This general report describes shortly the recent researches carried out so far in the geomechanics and geotechnology concerning deep underground excavations, especially tunnels, coal mining and ground subsidence caused by them, which are the topics under the Sub-Theme C2, C3 and C4in this Congress, and introduces the important part of the papers submitted to this Congress under these Sub-Themes to suggest particular area for discussion.
Dieser allgemeine Bericht beshreibt kurz die neuesten geomechanischen und geotechnischen Untersuchungen ueber tiefunterirdischen Ausschachtungen, besonders bei Tunnel- und Kohlenbergbau und die dadurch verursachten Bodensenkungen, welche Gesprachstoffe unter Sub-Them a C2, C3 und C4 dieses Kongresses sind, und leitet den wichtigen Teil der an diesen Kongress unter den vorgenannten Nebenthemen vorzutragenden Referate ein, um besondere Diskussionsbereiche vorzuschlagen.
Ce rapport general descrit brièvement des recherches recentes qui ont ete effectuees dans les domaines de geomecanique et de geotechnique, sur des excavations souterraines et profondes, notamment, des tunnels, l'exploitation minière des charbons et des affaissements du terrain causes par ces premiers, ceus qui sont les sujets des sous-thèmes C2, C3 et C4 dans ce congres, et introduit des parties importantes des etudes qui ont ete presentees à ce congres sous ces sous-thèmes pour but de suggèrer des zones particulières pour discussion.
Tunnel engineering techniques are very closely related to rock mechanics. It is not possible to summarize here the vast amount of informations now available on this subject, therefore only a few comments will be presented.. Research works on the tunnel engineering may be classified into two broad categories: one, of theoretical nature, which aims at explaining the process of deformation and failure of tunnels, and the other, of more practical nature, which deals with the design and construction of tunnels. Researches on rock mechanics related to these two categories of tunnel engineering are summarized as shown in Fig. 1.1. Studies belonging to the first category do not have direct relationship with design and construction at the present time. They are, however, works of basic research and highly important for the development of tunnel engineering in the future. The basic research of the tunnel engineering contains many different approaches. In the first approach the natural ground is studied by transforming it into a mechanical model, followed by analysing stress, strain, displacement and stability. If the ground is presumed to be a continuous body, the analysis can be carried out by applying the continuum mechanics, i.e. the theory of elasticity, of plasticity and of visco-elasto-plasticity. An analytical solution may be possible in this case, provided that the boundary conditions are simple. If the boundary conditions are complex, numerical analysis by the newly developed, digital computer must be carried out. The same goes true when complicated material properties must be taken into consideration. This approach, however, cannot be applied unless the crack spacing is much smaller than the size of the tunnel so that the natural ground can be considered as being a homogeneous body. The continuum mechanics approach can also be applied, with some effort and modification, to the grounds where the rock bolts or rock anchors exist. It cannot, however, be employed if the crack spacing is of similar order as the size of the tunnel opening. In such a case, the other approach which takes into account the existence of discontinuity is necessary. It is not possible to carry out these analyses without numerical techniques. Cundall (1974) and also Kawai (1977) already put forward a method of numerical analysis of discontinuity by simulating a rock mass with rigid or deformable blocks. For example the analysis of stability for the ground where joints appear at the crown of a tunnel was conducted by Shi (1981) considering the equilibrium of the forces acting on each block. As for the researches belonging to the second category, the majority deals with field measurements. A great deal of measuring results, including the development of new measuring methods and their evaluation, have already been reported (Sakurai, 1981). Many of these reports are concerned with the NATM technique. In addition, ambitious studies dealing with the decision-making in designing stage have been done. These studies collect the results of previous measurements and apply them to the decision-making with the help of the procedure based on statistics and the probability theory (Einstein, 1978; Ashley, 1981). In the tunnel engineering, the problems concerned with underground water cannotbe forgotten. The underground water flow will influence the stability of openings especially when the rock mass is fractured and sheared. Recently the hydro-mechanical analysis has been introduced to develop new numerical techniques. Having surveyed the state of research on the tunnel engineering, now several topics in relation to tunnelling will be introduced including the Seikan tunnel, 53.85 km undersea tunnel of which pilot tunnel was completed in January 1983.