As large scale caverns were being excavated, measurements of rock deformation, lining stress and other pertinent observations were carried out. From these measurements, the mechanism of rock behavior has been clarified: 1) deformation of rocks consists of "opening displacement" and "strain displacement", 2) ratio of these two displacements differs by types of rock, and 3) underground structures should be designed on the basis of "deformation" of rocks.


Les cavernes de grande dimension on ete construites et des mesures de la deformation de roches, la tension de revêtement et d'autres mesures on ete executees durant I'excavation. Le mecanisme du comportement des roches a ete eclairci à travers ces mesures: 1) La deformation des roches consiste en un "deplacement d'ouverture" et un "deplacement de tension", 2) Le rapport de ces deux deplacements varie selon Ie type de roche, 3) Les structures souterraines devraient être designees sur base de "deformation" des roches.


Groβe Aushöhlungen wurden gebaut und Messungen der verformung der gesteinsmasse, der Panzerungsbelastung und andere wurde bei der Ausgrabung ausgefuehrt. Durch die Messungen der Mechanik des Gesteinsverhaltens wurde folgendes festgestellt: 1) Die Deformation des Gesteins besteht aus einer "Offnungsverschiebung" und einer "Belastungsverschiebung", 2) Das Varhaltnis dieser beiden Verschiebungen ist je nach Gesteinsart unterschiedlich, 3) Untergrundbauprojekte sollten so entworfen werden, daβ sie die "Verformung" des Gesteins beruecksichtigen..


When a large scale cavern is under excavation, deformation of the surrounding rock occurs, and in the extreme case, it leads to a collapse of the cavern. The deformation of rock mass depends on not only the deformability of rock but also on its geological features, e.g., faults, seams, joints, and other cracks. Because of the complicated deformation process, it is necessary to perform in-situ measurement in order to clarify the deformation process. Many large scale caverns for underground pumped storage power station have been excavated in the last few decades. We have studied the stability of such large scale caverns by both numerical analysis and in-situ measurements while in excavation. This paper aims to discuss the characteristics of rock mass behavior from the results of the in-situ measurement (Hibino and Motojima 1993).

Shape of cavern, initial rock condition and types of measurement

The shape of a typical cavern of underground pumped storage power station discussed here is shown in Figure 1. The cavern is 25m in width, 100m to 150m in length and 50m in height. Dimensions of the existing caverns and the initial conditions of rocks are shown in Table 1. As shown in Figure 1, various types of measurement are performed on large scale caverns. Among them, displacement of rock mass, convergence, reinforcement stress in arched concrete lining, concrete strain, and temperature are usually measured. For the cavern which has 100m to 150m in length, 3 to 5 cross sections are usually prepared for the measurements. In some cases measurements of elastic wave velocities, measurement of permeability coefficient and observation by borehole TV are performed. Figure 2 shows a typical record of the subsidence of ceiling rocks due to excavation. It is obvious that the subsidence of ceiling rocks was caused during the excavation of the arch part and not by the excavation of the main part. Figure 3 also shows a record of the relative horizontal displacements. There is a clear indication that the horizontal displacement of cavern wall continued to increase throughout the excavation of the cavern, but stopped increasing just after the completion of excavation.

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