In Colorado’s resorts, where land values are often as steep as some of the building sites, terra firma can literally be a moving target and provide builders and developers with some special challenges.
Soils in the Rockies can range from solid rock to glacial debris, and can be anything but firm. Building a building or home on them can be a challenge as veteran resort builder Bob Warner of Warner Developments in Avon discovered when two of the seven luxury slope-side homes at the McCoy Springs neighborhood at Arrowhead moved, despite having deep foundations.
The recommended approach of using deep foundations had failed.
That caused the buildings to settle, cracking drywall and making doors and window difficult to open and close. It’s the first time in the 35 years of building in Eagle County that Warner had experienced a geotechnical challenge of this magnitude.
But Warner didn’t hesitate to make good once he discovered the problem and called Denver-based geotechnical-repair firm Hayward Baker for a solution.
Using state-of-the-art micropile technology, the company, which handles all manner of geotechnical and other issues, bored a series of holes for a new foundation using specialized drilling rigs. The largest bores were five-and-one-half in. in diameter and smaller bores, made inside the homes, were three-and-one-half in. in diameter. One of the homes required more than 50 boreholes.
Those micropiles were taken as deep as 97 ft, and 25 ft of that was into bedrock to create a secure “rock socket” beneath the home. Boring each hole took an average of three hours. The holes were sleeved with steel pipe, and coupled single strand #10 rebar was inserted into the smaller bores and #14 rebar was inserted into the larger boreholes. That beefy #14 rebar is one-and-three-quarters in. in diameter and commonly used in the slabs of metropolitan parking structures and bridges.
The boreholes were pumped full of grout, using approximately a ton in each, solidifying each pile to bedrock. Once the piles were in place, the building was gently releveled with multiple hydraulic rams, and the existing foundation was tied to the massive concrete and steel micropile cap. The entire remedy is out of sight beneath grade.
“It was a challenge, “ said project engineer Spencer Mills of Hayward Baker. “We had limited access on a steep slope next to luxury homes that we had to be aware of at all times.”
Carrying a price tag of more than $1 million per home, the result was a geotechnical solution carrying some pretty impressive engineering statistics. The work was completed over a two-year span, working around the busy resort seasons and finished just before the slopes at Arrowhead opened.
Each home, at approximately 7,700 sq ft, weighs in excess 1 million lb furnished.
The new micropile foundations, with approximately 50 tons of grout and steel apiece, have a load capacity five times the weight of the homes. For a better visual of what that means, it’s a structure capable of supporting 65 semi-trucks, each 75 ft long and weighing 80,000 lb.
Placed end-to-end, those trucks would stretch 4,800 ft or the length of 15 average city blocks.
Even the neighbors living next to the homes getting the foundation makeover were impressed with both the structural integrity of the solution and the personal integrity demonstrated by Warner in getting the job done.
Once the geotechnical fix was completed, Mills took a little time to look around at something besides the drill rigs and the hydraulic jacks and decided he liked what he saw.
“I would love a chance to live in a house like those,” he said. “They’re luxury homes, and it’s a perfect location.”
And the homes aren’t going anywhere. Warner is confident enough of that, that he is offering buyers a three-year structural warranty: “It’s the right thing to do,” he said.
In addition to that, Warner and Alpine Bank will team up to offer financing.
“With the economy and the history of the property, it’s the prudent thing to do,” he said. “They’re great homes and they’re they’ll be there for generations.”
Warner said he’s got one more home to build at McCoy Springs in the coming years, and he’s already decided he’ll use a micropile foundation to make sure it stays put.