Going Underground

Underground space is utilized primarily for utilities, sewers, and building foundations; transportation tunnels and subways, parking facilities, underground pedestrian malls, and floor space round out the uses. The underground development of floor space appears limited both by revenue and cost considerations. The revenue side involves light and air amenities; the existence of "bargain basements" seems to correspond to a generally held notion of lower quality as one descends. On the cost side, Jay S. Berger notes that the cost of subterranean parking increases in geometric progression when more than two levels are required.

Multiple use, an important aspect of underground space utilization, has two senses. The first involves the achievement of more than one purpose, so that joint production is involved; the second involves the separation and segregation of presumably conflicting activities, such as pedestrian and vehicle traffic, by means of devoting above-ground space to one activity and below-ground space to the other.

With respect to multipurpose uses of underground space, it has been suggested that such space could furnish fallout and nuclear attack shelters; manufacturing space free from vibration, temperature, and humidity fluctuations; the storage of surface water in floods; and the disposal of solid wastes (though contamination of underground water would be of concern).

In 100 Russian cities, 35 per cent or more of investment in structures is underground. Sweden has an extensive underground development program for civil defense purposes. About two billion dollars has been spent so far for underground installations, of which half are military, half civilian. Virtually all new buildings are constructed with underground shelters; present mass shelters are used for underground parking, convention rooms, and civic centers. Sweden has one of Europe's great aircraft plants located 200 feet underground; a number of other manufacturing operations and sewage disposal plants are located underground, as is the bulk of the air force. A comparative study of an aboveground and an underground plant (with 500 workers each) revealed:

• absenteeism caused by illness was greater above ground; the accident rate was markedly lower below ground, but headaches and psychosomatic problems were greater below ground.
• the capital cost of putting a plant underground was 10 to 15 per cent greater than that of the conventional plant. However, operating and maintenance costs were so much lower that the underground plant was the better investment. (There were no exteriors to paint or repair and little heat was needed.)

On a less dramatic level there are economies to be had by the coordination of utility installation; in particular, this involves installing all utilities in one trench or tunnel. Thus, in Oakland, California, the cost of putting electric services underground dropped from around $1,000 per lot to about $225 as a consequence of such coordination.

Turning to the separation and segregation of conflicting activities, a number of developments may be noted. Several cities have built underground garages beneath a central-area park. Rockefeller Center pioneered in the use of the first basement level of all its buildings as an underground pedestrian thoroughfare and shopping arcade. Escalators lead to the first floors of all buildings. This was seen as a means of reducing pedestrian traffic on the streets.

The Rockefeller Center underground network links about 17 acres of buildings. A much larger area will be served by an underground system in Montreal, which now connects 50 acres of downtown structures and will eventually serve 100 acres.

Particular levels are devoted to subway transit, passenger trains, garages, pedestrian concourses and shopping, and to surface traffic. The first phase of the development is under the Place Ville-Marie; the shopping level here has fifty stores fronting on air-conditioned promenades through which an estimated 80,000 persons pass daily. Foot traffic at major intersections above ground has fallen by roughly 70 percent. Office buildings tied into the underground network rented faster than those that were not. The total length of the pedestrian concourses is projected at 6 miles by 1977. The Eaton Center project in Montreal is a parallel development and a master plan for Philadelphia exhibits similar features, including a five-block underground shopping mall, a concourse connecting the mall and major department stores, and a transportation center connected by escalators to the mall, the streets, and underground parking facilities.

A number of technical advances may bring about greater utilization of underground space. Thus, underground transmission systems are falling in cost relative to overhead lines and increased underground installation of utility lines can be expected. Advances are occurring in tunneling and some important consequences are possible.

Thomas E. Howard argues that surface excavation is the only acceptable option for building substructures and most highways, but for other cases, tunneling may become more economic. The bitter controversy surrounding urban expressway routing might vanish if there were a feasible subsurface alternative. This alternative may appear in the form of the continuous tunnel borer, or mechanical mole, now under development, which simultaneously breaks away rock and scoops up fragments. By 1964, the borer had been used successfully in some cases, but these were limited to tunneling through soft or medium rock.

Research is also being carried out on the use of laser beams in splitting rock; however, practical application appears to be twenty years away at the earliest.

Costs of urban expressways and underground automobile tunnels were compared over time by George A. Hoffman, who discerned a rise in the cost of the former and a fall in that of the latter. He expected these cost trends to continue, with tunnel costs falling below expressway costs in the not too distant future.