21 are connected and fixed.

[0087] In order to improve the support strength of the string truss 3, several cross beams 34 are connected between the two curved beams 3. At the same time, the two column brackets 2 are provided with first cables 32 directly below the two curved beams 31. The two curved beams 32 are respectively connected to the first cables 32 through several inclined rods 33. A second cable 35 is connected between each curved beam 31 and the corresponding column bracket 2 near the two end positions.

[0088] The steel cylinder foundation 1 includes a steel cylinder 11 and a cap 12. The upper and lower ends of the steel cylinder 11 are open. It is designed based on factors such as the mudflat foundation soil, wind force, and waves. After the overall stability of the structure is verified, the diameter of the steel cylinder is between 2 and 4 meters, the wall thickness is 10 to 15 mm, and the depth is 10-30 meters. Several auxiliary grids 13 are set in the circumferential direction of the upper end of the inner wall of the steel cylinder 11, such as Figure 5 As shown, the auxiliary grid 13 is vertically provided with a T-shaped slot 131, the upper end of the T-shaped slot 131 is open and the lower end is closed. In order to improve the strength of the steel cylinder 11 itself and prevent the cylinder wall from deforming, the inner wall of the steel cylinder 11 is vertically and circumferentially provided with a reinforcing steel plate beam 15. The structure of the cap 12 is as follows Figure 6 As shown, the cap 12 is a cylindrical structure, with a reserved hole on the top surface for installing the column bracket 2, and a T-shaped plug plate 14 is provided on the side corresponding to the T-shaped slot of the sub-grid 13. When the cap 12 and the steel cylinder 11 are assembled, the cap 12 is inserted into the upper port of the steel cylinder 11, and the T-shaped plug plate 14 is inserted and fixed in the corresponding T-shaped slot, so that the cap 12 and the steel cylinder 11 are stably connected.

[0089] The above is a description of an embodiment of a tidal flat photovoltaic support structure of a composite foundation string structure in the present invention. The following is a description of its construction method:

[0090] A method for constructing a tidal flat photovoltaic support structure with a composite foundation string structure comprises the following steps:

[0091] S10: During high tide, use a transport ship to transport the steel cylinder foundation related components to the tidal flat operation area;

[0092] S20. When the water level is low or the tide is low, the steel cylindrical piles are inserted into the set position of the tidal flat foundation by their own weight, and the plane position and verticality of the steel cylindrical piles are detected by a total station to ensure that the plane position and verticality of the steel cylindrical piles meet the requirements;

[0093] S30: Use a hydraulic vibratory hammer to vibrate and sink the steel cylinder until the depth of the steel cylinder meets the set requirements. The starting frequency of the vibratory hammer is 15Hz, and it is increased to 20Hz after 1 minute. During the vibration and sinking of the steel cylinder, monitor its plane position and verticality, and control the position deviation within 15cm, and the verticality deviation ≤0.5‰; if excessive displacement and deformation occur, stop vibration immediately, and take measures such as pulling up and sinking alternately and repeatedly until the displacement and deformation are less than the control value, and then restart vibration and sinking;

[0094] When the vibration sinking is close to 0.5m, adopt short-term (within 10s) vibration, one or two times can reach the allowable range of elevation;

[0095] S40. The cap is lifted by a crane ship and inserted into the upper port of the steel cylinder. The T-shaped plug plate of the cap is inserted into the T-shaped groove of the steel cylinder sub-grid. The cap mainly sinks by its own weight. When it is difficult to sink, static ballast can be used to assist. After the cap is installed in place, quick-setting sulphoaluminate concrete is injected into the sub-grid. After waiting for 30 minutes for final setting, the T-shaped plug plate and the sub-grid are fixed to complete the construction of the steel cylinder foundation.

[0096] S50. Install column brackets on the top of the steel cylinder foundation;

[0097] S60, assemble the tensioned trusses, and after tensioning each truss, hoist it as a whole and connect and fix it to the corresponding column brackets; complete the construction of the tidal flat photovoltaic bracket structure, and then lay the photovoltaic panels.

[0098] Before construction, the size of the steel cylinder structure is determined first, and the design process is as follows:

[0099] a10: Determine the stress condition of the steel cylinder foundation: bear the deadweight of the upper structure, wind load, and current load at high tide;

[0100] The deadweight of the superstructure is the sum of the weight of the column supports, the string truss and the installed photovoltaic panels;

[0101] The wind load is the sum of the wind loads on the windward side of the photovoltaic panel and the windward side of the column above the water surface;

[0102] a20: Calculation of wind load and current load on steel cylinder foundation:

[0103] Calculation of wind loads:

[0104] F 风 =KK2P0A(N)

[0105] Where:

[0106] K- wind load shape factor, which is 0.5 for columns and 1.0 for photovoltaic panels;

[0107] K2- offshore wind pressure height variation coefficient, refer to the provisions of the offshore wind pressure height variation coefficient in the "Regulations for Classification and Construction of Offshore Fixed Platforms";

[0108] P0-basic wind pressure (Pa), refer to the relevant provisions of the "Regulations for Classification and Construction of Offshore Fixed Platforms";

[0109] A-wind-exposed area, the contour projection area perpendicular to the wind direction (m 2 );

[0110] According to this formula, the wind loads on the windward side of the photovoltaic panel and the windward side of the column above the water surface are calculated respectively, and then the two are added together to obtain the wind load size of the steel cylinder foundation.

[0111] The calculation of ocean current load is based on the formula:

[0112]

[0113] Where:

[0114] C D -Drag coefficient 0.6-1.0;

[0115] ρ-seawater density (kg / m 3) ;

[0116] U C - Design current velocity, using the maximum current velocity that may occur during the use of the structure (m / s);

[0117] A-projection area of ​​the component perpendicular to the direction of the ocean current (m 2 );

[0118] a30: Calculate the vertical and horizontal forces on the steel cylinder foundation based on the deadweight of the upper structure of the steel cylinder foundation, the wind load and the current load it bears;

[0119] a40: Initially set the steel cylinder diameter D, side wall thickness t and driving depth L, and calculate its vertical and horizontal bearing limit conditions based on the initial set size of the steel cylinder:

[0120] Among them, the vertical bearing limit of the steel cylinder is mainly considered to be provided by the bearing capacity of the cylinder tip and the supporting force of the soil inside the cylinder. It is stipulated that when the vertical deformation reaches 0.05D (steel cylinder diameter), it is the vertical bearing limit:

[0121]

[0122] Where:

[0123] c-soil cohesion (kPa);

[0124] D-diameter of steel cylinder (m);

[0125] L- steel cylinder driving depth (m);

[0126] γ-Heavyness of foundation soil at the bottom of steel cylinder (kN / m 3 );

[0127] γ0-weighted average density of soil above the bottom of the steel cylinder (kN / m 3 );

[0128] N c 、N q 、N r — is a dimensionless constant determined by the friction angle φ in the soil:

[0129]

[0130] Horizontal bearing limit of steel cylinder foundation: The horizontal bearing capacity considers the soil in the cylinder and the steel cylinder as a rigid whole, and the horizontal soil resistance of the barrel foundation obeys the Winkler assumption, which stipulates that when the rotation angle of the cylinder reaches 0.02rad, it is the horizontal bearing limit:

[0131]

[0132] Where:

[0133] c-soil cohesion (kPa);

[0134] D-diameter of steel cylinder (m);

[0135] L- steel cylinder driving depth (m);

[0136] k- rotation angle of steel cylinder under external load (rad);

[0137] m- Proportional coefficient of soil horizontal foundation resistance coefficient with depth growth (kN / m 4 ), refer to the provisions on horizontal foundation resistance coefficient in the "Code for Design of Wharf Structures";

[0138] C0-vertical foundation reaction coefficient of soil at the bottom of the cylinder (kN / m 3 ), refer to the Technical Specifications for Raft and Box Foundations of High-Rise Buildings, and use plate load test, back calculation of average foundation settlement, and empirical value method to determine;

[0139] t- steel cylinder thickness (m);

[0140] a50: Compare F 竖向 Compared with the vertical force of the steel cylinder foundation obtained in a30, F 水平 and the horizontal force on the steel cylinder foundation obtained in a30, if F 竖向 Greater than the vertical force of the steel cylinder foundation, F 水平 If it is greater than the horizontal force acting on the steel cylinder foundation, it means that the diameter D of the steel cylinder meets the requirements; otherwise, it means that the bearing capacity of the steel cylinder with this diameter is insufficient and the diameter of the steel cylinder needs to be increased until the calculation result meets the requirements.

[0141] The design and verification of steel cylinder structures can be carried out by three-dimensional numerical modeling:

[0142] Three-dimensional numerical modeling is used to calculate the load-displacement deformation of the initially designed steel cylinder structure under single load and combined load.

[0143] The finite element analysis of the structure and foundation coupling system is carried out as a whole. The soil structure can adopt a linear elastic constitutive model, and the steel cylinder structure can be regarded as a rigid body.

[0144] The calculation range of the finite element model can be 10 times the diameter of the steel cylinder in the horizontal direction and 5 times the length of the steel cylinder in the vertical direction.

[0145] The main numerical simulation calculation process includes: establishing a geometric model, defining the structure and soil material properties, dividing the grid, establishing the analysis and calculation steps, initial stress balance, applying loads, and obtaining load-displacement deformation results.

[0146] The calculation results focus on the vertical and horizontal displacements and inclinations of the steel cylinder, the stress distribution of the steel cylinder structure and the displacement and deformation of the foundation soil, to determine whether the shear stability, anti-sliding stability, foundation bearing capacity, settlement and overall stability of the cylinder bottom meet the requirements.

[0147] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A tidal flat photovoltaic support structure with a composite foundation string structure, characterized in that: It includes a plurality of photovoltaic support units arranged in parallel, each photovoltaic support unit including at least one cross-support structure; Each span support structure comprises two steel cylinder foundations (1) and a chord truss (3) for installing photovoltaic panels. The two steel cylinder foundations (1) are inserted into the tidal flat foundation. A column support (2) is respectively arranged on the top of the two steel cylinder foundations (1). The two ends of the chord truss (3) are connected and fixed to the two column supports (2).

2. According to the composite foundation string structure of the tidal flat photovoltaic support structure of claim 1, it is characterized by: The string truss (3) comprises two curved beams (31) arranged one in front of the other and each of which is arched upwards, the two curved beams (31) are connected to two column supports (2), and the arch height of the rear curved beam (31) is greater than the arch height of the front curved beam (31), and a plurality of cross beams (34) are connected between the two curved beams (31); The two column brackets (2) are provided with first cables (32) directly below the two curved beams (31), and the two curved beams (31) are respectively connected to the first cables (32) via a plurality of inclined tie rods (33).

3. The tidal flat photovoltaic support structure of the composite foundation string structure according to claim 2 is characterized by: A second cable (35) is connected between each curved beam (31) near the two end positions and the corresponding column bracket (2).

4. The tidal flat photovoltaic support structure of the composite foundation string structure according to claim 1 is characterized by: The steel cylinder foundation (1) comprises: The steel cylinder (11) is open at both the upper and lower ends. A plurality of auxiliary grids (13) are arranged in the circumferential direction of the upper end of the inner wall of the steel cylinder (11). The auxiliary grids (13) are vertically arranged with T-shaped grooves, the upper ends of the T-shaped grooves are open and the lower ends are closed. The cover cap (12) is arranged corresponding to the upper end of the steel cylinder (11). The cover cap (12) is a cylindrical structure, and a T-shaped insert plate (14) is arranged on the side surface of the cover cap corresponding to the T-shaped slot of the auxiliary grid (13). The T-shaped insert plate (14) is inserted into and fixed in the corresponding T-shaped slot, and the cover cap (12) and the steel cylinder (11) are connected and fixed.

5. The tidal flat photovoltaic support structure of the composite foundation string structure according to claim 4 is characterized by: The inner wall of the steel cylinder (11) is provided with reinforcing steel plate beams (15) in the vertical and circumferential directions respectively.

6. The tidal flat photovoltaic support structure of the composite foundation string structure according to claim 4 is characterized by: The steel cylinder (11) has a wall thickness of 10-15 mm, a diameter of 2-4 m, and a driving depth of 10-30 m.

7. The tidal flat photovoltaic support structure of the composite foundation string structure according to claim 1 is characterized by: When each photovoltaic support unit is provided with a support structure of two or more spans, adjacent ends of two adjacent spans of the support share a steel cylindrical foundation (1), and the diameter of the shared steel cylindrical foundation (1) is greater than the diameter of the steel cylindrical foundations (1) at both ends of the photovoltaic support unit.

8. A construction method for a tidal flat photovoltaic support structure, characterized in that: The following steps are involved: S10: During high tide, use a transport ship to transport the steel cylinder foundation related components to the tidal flat operation area; S20. When the water level is low or the tide is low, the steel cylindrical piles are inserted into the set position of the tidal flat foundation by their own weight to ensure that the plane position and verticality of the steel cylindrical piles meet the requirements; S30: Use a hydraulic vibrating hammer to vibrate and sink the steel cylinder until the depth of the steel cylinder meets the set requirements. During the vibration and sinking process of the steel cylinder, monitor its plane position and verticality. The position deviation is controlled within 15cm and the verticality deviation is ≤0.5‰; S40, lift the cap, insert the cap into the upper port of the steel cylinder, insert the T-shaped plug plate of the cap into the T-shaped slot of the steel cylinder sub-grid and fix it, and complete the construction of the steel cylinder foundation; S50. Install column brackets on the top of the steel cylinder foundation; S60. After each string truss is tensioned, it is hoisted as a whole and connected and fixed to the corresponding column bracket to complete the construction of the tidal flat photovoltaic bracket structure.

9. The construction method of a tidal flat photovoltaic support structure according to claim 8, characterized in that: The steel cylinder structure design process includes the following steps: a10: Determine the stress condition of the steel cylinder foundation: bear the deadweight of the upper structure, wind load, and current load at high tide; The deadweight of the superstructure is the sum of the weight of the column supports, the string truss and the installed photovoltaic panels; The wind load is the sum of the wind loads on the windward side of the photovoltaic panel and the windward side of the column above the water surface; a20: Calculation of wind load and current load on steel cylinder foundation: Calculation of wind loads: F 风 =KK2P0A(N) Where: K- wind load shape factor, which is 0.5 for columns and 1.0 for photovoltaic panels; K2-coefficient of variation of wind pressure height at sea; P0-basic wind pressure (Pa); A-wind-exposed area, the contour projection area perpendicular to the wind direction (m 2 ); According to this formula, the wind loads on the windward side of the photovoltaic panel and the windward side of the column above the water surface are calculated respectively, and then the two are added together to obtain the wind load size of the steel cylinder foundation. The calculation of ocean current load is based on the formula: Where: C D -Drag coefficient 0.6-1.0; ρ-seawater density (kg / m 3) ; U C - Design current velocity, using the maximum current velocity that may occur during the use of the structure (m / s); A-projection area of ​​the component perpendicular to the direction of the ocean current (m 2 ); a30: Calculate the vertical and horizontal forces on the steel cylinder foundation based on the deadweight of the upper structure of the steel cylinder foundation, the wind load and the current load it bears; a40: Initially set the steel cylinder diameter D, side wall thickness t and driving depth L, and calculate its vertical and horizontal bearing limit conditions based on the initial size of the steel cylinder: Among them, the vertical bearing limit of the steel cylinder is: Where: c-soil cohesion (kPa); D-diameter of steel cylinder (m); L- steel cylinder driving depth (m); γ-Heavyness of foundation soil at the bottom of steel cylinder (kN / m 3 ); γ0-weighted average density of soil above the bottom of the steel cylinder (kN / m 3 ); N c 、N q 、N r — is a dimensionless constant determined by the friction angle φ in the soil: Horizontal bearing limit of steel cylinder foundation: Where: c-soil cohesion (kPa); D-diameter of steel cylinder (m); L- steel cylinder driving depth (m); k- rotation angle of steel cylinder under external load (rad); m- Proportional coefficient of soil horizontal foundation resistance coefficient with depth growth (kN / m 4 ); C0-vertical foundation reaction coefficient of soil at the bottom of the cylinder (kN / m 3 ); t- steel cylinder thickness (m); a50: Compare F 竖向 Compared with the vertical force of the steel cylinder foundation obtained in a30, F 水平 and the horizontal force on the steel cylinder foundation obtained in a30, if F 竖向 Greater than the vertical force of the steel cylinder foundation, F 水平 If it is greater than the horizontal force acting on the steel cylinder foundation, it means that the diameter D of the steel cylinder meets the requirements; otherwise, it means that the bearing capacity of the steel cylinder with this diameter is insufficient and the diameter of the steel cylinder needs to be increased until the calculation result meets the requirements.

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