Underground space is increasingly regarded as an economic resource and a developmental opportunity, rather than a technology of last resort to be used when aboveground solutions fail. Geotechnical investigations are needed in early stages of industrial and urban planning to define opportunities and avoid difficulties and conflicts in the use of underground space. The need to manage conventional energy resources and capture wasted or renewable energy resources is creating new uses for underground space. The energy-related functions of underground space are fuel storage and management, energy capture and storage, energy conservation, and nuclear waste isolation. Fuel storage is a developed industry. Energy storage is rapidly developing. Geotechnical classifications of mined space and porous rock storage systems and functional classifications of fuel and energy storage systems are presented. The Rockstore conferences of 1977 and 1980 establish an historical precedent which should not go unnoticed. In these conferences, for perhaps the first time, the use of underground space is systematically treated as an opportunity driven by economic advantage, rather than a necessity forced by other considerations. Historically underground space has often been constructed in difficult t and extraordinary geologic conditions. Ore deposits commonly occur in zones of sheared and shattered, badly altered rock. Coal mines must cope with weak rocks and gas. Most major cities have been situated on rivers, estuaries and bays, giving access to water, but often placing them on water-saturated deposits of mud, silt and sand. Truly, geotechnology has been developed and tested in the crucible of adversity. It has won renown for heroically surmounting obstacles when ordinary, aboveground solutions fail, but in doing so, it has acquired the image of a technology of last resort -- a dragon slayer to be called on for heroic measures only when conventional champions have left the field. It is fitting now that this young Beowulf* of technology should come of age in Scandinavia. Here a number of cities and major industrial sites are located on strong, massive rock. This, coupled with a long tradition of hard-rock mining, certain strategic needs and a high value placed on preservation of environmental amenities, has led to the happy discovery that in appropriate settings underground construction can be quite simply the most economical solution to large space needs, not an adventure to be undertaken as a last resort. Our geotechnical Beowulf need no longer be dedicated to slaying dragons. He can, so to speak, beat his sword into a plowshare and cultivate a garden. However, cultivating gardens requires a certain sensitivity to natural conditions that is not demanded by dragon slaying. If we are to avoid Grendel's fearsome caverns, we need to know the ground before we start to dig, and the ground must be adapted to the use we plan to make of it. In other words, underground space is an economic resource if careful geotechnical investigation has shown that the geology is right. As with other earth resources, it must be explored and mapped. It is a resource that is not available everywhere in like degree. Moreover, underground space is not a single resource or commodity. There are a number of different uses to be made of the storage capacity of the ground, each having somewhat different, or even radically different, geologic and geotechnical requirements. If underground space is to be developed as a resource, its availability must be carefully investigated and considered just as other resources are considered.

Economic and engineering evaluations of energy-storage potential in certain USA aquifers are being conducted. Particularly detailed evaluations have been made for compressed air energy storage (CAES), using off-peak power from nearby nuclear power stations. In ''current studies, we are examining thermal energy storage and utilization prospects, using solar power or, alternatively, off-peak, low-cost nuclear power as the heat source. Economic and energy-saving aspects of selected combinations of sources, storage media, and uses are ranked with respect to various selection criteria. INTRODUCTION The current U.S. interest in underground storage of energy grows out of a number of environm7ntal, economic, and political factors. Environmental considerations create particular difficulties for nuclear power and coal. Economic and political problems are clouding the prospects for continued supply of energy needs from outside sources of petroleum. According to the National Academy of Sciences, nuclear-fusion, solar, and geothermal energy remain at present in a primitive state of development. This and other conclusions of a four-year study are set forth in a report "Energy in Transition, 1985–2010," recently published by the Academy''s Committee on Nuclear and Alternative Energy Systems. The study also concluded that conservation and energy efficiency are essential elements of the national energy policy. Efficiency can be realized through generation of energy at a time when surplus capacity is available and storing it for use when demand exceeds capacity. One such procedure involves storage of energy in aquifers, which constitute convenient natural near-surface reservoirs for fluid storage and recovery. AQUIFER STORAGE Although aquifer storage has been primarily employed for natural gas, storage of compressed air for use in the generation of electrical energy is in an active stage of development. Also, thermal storage, by means of hot or cold water injection, is under serious consideration, with initiation of experimental studies funded by the U.S. government anticipated at several locations in 1980. Texas A&M University and Auburn University are operating small thermal storage projects at present. Porosity and permeability are critical rock characteristics in storage considerations. Porosity is a measure of the volume available for fluid storage, expressed in percent of the total volume of solids plus voids for a representative portion of the storage medium. Permeability is a measure of the ability of fluids to flow through the aquifer. It is usually expressed in terms of darcys or millidarcys (mD), with the higher numbers indicating greater permeability -- that is, greater ease with which a given rock will accept, transmit, and deliver fluids. For example, natural gas is stored in aquifers having permeabilities from 7 mD up to about 7,000 mD. For compressed air storage, reservoirs with very high permeability are desirable -- several thousand millidarcys, if possible. ILLINOIS AQUIFERS Two aquifers in southern Illinois have been acquired for energy-storage purposes by the URS Corporation. These are anticlinal structures in Devonian-age carbonate rocks, at depths of about 600 ft, as shown in Fig. 1. Characteristics, as determined from well logs and other geologic data, are set forth in Table 1.

In this first phase of the study, the heat losses of an earth-sheltered dwelling through transmission have been studied by means of a mathematical model. These results have been supplemented by approximate values for passive solar heating and other energy sources. The calculated energy demand of the studied house is 90 kWh/m2/year. A similar house, though not earth-sheltered, would demand some 110 kWh/m2/year. A number of other test projects on energy conservation also indicate energy demand in the region of 110 kWh/m2/year. The average Swedish detached house consumes 28 000 kWh/year, corresponding to 250 kWh/m2/year. It seems that improvements to the house studied are possible and that these would result in a further significant reduction in energy demand. INTRODUCTION The idea of earth-sheltered housing has met with considerable interest in the U.S. The Underground Space Center at the University of Minnesota has given itself the task ot studying the concept and of disseminating information about it. The Swedish Council for Building Research, in cooperation with the Underground Space Center, has awarded a research grant to VBB AB and Hagconsult AB, for a study project on the characteristics of earth-sheltered housing in Scandinavian climate and geology. EARTH-SHELTERING Earth-sheltering can vary between conventional houses with grass on their roofs to fully recessed houses which receive their daylight via an atrium. The Swedish study concerns a house on a sloping site, the roof and three walls of which are covered with at least So cm of earth. The exposed fourth wall faces south in order to receive maximum passive solar heating. This basic model is applied rather strictly - the effects of alterations may be studied in projects to come. The house, see Fig. 1, is a concrete structure with sufficient styro insulation to meet the requirements demanded by the Building Code. Where the earth shelter is greater than 3 metres, no insulation is necessary. CLIMATIC DATA In the Stockholm area, the monthly mean temperature varies between -3.2 and +17.5°C. Most of the earth around the house is only subject to minor variations in temperature, from +70C which is the average temperature over the year. The latitude of Stockholm is S90N, where the solar angle varies between 7 and 55 0. ENERGY AND POWER DEMAND Heat losses due to transmission through the earth have been calculated by means of a finite element model, as shown in Fig. 2. The two-dimensional heat flow is calculated for a section of the house. The effects at the two ends of the house are not included, but they will not, however, significantly affect the results obtained. The model must be extended 20 m outside the structure of the house itself. The heat losses depend on the geological conditions. For calculation purposes, they have been assumed to be as is shown in Fig. 3. At an indoor temperature of 200C and an outdoor temperature of 7°C (mean yearly temperature) transmission losses will be 70 W/m house.

The disparity between energy production and demand has led to increased research into the use of aquifers for the long-term, large-scale storage of thermal energy. Currently, there are several field experiments and feasibility studies under way in which the technical, economic, and environmental aspects of aquifer storage are being researched. The present paper surveys the recent theoretical efforts in aquifer storage research and the impact their results may have on these field projects. Major work is highlighted according to three categories: semianalytic studies, numerical modeling studies, and site-specific studies. INTRODUCTION The need for energy storage arises from the disparity between energy production and demand. The development of viable storage methods will play a significant role in our ability to implement alternative energy technologies and use what is now waste heat. The ability to provide heat at night and during inclement weather is a key factor in the development of solar energy. Conversely, winter cold, in the form of melted snow or water cooled to winter air temperatures, can be used as a coolant or for air-conditioning. Practical storage systems would also allow us to capture the heat that occurs as a by-product of industrial processes and power production. Industrial plants and electric utilities generate tremendous amounts of waste heat, which is usually dissipated through an expensive network of cooling towers or ponds to avoid thermal pollution. Because periods of heat demand do not generally coincide with electricity generation or industrial production, a viable storage method is essential if this heat is to be used. Such a method would not only provide for the use of what is now waste heat, but would significantly decrease the necessary investment in cooling and backup heating systems. In recent years, aquifers have been studied as a very promising means for the long-term, large-scale storage of thermal energy. Aquifers are porous underground formations which contain and conduct water. Confined aquifers are bounded above and below by impermeable clay layers and are saturated by water under pressure. They are physically well suited to thermal energy storage because of their low heat conductivities, large volumetric capacities (on the order of 109m 3 ), and their ability to contain water under high pressures. Aquifers are also attractive storage sites because of their widespread availability. Aquifer storage is not a new concept. Over the last few decades aquifers have been used to store fresh water, oil products, natural gas, and liquid wastes. However, it has only been in recent years that their use for thermal energy has been suggested. Initial studies were conducted by Rabbimov, Umarov, and Zakhidov (1971), Meyer and Todd (1972), Kazmann (1971), and Hausz (1974). A good source of information about more recent work is the proceedings of the Thermal Energy Storage in Aquifers Workshop (Berkeley, 1978). Current research and development activities are reviewed in the quarterly ATES Newsletter prepared by Lawrence Berkeley Laboratory. Recent work includes field experiments at Mobile, Alabama (USA), Gaud (Fance), Bonnaud (France), College Station (USA).

The rationale for using subsurface space applies to developing nations but very little has been done. Using mined-out space for food storage may help solve the serious problems of post-harvest food losses and hunger. Much of the mined-out space in the developing nations is unsuited to secondary use but investigations are needed to determine what and where the potential is. INTRODUCTION In exploring the concept of using underground space for storage in the developing countries of the world, certain observations became apparent. Underground development is gaining great momentum in business, academic, and governmental circles. Even the public, in parts of the United States, is developing earth-sheltered housing at an astonishing rate. A new regard for basic resources has caused attention to be focused on earth-sheltered housing. They cost less to build, to heat, to cool, and to maintain. Today, we must move from a philosophy of waste and exploitation of non-renewable resources towards conservation. It was inevitable that sooner or later we would begin to truly and appropriately value the basic resources on this planet, including subsurface space. This symposium has as its focus three primary advantages of subsurface space. I would like to look at these for a moment and consider how they might apply to the developing countries. ENERGY SAVINGS We tend to think of the developing countries as having low-energy economies, and compared to the industrialized nations, this is true. But the high cost of energy of the past few years has hit the developing nations very hard. It has caught them when popular expectations were beginning to rise with standards of living. Now, high-cost energy is draining their treasuries of the precious foreign reserves and capital required to maintain their economic growth. Agricultural development, industrial and technical advances, and improved social services are also being impaired. During this century, the process of modernization has been largely subsidized by cheap energy. Except for the oil-rich, this is no longer possible; and yet for the present, we have no replacement. So while it is true that long and quick-tempered lines at the gas pump will probably not appear in the villages of Zambia, Thailand, and Honduras, it is also true that energy conservation is as important in the developing countries as in the industrialized nations. PROTECTION OF THE URBAN ENVIRONMENT Since World War II, probably the greatest human migration in history has been occurring in the developing countries--the migration from the countryside to the cities. It goes on still, creating gigantic urban centers where once only large towns stood. New Delhi has increased its population over 400% in this period. No wonder they are thinking of building an underground transit system. Calcutta's, by the way, is already under construction. Trying to deal with such logistical problems on the surface was really quite out of the question. So I don't think there is any doubt that the great cities of the developing world will be looking underground to solve some of their problems. In fact, architect Jannson of Sweden (1974) predicts that urban subsurface construction will double every ten years in both the developed and developing countries.

Progress in mining technology and excavation methods has made subsurface space more readily accessible. This development has opened exciting opportunities for engineering science and technology. Among these are the use of the underground for the production, storage, conversion, transportation and final use of energy- including the ultimate disposal of radioactive waste products from nuclear power plants. Improved methods for the production of primary energy by conventional means such as drilling for petroleum and mining for coal are now supplemented with in situ processes. These mean enhanced recovery and will make currently non accessible sources of fossil fuel available for future exploitation. Oil importing countrie's desire to hedge against sudden supply shortages make huge underground cavities necessary for the storage of petroleum. With respect to natural gas the necessity to cope with large load variations calls for short term storage facilities. Here liquid natural gas in underground caverns may offer attractive solutions both from the economical point of view and when safety aspects are considered. Long term storage of solar energy as well as the tapping of geothermal heat flows implies large underground storage cavities as well as subsurface heat extraction methods. Medium to small thermal nuclear plants may be safely located nearby or even within urban centers to be used for district heating. It has also been suggested that nuclear reactors for power generation should be placed underground both for the sake of public safety and for economical reasons. Using water as an energy vector for fairly long distance transportation of heat in unlined rock tunnels is already a proven technology. This offers economically alternative means for the utilization of waste heat from nuclear power plants. The method applies to district heating and to consumers of low temperature heat such as green houses. For energy intensive industrial applications surface location may be excluded in built up areas. Here the subsurface space may provide unconventional siteing possibilities. The final disposal of radioactive waste presents a serious problem for which subsurface space at present seems to offer the only viable solution. In 1975 the World Energy Conference established a Conservation Commission with representatives from developed as well as developing nations, from centrally planned economies as well as from market economies, and with delegates from international organizations such as United Nations, The World Bank and the Economic Commission for Europe. According to its rather broad and general terms of reference the Conservation Commission should study the long range energy prospects for the world at large as well as Io r various different regions in the world. It was decided that the time horizon should stretch to the year 2020 and that the investigation should cover production potentials of all sorts of primary energy including new, unconventional alternatives, such as solar energy, fusion and geothermal. The Commission should explore the possibilities to conserve energy and improve the efficiency in its usage. The Conservation Commission was also asked to forecast future energy demands in various parts of the world and how these will develop with time.

This paper discusses the current activity ann, in particular, the current research efforts in the area of earth sheltered building design, construction, and acceptance in the U.S. INTRODUCTION Interest in the use of earth sheltered buildings has expanded greatly in the past 6 years, and particularly in the last 2 years. Prior to 1973, there were only a few isolated earth sheltered houses and scattered commercial and institutional examples of underground buildings in the United States. These were mostly built for design aesthetics or environmental reasons. Since then the number of earth sheltered buildings and houses being built has increased very rapidly. Since earth sheltering is not yet a term that is universally understood, it would perhaps be well to further define the concept before embarking on a discussion of what research is currently underway in the field. In broad terms, earth sheltering uses the earth as a barrier and a moderator. The earth Moderates temperature extremes in the air, and moderates surface vibrations and airborne noise. It acts as a barrier to storm and wind effects, ultraviolet degradation, and an undesirable visual environment. It has a large thermal mass that can work well with an intermittent energy supply such as solar energy. The earth is also a natural element which supports vegetation and, hence, the other life processes on which we ultimately depend. Using the earth to shelter a house or building, then, is a means of providing a natural barrier to many undesirable climatic and man-made features of a particular area. The impact of the building on the surrounding environment will also be lessened, allowing more of the land's surface to remain in a natural state. Furthermore, and of particular importance at the present time, earth sheltering serves as a massive means of decreasing the dependence of the building on artificial methods of climate control derived from fossil fuel energy. Naturally, there are also some disadvantages to earth sheltered structures. These relate primarily to the heavier and stronger structure required, tile need for high quality waterproofing and insulation to combat exposure to ground moisture, and the need for a higher level of design and supervision in small scale construction. Although earth sheltered designs are not limited to any fixed definitions, it will perhaps be helpful to explain two of the basic layouts that are typical of earth sheltered construction. A typical design that is very appropriate for colder climates is the elevational design in which windows and openings are grouped on one side of the structure, with the remaining three sides and roof earth-covered. When the windows do face south, a maximum amount of passive solar heating can be achieved to combine with the low energy requirements of the structure. A courtyard or atrium design is quite common and is a very appropriate design for a flat site or a warm climate. The courtyard does not have to be totally enclosed. Using a U-shaped courtyard allows an easier transition and visual connection to the surrounding ground.

Storage of heated water in rock caverns is judged to be an interesting alternative for solving the storage problems connected to large-scale utilization of solar energy and surplus industrial heat. For verifying and demonstrating the technique, a test plant with a storage volume of 15 000 m 3 will be constructed, in which a comprehensive research programme will be carried through. The effects of various time/temperature cycles will be studied. Main items on the research programme are: heat losses, rock stability, heat exchange and material questions, water layer studies, and influence on the environment. INTRODUCTION The use of solar and wind energy as well as surplus or waste heat from industrial processes, power production, sewage water etc is judged to be an important way of reducing the very strong dependency on oil for heating purposes in Sweden. The increasing price on oil and the risk of disturbances of the supply together with the political decision on the limitation of use of nuclear power have lead to very strong efforts in Sweden to develop new techniques for the use of new energy sources and to reduce the need for energy. As the main part of solar and waste heat is normally available only during summer, this technique nessecitates seasonal storage. Extremely inexpensive methods will have to be used to make seasonal storage of low temperature energy economical. For large scale storage there are today few other choices available than storage in water or rock and soil. Since the "energy density" of such ·magazines is low, huge volumes will be needed to cover even a small part of the energy requirement for heating in Sweden. In particular storage of heated water in rock caverns or storage of heat direct in penetrated rock masses are judged to be most interesting due to common occurrence of suitable rock formations in Sweden and the possibilities this entails for optional localization of the storage close to the producer or user of the heat. The storage of heated oil in large rock caverns used in Sweden for many years has shown us that the use of rock caverns offers storage at low costs and that the energy consumption for heating the oil is small compared to the above ground alternatives. It was therefore natural to choose the same concept for the first heat storage facility in Sweden. The conditions for storing heated water in rock caverns have been studied in several R&D-projects in the 1970's. These investigations indicate that a large-scale storage in rock caverns can be advantageous from both technical, economical and environmental points of view compared to storage above ground. So far the technique has not been tested on a large scale. Research and demonstration plant For verifying the results of earlier investigations and for demonstrating the technique under realistic circumstances, full scale tests are necessary. For this purpose a test cavern, equipped with a comprehensive instrumentation for research, is now being designed.

The paper discusses the energy-saving potential of earth-sheltered buildings and the U.S. Department of Energy's research, development and demonstration activities and plans regarding their commercialization. INTRODUCTION The subject of my presentation--earth-sheltered buildings--involves a happy intersection of a problem and a potential. The problem is well recognized--the scarcity of energy and its rising price. The problem requires that we undertake effective energy conservation programs. In the United States, fully 37 percent of the nation's energy is used in the residential and commercial building sector. This underscores the importance of U.S. building energy conservation programs. The potential is not so broadly recognized. It is the potential of earth-sheltered designs to reduce by up to 30 to 60 percent or more the energy required for the heating and cooling of buildings. The U.S. Department of Energy regards earth-sheltered buildings as the promising alternative it is considering in its innovative structures program. The Department has monitored earth-sheltered building trends, supported research, identified barriers to commercialization, disseminated information, and is applying earth-sheltered designs to one of its own new buildings. HISTORY The term, earth-sheltered buildings, has not been captured by a formal definition. A good working definition applies the term to buildings with earth protection for 50 percent or more of the area of their roofs and exterior walls. Few of the buildings are entirely underground. but all use the earth to improve their energy performance. The current interest in earth-sheltered buildings is simply the latest chapter in man's continuing struggle to adapt to his environment. The first chapter was the caves inhabited at the dawn of human history. A more elegant version are the homes found in Ajanta, India, that date back to the 5th and 6th Centuries, A.D. A few centuries later, refugees from a crumbling Roman Empire, carved houses into soft, cone-shaped rocks in Cappadocia, Turkey. The Tunisian atrium houses through the century have provided protection from that area's extreme heat. The sod houses of the pioneers of the American prairie were another practical application of earth-sheltered design to cope with severe weather conditions where other building materials were not easily available. A rebirth of interest in earth-sheltered buildings has occurred in the United States during the past two decades. It has been nurtured by various themes. In the early phase, fear of atomic war led to habitable fallout shelters. In the later 1960's and 1970's, the environmental movement led architects to create earth-sheltered designs that were in harmony with the natural environment. The energy-saving benefits of earth-sheltered designs have fanned the rapidly spreading interest in the last half of the 1970's. As director of the Minnesota Energy Agency from 1975 to 1979 when I joined the U.S. Department of Energy, I participated in Minnesota's leadership in the support of earth-sheltered buildings. In the past few years, a state-sponsored guidebook, "Energy Sheltered Housing Design," (Underground Space Center, 1978) has become a best seller, selling more than 100,000 copies. A map of earthsheltered buildings is speckled with activity in all parts of the country with concentrations in Minnesota, Wisconsin and Oklahoma (Vadnais, 1980).