A large span underground facility, adjacent to the underground Palmaz winery in Napa, California, has a plan area of approximately 1000 square m (10,800 square feet), with dimensions of 20 by 50 m (66 by 164 feet). One of the design objectives was to maximize the available open space to facilitate the storage and display of an exotic car collection. The facility was constructed in a lahar formation comprised of fresh, angular andesite clasts in a matrix of highly weathered rhyolite. Cover over the facility ranges from 2 to 14 m (6 to 46 feet), with an average thickness of 8 m (26 feet). The design was predicated on the use of the Sequential Excavation Method (SEM) and involved the development of ground support details and a comprehensive sequence of excavation and support installation. Numerical modeling was used to develop an optimal geometry and construction sequence and to ensure minimal construction impact on the previously constructed adjacent underground fermentation dome located approximately 9 m (30 feet) from the proposed opening. Six horseshoe-shaped tunnels, 4 m (13 feet) wide by 5 m (16 feet) high and approximately 20 m (66 feet) long, were excavated to install the main steel arch support frames and associated foundations. The ground in between these drifts was then excavated in rounds and supported by steel ribs and shotcrete. The final lining consisted of steel members encased in reinforced concrete or shotcrete, including post-tensioned foundations, designed to reduce lateral load transfer into the surrounding ground.
The heart of the winemaking industry in northern California is located in the Napa Valley and the adjacent Sonoma Valley. This region has seen tremendous growth in the last 40 years, and especially in the field of viticulture, which has put a premium on land available for vineyards. The winemaking process also requires significant cellar space for fermentation and then maturing of wine in barrels. Cellar facilities take up valuable land and the operational costs can be significant. These considerations have resulted in increased use of underground space for wineries and experience has shown that the construction cost of a typical wine cave can be comparable to that of an above ground facility. However, the advantages of underground wine caves include naturally occurring low temperatures and high humidity with very small seasonal variations resulting in reduced utility costs and a substantial reduction of wine loss due to evaporation from the barrels. These cost savings can pay for the cost of wine cave construction in 6 to 8 years, and thus wine caves can be considered to pay for themselves over time. In addition, the environmental and permitting process has made the construction of new conventional wine cellars a very tedious and costly undertaking, while very few constraints are placed on underground construction. The above-mentioned factors and the economic benefits of fermenting and storing wine underground have resulted in the construction of more than 50 wine caves in Napa Valley, most of which have been built in the last 30 years.
