The Shin-Kanmon Undersea Tunnel is the railway tunnel on the Shinkansen, the thirdundersea tunnelconnecting Honshu and Kyushu across the Kanrnon Straits, its total length being 18.7km. Although theunderwater portion is 880m long or only five per cent of the total, it was very difficult to construct the tunnelbecause of the clayey and crashed fault zone underwater, abount 30m in width. This paper deals with the surveys made on the underwater portion and the application of the results forthe selection of the route and for the planning of the construction of the tunnel.It refers to the surveymethods adopted-super-sonic and seismic wave prospecting, and long horizontal boring-as well as to the pilottunnel.
The Upper Cretaceous Izumi Group in the vicinity of Naruto Strait, consists mainlyof sandstone and shalealternation and shows the monoclinic geologic structure. Well stratified bedding plane forms a distinct geologicdiscontinuous plane, developing cross joints nearly perpendicular to the bedding plane. The authors studied both a theoretical simple slope model by TERZAGHI and the actual conditions of manyroad cuts. Stability of stratified Izumi Group depends primarily on the bedding plane orientation with referenceto the slope. Further, slope stability is affected by continuous joints and small faults which is difficult topredict its presence before cutting.
Joint planes used in this experimental study consisted of three artificial joints of extension fractured surface (EFS), sawn-cut surface (SCS), and polished surface (PS). Shearing experiment with test pieces about 60 mm in diameter were performed under normal stress σN from 0.2 to 120kg/cm2. The roughness of above three planes and natnral joints was measured by surface roughness meter (SE-0) as shown in Fig.2. The relation between shearing strength τf and σN is shown in Figs. 4 and 5 for virgin shear of EFS, in Figs. 6 and 7 for repeated shear at first and second cycles of EFS, in Fig.9 for SCS, and in Figs.11 and 12 for PS. Power law of friction may be suitable to express τf-σN relations (see Figs.8 and 10). The dependence of frictional properties on normal stress is summarized in Fig. 13. From Fig. 13 the true frictional angle φu may be about 25°-26°. Dilation angle dn° at peak shear stress has non-linier relation to secant frictional angle φs of tan-1 (τf/σN) in Fig.19, which showes, though widely scattered, an important relation between φs and dn. The effect of filling materials on frictional resistance of joint is summarized in Fig.21 according to surface roughness, particle size and moisture condition. Weathering less than about 7% in porosity may be negligible effect on shear strength, but effective on deformation properties.
On the excavation of such a under ground condition as encountering sand quick phenomenon, well-point method to lower the water-table or deep-well method to reduce the water pressure at heading is ordinally adapted. When the water-table revive after lining, sometimes leakage and piping of water cause a serious problem. This paper reports the piping phenomenon of Obara tunnel in Tokaido-Shinkansen and the counerplans for leakage and drainage of Higuchiyama tunnel in Sanyo-Shinkansen.
Shirasu distributed in southern Kyushu, Japan, is the great deposits caused by volcanic activities of Aira and Ata calderas. Shirasu has many problems to settle from the standpoint of engineering practice and prevention of disaster, because it is structurally unstable. The main purpose herein is to present a method of the identification and classification of Shirasu from the standpoint of soil engineering with its geological aspects in consideration. Shirasu deposit has the hardness ranging from soft soil to weakly welded tuff, and its hardness may be used to as a criterion of the identification and classification for engineering purposes. It is proposed in the research that the hardness of Shirasu is given by the index hardness of its matrix, and is measured by applying Yamanaka's soil hardness tester with the spring pressure of 8.0 kg. Here the author investigated the hardness of Shirasu matrix measured at 145 locations in southern Kyushu and classified Shirasu deposits into five distinct groups as soft decomposed Shirasu, decomposed one, proper one, hard one, and welded tuff. The index hardness of soft decomposed Shirasu is lower than 20 mm. Decomposed Shirasu has the index hardness ranging from 20 to 26 mm, proper Shirasu has 26 to 31 mm, and hard Shirasu has 31 to 35 mm. Welded tuff is higher in the index hardness than 35 mm. The dry density of soft decomposed Shirasu is smaller than 0.80 t/m3, that of decomposed Shirasu is in the range of 0.80 to 1.10 t/m3, proper Shirasu is in 1.00 to 1.25 t/m3, hard Shirasu is in 1.15 to 1.35 t/m3, and welded tuff is larger than 1.35 t/m3. The propriety of the method proposed as the identification and classification of Shirasu for engineering purpose is ascertained statistically by means of x2, F, and t tests. There also is the correlation among hardness, dry bulk density, and moisture content. The hardness increases with an increase in the dry bulk density of Shirasu. Finally the chart of identification and classification of Shirasu is established on the basis of the relationship between index hardness and dry bulk density.
The Daito granodiorite mass is widely exposed in Kisuki-Daito district. This rock has a somewhat homogeneous composition and is medium to coarse-grained rock consisting chiefly of plagioclase, quartz, orthoclase, biotite and hornbelnde, accompanied by small quantites of apatite, magnetite, zircon and sphane. Whole rock and their biotite were examined by X-ray powder diffraction method and chemical analysis. The grade of chemical weathering that have taken place in rocks was determined by A.D.F. proposed by present writer. The amount of leaching from the parent rocks, relating to the cation, have intimate relations with A.D.F. By weathering reaction, biotite is altered to the mixed matters composed of biotite and kaolinite at about 15 in A.D.F., passing through the mixed matters composed of unstable biotite, interstratified biotite-vermiculite mineral and kaolinite at about 89, interstratified vermiculite-montmorillonite mineral, interstratified biotitevermiculite mineral and kaolinite at about 77, interstratified biotite-(vermiculitechlorite intergrade) mineral and kaolinite at about 19 in A.D.F. value. The results indicates that the altered products of biotite gives a measure of the proceeding on the weathering process of parental rock.