Helical Anchor Case Study: 1,240 Solar Tracker Bases on Shrink-Swell Clay

A solar contractor had 1,240 tracker posts to found across 40 hectares of shrink-swell clay. The ground cracked open in the dry season and heaved after rain, so any shallow footing moved with it. A pile rig would have refused on scattered gravel lenses, and concrete meant water trucks the site did not have. We manufactured 1,240 helical anchors to a single drawing. The foundation package finished in 16 days, with no concrete placed anywhere on the plot.

Project Snapshot

The Problem: Ground That Moves Twice a Year

Solar sites get chosen for irradiance and land price, not for soil. This plot was heavy clay that behaves differently in each season. Through the dry months it cracks to roughly a metre deep. After rain, the same clay swells and lifts. A footing that sits in that active layer will rise and fall with it, and tracker rows do not tolerate movement.

A second constraint arrived with the geotechnical report. Gravel lenses sat at random depths across the plot, so a driven pile would refuse early on some rows and drive deep on others. That variability breaks pile spacing and pushes the tracker rail out of line. Meanwhile the foundation window was ten weeks, and the weather window was shorter than that.

Why We Chose Helical Anchors Over Piles, Pads and Ballast

The engineering team compared four options.

Driven steel piles. Excluded. Refusal on gravel lenses would leave piles at different depths along the same row, and the rig could not work on the soft sections after rain without matting.

Cast-in-place concrete pads. Excluded. The site had no borehole, so water would have come by road, and every pad would need a week of curing before the tracker could be mounted. For 1,240 posts that is a large volume of concrete and a long idle period.

Ballasted precast blocks. Excluded. Freight alone was heavy, and the blocks would have loaded clay that was already moving. They also invite tampering on an open plot with no fence line.

Helical anchors. Selected. They install by rotation, so they need no water, no excavation and no curing. Depth is controlled through extension shafts, and the anchor can be proof loaded the same day.

The Helical Anchors We Manufactured

Our plant in Handan, Hebei produced all 1,240 units from one approved drawing. Each anchor begins as a Q235 carbon steel shaft, cut to length in a round or square section. The helix plates are pressed, then welded to full strength, and every weld is inspected before the part moves down the line.

Hot-dip galvanizing follows welding, which matters because the coating has to reach the plate faces and the shaft as one continuous layer. Galvanized steel also resists the scrapes that come with powered rotation, so the corrosion barrier survives installation.

The array needed two configurations. Inner rows took a mid-range unit, while the perimeter rows, where wind uplift peaks, took a heavier plate set. We also supplied the top brackets so the anchors bolted straight to the post bases with no drilling on site. Every unit was marked and packed to the contractor's row schedule.

Installation: How the Work Ran

Installation followed one fixed loop, and the loop is what keeps results stable.

The crew marked each position, then set a drive head on a mini-excavator over the mark. The operator rotated the anchor at roughly 5 to 15 rpm and watched the torque readout continuously. As the anchor went deeper, the crew added extension shafts, so depth stayed under control instead of being guessed. When torque reached the value set in the foundation design, the anchor had found competent material and rotation stopped. The shaft was then cut to height and the bracket bolted down.

No curing meant no waiting. Two crews placed about 80 anchors a day between them, which put the whole plot at 16 working days. Each post was bonded to the earthing system on the same pass using earth rods and ground pin clamps, so no separate trade had to come back later.

Testing and Quality Control

Three checks ran before shipment. We screened incoming steel for grade and section, inspected every weld, and measured coating thickness on samples from each batch. A unit that failed any check never reached a truck.

On site, the crew logged torque for every single anchor, which leaves a record that can be reviewed against the design value months later. Twelve anchors, about one per cent, were pulled to proof load as a spot check, and all twelve held. Because the wetter rows along the drainage line carry the highest corrosion risk, we specified a heavier coating there. The combiner structures used galvanized cross-arm angle steel with the same finish.

Results: What the Numbers Show

All 1,240 anchors were installed and passed proof load with no rework. The foundation package closed in 16 days, against a ten-week allowance, and nothing had to be batched, pumped or cured on site. Tracker mounting started the day after the last anchor was torqued, which is the real gain: the mechanical crews were never blocked.

Through the first completed wet season, no row needed re-torquing and the survey found no post movement. The clay still moves. The anchors sit below the active layer, so it no longer matters.

What This Case Means for Your Project

Ground that swells and cracks does not have to become a construction problem. A helical anchor foundation reduces the job to a plain sequence: rotate, read torque, lock depth, bolt down, test. We manufacture every unit in our own plant, galvanize it for the conditions it will meet, and match the shaft and plate set to your load case and soil report.

If your site sits on clay, silt or ground a rig cannot reach, send us the drawing and the soil data. Our team will size the anchor, the plate and the finish, then quote and ship. You can also review how mixed orders are handled by contacting our team while the foundation design is still open.