Cities all over the world are confronted with ever growing problems in keeping alive and functioning. This means that at an ever increasing speed the underground has got to be used where there are no good solutions anymore above ground for many vital elements. Subsurface construction used to be too expensive in many cases but now gives a much wider scope because of new developments in building techniques and because of a growing awareness of what should be put underground to preserve precious space above ground for people to use to its best advantage. Problems to be solved both in hardrock and in soft ground are often very big since the city has got to remain functioning and both construction as well as maintenance should be done as un-obstrusively as possible. Examples from Oslo Norway, and Amsterdam Netherlands will be given.
The City of Oslo, surrounded by hills, is situated at the end of the Oslo fjord(Fig. 1). The built up areas of the central part of Oslo consist mainly of 4–5 storeyed buildings which were erected in the later half of the 19th century. The greater part of these buildings are founded on clay deposits. Newer buildings can be considerably higher, but are then founded on rock. As in most established cities planning and building of new highways, a public transport system, and transportation systems for sewage and storm water drainage confronts the city planners and engineers with many problems. Very often the only solution is subsurface constructions. This chapter will deal with the more important aspects of rock constructions under urban areas with reference to experience gained by various public works departments in the Municipality of Oslo. Especially in two fields much new practical knowledge has been obtained recently, i.e. in the use of full face tunnel boring machines (TBM) and in grouting techniques against ground water leakage.
The geological conditions in Oslo are known to be very complex(Fig. 2). The rocks originate from three different geological periods. The oldest are the pre-Cambrian gneisses (1800 million years old). We find these mainly in the eastern parts of town, but they also form the foundation for Akershus Castle which lies in the centre of the town. The cillnbro-silurian sedimentary rocks arc about 570 to 350 million years old. These rocks consist mainly of different kinds of shale and limestone. These appear in the western and central part of town. The youngest rocks are the permian rocks which are about 250 million years. During the permian age the area around Oslo underwent great changes including large volcanic activities. The rocks from this period consist of java, basalt, syenite and porphyrite. These igneous rocks are found in the northern part of the town and also in the form of sills and dykes penetrating the sedimentary rocks and even the pre-cambrian bed-rock. There are large differences in the compressive strength of the different types of rocks. Some examples will show this: