Cave Drill at Neibaum/Coppola

Hard Rock or Soft Rock?

The geology is the largest variable in the building cost of wine caves according to William A. Fuchs, Ph.D. and registered California geologist. "Cave builders like some rocks and don’t like others."

That is why a geotechnical investigation is essential as a first step in the planning process. "California has some of the best tunneling ground and some of the worst. Much of the ground is weathered, decomposed, faulted and jointed rock with variable amounts of soil overburden. So different sites can make a big difference in the feasibility and cost," says Scott Lewis, Principal Engineering Geologist and Senior Tunneling Consultant with Condor Earth Technologies.

Wine caves inherently have a fairly wide span and low cover which creates some design and construction challenges in weak rock. "The size of a typical wine barrel storage cave is 13 to 18 ft (4 to 5.5 m) wide and 10 to 13 ft (3 to 4 m) high. Constructed caves, however, range up to 85 ft (30 m) in width and 50 ft (15 m) in height; difficult to achieve in poor quality rock," says Lewis.

As in mining, wine cave construction involves a tunneling process so engineering is done at the same time as excavation rather than entirely before construction. "After some actual digging, the knowledge base increases dramatically. If the client is flexible, new information can allow the contractor to make design changes that will result in cost savings (value engineering)," according to Dr. Fuchs.

And because wine caves bore into the earth, it is impossible to predict what construction and design challenges will be encountered in digging. As Daniel D’Agostini points out in his coffee table book on wine caves, Into the Earth, "Despite the intense study of the geology, an unexpected seam of mud or current of water or gargantuan boulder may be encountered, shifting the whole approach and design. Digging a wine cave, therefore, is part art, part science."

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