Photovoltaic composite foundation suitable for plain liquefied soil and construction method thereof

Abstract

The present application relates to the technical field of photovoltaic ground engineering, and particularly relates to a photovoltaic composite foundation suitable for plain liquefied soil and a construction method thereof. The construction method comprises the following steps: site geological survey, determining the distribution range, thickness and groundwater corrosivity grade of the liquefied layer, and determining the soil penetration depth parameter of the concrete precast pile and the arrangement range of the vibro-replacement stone column according to the thickness and liquefaction grade of the liquefied layer; vibro-replacement stone column construction, constructing the vibro-replacement stone column at the preset pile position according to the arrangement range to form a liquefaction-resistant grid; implanting the concrete precast pile into the preset position to form a main load-bearing structure; and performing corrosion protection treatment on the concrete precast pile, including brushing a permeable corrosion-resistant coating on the outer surface of the concrete precast pile, and arranging a rubber corrosion-resistant pad at the connection between the top of the pile and the photovoltaic support. The technical scheme can adapt to the characteristics of plain liquefied soil, take into account high load bearing and liquefaction resistance, and has targeted corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic foundation engineering technology, specifically to a photovoltaic composite foundation adapted to liquefied soil in plains and its construction method. Background Technology

[0002] Agro-solar hybrid technology, as a land-use hybrid model that organically combines agricultural production with photovoltaic power generation, has been widely promoted and applied. Plains areas, due to their flat terrain, abundant land resources, and superior sunlight conditions, have become important locations for photovoltaic projects. However, some plains areas widely contain liquefaction-sensitive strata such as liquefiable sandy soil and silt. These soils are highly susceptible to liquefaction under dynamic forces such as earthquakes and vibration loads, leading to a rapid loss of foundation bearing capacity, uneven settlement, or even overall instability, posing a serious threat to the safety of the upper photovoltaic support structure. Simultaneously, groundwater in some plains areas exhibits weak corrosiveness; the sulfates and chloride ions in the water continuously erode the foundation structure, accelerating concrete carbonation and steel reinforcement corrosion, severely affecting the long-term stability and service life of the photovoltaic support system.

[0003] Currently, photovoltaic power station foundation treatment technologies are mostly designed and constructed for conventional geological conditions, primarily employing single-pile foundations or simple composite foundations. Among these, precast concrete piles are widely used due to their fast construction speed and high bearing capacity; however, they rely mainly on the pile itself to bear the superstructure load, lacking specific design for liquefaction resistance in liquefiable soils. There is a lack of effective coordinating and densification mechanisms between the pile and the surrounding soil, meaning that under dynamic loads such as earthquakes, the liquefied soil around the pile cannot provide lateral restraint, resulting in weak overall liquefaction resistance of the foundation. While bored piles are more adaptable, they have long pile-forming cycles, are difficult to manage with mud, and also suffer from insufficient liquefaction resistance design. Crushed stone pile composite foundations, through processes such as vibro-compaction to form crushed stone columns in the soil, can effectively densify sand and improve liquefaction resistance, but their bearing capacity is relatively limited and cannot alone meet the high load-bearing requirements of photovoltaic supports. Some technical solutions attempt to combine crushed stone piles with cement-soil piles to form a composite foundation, which to some extent takes into account both load-bearing and liquefaction resistance. However, cement-soil piles have poor durability in groundwater environments, and this combination does not fully consider the differentiating effects of parameters such as liquefaction layer thickness and liquefaction level on pile arrangement, resulting in insufficient design refinement.

[0004] Current photovoltaic (PV) foundation technologies typically only design conventional concrete protective layers for the piles or use ordinary anti-corrosion coatings, failing to develop systematic anti-corrosion solutions for the weakly corrosive groundwater environment in plains. Corrosion is particularly pronounced in the area where the pile top connects to the PV support, due to unfavorable conditions such as contact between dissimilar materials, stress concentration, and rainwater infiltration. Conventional anti-corrosion measures are insufficient to effectively address the long-term corrosion risks in this area. While some technical solutions involve anti-corrosion treatment, these are mostly remedial measures.

[0005] For example, the existing technology of "FRP-steel honeycomb web photovoltaic pile foundation for solidified soft soil bearing layer" (CN119411574B) improves the bearing capacity and bending resistance of soft soil foundations by combining FRP composite materials with steel honeycomb webs. However, this technology focuses on the solidification and improvement of soft soil and does not involve the anti-liquefaction mechanism and design method of liquefiable soil under dynamic loads. Moreover, FRP composite materials are expensive and have complex construction processes, making it difficult to promote economically in large-scale plain photovoltaic projects. Another example is conventional precast concrete pile photovoltaic foundations, which rely solely on the pile body for load bearing without anti-liquefaction treatment of the soil between the piles. When applied in plain liquefiable soil areas, liquefaction of the soil around the piles under seismic action leads to a significant reduction in side friction, making the pile body prone to settlement and instability, and compromising the safety of the upper photovoltaic support structure. Summary of the Invention

[0006] The purpose of this invention is to propose a photovoltaic composite foundation and construction method adapted to liquefied soil in plains, which can adapt to the characteristics of liquefied soil in plains, take into account both high load-bearing capacity and liquefaction resistance, and have targeted anti-corrosion capabilities.

[0007] To achieve the above objectives, in a first aspect, the present invention proposes a construction method for photovoltaic composite foundations adapted to liquefiable soils in plains, comprising: Site geological survey to determine the distribution range, thickness and groundwater corrosivity level of the liquefaction layer, and determine the penetration depth parameters of precast concrete piles and the layout range of vibratory crushed stone piles based on the thickness and liquefaction level of the liquefaction layer. Vibro-compacted stone pile construction involves constructing vibro-compacted stone piles at pre-set pile locations according to the layout area to form an anti-liquefaction grid. Precast concrete piles are inserted into predetermined positions to form the main load-bearing structure; The precast concrete piles are subjected to anti-corrosion treatment, including applying a penetrating anti-corrosion coating to their outer surface and installing a rubber anti-corrosion pad at the connection between the pile top and the photovoltaic support.

[0008] Beneficial effects of the basic scheme: Through precise geological surveys in the early stage, the distribution, thickness and liquefaction level of the liquefaction layer are clearly defined, and the depth of precast concrete piles and the layout range of vibro-compacted stone piles are precisely matched, adapting to the characteristics of liquefiable soil in plains. The vibro-compacted stone piles form an anti-liquefaction grid, which can effectively compact the loose liquefiable soil layer, dissipate the pore water pressure of earthquakes, and inhibit soil liquefaction settlement and slippage from the source, ensuring the overall stability of the photovoltaic foundation.

[0009] A composite system of vibro-compacted stone pile anti-liquefaction grid and precast concrete pile main load-bearing structure is adopted. Synergistic effect is achieved through the three-element coupling of soil-stone pile-precast pile: During the vibro-compacting process, the vibro-compacted stone pile generates a radial compaction effect on the liquefiable soil layer, which increases the density of the soil around the pile and reduces the void ratio. Thus, after the precast pile is implanted, the side friction resistance of the pile-soil interface is significantly enhanced. At the same time, the precast pile is embedded as a rigid core in the composite foundation after the stone pile is densified, forming a spatial constraint structure of stone pile enclosure and precast pile load-bearing, which effectively suppresses the horizontal lateral deformation of the stone pile during earthquakes and prevents the stone pile from losing its anti-liquefaction performance due to excessive lateral displacement. The two components do not work independently, but rather achieve mutual enhancement of mechanical properties through changes in soil density: the increased density of the crushed stone piles provides higher lateral friction resistance for the precast piles, while the precast piles provide lateral constraint boundaries for the crushed stone piles. Together, they form a composite foundation with high bearing capacity, high liquefaction resistance, and low settlement, suitable for the stringent requirements of foundation uniformity and seismic resistance in large-area array layouts of photovoltaic power stations. Through a dual anti-corrosion design—applying a penetrating anti-corrosion coating to the outer surface of the piles and adding a rubber anti-corrosion pad at the connection between the pile top and the photovoltaic support—it can resist the erosion and damage of the concrete precast piles by groundwater corrosion media, and also isolate the electrochemical corrosion caused by the contact between the metal support and the pile body, buffering structural connection wear. This makes it suitable for the harsh service environment of outdoor photovoltaic projects, reducing subsequent operation and maintenance costs.

[0010] By applying a penetrating anti-corrosion coating to the outer surface of the pile and adding a rubber anti-corrosion pad at the connection between the pile top and the photovoltaic support, the double anti-corrosion design can not only resist the erosion and damage of the concrete precast pile by the corrosive medium of groundwater on the site, but also isolate the electrochemical corrosion caused by the contact between the metal support and the pile body and buffer the wear of the structural connection. It is suitable for the harsh service environment of outdoor photovoltaic projects and reduces the later operation and maintenance costs.

[0011] The construction process involves first reinforcing the soil against liquefaction, and then implanting the main load-bearing piles. The process is logically clear and facilitates standardized on-site construction. By relying on geological survey parameters, the pile positions, depths, and layout ranges can be accurately determined, avoiding blind construction, saving building materials and construction time. This approach is suitable for the large-scale promotion and application of photovoltaic power stations in plains with large areas of liquefiable soil.

[0012] As a feasible and preferred option, site geological investigation includes the following: Use drilling rigs to arrange exploration holes in a grid pattern within the project site, with a hole spacing of no more than 20m. Each exploration hole should penetrate the liquefaction layer and enter the stable bearing layer at a depth of no less than 1m. Standard penetration tests were conducted in each exploration borehole, with a test point spacing of no more than 5m. The number of test points in each liquefaction layer distribution area was no less than 3. Standard penetration tests were used to identify liquefaction and classify liquefaction levels. Groundwater samples were collected from each exploration borehole for corrosivity analysis to determine key indicators such as pH value and chlorine content of the groundwater. Based on the exploration and test results, a distribution map of the liquefaction layer was drawn to determine the penetration depth of precast concrete piles and the layout range of vibro-compacted stone piles.

[0013] As a feasible and preferred option, the liquefaction level classification is calculated using the liquefaction index:

[0014] In the formula: , For the measured and critical values ​​of the standard penetration test (SPT) blow count at point i, Let be the thickness of the soil layer represented by point i. The layer influence weight function value per unit thickness of the i-th soil layer; Liquefaction grade classification: ≤5 indicates slight liquefaction, 5< ≤15 indicates moderate liquefaction. >15 indicates severe liquefaction.

[0015] As a feasible and preferred option, the formula for calculating the embedment depth H of precast concrete piles is:

[0016] in, h For the thickness of the liquefaction layer, The depth at which the pile tip is embedded in the stable bearing layer; The adaptation factor is determined based on the liquefaction level: Slight liquefaction zone =1.5~1.8, medium liquefaction zone =1.8~2.2, severely liquefied area =2.2~2.5; the fitting coefficient k is corrected according to the number of blows N in the standard penetration test.

[0017] As a feasible and preferred option, vibro-compacted stone pile construction includes the following: Based on the geological survey results, the vibratory compaction stone pile positions are arranged in an equilateral triangle pattern within the site, with the pile spacing being 2.0 to 3.0 times the pile diameter. The specific values ​​are determined based on the thickness of the liquefaction layer and the design seismic acceleration. Excavate a guide pit with a depth of 0.5m at each pile location, fill it with graded crushed stone and level it; Lower the vibratory compactor to the designed depth and perform vibratory compaction at a lifting speed of 1-2 m / min. At the same time, fill the hole with graded crushed stone to ensure that the compaction degree of the pile body is not less than 0.85. After the vibratory compaction operation is completed, curing shall be carried out for no less than 72 hours.

[0018] As a feasible and preferred option, precast concrete piles are inserted into predetermined positions to form the main load-bearing structure, including the following: After the vibratory crushing stone piles have been cured, the pile positions are checked. A static pressure pile driver is used to press precast concrete piles into the preset positions, ensuring that the pile tip is embedded at least 1m into the stable bearing layer. The verticality of the pile is monitored in real time during the pile driving process, and the deviation is no more than 0.5%. If the pile length exceeds the length of a single pile section, pile splicing shall be carried out, and the joint shall be welded or mechanically connected and coated with anti-corrosion paint. After the piles were installed, the low-strain reflected wave method was used to test the integrity of the pile body, with a testing rate of 100%.

[0019] As a feasible and preferred option, the precast concrete piles are subjected to anti-corrosion treatment, including the following: Clean the outer surface of the precast concrete pile; Apply fluorocarbon primer to a thickness of 20-30μm; After the primer has dried and cured, apply fluorocarbon intermediate paint with a thickness of 30-40μm; After the intermediate paint has dried and cured, apply the fluorocarbon topcoat with a thickness of 30-50μm. Install a nitrile rubber anti-corrosion pad with a thickness of 10-15mm at the connection between the top of the precast concrete pile and the photovoltaic support.

[0020] As a feasible and preferred option, this also includes verifying whether the foundation bearing capacity meets the design requirements and monitoring foundation settlement, including the following: 3% of the precast concrete piles within the project area, with a minimum of 3 piles, were randomly selected for static load testing. The load was applied in stages up to 1.5 times the design bearing capacity, and the load was held for at least 2 hours. Typical areas within the project area were selected for liquefaction resistance simulation tests. Seismic dynamic loads were simulated using a shaking table to monitor the liquefaction of the foundation and the amount of settlement. During the project's operation, long-term monitoring of foundation settlement will be conducted, settlement observation points will be set up, and settlement data will be measured and recorded regularly.

[0021] Secondly, the present invention also provides a photovoltaic composite foundation adapted to liquefiable soil in plains, and applies to the above-mentioned construction method of a photovoltaic composite foundation adapted to liquefiable soil in plains, including a precast concrete pile main load-bearing structure, a vibro-compacted crushed stone pile anti-liquefaction structure, and an anti-corrosion system.

[0022] As a feasible preferred solution, the vibratory crushed stone pile is provided with a graded permeable drainage channel inside, with a layer of permeable screen installed every 2m along the length of the pile. The permeable screen is connected to the drainage hole reserved in the center of the pile body through an inclined guide pipe. An anti-clogging device is installed at the top of the drainage hole. The anti-clogging device includes a detachable filter cap and a check valve. The opening pressure of the check valve is 0.05-0.1MPa. Attached Figure Description

[0023] Figure 1 This is a logical schematic diagram of a photovoltaic composite foundation adapted to liquefied soil in plains and its construction method. Detailed Implementation

[0024] To make the technical solution and advantages of this application clearer, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. It is understood that the specific embodiments described herein are only some embodiments of the present invention, and are only used to explain this application, not to limit it. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated; they can be combined with each other to achieve better technical effects. The same reference numerals appearing in the accompanying drawings of the following embodiments represent the same features or components, and can be applied to different embodiments.

[0025] Furthermore, unless otherwise defined, the technical or scientific terms used in this invention description shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains.

[0026] The present invention will now be described in further detail with reference to the accompanying drawings.

[0027] Reference Figure 1 This disclosure provides a photovoltaic composite foundation adapted to liquefiable soil in plains and its construction method. The composite foundation includes a precast concrete pile main load-bearing structure, a vibro-compacted crushed stone pile anti-liquefaction structure, and an anti-corrosion system. Through a dual-pile synergistic reinforcement design, the foundation's load-bearing capacity and anti-liquefaction ability are simultaneously improved, and the anti-corrosion treatment extends its service life.

[0028] The specific technical solution is as follows: Precast concrete piles: 300mm in diameter, C80 strength grade, with a pile tip penetration depth to ground depth ratio of not less than 1.5:1. When the ground liquefaction layer thickness is 7m, the precast concrete pile penetration depth should be not less than 10.5m. The pile top is connected to the bottom of the photovoltaic support structure.

[0029] Vibro-compacted stone piles: These piles are arranged in an equilateral triangle around the precast concrete piles, with a diameter of 1m and a length of 10m. The spacing between adjacent vibro-compacted stone piles is 2.5m. The vibro-compacted stone piles use graded crushed stone filler to ensure that the pile density is not less than 0.85.

[0030] Anti-corrosion system: including a penetrating anti-corrosion coating (fluorocarbon coating, 80-120μm thick) applied to the outer surface of the precast concrete pile, and a rubber anti-corrosion pad (nitrile rubber material, 10-15mm thick) installed at the connection between the top of the precast concrete pile and the photovoltaic support.

[0031] In one embodiment, a graded permeable drainage channel is added inside the vibratory crushed stone pile to further improve the liquefaction resistance of the composite foundation. Specifically, a permeable screen is installed every 2m along the pile length. The screen mesh has a diameter of 5-8mm and is made of woven stainless steel wire with a diamond-shaped mesh arrangement. The edge of the screen is fixedly connected to the inner wall of the pile by binding or welding. A 100mm diameter drainage hole is reserved in the center of the pile, extending 0.5m below the bottom of the liquefaction layer. The inner wall of the drainage hole is provided with a longitudinal guide groove, 3mm deep and 5mm wide, with 6 grooves evenly distributed along the circumference. The permeable screen is connected to the drainage hole by an inclined guide pipe with a diameter of 30mm and an inclination angle of 15°-30° to ensure that pore water can quickly collect in the drainage hole under vibration load. An anti-clogging device is installed at the top of the drainage hole, including a detachable filter cap and a check valve. The filter cap has a diameter of 2-3mm, and the check valve has an opening pressure of 0.05-0.1MPa to prevent surface water backflow while ensuring the smooth discharge of excess pore water pressure.

[0032] The precast concrete piles are equipped with an adaptive drainage structure in the section crossing the liquefaction layer. The drainage holes have a diameter of 20mm, a spacing of 300mm, and are arranged in a quincunx pattern, with 3-4 drainage holes per row and a row spacing of 600mm. The drainage holes are filled with a penetrating waterproof sealant, which is a composite of polyurethane foam and expanded rubber. Under normal compression, the sealing pressure is ≥0.3MPa, and the expansion rate upon contact with water is 150%-200%. When liquefaction occurs and the pore water pressure around the pile reaches 0.2-0.25MPa, the sealant ruptures, forming a drainage channel to help dissipate the pore water pressure around the pile. The effective diameter of the drainage channel after rupture is ≥15mm. The inner wall of the drainage hole is coated with an anti-corrosion coating with a thickness of ≥200μm, using an epoxy coal tar coating, to prevent the drainage hole from becoming a corrosion channel.

[0033] In one embodiment, a pressure-bearing anti-corrosion pad is also included. This pad adopts a composite structure of nitrile rubber and carbon fiber reinforcement layer. The rubber layer is 10-15mm thick, with a 1mm thick carbon fiber reinforcement layer embedded in the middle. The edge of the anti-corrosion pad is provided with annular pressure-bearing protrusions that precisely match the grooves of the photovoltaic support base. Furthermore, an anti-corrosion pressure-bearing cover plate, made of stainless steel and 10mm thick, is added to the top of the precast pile. The cover plate is connected to the pile top by anti-corrosion bolts, and a positioning groove matching the anti-corrosion pad is provided on the cover plate. This design not only prevents rainwater and soil impurities from entering the pile top connection point but also further disperses the load on the support.

[0034] The connection between the pressure-bearing anti-corrosion pad and the pile top is made of M16 stainless steel anti-corrosion bolts. The bolts are made of 316L stainless steel with fine threads (1.5mm pitch). The bolt preload is controlled at 80-100 N·m. A 2mm thick polytetrafluoroethylene gasket is placed between the pressure-bearing anti-corrosion pad and the pile top. The outer diameter of the gasket is the same as the outer diameter of the cover plate, and the inner diameter is the same as the bolt hole diameter. The edge of the cover plate is provided with an outward flange with a flange height of 15mm, which overlaps with the outer surface of the pile body. The overlap length is ≥20mm to form a sealing structure.

[0035] The construction method adopts a "exploration before construction" process, sequentially completing geological exploration, vibro-compacted stone pile construction, precast pile implantation, and bearing capacity verification. This includes the following steps.

[0036] Step S100: Site geological investigation to determine the distribution range and thickness of the liquefaction layer and the corrosivity level of groundwater, and to clarify the penetration depth parameters of precast concrete piles and the layout range of vibro-compacted stone piles. This includes: Drilling rigs were used to create a grid pattern of exploration boreholes within the project site, with a spacing generally not exceeding 20 meters, to ensure coverage of the entire project area. Each exploration borehole must penetrate the liquefaction layer and reach a stable bearing layer at least 1 meter deep.

[0037] Standard penetration tests (SPTs) were conducted in each exploration borehole, with test point spacing not exceeding 5 meters, and at least three test points in each liquefaction layer distribution area. Liquefaction was determined and liquefaction levels were classified using the SPT. The critical value for the SPT blow count was calculated using the following formula:

[0038] in, The standard penetration test blow count is used as the benchmark value for liquefaction discrimination criteria. It is taken as 12 when the design seismic acceleration is 0.20g and 16 when it is 0.30g. To adjust the coefficients, the design earthquake coefficients are set to 0.80 for the first group, 0.95 for the second group, and 1.05 for the third group. The standard penetration depth (m) of saturated soil. The depth of the groundwater level (m); The percentage of clay content, when When the value is less than 3, take 3.

[0039] Liquefaction Index Calculation:

[0040] In the formula: , For the measured and critical values ​​of the standard penetration test blow count at point i; Let be the soil layer thickness (m) represented by point i, which is half the difference in depth between adjacent liquefaction points above and below that point, with the upper limit not exceeding the groundwater level depth and the lower limit not exceeding the liquefaction depth. The layer influence weight function value per unit thickness of the i-th soil layer (m) - ¹), when the depth of the midpoint of the layer is ≤5m, take 10, when it is =20m, take 0, and for 5-20m, take the value by linear interpolation.

[0041] Liquefaction grade classification: ≤5 indicates slight liquefaction, 5< ≤15 indicates moderate liquefaction, I >15 indicates severe liquefaction.

[0042] In one embodiment, this disclosure also provides a quantitative adaptation method for liquefied soils in plains to ensure the stability of the foundation.

[0043] Quantitative model of pile tip penetration depth: Pile tip penetration depth The formula for calculating (m) is: .

[0044] in, h The thickness of the liquefaction layer is in meters (m). The depth (m) into which the pile tip is embedded in the stable bearing layer; and d≥1 m. The adaptation factor is determined based on the liquefaction level: Slight liquefaction zone =1.5~1.8, medium liquefaction zone; =1.8~2.2, severely liquefied area =2.2~2.5. Preferably, the k value can be corrected according to the number of blows in the standard penetration test; N, the correction logic is: for every 5 increase in N, the k value decreases by 0.1.

[0045] Groundwater samples were collected from each exploration borehole and sent to the laboratory for corrosivity analysis to determine key indicators such as pH value and chlorine content of the groundwater.

[0046] Based on the exploration and test results, a distribution map of the liquefaction layer was drawn to determine the penetration depth of precast concrete piles and the layout range of vibro-compacted stone piles.

[0047] Step S200: Vibro-compacted stone pile construction. Vibro-compacted stone piles are constructed at the pre-set pile locations to form an anti-liquefaction grid and improve soil compaction. This includes: Based on the geological survey results, the vibratory compaction stone pile positions were arranged in an equilateral triangle pattern within the site, with a pile spacing of 2.5m. A total station was used for precise layout to ensure accurate pile positions.

[0048] A guide pit with a depth of 0.5m was excavated at each pile location, filled with graded crushed stone and leveled to provide a stable working platform for the vibratory compactor.

[0049] Hoist the vibratory compactor to the top of the guide pit and slowly lower it to the designed depth. Start the vibratory compactor and perform vibratory compaction at a lifting speed of 1-2 m / min, while simultaneously filling the hole with graded crushed stone.

[0050] During vibro-compaction, graded crushed stone is continuously filled to ensure that the pile density is not less than 0.85. Heavy dynamic penetration tests are used to test the pile density, with one test conducted for every 20 piles.

[0051] After the vibratory compaction operation is completed, turn off the vibratory compactor and slowly lift it out of the ground. The vibratory compacted stone piles should then be cured for at least 72 hours.

[0052] Step S300: Precast concrete pile installation. Precast concrete piles are installed in predetermined positions to form the main load-bearing structure. This includes: After the vibratory crushing stone piles have been cured, the pile positions are checked to ensure that they are accurate.

[0053] A static pressure pile driver is used to slowly press the precast concrete piles into the preset positions, ensuring that the pile tip is embedded at least 1 meter into the stable bearing layer. During the pile driving process, the verticality of the pile is monitored in real time, and the deviation is no greater than 0.5%.

[0054] If the pile length exceeds the length of a single pile section, pile splicing is required. When splicing, ensure that the axes of the upper and lower pile sections are aligned, use welding or mechanical connection at the joint, and apply anti-corrosion coating.

[0055] After the piles are installed, the low-strain reflected wave method is used to test the integrity of the pile body, with a testing rate of 100%. This ensures that the pile body is free of defects.

[0056] Vibro-compacted stone piles and precast concrete piles together form a composite foundation system, achieving significant synergistic effects through a three-dimensional coupling of soil, stone piles, and precast piles. During pile formation, vibro-compacted stone piles generate a strong radial compaction effect on the surrounding liquefiable soil layer, effectively increasing the density of the soil around the pile and reducing the void ratio. This significantly enhances the lateral friction resistance at the pile-soil interface after the precast concrete piles are implanted. Simultaneously, the precast concrete piles, as rigid cores, are embedded in the composite foundation reinforced by stone piles, forming a spatial constraint structure of stone pile retaining walls and precast pile bearing capacity. This effectively suppresses the horizontal lateral deformation of the stone piles under dynamic loads such as earthquakes, preventing them from losing their anti-liquefaction performance due to excessive lateral displacement.

[0057] The aforementioned synergistic mechanism is not a simple functional superposition, but rather a mutual enhancement of mechanical properties by changing the physical state of the soil. The crushed stone piles provide a foundation with high lateral friction resistance for the precast piles, while the precast piles provide key lateral constraint boundaries for the crushed stone piles. Together, they construct an integrated foundation system with high bearing capacity, high liquefaction resistance, and low settlement risk, perfectly adapting to the stringent requirements of large-area array layout of photovoltaic power stations for foundation uniformity and seismic stability.

[0058] Step S400, anti-corrosion treatment, involves applying a penetrating anti-corrosion coating to the outer surface of the precast concrete pile and installing a rubber anti-corrosion pad on the pile top to extend the service life of the foundation, including: Clean the outer surface of the precast concrete piles to remove oil, dust, and other impurities. Rinse the pile body with a high-pressure water gun and allow it to dry.

[0059] Fluorocarbon primer should be selected, mixed according to the specified ratio, and then evenly applied to the surface of the pile. The coating thickness should be controlled at 20-30μm to ensure a uniform and complete coating.

[0060] After the primer has dried and cured (curing time no less than 24 hours), apply the fluorocarbon intermediate coat. The coating thickness should be controlled at 30-40 μm to ensure good adhesion between the intermediate coat and the primer.

[0061] After the intermediate coat has dried and cured (curing time no less than 12 hours), apply the fluorocarbon topcoat. The coating thickness should be controlled at 30-50 μm to ensure a smooth and even topcoat.

[0062] A nitrile rubber anti-corrosion pad is installed at the connection between the top of the precast concrete pile and the photovoltaic support. The anti-corrosion pad is 10-15mm thick, its size matches the cross-section of the pile top, and its surface has an anti-slip texture.

[0063] Step S500: Verify whether the foundation bearing capacity meets the design requirements and monitor foundation settlement. This includes: Randomly select 3% (but no fewer than 3) of the precast concrete piles within the project area for static load tests. Apply load to the pile top using jacks and reaction devices, gradually increasing the load to 1.5 times the design bearing capacity, and hold the load for at least 2 hours. Record the pile top settlement and plot the load-settlement curve.

[0064] Typical areas within the project area were selected for liquefaction resistance simulation tests. Seismic dynamic loads were simulated using a shaking table to monitor foundation liquefaction and settlement.

[0065] During project operation, long-term monitoring of foundation settlement will be conducted. Settlement observation points will be set up, and settlement data will be measured and recorded regularly. If abnormal settlement is detected, reinforcement measures will be taken promptly.

[0066] Example 2 The technical feature that distinguishes this embodiment from Embodiment 1 is that, for highly corrosive groundwater environments, this embodiment adds a dual anti-corrosion strategy that combines cathodic protection and anti-corrosion coating.

[0067] A zinc alloy sacrificial anode is installed at the bottom of the precast concrete pile. The anode specifications are ZP-10 type (10kg / pile) or ZP-15 type (15kg / pile), and the anode size is 200mm×100mm×50mm.

[0068] A copper core cable with a cross-sectional area of ​​16mm² is used for connection. The cable is protected by a PVC pipe. The connection point is located 0.5m above the bottom of the pile. The connection method is copper welding or mechanical crimping. The contact resistance is ≤0.01Ω.

[0069] The consumption rate of zinc alloy anodes in seawater is approximately 11.88 kg / (A·year), and in highly corrosive groundwater it is calculated to be 15 kg / (A·year). With a design life of 25 years, the anode mass m = 15 × I × 25, and the protection current density is taken as 10-30 mA / m².

[0070] The anode needs to be replaced when the remaining mass of the anode is less than 20% of the initial mass or when the protection potential shifts positively to -0.75V (vs Cu / CuSO4).

[0071] Meanwhile, the anti-corrosion coating structure was optimized by using three layers: epoxy primer, polyurea intermediate coat, and fluorocarbon topcoat, increasing the total thickness to 150-180μm, with the polyurea intermediate coat being 60-80μm thick, thus enhancing the coating's corrosion resistance and impact resistance.

[0072] Example 3 The technical feature that distinguishes this embodiment from Embodiment 1 is that, for the complex soil environment of seasonal freeze-thaw and liquefaction in cold northern regions, this embodiment adds a synergistic design for freeze-thaw protection and liquefaction prevention.

[0073] Freeze-thaw protection for precast piles includes the following: In the section where the precast piles pass through the freeze-thaw layer (from 0.5m below the ground surface to 0.5m below the bottom of the freeze-thaw layer), a polyurethane insulation layer with a thickness of 50mm, a density of 40-60kg / m³, a thermal conductivity ≤0.024W / (m·K), and a compressive strength ≥200kPa is wrapped around it.

[0074] The insulation layer is wrapped with SBS modified bitumen waterproof membrane with a thickness of ≥4mm and an overlap width of ≥100mm. The overlap is constructed using the hot-melt method, and the peel strength of the joint is ≥1.5N / mm.

[0075] The waterproof layer is wrapped with a fiberglass protective shell, 3-5mm thick, with a resin content ≥60% and a tensile strength ≥150MPa, to prevent construction damage.

[0076] A compressible deformation section is set in the freeze-thaw zone of the precast pile, using a corrugated steel pipe sheath with a corrugation depth of 10mm and a corrugation pitch of 50mm, allowing radial deformation ≥5mm to release frost heave force. The space between the deformable section and the pile body is filled with a flexible material, preferably polyurethane foam or rubber granules, with a compression modulus of 5-10 MPa, which allows for deformation while maintaining the stability of the pile body.

[0077] The freeze-thaw resistance of vibratory compaction stone piles includes the following: Adding 5%-8% volcanic ash (fly ash or silica fume) to graded crushed stone, with a volcanic ash fineness (45μm sieve residue) ≤20% and an activity index ≥70%, improves the frost resistance and density of the pile body.

[0078] Drainage blind ditches are installed at the bottom of the freeze-thaw layer (0.3m below the bottom surface of the freeze-thaw layer). The cross-sectional dimensions of the blind ditches are 300mm×300mm. They are filled with crushed stone with a particle size of 20-40mm and wrapped with geotextile (200g / m²). The slope of the blind ditches is ≥1%, and they are connected to the drainage holes of the crushed stone piles.

[0079] A sump well is installed at the outlet of the blind drain. The well has a diameter of 600mm and a depth of 1.0m. The well wall is made of concrete with a thickness of 150mm. A submersible pump is installed at the bottom of the well to automatically pump out the freeze-thaw water.

[0080] Specifically, in the section where the precast piles pass through the freeze-thaw zone, a 50mm thick polyurethane insulation layer is wrapped around it, and a waterproof membrane is wrapped around the insulation layer to prevent the concrete of the pile from cracking due to freeze-thaw cycles.

[0081] Meanwhile, 5%-8% volcanic ash is added to the vibratory compaction stone pile filler to improve the pile's frost resistance and density, preventing a decrease in pile strength due to freeze-thaw cycles. A drainage ditch is installed at the bottom of the freeze-thaw layer, connected to the drainage holes of the stone piles, to promptly drain groundwater generated during freeze-thaw cycles.

[0082] Example 4 The technical feature that distinguishes this embodiment from Embodiment 1 is that, for the scenario of photovoltaic agriculture composite utilization, this embodiment combines composite foundation design with agricultural photovoltaic complementary system to realize multi-functional land utilization.

[0083] The preferred height of the photovoltaic support frame is ≥1.5m at the front end, ≥2.5m at the rear end, and ≥4.0m between the supports to meet the space requirements for agricultural machinery operation.

[0084] Planting areas are divided according to the average daily cumulative photosynthetically active radiation (PPFD): Shade-loving plant planting area (PPFD < 50 μmol·m - ²·s - ¹): Plant shade-tolerant crops, such as edible fungi, ginger, and pinellia. Neutral plant planting area (50≤PPFD<200μmol·m - ²·s - ¹): Plant neutral crops, such as soybeans, peanuts, and vegetables; Sunlight-loving plant cultivation area (PPFD ≥ 200 μmol·m - ²·s - ¹): Plant light-loving crops, such as corn, sorghum, and pasture.

[0085] Drip irrigation or micro-sprinkler irrigation pipelines with diameters of De63-De110 and working pressures of 0.1-0.3MPa are laid within the maintenance channel. Irrigation water sources are preferentially sourced from groundwater pumps driven by photovoltaic power generation, or rainwater collected from photovoltaic panels and filtered and then used. Soil moisture monitoring: Soil moisture sensors are installed at depths of 0-20cm, 20-40cm, and 40-60cm to automatically control irrigation start and stop.

[0086] After the photovoltaic array occupies the land, the topsoil reserved in the excavation is used to cover it with soil, with a thickness of 15-25cm, and beneficial microbial agents (such as rhizobia, mycorrhizal fungi, and photosynthetic bacteria) are inoculated. Mixed planting is adopted, and native plants that are drought-resistant, tolerant of poor soil, and shade-tolerant are given priority, such as alfalfa, white clover, and ryegrass. Soil quality (pH, organic matter, nutrients), vegetation growth (coverage, biomass, diversity) and ecological functions (soil and water conservation, carbon sequestration) are monitored regularly.

[0087] The above content is merely an embodiment of the present invention. Commonly known structures and characteristics of the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can improve and implement this solution based on the guidance provided in this application and their own capabilities. Typical well-known structures or operating methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains, characterized in that, include: Site geological survey to determine the distribution range, thickness and groundwater corrosivity level of the liquefaction layer, and determine the penetration depth parameters of precast concrete piles and the layout range of vibratory crushed stone piles based on the thickness and liquefaction level of the liquefaction layer. Vibro-compacted stone pile construction involves constructing vibro-compacted stone piles at pre-set pile locations according to the layout area to form an anti-liquefaction grid. Precast concrete piles are inserted into predetermined positions to form the main load-bearing structure; The precast concrete piles are subjected to anti-corrosion treatment, including applying a penetrating anti-corrosion coating to their outer surface and installing a rubber anti-corrosion pad at the connection between the pile top and the photovoltaic support.

2. The construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains according to claim 1, characterized in that, Site geological investigation, including the following: Use drilling rigs to arrange exploration holes in a grid pattern within the project site, with a hole spacing of no more than 20m. Each exploration hole should penetrate the liquefaction layer and enter the stable bearing layer at a depth of no less than 1m. Standard penetration tests were conducted in each exploration borehole, with a test point spacing of no more than 5m. The number of test points in each liquefaction layer distribution area was no less than 3. Standard penetration tests were used to identify liquefaction and classify liquefaction levels. Groundwater samples were collected from each exploration borehole for corrosivity analysis to determine key indicators such as pH value and chlorine content of the groundwater. Based on the exploration and test results, a distribution map of the liquefaction layer was drawn to determine the penetration depth of precast concrete piles and the layout range of vibro-compacted stone piles.

3. The construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains according to claim 1, characterized in that, The liquefaction level classification is calculated using the liquefaction index: In the formula: , For the measured and critical values ​​of the standard penetration test (SPT) blow count at point i, Let be the thickness of the soil layer represented by point i. The layer influence weight function value per unit thickness of the i-th soil layer; Liquefaction grade classification: ≤5 indicates slight liquefaction, 5< ≤15 indicates moderate liquefaction. >15 indicates severe liquefaction.

4. The construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains according to claim 1, characterized in that, The formula for calculating the embedment depth H of a precast concrete pile is: in, h For the thickness of the liquefaction layer, The depth at which the pile tip is embedded in the stable bearing layer; The adaptation factor is determined based on the liquefaction level: Slight liquefaction zone =1.5~1.8, medium liquefaction zone =1.8~2.2, severely liquefied area =2.2~2.5; the fitting coefficient k is corrected according to the number of blows N in the standard penetration test.

5. The construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains according to claim 1, characterized in that, Vibro-compacted stone pile construction includes the following: Based on the geological survey results, the vibratory compaction stone pile positions are arranged in an equilateral triangle pattern within the site, with the pile spacing being 2.0 to 3.0 times the pile diameter. The specific values ​​are determined based on the thickness of the liquefaction layer and the design seismic acceleration. Excavate a guide pit with a depth of 0.5m at each pile location, fill it with graded crushed stone and level it; Lower the vibratory compactor to the designed depth and perform vibratory compaction at a lifting speed of 1-2 m / min. At the same time, fill the hole with graded crushed stone to ensure that the compaction degree of the pile body is not less than 0.

85. After the vibratory compaction operation is completed, curing shall be carried out for no less than 72 hours.

6. The construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains according to claim 1, characterized in that, Precast concrete piles are inserted into predetermined positions to form the main load-bearing structure, including the following: After the vibratory crushing stone piles have been cured, the pile positions are checked. A static pressure pile driver is used to press precast concrete piles into the preset positions, ensuring that the pile tip is embedded at least 1m into the stable bearing layer. The verticality of the pile is monitored in real time during the pile driving process, and the deviation is no more than 0.5%. If the pile length exceeds the length of a single pile section, pile splicing shall be carried out, and the joint shall be welded or mechanically connected and coated with anti-corrosion paint. After the piles were installed, the low-strain reflected wave method was used to test the integrity of the pile body, with a testing rate of 100%.

7. The construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains according to claim 1, characterized in that, The anti-corrosion treatment of the precast concrete piles includes the following: Clean the outer surface of the precast concrete pile; Apply fluorocarbon primer to a thickness of 20-30μm; After the primer has dried and cured, apply a fluorocarbon intermediate coat with a thickness of 30-40μm. After the intermediate paint has dried and cured, apply the fluorocarbon topcoat with a thickness of 30-50μm. Install a nitrile rubber anti-corrosion pad with a thickness of 10-15mm at the connection between the top of the precast concrete pile and the photovoltaic support.

8. The construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains according to claim 1, characterized in that, This also includes verifying whether the foundation bearing capacity meets the design requirements and monitoring foundation settlement, including the following: 3% of the precast concrete piles within the project area, with a minimum of 3 piles, were randomly selected for static load testing. The load was applied in stages up to 1.5 times the design bearing capacity, and the load was held for at least 2 hours. Typical areas within the project area were selected for liquefaction resistance simulation tests. Seismic dynamic loads were simulated using a shaking table to monitor the liquefaction of the foundation and the amount of settlement. During the project's operation, long-term monitoring of foundation settlement will be conducted, settlement observation points will be set up, and settlement data will be measured and recorded regularly.

9. A photovoltaic composite foundation adapted to liquefiable soil in plains, characterized in that: A construction method for a photovoltaic composite foundation adapted to liquefiable soil in plains, as described in any one of claims 1-8, includes a precast concrete pile main load-bearing structure, a vibro-compacted crushed stone pile anti-liquefaction structure, and an anti-corrosion system.

10. A photovoltaic composite foundation adapted to liquefied soil in plains according to claim 9, characterized in that: The vibratory crushed stone pile is equipped with a graded permeable drainage channel. A permeable screen is set every 2m along the length of the pile. The permeable screen is connected to the drainage hole reserved in the center of the pile body through an inclined guide pipe. An anti-clogging device is set at the top of the drainage hole. The anti-clogging device includes a detachable filter cap and a check valve. The opening pressure of the check valve is 0.05-0.1MPa.

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