The floor has a 48-in. manhole-like cave access pipe, which will be level with the completed floor.

The fill sand was funneled into the sinkhole via a conveyor belt, reversing the process for removing the dirt earlier.

For safety reasons, crane operators stayed at the top and used remote controls to operate a pair of Bobcats that were lowered into the hole with a crane, says Mike Murphy, chief executive officer of Scott, Murphy & Daniel.

The Skydome also has been home, at times, to a pair of 35-ton cranes, a long-reach excavator, a telehandler and the Bobcats, one a front-loader and one with rollers to compact the sand.

Since there's limited access to the site—a 14-ft-wide, 10.5-ft-high hole cut in the exterior wall—some machines' tires were partially deflated so they could make it in and out, Murphy says.

After installing the micro piles crews will lay two layers of rebar before placing the slab beams and 8-in. floor this spring. The new floor will accommodate 38 Corvettes when it is finished in June.

The museum, which initially considered leaving the hole open so visitors could view it, will have a camera-based exhibit that allows them to see the caves.

Creative Arts Unlimited Inc. will construct a kiosk with the camera controller in a hallway leading into the Skydome, says Katie Frassinelli, museum spokeswoman. The sinkhole and eight recovered Corvettes on display drew a record 251,258 visitors last year, but officials predict 165,000 this year, she says. That's up from 150,461 in 2013.

Three Corvettes—the2009 ZR1 that was first retrieved from the hole, the 1992 millionth-production car and the 1992 black coupe that had a slab of concrete on its hood—will be repaired, and all eight will be on exhibit.

The museum continues to take advantage of sinkhole-related interest. The gift shop is selling jars of dirt and rock from the hole, and Corvette fans have bought more than 1,600 at $10 a jar.