Establishing a utility-scale mechanical foundation across challenging Butte County terrain.
Located in Oroville, California, this greenfield utility-scale installation required complete mechanical ground-mount construction across raw, undeveloped terrain. Mobilizing as the lead mechanical contractor, Sunstall was tasked with translating civil engineering drawings into an OEM-warranted tracker foundation. Early site work confirmed shallow, fractured rock strata across the footprint, meaning foundation integrity, embedment depth, and strict structural alignment would dictate the success of the entire mechanical phase.
Sunstall managed the entire mechanical critical path, coordinating ground-level execution through structured milestones:
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Civil Layout & Surveying: Mapping engineer-of-record coordinate points across native contours to establish table centerlines and tracker baselines.
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Structural Foundation Installation: Driving heavy-gauge steel piles to mandated embedment depths to satisfy site-specific wind and seismic load tolerances.
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Tracker & Racking Assembly: Erecting bearing assemblies, mounting torque tubes, and securing purlins within strict OEM mechanical tolerances.
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Robotic Module Placement & Mechanical QC: Deploying automated mechanical lifters and robotic module installation systems to place panels efficiently, true the tables, and eliminate angular run-out before mechanical completion.
1938
Hours of Work
Aug 2026
Construction Date
2.43
Size[MW]
Butte County, CA
Location
Navigating layout deflection, 123 rock refusals, and racking drift under tight tolerances.
Field crews hit high-density subterranean rock that disrupted standard installation workflows:
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Manual Layout Deflection: Subsurface cobble repeatedly bent steel survey pins and ground markers (“birdies”), making traditional manual pinning unreliable across dense rock sections.
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123 Pile Refusals: Conventional driving rigs encountered impenetrable rock shelves, logging 123 structural refusals where piles halted well short of target engineering depth.
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Lateral Pile Drift: As pile tips deflected off subterranean boulders, several foundations shifted out of plumb and lateral alignment, threatening table geometry for downstream racking.
Applying specialized pre-drilling, field realignments, and robotic installation to safeguard tolerances.
Rather than letting subterranean friction disrupt the construction schedule, Sunstall adapted its tooling and connection strategy on the fly:
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Targeted Pre-Drilling Operations: Specialized drill rigs were mobilized to core through the bedrock at refusal locations, allowing piles to achieve 100% specified embedment depth.
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Field-Adapted Racking Realignment: To correct for underground pile deflection, crews executed controlled purlin adjustments and supplemental hole drilling, bringing table alignment back within millimeter-level manufacturer limits.
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Automated Precision at Scale: Transitioning from manual module handling to robotic module placement allowed the team to recover schedule velocity lost during pre-drilling, seating panels with consistent torque and zero micro-fracturing risk.
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Execution Agility: Greenfield geotechnical reports rarely capture every rock shelf. Sunstall’s ability to troubleshoot ground refusals, adjust steel tolerances in the field, and deploy robotics during panel placement delivered an OEM-compliant, warrantable racking foundation ready for electrical balance-of-plant teams.
