Case Study: 1.5MW Ground-Mounted Solar Structure Piling Project in Madurai
Project Overview
- Capacity: 1.5 MWp
- Location: Thirumangalam Agricultural Zone, Madurai, Tamil Nadu
- Terrain: Open flat farmland (Category 2 terrain)
- Target Wind Speed: 39 m/s (Zone 2, IS 875 wind zone)
- Structural Solution: Rammed C-channel steel piling foundations with Hot-Dip Galvanized (GI) seasonal tilt structures.
The Engineering Challenge
The client required a 1.5 MW ground-mounted utility array built on former agricultural land. The geotechnical survey revealed a highly variable soil profile: the top $600\text{mm}$ consisted of loose clayey black cotton soil (which expands and contracts during seasonal water table shifts), followed by medium-stiff gravelly sand underneath.
Traditional concrete pedestal block foundations would require significant manual excavation, cement transit mixing, and 28 days of curing time, delaying the project timeline.
To meet the commissioning deadline, the EPC required a concrete-free piling solution that could anchor the structures directly into the variable soil layer.
Structural Design & Solution
The SOLBE engineering team selected a Direct-Ramming Steel Pile Foundation:
1.5MW RAMMED PILING GROUND PROFILE
[ PV Module Table ]
[ HDG Steel Columns (IS 2062 steel) ]
═════════════════════════════════ <- Soil Surface (Black Cotton Soil)
│ Loose soil layer (600mm) │
├────────────────────────────────┤
│ Rammed pile depth (1.8m) │ <- Hydraulic piling into gravelly sand
└────────────────────────────────┘- Direct Hydraulic Piling: Using a crawler-mounted hydraulic pile rammer, we drove galvanized steel C-channel columns ($120\text{mm} \times 60\text{mm} \times 3.0\text{mm}$ thickness) directly into the soil to a depth of $1.8\text{ meters}$. This bypassed the loose topsoil layer and anchored the columns securely inside the gravelly sand matrix.
- Pull-Out Tension Testing: In-situ physical pull-out testing was executed on 2% of the installed piles using a calibrated hydraulic jack. Piles successfully withstood a tension force of $12.8\text{ kN}$ (well above the design wind uplift limit of $8.2\text{ kN}$).
- Seasonal Tilt Adjustment: The A-frame rafter connections were designed with seasonal tilt joints, allowing the maintenance crew to manually adjust the array tilt between $11^\circ$ (summer orientation) and $25^\circ$ (winter orientation) to maximize annual yield.
Key Performance Metrics
- Foundation Cost Savings: Saved ₹4,20,000 on concrete excavation and cement logistics.
- Installation Velocity: Hydraulic piling averaged 85 piles per day, completing all foundation works within 14 days (saving 3 weeks of concrete curing wait times).
- Solar Yield Efficiency: The manual seasonal tilt adjustment achieved a 3.8% increase in annual generation compared to fixed-tilt installations.
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