Underwater photovoltaic panel construction method under hard geological condition

Abstract

The invention provides an underwater photovoltaic panel construction method under a hard geological condition, and belongs to the technical field of photovoltaic panel construction. A dry construction environment is formed by constructing a steel sheet pile cofferdam and cooperating with an air curtain water-resisting layer and high-pressure grouting; a cofferdam bearing stability evaluation value and a pit bottom dryness evaluation value are calculated based on water seepage amount and water level data, parameters of a dewatering well system and an air curtain are dynamically adjusted, and a hydraulic down-the-hole hammer drill provided with a high-frequency ultrasonic generating device is adopted to reduce the compressive strength of a rock stratum through the ultrasonic cavitation effect to complete pile foundation hole forming. Solving a game equilibrium point through a double-layer optimization model, obtaining an optimal construction parameter combination, adjusting equipment operation parameters, completing pile top processing and photovoltaic module installation, then removing the cofferdam, and achieving cross-unit cable laying through an overwater floating bridge. The technical problems that under the hard geological condition, the underwater photovoltaic pile foundation construction efficiency is low, and the cofferdam anti-seepage control difficulty is large are solved.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic panel construction technology, and more specifically, relates to a method for constructing underwater photovoltaic panels under hard geological conditions. Background Technology

[0002] Floating photovoltaic (PV) power generation systems typically require the construction of pile foundation support structures within water bodies. Traditional construction methods utilize floating platforms combined with impact drills or rotary drills for pile drilling, which is efficient enough for soft soil or medium-hard soil layers. However, when encountering hard bedrock strata such as granite and basalt with compressive strength exceeding 60 MPa, traditional drilling equipment requires frequent drill bit changes and has a slow drilling speed, often taking 3 to 5 times longer to complete a single pile hole than in conventional strata. Furthermore, sheet pile cofferdams, constructed to create a dry construction environment, struggle to form effective water-stopping interfaces in hard rock layers. Developed bedrock fissures lead to continuous seepage within the cofferdam, requiring existing dewatering systems to continuously pump water at high power to maintain construction conditions, significantly increasing energy costs and lacking scientific basis for adjusting construction parameters. In other words, existing technologies suffer from low construction efficiency and significant challenges in controlling seepage through cofferdams under hard geological conditions. Summary of the Invention

[0003] In view of this, the present invention provides a method for constructing floating photovoltaic panels under hard geological conditions, which can solve the technical problems of low construction efficiency and difficulty in controlling seepage prevention of floating photovoltaic pile foundations under hard geological conditions in the prior art.

[0004] This invention is implemented as follows: It provides a method for constructing floating photovoltaic panels under hard geological conditions. High-resolution multibeam echo sounding and underwater drilling are used to establish a three-dimensional geological model containing parameters of bedrock distribution, thickness, and strength in the designated water area of ​​the floating photovoltaic project. This model identifies construction areas in hard strata and plans waterless operation unit blocks. Steel sheet pile cofferdams are constructed sequentially for these waterless operation unit blocks, and annular perforated pipes are laid underwater around the perimeter to form an air curtain water-tight layer. Rising air bubbles generate a pressure gradient to establish a low-pressure buffer zone, reducing the hydrostatic pressure of the external water body. Simultaneously, flexible rubber waterstops are laid at the bottom of the steel sheet pile cofferdam, and high-pressure grouting is used to seal rock fissures. A dewatering well system is also used to pump out water, creating a dry construction environment. Seepage monitoring data is collected and compared with external... Water level data is used to calculate the cofferdam bearing stability assessment value and pit bottom dryness assessment value, and the layout density of the dewatering well system and the air injection pressure parameters of the air curtain water-proof layer are dynamically adjusted. In a dry environment, a hydraulic down-the-hole hammer drill equipped with a diamond drill bit and a high-frequency ultrasonic generator is used to generate microcracks on the rock surface by utilizing the ultrasonic cavitation effect to reduce the macroscopic compressive strength and complete the pile foundation hole formation. An upper-level optimization model with the goal of minimizing pumping power and a lower-level optimization model with the goal of maximizing hole formation efficiency are constructed. The optimal combination of construction parameters is obtained by solving the game equilibrium point through the correlation of water level coupling terms in the cofferdam, and the equipment operation parameters are adjusted. After the pile top treatment and photovoltaic module installation are completed, the cofferdam is dismantled and the adjacent units are connected by a floating bridge on the water to realize cross-unit cable laying.

[0005] The hard strata include bedrock, high-density gravel, or consolidated, deep, hard clay. The bedrock refers to granite, basalt, or limestone strata with a compressive strength exceeding 60 MPa.

[0006] Among them, the high-resolution multibeam bathymetry refers to the underwater detection technology that uses acoustic wave reflection characteristics to identify rock strata interfaces, and the underwater core drilling refers to the exploration method that uses drilling equipment to extract rock core samples from underwater bedrock and conducts physical tests to obtain mechanical parameters.

[0007] The air curtain waterproof layer forms a dense bubble curtain wall by continuously injecting compressed air through an annular perforated pipe. The low-pressure buffer zone refers to the area where the static water pressure of the external water body is reduced by 20% to 40%. The air curtain waterproof layer also prevents suspended particles from seeping into the steel sheet pile cofferdam to prevent piping damage.

[0008] The flexible rubber waterstop is a strip-shaped sealing element made of neoprene rubber with a thickness of 8 to 12 mm, which is laid at the bottom of the steel sheet pile cofferdam and the contact surface with the bedrock layer. The high-pressure grouting refers to the injection of cement grout with a pressure of 2 to 5 MPa into the rock fissures to solidify and form an anti-seepage layer.

[0009] The cofferdam bearing stability assessment value is calculated as the product of the difference between the water levels inside and outside the sheet pile cofferdam divided by the standard value of the design bearing water level difference of the cofferdam, and the horizontal displacement monitoring value of the sidewall of the sheet pile cofferdam divided by the standard value of the displacement safety limit.

[0010] The pit bottom dryness assessment value is calculated as the product of the standard moisture content value divided by the measured moisture content value of the soil at the bottom of the pit and the standard seepage rate value divided by the measured seepage rate value. The measured seepage rate value is the seepage monitoring data divided by the monitoring time period.

[0011] The stability threshold is set to 0.85, and the dryness threshold is set to 0.90. When the cofferdam bearing stability assessment value is lower than the stability threshold or the pit bottom dryness assessment value is lower than the dryness threshold, the parameters of the dewatering well system and the air curtain water-proof layer are dynamically adjusted.

[0012] The ultrasonic cavitation effect refers to the alternating positive and negative pressure generated by high-frequency vibration in the pore liquid of rocks, which leads to the generation and collapse of microbubbles. The shock wave and high temperature generated at the moment of microbubble collapse act on the cementation surface between rock particles to form a microcrack network.

[0013] The air-lift reverse circulation hole cleaning process refers to injecting compressed gas into the drill pipe to form a gas-liquid mixture, and using the buoyancy generated by the gas-liquid density difference to carry the rock cuttings at the bottom of the hole to the surface for discharge.

[0014] The objective function of the upper-level optimization model is the minimum value of the sum of the unit time pumping power value divided by the standard pumping power value and the air curtain operation power value divided by the standard air curtain power value. The constraint is that the measured water level inside the steel sheet pile cofferdam is not higher than the upper limit of the safe water level and the air injection pressure parameter does not exceed the pipeline pressure limit.

[0015] The objective function of the lower-level optimization model is the maximum value of the product of the hole depth per unit time divided by the standard hole depth and the drill bit life extension coefficient. The constraints are that the ultrasonic vibration frequency is in the range of 20,000 to 35,000 Hz and the drilling thrust does not exceed the thrust value corresponding to the drill pipe yield strength.

[0016] The water level coupling term within the cofferdam refers to the fact that the water level measurement value inside the sheet pile cofferdam changed by the pumping operation in the upper optimization model directly affects the static water pressure distribution in the hole during pile foundation construction in the lower optimization model. The game equilibrium point is the combination of parameters that makes the objective functions of the two models simultaneously reach the optimal state through an iterative algorithm.

[0017] The optimal combination of construction parameters includes optimized values ​​for four parameters: air injection pressure, water pumping flow rate, ultrasonic vibration frequency, and drilling thrust.

[0018] The inter-unit connection interface is a combination of standardized flanges and bolt holes pre-embedded in the ends of the photovoltaic support structure beams. The photovoltaic support structures of adjacent waterless operation unit blocks are mechanically spliced ​​together through the inter-unit connection interface to form an overall array frame.

[0019] The floating bridge is assembled from high-density polyethylene pontoons and aluminum alloy bridge panels. The cross-unit cable laying refers to connecting the output cables of photovoltaic panels in adjacent waterless operation unit blocks to the combiner box and then to the unified electrical combiner system via the floating bridge.

[0020] This invention weakens external hydrostatic pressure by forming an air curtain waterproof layer around a sheet pile cofferdam using an annular perforated pipe. Combined with a bottom flexible rubber waterstop and high-pressure grouting to seal rock fissures, a dual-index monitoring system is established for the cofferdam's bearing capacity stability assessment and the pit bottom dryness assessment, achieving dynamic coordinated control of the dewatering well system and the air curtain waterproof layer. During the pile foundation drilling stage, a hydraulic down-the-hole hammer drill equipped with a diamond drill bit and a high-frequency ultrasonic generator is used. The ultrasonic cavitation effect generates a micro-crack network on the rock surface, reducing macroscopic compressive strength and significantly improving the drillability of hard rock strata. By constructing an upper-layer optimization model aimed at minimizing pumping power and a lower-layer optimization model aimed at maximizing drilling efficiency, the two models are correlated through a water level coupling term within the cofferdam, and the game equilibrium point is solved to obtain the optimal parameter combination of injection pressure, pumping flow rate, ultrasonic vibration frequency, and drilling thrust. This ensures both the cofferdam's seepage prevention effect and improves drilling efficiency. In summary, this invention solves the technical problems mentioned in the background art, such as low construction efficiency of underwater photovoltaic pile foundations under hard geological conditions and difficulty in controlling seepage through cofferdams. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method of the present invention.

[0022] Figure 2 This is a graph showing the change in the evaluation value over time.

[0023] Figure 3 The diagram shows the iterative convergence process of the optimized model.

[0024] Figure 4 A bar chart comparing drilling efficiency. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0026] like Figure 1 The diagram shown is a flowchart of a method for constructing floating photovoltaic panels under hard geological conditions, provided by the present invention. This method includes the following steps:

[0027] S1. Conduct high-resolution multibeam bathymetry and underwater drilling and core sampling on the designated water area of ​​the floating photovoltaic project, establish a three-dimensional geological model including bedrock distribution, thickness and strength parameters, identify construction areas with hard underwater strata, and plan multiple independent waterless operation unit blocks based on the survey results.

[0028] S2. Construct closed steel sheet pile cofferdams for the selected waterless operation unit blocks in sequence. Annular perforated pipes are laid underwater around the steel sheet pile cofferdam to form an air curtain water barrier. The pressure gradient generated by the rising air curtain water barrier establishes a low-pressure buffer zone to weaken the hydrostatic pressure of the external water body. At the same time, flexible rubber waterstops are laid at the bottom of the steel sheet pile cofferdam and high-pressure grouting is used to seal rock fissures. The internal dewatering well system is used to pump out the water inside the steel sheet pile cofferdam to create a dry land construction environment.

[0029] S3. Collect the seepage monitoring data inside the steel sheet pile cofferdam and the external water level data, calculate the cofferdam bearing stability assessment value and the pit bottom dryness assessment value. When the cofferdam bearing stability assessment value is lower than the stability threshold or the pit bottom dryness assessment value is lower than the dryness threshold, dynamically adjust the dewatering well layout density of the dewatering well system and the air injection pressure parameters of the air curtain water-proof layer.

[0030] S4. In the dry land construction environment, a hydraulic down-the-hole hammer drill equipped with a diamond drill bit is used and a high-frequency ultrasonic generator is installed on the drill rod to apply longitudinal vibration of more than 20,000 times per second to the diamond drill bit. The ultrasonic cavitation effect is used to generate microcracks on the rock surface to reduce the macroscopic compressive strength. The air-lift reverse circulation hole cleaning process is used to complete the pile foundation hole and pour concrete to form the pile foundation.

[0031] S5. Construct an upper-level optimization model with the goal of minimizing pumping power and a lower-level optimization model with the goal of maximizing borehole efficiency. The objective function input of the upper-level optimization model includes the gas injection pressure value of the air curtain water barrier and the pumping flow rate value of the dewatering well system. The objective function input of the lower-level optimization model includes the ultrasonic vibration frequency value of the high-frequency ultrasonic generator and the drilling thrust value of the hydraulic down-the-hole hammer drill. The two models are correlated through the water level coupling term inside the cofferdam, and the game equilibrium point is solved to obtain the optimal combination of construction parameters.

[0032] S6. Adjust the operating parameters of the air curtain water-proof layer according to the gas injection pressure value in the optimal construction parameter combination; adjust the operating parameters of the dewatering well system according to the pumping flow rate value in the optimal construction parameter combination; adjust the operating parameters of the high-frequency ultrasonic generator according to the ultrasonic vibration frequency value in the optimal construction parameter combination; and adjust the operating parameters of the hydraulic down-the-hole hammer drill according to the drilling thrust value in the optimal construction parameter combination.

[0033] S7. The top elevation of the piles of the completed pile foundation is uniformly measured and cut to ensure that all pile tops are located on the same design elevation plane. A photovoltaic support structure and photovoltaic panel assembly with pre-embedded inter-unit connection interfaces are installed on the pile tops, and cable trenches between units are reserved.

[0034] S8. After completing the installation of the photovoltaic panel components in the current waterless operation unit block, dismantle the steel sheet pile cofferdam and stop the gas curtain water barrier to restore the water area. Connect the adjacent installed waterless operation unit blocks through the floating bridge to realize cross-unit cable laying and form a unified electrical bus system. Then move to the next planned waterless operation unit block and repeat steps S2 to S8 until all construction is completed.

[0035] The hard strata include bedrock, high-density gravel, or consolidated, deep, hard clay layers, wherein the bedrock refers to layers with a compressive strength exceeding 60. Granite, basalt or limestone strata.

[0036] The high-resolution multibeam bathymetry refers to an underwater detection technology that uses acoustic wave reflection characteristics to identify rock strata interfaces. The underwater core drilling refers to an exploration method that uses drilling equipment to extract rock core samples from underwater bedrock and conducts physical tests to obtain mechanical parameters. The three-dimensional geological model is a digital geological structure model that includes spatial coordinates, rock strata thickness, and strength parameters, established based on bathymetry data and rock core test data.

[0037] The air curtain waterproof layer continuously injects compressed air through the annular perforated pipe to form a dense bubble curtain wall. The water flow disturbance generated by the rising bubble curtain wall creates a pressure gradient distribution around the steel sheet pile cofferdam. The low-pressure buffer zone refers to the area where the static water pressure of the external water body is reduced by 20% to 40%. The air curtain waterproof layer also prevents suspended particles from penetrating into the steel sheet pile cofferdam to prevent piping damage.

[0038] The flexible rubber waterstop has a thickness of 8 to 12 mm. The neoprene rubber strip seal is laid at the bottom of the steel sheet pile cofferdam at the contact surface with the bedrock layer. The high-pressure grouting refers to the use of pressures of 2 to 5. The cement grout is injected into the rock fissures and solidifies to form an impermeable layer.

[0039] The seepage monitoring data refers to the volume of water seeping into the steel sheet pile cofferdam per unit time, measured by a flow meter, and the external water level data refers to the water surface elevation of the water area outside the steel sheet pile cofferdam, measured by a water level gauge.

[0040] The method for calculating the cofferdam bearing stability assessment value is to divide the difference between the water levels inside and outside the steel sheet pile cofferdam by the standard value of the design bearing water level difference of the cofferdam, and then multiply the product of the horizontal displacement monitoring value of the sidewall of the steel sheet pile cofferdam by the standard value of the displacement safety limit. The method for calculating the pit bottom dryness assessment value is to divide the standard moisture content value by the measured moisture content value of the soil at the bottom of the pit, and then multiply the product of the standard seepage rate value by the measured seepage rate value.

[0041] The water level difference between the inside and outside of the sheet pile cofferdam is the external water level data minus the measured water level inside the sheet pile cofferdam. The horizontal displacement monitoring value of the sidewall of the sheet pile cofferdam is obtained in real time by a displacement sensor. The measured moisture content of the soil at the bottom of the pit is determined by the sampling and drying method. The measured seepage rate is the seepage monitoring data divided by the monitoring time period.

[0042] The stability threshold is set to 0.85, and the dryness threshold is set to 0.90. When the cofferdam bearing stability assessment value is lower than the stability threshold or the pit bottom dryness assessment value is lower than the dryness threshold, it indicates that the construction conditions do not meet the requirements and adjustments need to be made.

[0043] The precipitation well layout density refers to the number of precipitation wells deployed per unit area within the waterless operation unit block, and the air injection pressure parameter refers to the input pressure value of compressed air in the annular perforated pipe.

[0044] The ultrasonic cavitation effect refers to the alternating positive and negative pressure generated by high-frequency vibration in the pore liquid of rocks, which leads to the generation and collapse of microbubbles. The shock wave and high temperature generated at the moment of collapse of the microbubbles act on the cementation surface between rock particles to form a microcrack network. The macroscopic compressive strength is reduced by 15% to 30%.

[0045] The air-lift reverse circulation hole cleaning process refers to injecting compressed gas into the drill pipe to form a gas-liquid mixture, and using the buoyancy generated by the gas-liquid density difference to carry the rock cuttings at the bottom of the hole to the surface for discharge. Compared with the traditional mud circulation hole cleaning process, the speed is increased by more than 50%.

[0046] The objective function of the upper-level optimization model is expressed as the minimum value of the sum of the unit-time pumping power value divided by the standard pumping power value and the air curtain operation power value divided by the standard air curtain power value. The constraint is that the measured water level inside the steel sheet pile cofferdam is not higher than the upper limit of the safe water level and the air injection pressure parameter does not exceed the pipeline pressure limit. The objective function of the lower-level optimization model is expressed as the maximum value of the product of the unit-time hole depth value divided by the standard hole depth value and the drill bit life extension coefficient. The constraint is that the ultrasonic vibration frequency value is between 20,000 and 35,000. The range and the drilling thrust value does not exceed the thrust value corresponding to the drill pipe yield strength.

[0047] The pumping power per unit time is calculated based on the pumping flow rate and the water level difference between the inside and outside of the sheet pile cofferdam. The air curtain operation power is calculated based on the air injection pressure parameter and the air injection flow rate. The hole depth per unit time is obtained based on the drilling rate corresponding to the drilling thrust and the ultrasonic vibration frequency. The drill bit life extension coefficient is determined based on the influence of the ultrasonic vibration frequency on the drill bit wear rate.

[0048] The water level coupling term within the cofferdam refers to the fact that the water level measurement value inside the steel sheet pile cofferdam, which is changed by the pumping operation in the upper optimization model, directly affects the static water pressure distribution inside the hole during the pile foundation construction in the lower optimization model, thereby affecting drilling efficiency and hole wall stability. The game equilibrium point is the parameter combination that makes the objective functions of the two models simultaneously reach the optimal state through an iterative algorithm.

[0049] The optimal combination of construction parameters includes optimized values ​​for four parameters: the gas injection pressure, the pumping flow rate, the ultrasonic vibration frequency, and the drilling thrust.

[0050] The inter-unit connection interface is a combination of standardized flanges and bolt holes pre-embedded in the ends of the photovoltaic support structure beams. The photovoltaic support structures of adjacent waterless operation unit blocks are mechanically spliced ​​together through the inter-unit connection interface to form an overall array frame.

[0051] The floating bridge is constructed from high-density polyethylene pontoons and aluminum alloy deck panels, with a load-bearing capacity of no less than 500 tons. The cross-unit cable laying refers to connecting the output cables of the photovoltaic panels of adjacent waterless operation unit blocks to the combiner box and then to the unified electrical combiner system via the floating bridge.

[0052] The specific implementation methods of the above steps are described in detail below.

[0053] The specific implementation of step S1 is as follows: First, a high-resolution multibeam echo sounder system is deployed in the designated water area of ​​the floating photovoltaic project. Acoustic signals of different frequencies are emitted underwater using acoustic transmitting and receiving devices. The difference in reflection time at the interface of media with different densities is used to identify the underwater topography and bedrock layer distribution characteristics. The abrupt change in acoustic reflection intensity corresponds to the location of the top surface of the bedrock layer. A digital elevation model of the underwater topography is constructed through spatial interpolation of data from multiple measuring points. Subsequently, underwater drilling and core sampling are carried out in the identified bedrock area. After the drilling equipment penetrates the water to reach the bedrock layer, cylindrical rock core samples are extracted. Uniaxial compressive strength and shear strength tests are performed on the rock cores to obtain rock mechanical parameters. The echo sounder data and rock core test data are input into geological modeling software. The Kriging interpolation algorithm is used to spatially continuousize the discrete measuring point data, generating a three-dimensional geological model that includes the bedrock layer burial depth distribution, thickness variation, and compressive strength spatial distribution. Based on the three-dimensional geological model, the bedrock layer burial depth is divided into areas less than 5 km. And compressive strength greater than 60 The area is designated as a construction zone with hard strata, and the working radius of a single land pile foundation construction device is 15 to 20 meters based on the photovoltaic array layout module and the working radius of the single land pile foundation construction equipment. The constraints limit the construction area in hard strata to be divided into sections with sides of 30 to 50 mm. Rectangular waterless operation unit blocks are defined to ensure that the geological conditions within each waterless operation unit block are uniform enough to meet construction requirements.

[0054] The specific implementation of step S2 is as follows: First, steel sheet piles are driven into the perimeter of the selected waterless operation unit block according to the rectangular boundary line to form a closed retaining structure. The steel sheet piles are made of U-shaped or Z-shaped steel. The steel sheet piles are driven one to two meters below the top surface of the bedrock layer using a hydraulic pile hammer. The depth is such that adjacent sheet piles are connected by interlocking joints to form a continuous water-retaining wall. A diameter of 100 to 150 mm is laid underwater along the perimeter of the outer side of the sheet pile cofferdam. A ring-shaped perforated pipe, with evenly distributed holes of 5 to 8 mm in diameter. The air outlets and pipe spacing are 2 to 3. The system is configured to continuously inject pressure of 0.3 to 0.5 kPa into the annular perforated pipe using an air compressor. Compressed air is released from the vents, forming a dense cluster of rising air bubbles that constitute an air curtain impermeable layer. The buoyancy generated by these rising bubbles in the surrounding water creates a radial water flow from the outside in. This radial water flow establishes a pressure gradient reduction zone on the outside of the sheet pile cofferdam, reducing the hydrostatic pressure of the external water on the sheet pile cofferdam by 20% to 40%. Simultaneously, the air curtain prevents suspended sediment particles from migrating into the sheet pile cofferdam. A layer of 8 to 12 cubic meters thick is laid at the bottom of the sheet pile cofferdam where it contacts the bedrock layer. The chloroprene rubber flexible waterstop is fixed to the bedrock surface by pre-embedded anchors. The lower end of the steel sheet pile presses the waterstop to form the first seepage barrier. A high-pressure grouting pump is used to inject cement grout with a water-cement ratio of 0.5 to 0.8 at a rate of 2 to 5... Pressure is injected into the surface fissures of the bedrock layer. After the grout diffuses and solidifies within the fissures, it forms a continuous seepage barrier. This barrier is installed at a depth of 8 to 12 meters inside the sheet pile cofferdam. The dewatering wells are spaced 5 to 8 meters apart. Arranged in a quincunx pattern, submersible pumps continuously pump accumulated water and seepage water from inside the cofferdam to the external water area. The pumps operate until the water level inside the cofferdam drops to 0.5 meters below the design construction surface. The pumping was stopped to create a dry land construction environment.

[0055] The specific implementation of step S3 involves installing a flow meter inside the sheet pile cofferdam to monitor the infiltration rate per unit time. The flow meter is installed on the outlet pipe of the dewatering well to record the pumping flow rate data in real time. A water level gauge is installed outside the sheet pile cofferdam to measure the water surface elevation of the external water area. Displacement sensors are installed on the sidewalls of the sheet pile cofferdam to monitor changes in horizontal displacement. The data collection interval is 10 minutes. When calculating the cofferdam's bearing capacity stability assessment value, the difference between the external water level data and the measured water level inside the cofferdam is first calculated as the water level difference between the inside and outside of the sheet pile cofferdam. This water level difference is then divided by the standard value of the cofferdam's design bearing capacity water level difference (3). The dimensionless water level difference ratio was obtained, and the monitored value of the horizontal displacement of the steel sheet pile cofferdam sidewall was divided by the standard value of the displacement safety limit by 50. The dimensionless displacement ratio is obtained. Multiplying the two dimensionless ratios yields the cofferdam's bearing capacity stability assessment value. When calculating the pit bottom dryness assessment value, soil samples are taken from the pit bottom, dried, and the measured moisture content is determined. The standard moisture content value (8%) is divided by the measured moisture content of the pit bottom soil to obtain the reciprocal of the moisture content ratio. The seepage monitoring data is divided by the monitoring time period to obtain the measured seepage rate value. The standard seepage rate value is 0.5... / h divided by the measured seepage rate value yields the reciprocal ratio of the seepage rate. Multiplying the two reciprocal ratios gives the pit bottom dryness assessment value. The cofferdam bearing stability assessment value is compared with the stability threshold of 0.85. If the cofferdam bearing stability assessment value is lower than 0.85, it indicates that the steel sheet pile cofferdam has insufficient bearing capacity and is at risk of instability. The pit bottom dryness assessment value is compared with the dryness threshold of 0.90. If the pit bottom dryness assessment value is lower than 0.90, it indicates that the pit bottom moisture content is too high or the seepage rate is too high, which does not meet the requirements for land construction. When either assessment value is lower than the corresponding threshold, the stability of the cofferdam and the dryness of the pit bottom are improved by increasing the number of dewatering wells to increase the density of dewatering wells or increasing the air injection pressure parameter of the annular perforated pipe.

[0056] The specific implementation of step S4 involves transporting a hydraulic down-the-hole hammer drill rig to the pile location in a dry land construction environment. The drill rig is equipped with a diameter of 800 to 1200 mm. The diamond composite drill bit features diamond particles embedded in its cutting edge, providing high-hardness cutting capability. A high-frequency ultrasonic generator is fixedly installed on the outer wall of the drill pipe. This generator consists of a piezoelectric ceramic transducer and a power amplifier. The transducer generates mechanical vibration under an alternating electric field and transmits it to the drill pipe. During drilling, the ultrasonic generator applies a frequency of 20,000 to 35,000 to the drill pipe. Amplitude 0.05 to 0.15 The longitudinal vibration waves are transmitted through the drill pipe to the diamond drill bit, acting on the rock contact surface. High-frequency vibrations generate periodic alternating positive and negative pressures in the rock pore water. When the negative pressure amplitude exceeds the cavitation threshold of the water, a large number of micron-sized bubbles form in the pore water. These bubbles rapidly collapse during the positive pressure phase, releasing shock waves and localized high temperatures. The concentrated energy of the shock waves acts on the cementing material between rock particles, generating microcracks. The expansion of the microcrack network reduces the overall compressive strength of the rock by 15% to 30%, significantly reducing the drill bit's resistance to rock breaking. During drilling, pressure of 0.6 to 0.8 is injected into the bottom of the hole through the center hole of the drill pipe. Compressed air mixes with rock cuttings at the bottom of the borehole to form a gas-solid two-phase flow. Taking advantage of the fact that the density of gas is much lower than that of liquid, the gas-solid mixture rises to the surface along the annular space on the outer wall of the drill pipe under the action of buoyancy. The rock cuttings are carried out of the borehole by the airflow to complete the borehole cleaning operation. The air-lift reverse circulation borehole cleaning rate is more than 50% higher than that of traditional mud circulation. After the borehole reaches the design depth, the steel cage is lowered and concrete is poured to form the pile foundation.

[0057] The specific implementation of step S5 involves establishing a two-layer game optimization model to solve for the optimal combination of construction parameters. The upper-layer optimization model aims to reduce the total energy consumption of the pumping and drainage system and the air curtain system. The input parameters of the objective function include the air injection pressure of the air curtain water-tight layer and the pumping flow rate of the dewatering well system. The operating power of the air curtain is obtained based on the air injection pressure and flow rate using power calculation principles. The pumping power per unit time is obtained based on the pumping flow rate and the water level difference between the inside and outside of the steel sheet pile cofferdam using pump power calculation principles. The pumping power per unit time is then divided by the standard pumping power value of 50. Divide the operating power value of the air curtain by the standard air curtain power value by 30 The sum of is used as the objective function, and the constraint is set as follows: the measured water level inside the sheet pile cofferdam should not exceed the upper limit of the safe water level by -0.3. Furthermore, the gas injection pressure parameter does not exceed the pipeline's pressure limit value by 0.6. The lower-level optimization model aims to improve pile foundation drilling efficiency and extend drill bit lifespan. The objective function input parameters include the ultrasonic vibration frequency of the high-frequency ultrasonic generator and the drilling thrust of the hydraulic down-the-hole hammer drill. Based on the ultrasonic vibration frequency and drilling thrust, the drilling depth per unit time is calculated using the rock breaking mechanism. The drill bit life extension coefficient is determined based on the influence curve of ultrasonic vibration frequency on drill bit wear rate. Finally, the drilling depth per unit time is divided by the standard drilling depth value. The objective function is the product of / h and the drill bit life extension coefficient. The constraint is set as follows: the ultrasonic vibration frequency is between 20000 and 35000. Within the range and the drilling thrust value does not exceed 800 of the thrust value corresponding to the drill pipe yield strength. The two-layer model is linked by a water level coupling term within the cofferdam. In the upper-layer model, the pumping flow rate directly affects the water level measurement inside the sheet pile cofferdam. The water level measurement inside the cofferdam determines the hydrostatic pressure inside the hole during pile foundation drilling in the lower-layer model. Changes in the hydrostatic pressure inside the hole affect the hole wall stability and drilling efficiency. A sequential iterative algorithm is used to solve the two-layer game model. First, the parameters of the lower-layer model are fixed to solve for the optimal solution of the upper-layer model. Then, the optimal solution of the upper-layer model is substituted into the lower-layer model to solve for the optimal solution of the lower-layer model. The optimal solution of the lower-layer model is fed back to the upper-layer model for the next round of iteration. When the change in the objective function value between two consecutive iterations is less than 0.01, the game equilibrium point is determined to be reached. At this point, the corresponding gas injection pressure, pumping flow rate, ultrasonic vibration frequency, and drilling thrust constitute the optimal combination of construction parameters.

[0058] The specific implementation of step S6 involves extracting the values ​​of four parameters from the optimal combination of construction parameters. The air injection pressure value is input into the air compressor control system to adjust the compressor output pressure so that the pressure inside the annular perforated pipe is stabilized at the optimized value. The water pumping flow rate value is input into the dewatering well system controller to adjust the submersible pump speed or the number of pumps started and stopped so that the total water pumping flow rate reaches the optimized value. The ultrasonic vibration frequency value is input into the frequency adjustment module of the high-frequency ultrasonic generator to change the excitation voltage frequency of the piezoelectric ceramic vibrator. The drilling thrust value is input into the hydraulic system of the hydraulic down-the-hole hammer drill to adjust the hydraulic cylinder propulsion pressure and control the axial force of the drill bit on the rock. The closed-loop feedback control system monitors the deviation of each operating parameter from the set value in real time and makes dynamic adjustments to ensure that the operating parameters of each piece of equipment are always kept in the optimal state during the construction process.

[0059] The specific implementation of step S7 involves using a level to measure the top elevation of each pile, recording the elevation difference between the top of each pile and the design elevation plane. For piles exceeding the design elevation, a concrete cutting machine is used to cut the top, with the cutting depth determined based on the elevation difference, ensuring that the elevation error of all pile tops is controlled within ±10°. Within the scope, pre-embedded steel plates are welded to the top of the treated piles. The main beam of the photovoltaic support structure is then connected and fixed to the pre-embedded steel plates using high-strength bolts. Standardized flanges are pre-installed at the ends of the crossbeams of the photovoltaic support structure, forming inter-unit connection interfaces with the bolt holes. Photovoltaic panel modules are installed on the photovoltaic support structure and electrically connected. A width of 0.8 to 1.2 meters is reserved at the boundary between adjacent waterless operation unit blocks. The cable trenches are used for subsequent cross-unit cable laying.

[0060] The specific implementation of step S8 is as follows: After the photovoltaic panel modules of the current waterless operation unit are installed, the sheet pile extraction equipment is started to pull out and retrieve the sheet piles one by one. The air compressor is turned off to stop the injection of air into the annular perforated pipe, causing the air curtain water barrier to disappear. The surrounding water flows back to the construction area under the action of gravity, restoring the original water state. A floating bridge is erected between adjacent waterless operation unit blocks that have been installed. The floating bridge is supported by high-density polyethylene pontoons, and an aluminum alloy bridge deck is laid on the upper part of the pontoons to form a passage platform. The load-bearing capacity of the floating bridge is not less than 500. To meet the access requirements for personnel and cable laying equipment, the output cables of photovoltaic panels from adjacent unit blocks are introduced into the reserved cable trench and connected to the combiner box via a floating bridge. The output end of the combiner box is connected to the inverter to form a unified electrical combiner system. After the construction of the current area is completed, the construction equipment is transferred to the next planned waterless operation unit block. The construction process of steps S2 to S8 is repeated until the construction of all waterless operation unit blocks is completed.

[0061] It should be noted that the key technical concepts of this invention include air curtain-assisted dewatering technology, ultrasonic enhanced drilling technology, and dual-layer game parameter optimization technology. Air curtain-assisted dewatering technology forms a continuously rising bubble curtain around the cofferdam. The water flow disturbance induced by the bubble movement creates a pressure gradient transition zone around the cofferdam. Compared to the traditional method of relying solely on the cofferdam structure to bear all external hydrostatic pressure, the dynamic low-pressure buffer zone generated by the air curtain reduces the force of external water on the cofferdam by 20% to 40%, significantly reducing the stress level and deformation risk of the cofferdam structure. Simultaneously, the physical barrier effect of the bubble curtain on suspended particles reduces the infiltration of sediment into the cofferdam. Combined with the dewatering well system, this reduces the pumping power requirement by 30%, effectively preventing seepage damage phenomena such as piping. Ultrasonic enhanced drilling technology applies high-frequency longitudinal vibration to the drill rod. The vibration energy is transmitted to the rock interface through the drill bit, generating a cavitation effect. The shock waves released by the collapse of cavitation bubbles form a network of microcracks on the cemented surface of rock particles. Compared with the traditional method of simply relying on the mechanical cutting of the drill bit to break the rock, ultrasonic cavitation pretreatment reduces the macroscopic compressive strength of the rock by 15% to 30%, significantly reduces drilling resistance, and thus increases the hole formation rate. At the same time, high-frequency vibration reduces the frictional adhesion effect between the drill bit and the rock, extending the service life of the drill bit. It is particularly suitable for construction on high-strength bedrock such as granite. The two-layer game parameter optimization technique establishes separate optimization models for the pumping system and the borehole system as two mutually influential subsystems. The water level inside the cofferdam is used as a coupling variable to associate the objective functions of the two models. Compared with the traditional independent optimization method that optimizes the parameters of each subsystem separately, the two-layer game model considers the interaction mechanism that changes in the water level inside the cofferdam caused by pumping operations directly affect the hydrostatic pressure inside the borehole during drilling, thus affecting drilling efficiency and borehole wall stability. By solving the game equilibrium point through sequential iteration, the globally optimal parameter combination that balances energy consumption reduction and efficiency improvement is obtained, avoiding the overall system performance loss caused by local optimization. The synergistic effect of the three technologies is reflected in the fact that the air curtain depressurization technology reduces the difficulty of controlling the stability of the cofferdam and provides more adjustment space for the optimization of the pumping system; the ultrasonic enhancement technology improves the hole-forming rate, shortens the construction cycle of a single waterless operation unit block, and reduces the long-term pressure accumulation effect of the cofferdam; and the dual-layer game optimization technology coordinates the coupling relationship between the air curtain injection parameters, the pumping flow rate parameters, and the drilling process parameters. Compared with the traditional method of adjusting parameters one by one based on experience, the synergistic optimization improves the overall construction efficiency by more than 40% and increases the safety margin of the cofferdam by 25%, forming a systematic solution for waterborne photovoltaic construction under hard geological conditions.

[0062] It should be noted that this invention also solves the following technical problem: the difficulty in uniformly optimizing the construction parameters of multiple independent construction unit blocks under hard geological conditions. This invention identifies construction areas in hard strata by establishing a three-dimensional geological model including bedrock distribution, thickness, and strength parameters. Based on the exploration results, the entire water area is planned into multiple independent waterless operation unit blocks. Each block sequentially completes the entire process of cofferdam construction, pile foundation construction, photovoltaic module installation, and cofferdam dismantling. During the construction process of each block, a two-layer optimization model is used to solve for the equilibrium point based on the geological conditions and construction environment of the current block, obtaining the optimal combination of construction parameters for that block, thus achieving adaptive adjustment of construction parameters under different geological conditions. Adjacent blocks are mechanically spliced ​​to form an overall array frame through pre-embedded inter-unit connection interfaces, and cross-unit cable laying is achieved through floating bridges to form a unified electrical bus system. This ensures both targeted optimization of construction parameters for each block and system integration of the overall project, effectively solving the technical problem of the difficulty in uniformly optimizing the construction parameters of multiple units.

[0063] Specifically, the principle of this invention is as follows: This invention can solve the technical problems of low construction efficiency and difficulty in seepage control of underwater photovoltaic pile foundations under hard geological conditions. The principle lies in the pressure gradient generated by the air curtain water-stop layer, which forms a low-pressure buffer zone around the steel sheet pile cofferdam, reducing the static water pressure of the external water body by 20% to 40%, thus lowering the load-bearing requirements of the cofferdam structure. Simultaneously, the disturbance of the air curtain wall blocks the infiltration of suspended particles into the cofferdam, preventing piping damage. The flexible rubber waterstop can adapt to the irregular morphology of the bedrock surface to form a tight seal. High-pressure grouting allows cement slurry to penetrate into the rock fissures and solidify to form a seepage-proof layer. The synergistic effect of these two elements significantly reduces seepage. A high-frequency ultrasonic generator applies more than 20,000 longitudinal vibrations per second to the diamond drill bit, generating alternating positive and negative pressures in the rock pore fluid, causing the generation and collapse of microbubbles. The shock wave and high temperature at the moment of collapse act on the cementation surface between rock particles, forming a microcrack network, reducing the macroscopic compressive strength of the hard rock layer by 15% to 30%. Combined with the high-frequency impact of the hydraulic down-the-hole hammer, this significantly improves drilling efficiency. The dual-layer optimization model organically links seepage control with drilling operations through the water level coupling term within the cofferdam. Iteratively solving the game equilibrium point enables both pumping power and borehole efficiency to reach their optimal state simultaneously, thus achieving the scientific configuration of construction parameters.

[0064] The following provides a specific embodiment 1 of the present invention, and the specific implementation of each step in this embodiment 1 is described in detail below.

[0065] The specific implementation of step S3 involves collecting seepage monitoring data within the sheet pile cofferdam and external water level data, then calculating the cofferdam's bearing capacity stability assessment value and the pit bottom dryness assessment value to determine whether the construction conditions meet the requirements. The cofferdam's bearing capacity stability assessment value... The calculation formula is expressed as follows:

[0066] ;

[0067] In the formula, This is a dimensionless value representing the load-bearing stability assessment value of the cofferdam. External water level data, unit: ; This is a measurement of the water level inside the sheet pile cofferdam, in units of... ; This represents the standard value of the design bearing water level difference for the cofferdam, in units of... The empirical value is 8-12; These are the horizontal displacement monitoring values ​​of the sidewall of the sheet pile cofferdam, in units of... ; This refers to the standard value for displacement safety limits, in units of... The value is typically taken as 50-80. (Pot bottom dryness assessment value) The calculation formula is expressed as follows:

[0068] ;

[0069] In the formula, This is a dimensionless value for assessing the dryness of the pit bottom. This is the standard moisture content value, usually taken as 15-20%, expressed as a percentage. The measured moisture content of the soil at the bottom of the pit is expressed as a percentage. The standard seepage rate value is empirically estimated to be 0.5–1.0, and the unit is... ; The measured seepage rate value is given in units of... .in, The water level was measured in real time using a water level gauge. Data is acquired in real time through a displacement sensor. The measured seepage rate was determined by the sampling and drying method. The calculation formula is:

[0070] ;

[0071] In the formula, This is data on seepage monitoring, in units of... ; For monitoring time periods, the unit is 1. .when Below the stability threshold of 0.85 or When the aridity threshold of 0.90 is below, the density of the dewatering wells in the dewatering well system and the gas injection pressure parameters of the air curtain water barrier need to be dynamically adjusted.

[0072] The specific implementation of step S5 is to construct a two-layer optimization model to solve for the optimal combination of construction parameters. The objective function of the upper-layer optimization model is... The statement is as follows:

[0073] ;

[0074] In the formula, The objective function value of the upper-level optimization model is dimensionless; This represents the pumping power per unit time, in units of... ; Standard extraction power value, unit: The experience value is 80-120; This is the operating power value of the air curtain, in units of... ; This is the standard air curtain power value, in units of The default value is 50-75. This refers to the pumping power per unit time. The calculation formula is:

[0075] ;

[0076] In the formula, The density of water is 1000, and the unit is 1000. ; This represents the acceleration due to gravity, with a value of 9.8, and the unit is... ; This is the pumping flow rate value, in units of... ; The pump efficiency coefficient, typically taken as 0.75–0.85, is dimensionless; 1000 in the formula is a unit conversion factor. Air curtain operating power value. The calculation formula is:

[0077] ;

[0078] In the formula, This refers to the injection pressure parameter, in units of... ; This refers to the gas injection flow rate, in units of... ; The adiabatic index of the gas is taken as 1.4 for air, and is dimensionless; 1000 in the formula is a unit conversion factor. The constraints of the upper-level optimization model are: and ,in This is the upper limit of the safe water level, in units of... ; This represents the pipeline's pressure limit value, in units of... The objective function of the lower-level optimization model The statement is as follows:

[0079] ;

[0080] In the formula, The objective function value of the lower-level optimization model is dimensionless; This represents the hole depth per unit time, in units of... ; Standard hole depth value, unit: The empirical value is 1.5 to 2.5; This represents the drill bit life extension factor, which is dimensionless. Wherein, it represents the hole depth per unit time. The calculation formula is:

[0081] ;

[0082] In the formula, This is the drilling coefficient, with an empirical value of 0.02 to 0.05, in units of... ; This represents the drilling thrust value, in units of... ; This represents the ultrasonic vibration frequency value, in units of... Drill bit life extension factor value The calculation formula is:

[0083] ;

[0084] In the formula, This is the lifespan extension factor, typically ranging from 0.15 to 0.25, and is dimensionless. The reference ultrasonic vibration frequency value is 20000, and the unit is... The constraints of the lower-level optimization model are: and ,in This represents the thrust value corresponding to the drill pipe's yield strength, in units of... The water level coupling term within the cofferdam is determined through... By associating two-layer models and employing an iterative algorithm to solve for the game equilibrium point, the optimal combination of construction parameters is obtained, including... , , and Optimized values ​​for the four parameters.

[0085] To better understand and implement this invention, the following is a specific application scenario of the invention, Example 2: A technical team is carrying out a floating photovoltaic power station project in a large reservoir with a water area of ​​approximately 45,000 square meters. The water depth ranged from 6 to 12 meters. Underwater geological surveys revealed that the bedrock layer was granite with a compressive strength of 78 MPa, indicating typical hard geological conditions. The technical team used a high-resolution multibeam echo sounder to conduct a full-coverage scan of the designated water area. With the acoustic frequency set to 500 kHz, the depth measurement accuracy reached 0.05 meters, obtaining detailed data on underwater topography and bedrock distribution. Subsequently, underwater core drilling was conducted at 12 representative locations, with drilling depths ranging from 15 to 20 meters. Physical tests on the extracted core samples showed that the granite had a uniaxial compressive strength of 78 MPa, an elastic modulus of 42 GPa, and a Poisson's ratio of 0.26. Based on the depth measurement data and core test results, the technical team established a three-dimensional geological model including spatial coordinates, bedrock thickness, and strength parameters. This model accurately identified an area of ​​approximately 28,000 square meters where the bedrock burial depth was less than 2 meters. This area accounts for 62% of the total construction area. Based on the capacity of the construction equipment and the schedule requirements, the technical team divided the construction area into 8 independent waterless operation unit blocks, each with an area of ​​approximately 3,500 square meters. It has a rectangular layout, with a long side of 70m and a short side of 50m.

[0086] The technical team selected the first waterless operation unit for pilot construction, using U-shaped steel sheet piles (12m long, 0.4m wide, and 10mm thick) to construct a closed cofferdam. The sheet piles were made of Q345B steel with a yield strength of 345MPa. The sheet piles were driven using a hydraulic vibratory hammer, with a vibration frequency of 28Hz and an amplitude of 8mm. The driving time for a single sheet pile was approximately 25 minutes. The cofferdam had a circumference of 240m, and a total of 600 sheet piles were used. A ring-shaped perforated pipe was laid 3m underwater around the perimeter of the sheet pile cofferdam. The pipe was made of high-density polyethylene, with an outer diameter of 110mm, a wall thickness of 6mm, a perforation diameter of 2mm, a perforation spacing of 50mm, and a total pipe length of 250m. The perforated pipe connected to an onshore air compressor system with a rated power of 75kW, an output pressure of 0.6MPa, and an injection flow rate of 120... / min. Compressed air is continuously injected into the water through perforated pipes to form a dense air curtain water-proof layer. The air bubbles are 2 to 5 mm in diameter and rise at a speed of 0.3 m / s, forming an air curtain wall with a width of about 4 m around the cofferdam. Monitoring data shows that after the air curtain water-proof layer is in operation, the hydrostatic pressure of the water within 5 m outside the steel sheet pile cofferdam decreases by 32%, effectively weakening the lateral pressure of the external water on the cofferdam. The technical team laid a 10 mm thick neoprene rubber waterstop at the contact surface between the bottom of the steel sheet pile cofferdam and the bedrock. The waterstop is 600 mm wide, has a tensile strength of 18 MPa, and an elongation of 420%. After the waterstop is laid, a high-pressure grouting process is used to seal the cracks in the rock strata. The grouting material is a sulfoaluminate cement slurry with a water-cement ratio of 0.5. The grouting pressure is 3.5 MPa, the grouting volume per hole is 150 to 200 L, the grouting hole spacing is 3 m, and a total of 80 grouting holes are arranged at the bottom of the cofferdam. Forty-eight hours after grouting is completed, the grout solidifies to form a seepage barrier layer with a thickness of approximately 0.8 meters, and the permeability coefficient drops to [value missing]. cm / s.

[0087] After the cofferdam closure system was completed, the technical team installed a dewatering well system inside the cofferdam. The dewatering wells adopted a tubular well structure with a well diameter of 300mm, a filter pipe section length of 6m, and a wire-wound filter screen with an opening rate of 35%. Based on hydrogeological calculations, the water yield per well was approximately 15... / h, the technical team evenly deployed 12 dewatering wells within the block, with a well spacing of approximately 12m, resulting in a dewatering well density of 1000 per 1000 m. 3.4 wells were installed. Each well was equipped with a 5.5kW submersible pump, for a total pumping power of 66kW. After the dewatering system was activated, the water level inside the cofferdam dropped at a rate of 0.8m per hour. After 72 hours, the water inside the cofferdam was completely pumped out, creating a dry land construction environment. The moisture content at the bottom of the pit dropped to 8.5%, meeting the requirements for pile foundation construction. During construction, the technical team monitored the seepage rate inside the cofferdam in real time using flow meters. The initial seepage rate was 12... / h, as the dewatering well system continues to operate and the grouting layer solidifies, the seepage rate gradually decreases to 5 / h. Simultaneously, the water level outside the cofferdam was monitored. The water level gauge showed that the water surface elevation of the outer water area remained stable at an elevation of 85.6m. After pumping out water from inside the cofferdam, the bottom elevation of the pit was 78.2m, resulting in a water level difference of 7.4m between the inside and outside. The technical team calculated the cofferdam's load-bearing stability assessment value. The standard value for the design load-bearing water level difference of the cofferdam was 8.5m. Dividing the water level difference of 7.4m by the standard value of 8.5m yielded a ratio of 0.871. The monitored horizontal displacement value of the steel sheet pile sidewall was 18mm, and the standard displacement safety limit value was 25mm, resulting in a ratio of 0.720. Multiplying these two values ​​yielded the cofferdam's load-bearing stability assessment value of 0.627. In the calculation of the pit bottom dryness assessment value, the standard moisture content was set at 10%, the measured moisture content of the soil at the pit bottom was 8.5%, resulting in a ratio of 1.176, and the standard seepage rate was 6. / h, measured seepage rate value 5 / h, the ratio is 1.200, and the product of the two yields the pit bottom dryness assessment value of 1.411. Since the cofferdam's bearing stability assessment value of 0.627 is lower than the stability threshold of 0.85, the technical team adjusted the operating parameters of the dewatering well system, increasing the density of dewatering wells to per 1000 4.2 wells were installed, adding 3 new infill wells to the existing 12 wells. Simultaneously, the gas injection pressure in the gas curtain aquitard was increased to 0.75 MPa, and the gas injection flow rate was increased to 145 kWh. / min. After 24 hours of adjustment, the cofferdam's load-bearing stability assessment value increased to 0.892, and the pit bottom dryness assessment value remained at 1.385, both meeting the construction requirements. Figure 2 As shown.

[0088] After the arid terrestrial environment was established, the technical team used a hydraulic down-the-hole hammer drill equipped with a diamond drill bit for pile foundation drilling. The drill bit model was YQ-100, with a rated power of 110kW, a maximum drilling thrust of 180kN, a drill rod diameter of 89mm, a wall thickness of 9mm, and a yield strength corresponding to a thrust value of 195kN. The diamond drill bit had a diameter of 800mm, a matrix material of cobalt-based alloy, and diamond particles with a particle size of 0.3mm and a concentration of 60%. A high-frequency ultrasonic generator was installed on the drill rod. This device consisted of an ultrasonic transducer, a power amplifier, and a control system. The transducer used piezoelectric ceramic material, with a resonant frequency of 28000Hz and an output power of 3.5kW. The ultrasonic generator applied longitudinal vibration to the diamond drill bit at a frequency of 28000Hz, an amplitude of 0.08mm, and a vibration frequency of 28000 times per second. High-frequency vibrations generate alternating positive and negative pressures in the pore fluid of the rock, with a pressure amplitude of ±0.8 MPa. This leads to the formation and collapse of microbubbles, with bubble diameters ranging from 10 to 50 μm. The peak pressure of the shock wave generated at the moment of collapse reaches 500 MPa, and the local temperature instantaneously rises to 800℃. The shock wave and high temperature act on the cementation surface between rock particles, forming a network of microcracks with a width of 1 to 5 μm, a depth of 20 to 50 μm, and a microcrack density of 120 cracks per square centimeter. The ultrasonic cavitation effect reduces the macroscopic compressive strength of granite from 78 MPa to 56 MPa, a reduction of 28%, significantly improving drilling conditions. During drilling, a drilling thrust of 150 kN and a drill rod rotation speed of 45 r / min are used, increasing the drilling rate to 1.8 m / h, a 100% improvement compared to the traditional drilling rate of 0.9 m / h. After completing each pile hole, the technical team used an air-lift reverse circulation cleaning process to remove rock cuttings from the bottom of the hole. Compressed gas at a pressure of 0.4 MPa was injected into the drill pipe at a flow rate of 80. The flow rate is [speed] / min, forming a gas-liquid mixture with a gas-liquid volume ratio of 1:3. The density of the gas-liquid mixture is 1100 [units]. The density of the water outside the hole is 1000 lower than that of the surrounding water. The resulting buoyancy difference carries rock cuttings from the bottom of the borehole to the surface for discharge, achieving a borehole cleaning speed of 12m / h, which is 50% higher than the traditional mud circulation borehole cleaning speed of 8m / h. The first waterless operation unit requires 96 boreholes, with a diameter of 800mm, a pile length of 10m, and a matrix arrangement of 7m×8m pile spacing.

[0089] To optimize construction parameters, the technical team constructed a two-layer optimization model. The upper-layer model aims to minimize pumping power, with the objective function input including the air injection pressure parameters of the air curtain impermeable layer and the pumping flow rate parameters of the dewatering well system. The pumping power per unit time is calculated based on the pumping flow rate value of 180. The calculated power is 52.8 kW based on the water level difference of 7.4 m between the inside and outside of the cofferdam. The standard pumping power is set at 55 kW, with a ratio of 0.960. The air curtain operating power is based on the injection pressure parameter of 0.75 MPa and the injection flow rate of 145... The calculated power output per minute is 68.5 kW, and the standard air curtain power value is set at 70 kW, with a ratio of 0.979. The objective function value of the upper-level optimization model is the minimum of the sum of 0.960 and 0.979, which is 1.939. The constraints are that the measured water level inside the cofferdam should not exceed the upper limit of the safe water level elevation of 80.0 m, and the actual water level elevation of 78.2 m satisfies the constraints; the air injection pressure parameter of 0.75 MPa does not exceed the pipeline pressure limit of 1.2 MPa, which also satisfies the constraints. The lower-level optimization model aims to maximize the hole-forming efficiency. The objective function inputs include the ultrasonic vibration frequency parameters of the high-frequency ultrasonic generator and the drilling thrust parameters of the hydraulic down-the-hole hammer drill. The hole-forming depth per unit time is obtained based on the drilling rate of 1.8 m / h corresponding to a drilling thrust of 150 kN and an ultrasonic vibration frequency of 28000 Hz. The standard hole-forming depth is set at 1.5 m / h, with a ratio of 1.200. The drill bit life extension coefficient was determined to be 1.35 based on the influence of ultrasonic vibration frequency 28000Hz on drill bit wear rate. The objective function value of the lower optimization model is the maximum value of the product of 1.200 and 1.35, which is 1.620. The constraints are that the ultrasonic vibration frequency of 28000Hz is within the range of 20000 to 35000Hz, which is satisfied; and the drilling thrust of 150kN does not exceed the thrust value corresponding to the drill pipe yield strength of 195kN, which is also satisfied. The two models are linked through a water level coupling term within the cofferdam. In the upper model, the water level inside the cofferdam changed by the pumping operation directly affects the static water pressure distribution inside the borehole during pile foundation construction in the lower model. The static water pressure inside the borehole decreased from 73.6kPa initially to 7.2kPa during construction, a 90% reduction that improved borehole stability and increased drilling efficiency. Figure 3 and 4 As shown in Table 1, the technical team solved the game equilibrium point using an iterative algorithm. After 18 iterations, they obtained the optimal combination of construction parameters.

[0090] Table 1 Optimal combination of construction parameters

[0091]

[0092] The technical team adjusted the operating parameters of each system based on the optimal combination of construction parameters, increasing the air injection pressure of the air curtain waterproof layer to 0.82 MPa and the corresponding air injection flow rate to 155. / min, the pumping flow rate of the dewatering well system decreased to 165 The total pumping power was reduced to 48.5kW, resulting in energy savings of 7.3%. The vibration frequency of the ultrasonic generator was adjusted to 30500Hz, and the output power was increased to 3.8kW. The drilling thrust of the hydraulic down-the-hole hammer drill was increased to 158kN, and the drilling rate was further improved to 2.1m / h. After parameter optimization, the time to complete a single pile hole was shortened from 5.6 hours to 4.8 hours, and the total completion time for 96 pile holes in the first waterless operation unit was shortened from 18 days to 15 days, improving efficiency by 16.7%.

[0093] After the pile foundation holes were completed, the technical team poured C30 concrete into them. The concrete slump was 180mm, and 5.0g of concrete was poured into each pile hole. The pouring time was 40 minutes, the initial setting time of the concrete was 6 hours, and the final setting time was 10 hours. After 28 days of curing, the compressive strength of the concrete reached 32.5 MPa, meeting the design requirements. The technical team uniformly measured the top elevation of the completed piles using a total station with an accuracy of ±2 mm. The measurement results showed that the elevations of the 96 pile tops were distributed between 88.15 and 88.42 m, with a standard deviation of 0.08 m. To ensure that all pile tops were at the same design elevation of 88.20 m, the technical team used a diamond wire saw to cut the pile tops that were higher than the design elevation. The wire saw linear speed was 25 m / s, the cutting power was 15 kW, and the cutting time for a single pile top was 35 minutes. After cutting, the deviation of the pile top elevation was controlled within ±5 mm. A photovoltaic support structure with pre-embedded inter-unit connection interfaces is installed on the pile top. The support structure is made of hot-dip galvanized Q235B steel. The main beam has a rectangular steel tube with a cross-section of 200mm×150mm×8mm, and the secondary beam has a rectangular steel tube with a cross-section of 150mm×100mm×6mm. The main beam spans 7m, and the secondary beam spans 8m. The inter-unit connection interface is a standardized flange pre-embedded in the end of the crossbeam of the support structure. The flange has an outer diameter of 350mm, a thickness of 20mm, and 8 bolt holes with a diameter of 22mm and a center circle diameter of 300mm. The photovoltaic modules are monocrystalline silicon modules, with a single module size of 2100mm×1050mm×40mm, a rated power of 550W, and a photoelectric conversion efficiency of 21.2%. Each support unit is equipped with 20 photovoltaic panels, and the total installed capacity of the unit is 11kW. The technical team reserved cable trenches between units, with a trench width of 300mm and a depth of 200mm. Protective pipes were laid in the trenches, and the protective pipes were made of PVC, with a diameter of 110mm and a wall thickness of 3.2mm.

[0094] After the photovoltaic panel installation was completed in the first waterless operation unit, the technical team dismantled the sheet pile cofferdam. A hydraulic pile extractor was used to remove the sheet piles, with a pulling force of 120kN. The extraction time for a single sheet pile was approximately 15 minutes, and the removal of all 600 sheet piles took 6 days. After the sheet piles were removed, the air curtain waterproofing layer was stopped, and the water area naturally recovered. The water level rose to its original elevation of 85.6m within 48 hours. The installed photovoltaic support structure and photovoltaic panel components were 3.4m above the water surface, meeting flood control and navigation requirements. The technical team connected adjacent waterless operation units to a floating bridge. The floating bridge was assembled from high-density polyethylene pontoons and aluminum alloy deck panels. The pontoons were 2m long, 0.6m in diameter, and 8mm thick, with a buoyancy of 850kg per pontoon. The deck panels were 1.2m wide, 5mm thick, and had a load-bearing capacity of 520kg / m². The floating bridge is 75m long, connecting two adjacent blocks. Construction workers use the floating bridge to lay cables across units. The cables are YJV22 type copper core cross-linked polyethylene insulated steel tape armored PVC sheathed power cables, with a conductor cross-sectional area of ​​70... The rated voltage is 1kV and the current carrying capacity is 180A. The cable is led out from the first block combiner box, laid along the floating bridge to the second block combiner box, forming a unified electrical combiner system. The output current of the photovoltaic panels in each block is collected and connected to the onshore inverter. The inverter has a capacity of 250kW and a conversion efficiency of 98.5%. The technical team moved to the second planned waterless operation unit block and repeated the steps of steel sheet pile cofferdam construction, dewatering well system pumping, pile foundation drilling, concrete pouring, and photovoltaic support structure installation. The construction of the eight waterless operation unit blocks was completed in sequence, with a total construction period of 120 days. A total of 1,536 photovoltaic panels were installed, with a total installed capacity of 844.8kW and an annual power generation of approximately 1.06 million kWh.

[0095] This construction method represents a significant technological advancement compared to traditional offshore photovoltaic pile foundation construction techniques. Traditional methods utilize offshore drilling platforms, whose stability is affected by water flow and waves, making it difficult to control borehole verticality. Furthermore, drilling efficiency is low in hard bedrock conditions, and conventional drill bits have limited ability to break high-strength granite, resulting in a drilling rate of only 0.9 m / h. Severe drill bit wear leads to frequent replacements, increasing costs. This invention, by constructing a closed steel sheet pile cofferdam in conjunction with an air curtain waterproofing layer and high-pressure grouting technology, transforms the underwater construction environment into a dry terrestrial environment, eliminating water flow interference with the drilling rig. The borehole verticality accuracy is improved to 1 / 500, ensuring pile foundation quality. High-frequency ultrasonic-assisted drilling technology utilizes the ultrasonic cavitation effect to generate a microcrack network within the rock, reducing the macroscopic compressive strength of the rock at the microstructural level. This significantly improves the rock-breaking efficiency of the drill bit under the same thrust, increasing the drilling rate to 2.1 m / h. Simultaneously, ultrasonic vibration reduces direct friction and wear between the drill bit and the rock, extending drill bit lifespan by 35%. The dual-layer optimization model achieves coordinated optimization of the pumping and drilling systems through the water level coupling term within the cofferdam. This minimizes energy consumption and maximizes efficiency while ensuring construction safety and quality. Compared to empirical parameter setting methods, the optimized parameter combination reduces total energy consumption by 7.3% and shortens the construction period by 16.7%. The modular, waterless operation unit block division strategy and standardized connection interface design between units enable zoned construction and parallel operations, accelerating the overall project progress. Simultaneously, the mechanical splicing method between units forms an overall array frame that enhances the overall rigidity and wind and wave resistance of the photovoltaic support structure, ensuring the long-term safe and stable operation of the floating photovoltaic power station.

[0096] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing floating photovoltaic panels under hard geological conditions, characterized in that, High-resolution multibeam bathymetry and underwater drilling were used to establish a three-dimensional geological model of the designated water area for the floating photovoltaic project. This model included parameters such as bedrock distribution, thickness, and strength. Construction areas in hard strata were identified, and waterless operation units were planned. Steel sheet pile cofferdams were constructed sequentially for each waterless operation unit. A ring-shaped perforated pipe was installed underwater around the perimeter to form an air curtain impermeable layer. Rising air bubbles generated a pressure gradient to create a low-pressure buffer zone, reducing the hydrostatic pressure of the external water body. Simultaneously, flexible rubber waterstops were laid at the bottom of the steel sheet pile cofferdam, and high-pressure grouting was used to seal rock fissures. A dewatering well system was also used to pump out water, creating a dry construction environment. Seepage monitoring data and external water level data were collected to calculate the cofferdam's bearing capacity stability assessment value. Based on the assessment value of pit bottom dryness and the dynamic adjustment of the layout density of the dewatering well system and the air injection pressure parameters of the air curtain water-proof layer, a hydraulic down-the-hole hammer drill equipped with a diamond drill bit and a high-frequency ultrasonic generator was used in a dry environment to generate microcracks on the rock surface by utilizing the ultrasonic cavitation effect to reduce the macroscopic compressive strength and complete the pile foundation hole formation. An upper-level optimization model aimed at minimizing pumping power and a lower-level optimization model aimed at maximizing hole formation efficiency were constructed. The optimal combination of construction parameters was obtained by solving the game equilibrium point through the correlation of water level coupling terms within the cofferdam, and the equipment operating parameters were adjusted. After the pile top treatment and photovoltaic module installation were completed, the cofferdam was dismantled and the adjacent units were connected by a floating bridge on the water to realize cross-unit cable laying.

2. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 1, characterized in that, The hard strata include bedrock, high-density gravel, or consolidated, deep, hard clay layers. The bedrock refers to granite, basalt, or limestone strata with a compressive strength exceeding 60 MPa.

3. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 2, characterized in that, The high-resolution multibeam bathymetry refers to an underwater exploration technology that uses acoustic wave reflection characteristics to identify rock strata interfaces. The underwater core drilling refers to an exploration method that uses drilling equipment to extract rock core samples from underwater bedrock and conducts physical tests to obtain mechanical parameters.

4. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 3, characterized in that, The air curtain waterproof layer forms a dense bubble curtain wall by continuously injecting compressed air through an annular perforated pipe. The low-pressure buffer zone refers to the area where the static water pressure of the external water body is reduced by 20% to 40%. The air curtain waterproof layer also prevents suspended particles from seeping into the steel sheet pile cofferdam to prevent piping damage.

5. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 4, characterized in that, The flexible rubber waterstop is a strip-shaped sealing component made of neoprene rubber with a thickness of 8 to 12 mm, laid at the bottom of the steel sheet pile cofferdam and the contact surface with the bedrock layer. The high-pressure grouting refers to injecting cement grout with a pressure of 2 to 5 MPa into the rock fissures and solidifying it to form an anti-seepage layer.

6. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 5, characterized in that, The cofferdam bearing stability assessment value is calculated as the product of the difference between the water levels inside and outside the sheet pile cofferdam divided by the standard value of the design bearing water level difference of the cofferdam, and the monitoring value of the horizontal displacement of the sidewall of the sheet pile cofferdam divided by the standard value of the displacement safety limit.

7. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 6, characterized in that, The assessment value of the dryness of the pit bottom is calculated as the product of the standard moisture content value divided by the measured moisture content value of the soil at the bottom of the pit, and the standard seepage rate value divided by the measured seepage rate value. The measured seepage rate value is the seepage monitoring data divided by the monitoring time period.

8. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 7, characterized in that, The stability threshold is set to 0.85, and the dryness threshold is set to 0.

90. When the cofferdam bearing stability assessment value is lower than the stability threshold or the pit bottom dryness assessment value is lower than the dryness threshold, the parameters of the dewatering well system and the air curtain water-proof layer are dynamically adjusted.

9. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 8, characterized in that, The ultrasonic cavitation effect refers to the alternating positive and negative pressure generated by high-frequency vibration in the pore liquid of rocks, which leads to the formation and collapse of microbubbles. The shock wave and high temperature generated at the moment of microbubble collapse act on the cementation surface between rock particles to form a network of microcracks.

10. The method for constructing floating photovoltaic panels under hard geological conditions according to claim 9, characterized in that, The air-lift reverse circulation hole cleaning process refers to injecting compressed gas into the drill pipe to form a gas-liquid mixture, and using the buoyancy generated by the gas-liquid density difference to carry the rock cuttings at the bottom of the hole to the surface for discharge.

Images