The problem of land use pressures and related economic effects of high land prices are of great interest in the study of the potential uses of underground space. When surface space is fully utilized, underground space becomes one of the few development zones available. It offers the possibility of the adding needed facilities without further degrading the surface environment. Without high land prices, however, the generally higher cost of constructing facilities underground is a significant deterrent to their environmental, or social grounds-luxuries which many developing nation cannot afford at present and which developed nations are reluctant to undertake except in areas of special significance.
Planning of Underground Space
Effective planning for underground utilization should be an essential precursor to the development of major underground facilities. This planning must consider long-term needs while providing a frame work for reforming urban areas into desirable and effective environments in which to live and work. If underground development is to provide the most valuable long-term benefit possible , then effective zones beneath public rights-of-way in older cities around the world. The tangled wed of utilizes commonly found is due to a lack of coordination and the historical evolution in utility provision and transit system development.
The underground has several characteristics that make good planning especially problematical:
Once underground excavations are made, the ground is permanently altered. Underground structures are not as easily dismantled as surface buildings.
An underground excavation may effectively a large zone of the stability of the excavation.
The underground geologic structure greatly affects the type, size, and costs of facilities that can be constructed, but the knowledge of a region`s can only be inferred from a limited number of site investigation borings and previous records.
Large underground projects may require massive investments with relatively high risks of construction problem, delay, and cost overruns.
Traditional planning techniques have focused on two-dimensional representations of regions and urban areas . This is generally adequate for surface and aboveground construction but it is not adequate for the complex three-dimensional geology and built structures often found underground . Representation of this three-dimensional information in a form that can readily be interpreted for planning and evaluation is very difficult.
In Tokyo, for example, the first subway line (Ginza Line) was installed as a shallow line (10 meters deep) immediately beneath the existing layer of surface utilities. As more subway lines have been added, uncluttered zones can only be found at the deeper underground levels. The new Keiyo JR line in Tokyo is 40 meter deep. A new underground super highway from Marunouchi to Shinjuku has been proposed at a 50-meter depth. For comparison, the deepest installations in London are at approximately a 70-meter depth although the main complex of works and sewers is at less than 25 neters. Compounding these issues of increasing demand is the fact newer transportation services (such as the Japanese Shinkansen bullet trains or the French TGV) ofen require larger cross-section tunnels, straighter alignments, and flatter grades. If space is not reserved for this type of use, very inefficient layouts of the beneath urban areas can occur.
Environmental Benefits
Another major trigger for under ground space usage is the growing international concern over the environment, which has led to attempts to rethink the future of urban and industrial development. The major concerns in balancing economic development versus environmental degradation and world natural resource limitations revolve around several key issues. These are:
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