Full life cycle management of photovoltaic spiral piles: technical paths and practices from design to recycling

The value of photovoltaic spiral ground piles lies not only in their initial advantage of "easy installation," but also requires scientific management throughout their entire life cycle (design - construction - operation and maintenance - recycling) to achieve the goals of "long-term reliability, optimal cost, and eco-friendliness." Especially in extreme geological scenarios such as frozen soil and soft soil, full-lifecycle management directly determines the pile's bearing stability and project return on investment. This article focuses on key aspects of the spiral ground pile life cycle, analyzing technical optimization strategies and practical cases to fill the gap in extreme geological adaptation and recycling.

I. Design Phase: Geological Adaptation and Mechanical Optimization to Strengthen Foundation Performance

Design is the core prerequisite for the spiral ground pile's entire life cycle. It must integrate geological survey data with load requirements, and through coordinated optimization of the "geology - structure - materials" process, avoid bearing failures caused by design deviations later in life. (I) Specialized Design Solutions for Extreme Geology

Permafrost PV (e.g., Greater Khingan Mountains, Northeast China)

Geological Pain Points: Soil expansion during winter freezing (up to 5-15cm) and thawing and settling during summer can easily cause piles to tilt or pull out. Freeze-thaw cycles accelerate pile corrosion, shortening the lifespan of traditional piles to less than 15 years.

Design Optimization:

Pile Structure: A "variable diameter pile" (upper diameter 140mm, lower diameter 114mm) is used, with the lower portion embedded in the permafrost (buried at a depth of ≥3m) to avoid freeze-thaw effects. The blades feature a "spiral gradient angle design" (upper angle 15°, lower angle 10°) to enhance engagement with the permafrost and increase pullout resistance to over 30kN. Material Selection: Q460 steel with a zinc-aluminum-magnesium coating (thickness ≥ 80μm) is used, along with a polyurethane insulation layer (50mm thick) wrapped around the outside of the pile body to mitigate the thermal shock of freeze-thaw cycles, keeping the corrosion rate to less than 0.001mm/year.

Case Study: A 50MW photovoltaic project on frozen soil in Heilongjiang Province employed variable-diameter insulated spiral ground piles. After three freeze-thaw cycles (with a minimum temperature of -40°C), the piles maintained an inclination of ≤0.5° and a pull-out strength degradation rate of only 2%, meeting the 25-year design lifespan.

Soft Soil Photovoltaic Projects (e.g., the marshy areas of the Yangtze River Delta)

Geological Challenges: Low soil bearing capacity (≤80kPa) and prone to compression and settlement (settlement of up to 20cm). Traditional ground piles are prone to "pile sinking," resulting in deformation of the support. Design Optimization:

Foundation Reinforcement: A "composite foundation of spiral piles and cement-soil mixing piles" is used. Cement-soil mixing piles (600mm diameter, 4m length) wrap around the lower portion of the spiral piles, increasing the soil bearing capacity to over 150kPa. The spiral pile length is increased to 3.5-4m, and the number of blades is increased to four (300mm diameter), increasing the contact area with the soil and reducing settlement.

Load Distribution: An expanded flange (300mm diameter) is used at the top of the pile, combined with a 20mm thick rubber cushion to evenly transfer the support load to the pile, preventing localized stress concentration and pile bending.

Case Study: A 30MW soft-soil photovoltaic project in Jiangsu Province employed a composite foundation solution. Pile settlement was controlled to within 5cm, and the support flatness error was ≤3mm, reducing settlement risk by 80% compared to traditional pile solutions. (II) Mechanical Simulation and Digital Design Tools

Finite Element Analysis (FEA) is used to simulate the stress distribution of ground piles under different loads. For example, for ground piles equipped with dual-axis tracking brackets, the pile body stress under a wind load of 1.8 kN/m² is simulated to ensure that the maximum stress is ≤180 MPa (Q460 steel yield strength is 345 MPa), allowing for a sufficient safety factor.

BIM (Building Information Modeling) technology is introduced: geological data, ground pile parameters, and bracket models are integrated to visualize the positional relationship between ground piles, underground pipelines, and rock formations, thus avoiding conflicts with underground facilities during construction. (For example, in one project, BIM revealed that 30% of the ground piles overlapped with underground cables, allowing for preemptive design adjustments and reducing rework costs by 500,000 yuan.)

II. Construction Phase: Intelligent Equipment and Digital Quality Control Improve Installation Efficiency

The core of the construction phase is "precise placement and controlled quality." Intelligent equipment replaces manual operations, combined with digital monitoring methods to reduce human error and ensure that ground pile installation meets design requirements. (I) Intelligent Construction Equipment Upgrade

Unmanned Pile Driver

Comprising an unmanned crawler chassis, an automatic positioning system, and a hydraulic piling module, it automatically aligns pile positions using Beidou positioning (accuracy ±2cm), eliminating the need for manual adjustment. Pile driving parameters (speed 20-40 r/min, pressure 30-100 kN) are adaptively adjusted in real time based on the geology (sand and soil conditions automatically increase the speed to 35 r/min, and clay and soil conditions automatically increase the pressure to 80 kN).

Efficiency Comparison: Traditional manual pile drivers install an average of 200-300 piles per day, while unmanned pile drivers install 400-500 piles per day, representing an efficiency increase of over 60%. Furthermore, each unit requires only one person for remote monitoring, reducing labor costs by 70%. Case Study: A 200MW desert photovoltaic project in Inner Mongolia deployed 10 unmanned pile-driving units, completing the installation of 160,000 piles in 20 days, shortening the construction period by 15 days compared to manual methods and saving 1.2 million yuan in labor costs.

Miniature Customized Equipment

For narrow mountainous terrain (passage width ≤ 1m), a "foldable pile driver" (folded width 0.8m, weight 1.2 tons) was developed, which can be transported to the mountaintop via a cableway. An "electric hydraulic system" replaced diesel power, reducing exhaust pollution during mountain construction (carbon emissions were reduced by 90%).

For rooftop photovoltaic projects (such as those with parapet walls on flat roofs), a "portable pile driver" (weight 30kg, power 5kW) was developed. It is fixed to the roof using vacuum suction cups, eliminating the need for large-scale equipment and allowing a single pile to be installed in 8 minutes or less. (II) Digital Quality Control System
Real-time Data Monitoring: The pile driver is equipped with a "torque sensor + depth sensor," which uploads the installed torque (accuracy ±1N·m) and depth (accuracy ±1cm) to a cloud platform in real time. If the torque is abnormal (e.g., a sudden increase of 30%, possibly due to rock impact), the machine will automatically shut down and issue an alarm to prevent pile damage.
Blockchain Evidence Storage: The installation time, parameters, and test results of each pile are uploaded to the blockchain, making them tamper-proof and facilitating traceability for future operations and maintenance. (For example, if a pile tilted due to a typhoon on a project, retrieval of installation data through the blockchain quickly confirmed that it was geological subsidence rather than an installation error, shortening the time required to determine responsibility by three days.)

III. Operation and Maintenance Phase: Fault Warning and Precision Maintenance to Extend Service Life
Operation and maintenance of spiral piles should focus on "early warning, minimal intervention." By combining sensor monitoring with regular inspections, problems such as corrosion and subsidence can be detected promptly to prevent further failures. (I) Intelligent Monitoring System
Pile Health Monitoring Module
Fiber Bragg Grating Sensors (accuracy ±0.001mm) are embedded in the pile body to monitor pile strain (reflecting load changes) and temperature (correlating to freeze-thaw and corrosion risks) in real time. A tilt sensor (accuracy ±0.01°) is installed at the top of the pile to monitor pile tilt trends.

Early Warning Mechanism: When strain exceeds 200 MPa (or tilt angle exceeds 1°), the system automatically sends an alert to operations and maintenance personnel and generates a maintenance plan (e.g., recommending hydraulic jacking correction for tilted piles).

Case Study: A coastal photovoltaic power station in Fujian Province installed monitoring modules on 1,000 spiral piles. Over two years of operation, 12 piles were identified as experiencing abnormal strain due to salt spray corrosion. These piles were promptly replaced, preventing the risk of pile collapse and reducing losses by approximately 2 million yuan. Environmental Linked Monitoring

Combining meteorological station data (wind speed, rainfall) with ground pile monitoring data, an "environment-load" correlation model is established. For example, if wind speeds are predicted to be ≥ Level 10, a ground pile stress warning is issued in advance, allowing operations and maintenance personnel to preemptively reinforce the connection between the bracket and the ground pile to reduce wind load impact.

(II) Tiered Maintenance Strategy

Daily Maintenance (once per year): Check the torque of the flange bolts at the pile top (retighten with a torque wrench, ensuring that the torque of M16 bolts remains between 80-100 N·m); clear mud, sand, and weeds from the exposed portion of the pile top to prevent obstruction of the sensor.

Interim Maintenance (five times per year): Use an ultrasonic thickness gauge to measure pile wall thickness (if corrosion causes a reduction of more than 10% in wall thickness, reapply an anti-corrosion coating). For coastal projects, use a salt spray concentration meter to assess the surrounding environment. Increase the frequency of anti-corrosion maintenance if the concentration exceeds 80 mg/m³. Emergency Maintenance: For sinking piles, high-pressure grouting reinforcement is used (cement slurry is injected through pre-reserved holes in the pile body to fill soil voids and increase bearing capacity). For tilted piles, hydraulic jacks are used to push and correct them, and steel wedges are then inserted to secure them. The maintenance cost per pile is approximately 500 yuan, far lower than the replacement cost (3,000 yuan per pile).

Fourth, Recycling Phase: Technical Pathways and Circular Economy to Achieve an Ecologically Closed Loop

After the lifespan of a photovoltaic project (typically 25-30 years), the scientific recycling of spiral piles is key to eco-friendliness. This requires minimizing land damage while achieving material recycling. (I) High-Efficiency Recovery Technology
Hydraulic Pile Extraction Equipment
Using a "double-cylinder hydraulic pile extractor" (pulling force 50-100kN), the jaws clamp the flange at the top of the pile and extract it slowly and evenly (5-10cm/min), avoiding damage to the soil structure caused by violent pile extraction. Combined with a "vibration module" (frequency 20-30Hz), it reduces pile extraction resistance and is particularly suitable for clay layers (increasing pile extraction efficiency by 40%).
Recovery Efficiency: Traditional manual pile extraction recovers an average of 50-80 piles per day, while hydraulic equipment recovers an average of 200-300 piles per day, with a soil recovery rate of 98% (only holes with a diameter of ≤150mm remain after pile extraction, which can be manually backfilled and leveled). Material Separation and Recycling
Metal Recycling: Recycled ground piles are disassembled (flange, pile body, and blades are separated). Shot blasting is used to remove old coatings (rust removal rate ≥ 95%). Wall thickness is then tested (remaining wall thickness ≥ 70% of the design value allows for reprocessing). Q355 steel ground piles can be melted and recast into new pile bodies (material utilization rate over 80%). 316L stainless steel ground piles can be directly re-coated and reused (at only 30% of the cost of new piles).
Coating Treatment: Old coatings (such as zinc, aluminum, and magnesium layers) are removed through high-temperature incineration and pickling. The incineration exhaust is treated and discharged (pollutant emissions comply with GB 16297 standards). The pickling wastewater can be used to recover metals such as zinc and aluminum, achieving "zero wastewater discharge." (II) Economic and Ecological Benefits

Cost Comparison: The cost of recycling and reusing a single ground pile is approximately 100 yuan, a 60%-80% reduction compared to purchasing new piles (80-500 yuan). A 100MW project recycled 100,000 ground piles, saving approximately 8 million yuan in procurement costs through reprocessing.

Ecological Benefits: Recycling ground piles prevents metal waste from landfill (every ton of recycled steel reduces 1.5 tons of CO2 emissions). Once restored, the land can be reclaimed as farmland or grassland (for example, in a recycling project in Inner Mongolia, pasture yields recovered to 95% of pre-project levels).

V. Conclusion

The full lifecycle management of photovoltaic spiral ground piles is a deep integration of "technological innovation" and "ecological concepts"—geological adaptation during the design phase ensures a reliable foundation, intelligent construction improves efficiency, early warning maintenance during operation and maintenance extends lifespan, and recycling during the recycling phase achieves a closed-loop system. In the future, with the application of technologies such as "digital twin" (building a digital model of the pile's entire lifecycle to simulate performance changes under different operating conditions) and "bio-based anti-corrosion materials" (such as plant extract coatings that are naturally degradable), spiral piles will further break through extreme geological limitations, reduce full-lifecycle costs, and provide a more solid foundation for the "sustainable development" of the photovoltaic industry.