The paper describes the possibilities and consequences of district heating in densely populated urban areas. Special, attention is paid to the applications utilizing subsurface space for production, storage and transmission of heat. The theme is enlightened by certain typical realised projects and case studies of potential ones. Comparisons between ground level and subsurface alternatives are performed concerning their technical, economic and environmental effects. INTRODUCTION It is a necessity for the industrialized world to, save energy and to develop methods to substitute for fuel oil. Rapid rise of energy prices and unsteady availability of oil has forced us to concentrate our efforts on reaching these goals. Traditional technologies are found insufficient and inapplicable to the future situation. New solutions and applications are to be invented, and the old ones developed further, for the whole chain of energy supply system from the primary sources to the end use and for harmless returning of the energy flows and wastes back to the environment. One of the most important energy consumption sectors is the domestic heat supply. It constitutes a remarkable potential for energy savings in many countries. Future will bring radical changes also in this sector, and the trend is towards cheaper energy sources, better efficiency and centralized production of energy. District heating - especially at its advanced stage comprising combined heat and power generation - is an efficient way for long-term energy saving on a large scale. District heating systems offer highest benefits when supplying densely built city areas, but there they face alsosome problems, which are common to all city planning, such as land use and environmental problems. The available space for new service plants and distribution networks in cities is always very limited. The street grounds arein most casesfilled with traversing water mains, sewers, possibly gas pipes, electric and phone cables, and other lines. Especially in these cases the subsurface applications in district heating systems are very recommendable. Sometimes there are purely economic reasons favouring subsurface solutions - especially in connection with large and long-distance heat transmission. The heat production plant should always be placed as near the center of the heat load as possible-. In some cases it is necessary or preferable, for reasons relating to land use, environmental protection, safety, or economy, to place the plant underground. District heating has.any characteristics for the protection of environment and landscape, and the best result is often obtained by reasonable use of underground spaces. In this paper we present the possibilities of district heating for the heating of urban areas, and special attention is paid to the underground applications. First, a short survey on the general characteristics of the district heating is presented, and then the underground applications are described by means of typical examples of realized and projected cases. DISTRICT HEATING District heating is a very suitable method for serving densely populated areas. Its major advantages in energy production are: possibility to utilize cheaper fuels and combined heat and power production environmental protection. In most district heated cities, the heat is mainly produced by combined heat and power plants, and only peak heat demands are covered by water boilers.

Recent applications of the Q-system of rockmass classification are given. It is shown that Four potential storage sites with different rockmass conditions may have different optimal cavern dimensions. Support costs may increase disproportionately if dimensions are chosen that are smaller or larger than the theoretical optimum of 18 to 24 metres span. The Q-system is also used for mapping rockmass conditions during tunnel and cavern construction, to aid in the choice of permanent support. Examples include 25 m2 and 167 m2 headrace tunnels, and an underground sewage treatment plant constructed in 1 km of caverns, 16 m in span. Mapping of associated collector and outlet tunnels is also illustrated. The former is being excavated by full-face tunnel boring machines. Finally it is shown how the Q-value can give a preliminary estimate of the in situ deformation modulus, and the range of likely deformations. INTRODUCTION Estimates of support are required at three stages in a project: for the feasibility studies, for the detailed planning, and finally during excavation itself. In view of the potential economic importance of support costs it is preferable that the support estimates are as accurate as possible for all three stages. The accuracy will depend partly on the effectiveness of the geological investigations, and partly on the ability to extrapolate past experiences of support performance to new rockmass environments. Underground excavations are constructed with some confidence primarily because of all their successful predecessors. A practical method of extrapolating past experiences of support performance to new rockmass environments is the Q-system (Barton, Lien and Lunde, 1975). Several years experience by a number of users have shown it to be a useful aid in making design decisions. It has been used during feasibility and detailed planning work, and particularly during construction. Here it provides a logical system for quantitative geological mapping of tunnels and large excavations, and is helpful in indicating suitable permanent support. Several recent examples will be given later in this paper. THE Q-SYSTEM OF ROCKMASS CLASSIFICATION The Q-system is essentially a weighting process in which the positive and negative aspects of a rockmass are assessed quantitatively by evaluating six factors, i.e. number of joint sets, joint roughness, type of clay fillings, water inflow, stress levels etc. A store of experience is searched to find the most appropriate support measures, taking into account the rockmass quality (Q), the excavation dimensions, and the safety requirements (purpose of excavation, ESR). The rockmass descriptions and ratings for each of the six parameters are given in Table 1. Additional notes on the use of the classification system are given elsewhere. It is important to observe that the values of J r and J a relate to the joint set or discontinuity most likely to allow failure to initiate. The important influence of orientation relative to the tunnel axis is implicit. ROCKMASS REQUIREMENTS FOR PERMANENTLY UNSUPPORTED EXCAVATIONS A very interesting area of application for the Q-system is the recognition of rockmass characteristics required for safe operation of permanently unsupported openings.

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).

In some designs, the rock at the face of an unlined storage cavity may be stressed beyond its maximum strength, and the article presents how an analytical model can be used to describe the conditions of failure in the rock and their effects on stability. It is henceforth possible to use underground storage techniques at moderate depths in soft rocks or at great depths in hard, brittle rocks. INTRODUCTION Underground storage first developed by making use of very favourable geological conditions like those available in salt domes or large expanses of crystalline rock. The design of facilities to store oil, and liquified or gaseous gas is a relatively simple matter in this kind of context. Over the last decade or so, however, because of the move to capitalize on the unusually high standard of environmental protection and safety associated with underground storage, attention has been focused on extending it to a much wider range of stored products in much less favourable geological conditions and there are even cases of such projects now in the design stage. The new products to be stored produce very different stress conditions in the rock. Liquified natural gas and ethylene involve low-temperature stresses. Residual fuel oil, compressed air and nuclear wastes apply thermal stresses. The alternating and sudden pressure changes associated with the operation of compressed air storage facilities are a severe test of stability. The advantages of underground storage have induced engineers to examine its application in much less favourable geologies, and Geostock is currently engaged in conceptual and project design studies for facilities in weak to very weak soft rock, even down to almost unconsolidated clays. Such formations are very commonly found in the large alluvial plains where the world's major cities are built, so that safety is an obvious criterion. In such rock, it is quite possible that the cavities will not be inherently stable if rock strength is ina dequate to withstand the applied loads. Conventional design rules derived from theoretical rock me chanics models do not enable us to estimate the permissible limits in such design, or to optimize support. In order to provide a means of examining the feasibility of such projects, Geostock has been running a programme of research jointly with the Laboratoire de Mecanique des Solides of the Ecole Polytechnique in Paris since 1974, to investigate materials behaviour when stresses are equal to or in excess of their maximum strength as obtained from crushing tests. A set of experimental data has also been analysed to calibrate the results of this theoretical research, and check the accuracy of the findings. We shall first briefly review the shortcomings of conventional models before going on to describe the main features of the new model and compare findings with a variety of case histories. The article concludes with comments on the new opportunities offered by this model for designing underground storage facilities in poor engineering rock where stress conditions are complex, in strong rock where stresses are expected to exceed rock strength, or where support optimization is a prime consideration.