There are many faults in area of Kunnui Formation, but few in Kuromatsunai Formation. It seems to the reason of the geological age and of which Kunnui Formation is mainly underlain by solid character's rock (tuff, lapilli tuff, and tuff breccia) and Kuromatsunai Formation is fluid quality (mudstone). The biggest fault is F. 10 fault which appeared in about 33km. The thrust length seems to about five hundred meters, because Fukuyama Formation is in fault contact with Kunnui Formation (Kn 4). About one kilometer of Kunnui Formation (tuff and mudstone, Kn 2-Kn 4) near the fault is squeezing ground, and the maximum earth pressure amount to 2.0MPa. Excavating of main tunnel carried out by the circular short bench (with spring line drift) method after elavolate grouting. On the other hand, during the construction there were four accidents of water inrushing in the area of fault zone. Every restoration work took about five to twelve months. In the fault zone, as advance boring came to deadlock, investigation for proving was carried out by short drilling (coring and noncoring) from working face and side well. To prevent water inrushing, new technologies of measuring must be developed to grasp the process of seepaging and loosening of the ground. This is very important task for maintenance of tunnel. Meanwhile, chemical quality of seepage water is almost near that of sea water and is alteration sea-water type by exchange of ion, and partially is hot-spring type.
The Seikan Tunnel is located 100 meters below the seabed. The maximum depth of the sea above the tunnel is 140 meters, and there are strong currents of up to 8 knots. Because of the considerable depth and the strong currents, there were limits to the types of surveys which could be conducted from the sea surface. This was especially true of the central area of the straits, where both the number and precision of surveys were inadequate. Thus, it was necessary to supplement these surveys with surveys conducted from within the tunnel. The surveys were based mainly on pilot boring and daily investigation of the face. It is believed that the Seikan Tunnel project was the first project in which these methods were used on a daily basis. This report describes how underground geological surveys were conducted in the under sea tunnel during construction, explaining both the method employed and the results obtained. Furthermore, reconsiderations and suggestions from both the parties which conducted the geological survey and the parties which used the data from these surveys are also included.
In this work, an empirical equation that is derived from Ladanyi's shear strength theory of jointed rock masses is proposed. This equation is expressed as follows. While Ladanyi's equation is expressed as follow. In this empirical equation, the factor “β” that depends on the continuity of rock joints is considered. The value of this factor “β” can be found, β=1 for highly jointed rock masses, β=O for intact rock and O<β<1 (in many casies β=0.5-0.85) for the intermediate states of the rock masses. Theoretical shear strength curves are suggested by the combination of general φb (basic friction angle), i (dilation angle), σc (uniaxial compressive strength) and “β”. The relation between the theoretical shear strength carves and measured strength values which are obtained from in situ block shear test is examine in many casies.
Alteration, which weakens rock mass and reduces the dry density, is one of the essential subjects in the foundation engineering. Case study has been carried out in which the alteration zone was to be grasped by the estimation of the density with the mean of geostatistics. The distribution of the dry density in whole mass was estimated from measured data of limited numbers of cores bored vertically and compared with the data measured horizontally. The result shows that the shape of histogram of estimated density was very similar to the measured one, while the density itself was not estimated precisely. Therefore, the geostatistics is able to be applyed to estimate many properties of rock mass other than alteration.