Just after a landslide or landslip occurs, we can often observe in situ that ground water gushs out like a vein-stream from the main scarp or among deposits of the landslide or landslip area. By examining the relation between this phenomenon and the results of various investigations for ground water, such as tracer method, water-level, flowing layer detector, pumping test, water quality, and others, it is inferred that the ground water having a large influence on the landsilde movement or occurrence exists as the state of vein-streams in and around the landslide area.
In many cases the landslide seems to occur or move when the abnormal condition arised in vein-streams by some causes, such as heavy rain, thawing water, earthquakes, embankment, and others.
Accordingly in order to investigate the occurrence and movement mechanism of landslide or landslip phenomena, it is neccessary for us to estimate the existing places of vein-streams in and around landslide and landslip area as accurate as possible. Then the author proposed one new survey method “The underground temperature survey in one meter depth” for the vein-streams in and around them. It was shown, by both a theoretical study and experiments in situ, that this new method was useful one for surveying the ground water like a vein-stream.
By using both the new method to estimate the scales of vein-streams and some methods to obtain the displacement values of landslide soil-mass, it was found that the vein-stream had a large influence upon the landslide movement: As the scale of the vein-stream becomes larger, the displacement values of the soil mass increases; and the scale becoming smaller, the value decreases.

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The deformation and movement developed by the geological structure in some regions yield faults, fractures, folds and so on. Teref ore approach to the strength properties of rock mass is led by the understanding of the orientations of strength anisotropy of rocks due to these geological structures.
In this paper the authors described the result of an experimental study on the change of strength and deformation characteristics with water absorption, taking their anisotropy into account. On the one hand tensile strength of rocks has been determined by the point load test on untrimmed test specimens to know the influence of water absorption to strength. On the other hand elastic wave velocities of specimens have been measured and the dynamic moduli E_d have been calculated in view of their deformation anisotropy.
The tensile strength is denoted “σ_ta” and “σ_tc” respectively in the direction normal and parallel to the discontinuity planes such as joint surfaces. Similarly the dynamic modulus in the direction normal to the discontinuity planes is called “E_da” and that parallel to them “E_de”.
The results obtained as to the dynamic modulus and point load test are summarized as follows:-(1) Degree of strength anisotropy shown by point load test, “σ_ta/σ_tc” and that by dynamic modulus, “E_da/E_do” correlate nearly with a straight line.(2) While degree of anisotropy of dynamic modulus “E_da/E_dc” is decreased, that of strength anisotropy “σ_ta/σ_tc” is increased when water is taken into discontinuity planes.

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Soilの膨潤性や強度などの物理的性質はsoi1の粒度・鉱物組成・soil粒子と結合したりまた単にsoil粒子間にある水の量と深い関係があることは従来より知られている。鉱物組成は定性的であれば比較的容易に求めることができる。またsoil中の水は単に含水比として検討されてきた。しかし, soilの物理的性質は構成鉱物の定量的な組成, 粒度, soil粒子と間隙水の結合の度合といったものに支配される。
この研究はsoilの膨潤性と最も関係の深い構成鉱物, すなわち, 粒度が小さく, 比表面積が大きく, 界面活性度が高くそしてカチオンの置換容量が大きい粘土鉱物 (ここでは主としてモンモリロナイト) の含有量とそのsoilの膨潤性, 結合水量と膨潤性などについて, 第三紀泥岩を粉粋して作ったSoilについて検討したものである。

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The Enasan Tunnel is a vehicular tunnel with two lanes and a length of 8, 489 m from Iida city to Nakatsugawa city.
The geological survey of the Tunnel was started in 1957. On the basis of preliminary survey, many faults and sheared zones running from sounth to northward were recognized. Misaka fault have wide sheared zone about 700 m in width.
The pilot tunnel was first driven for the whole length of the tunnel. Its purpose was to explore the strata, fully and to simplify access, ventilation and drainage in the construction of the main tunnel. Geological conditions were much worse than anticipated. Tunnelers hat to bore through the mountain of granite and rhyolite crossed by over 130 faults and saturated with ground water. Maximum pressure ofgroundwater reached about 50 kg/cm².

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This report refers to some geotechnical experiences about the shaft work in Enasan-tunnel that is lately completed.
They contain following topics.
(1) location of the shaft
(2) geotechnical investigation fer design and operation
(3) a boring for drain and attendant works
(4) excavation in distress
(5) cracks in lining due to 440 m-fault gouge

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