Building On A Mile Of Solid Rock

The obstacles to building a visitor center on the most rugged mountain in Eastern America where winds regularly top 100 mph are intimidating. And the enormity of this challenge has perplexed and entertained Zeb Wells of Sutton, Kennerly & Associates Engineering in Asheville, Bill Dixon of Appalachian Architecture in Boone and Skip Greene of Greene Construction in Boone for many, many years.

Even as new life develops in the womb, Grandfather’s Top Shop has been gestating in boardrooms, design studios and the cabs of pickup trucks since the dawn of the new millennium. Now, as we perch ready to launch into the corporeal task of erecting the new structure, it is meaningful to review the cerebral twists and turns faced along the way.

The first question to be answered was where to locate the new building. Although Grandfather looks like one big solid rock, structural engineers know that the Mountain is actually a pile of cracked and fissured layers of rock. The challenge was to identify sites where the bedrock is solid and stable enough to support the weight of a three-story building.

The next big issue was water. Grandfather’s existing Top Shop has depended on a well located at the Black Rock parking area that pumps 25 gallons per minute. Pipes to that well must be drained in the winter, however, because the lines run so close to the surface of the ground that they freeze in winter.

A second well was drilled last year in hopes of increasing the water supply to the summit. After driving a 6-inch bore 1,200 feet (reaching to an elevation lower than the Entrance Gate), the new well delivers 3 gallons per minute. That output will hopefully be enough to meet demand at the new shop in winter, when traffic is slowest.

Handling wastewater was another concern. Soils on the peaks of Grandfather Mountain are only two or three inches deep. Locating a drain field on that terrain was not an option (and any locations near the ridge which might have met the requirements were off limits because they are permanently protected in a Nature Conservancy trust), so a solution was proposed that entails conveying wastewater from the Top Shop to a drain field lower on the Mountain.

Engineers were asked to investigate the feasibility of burying the power lines to the Top Shop. The response was that power lines are traditionally buried 3 feet beneath the surface, and as previously mentioned, Grandfather’s terrain consists of three inches of topsoil on a mile of cracked and fissured (but essentially solid) rock.

Because the new building has an elevator to access the Swinging Bridge, the new shop needs more electricity. The existing visitor center operates on single-phase power (one electric line strung from pole to pole to the top of the Mountain). The new shop will operate on three-phase power (three electric lines strung from pole to pole to the top of the Mountain). This necessitated setting new poles and clearing a much wider path up the Mountain. The greatest visual impact is where the power line crosses the road above Cliffside Overlook and where the power line crosses the Bridge Trail.

The next barrier to building atop Grandfather Mountain involved materials. I know you think I am going to talk about selecting materials that can withstand Grandfather’s wind and weather, but before materials can face the wind and the weather they first have to be delivered to the site!

How do you truck materials up a steep, narrow road with three hairpin turns at the finish? Keep all materials under 40 feet in length and plan all big deliveries for before the park opens in the morning or after the park closes at night.

Decisions about the actual building design were all “wind driven” (if you'll pardon the pun). Architects gave the building a curved roof to provide the wind somewhere to flow, and concrete was selected as the one roofing material that could endure Grandfather’s conditions.

Most of the exterior surface will be rock, a decision not made just for looks. Window selection was another challenge. Weather concerns affected not only the size of windows, but also the choice of fiberglass as the glazing material.

And after addressing all the barriers to designing a building for the top of Grandfather Mountain, architects then faced the challenge of moving guests from the third-floor elevator to the Mile High Swinging Bridge - with zero impact on the rare plant communities that make their home on Grandfather’s cliffs.

Whew!

And it all starts next week! We’ll keep you posted!

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