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For grasping the charactaristics of the Gotenyama landslide, we executed investigations bymeans of internal strain gauge, tiltoneter, extenso-meter, bedrock survey and electric survey.As the result of these, we got the following1) This area didn't move as one large mass, but as some small blocks, moving directions ofwhich were not the same.2) Sub-slide surface was moved by astimulation of the movement of upper slide mass.3) Movement of ground surface layer suffered remarkable effects of anow-fall

The authors have been observing the sediment yield in a mountain stream, HirudaniExperimental Watershed, at Hodaka Sedimentation Observatory.Present year, a more reliable facilities was used for picking considerably coarse gravelscontained in running water. Therefore following facts were proved:1. Sediment concentration decreases even while water discharge is constant after thepeak discharge.2. In some cases, the maximum size of sediments which is caught happenes fairlybefore and after the peak of sediment concentration are attained.3. The maximum of sediment concentration in a flood is likely to depend on theratio of peak discharge to base flow or the increasing rate of discharge than on the peakdischarge itself of the flood.

In order to know the nature of variations of the surface inclination at the landslide areaswhich were clasified into creep type when its occurred, the water-tube type inclinometers wherewere set at the suitable site were used.In this paper, the observational results on the small scale surface ground tilt at Kamenose, Muraoka and Myoban landslide areas were reported and some discussion were made.

All Japan Landslide Prevention Association is organized by the Prefectures whichare troubled by landslide. Recently, this Association collected the problems by enqu~temethod which are requested to settle in each Prefecture. In this paper, this authorclassifies and interpretates those problems.

The purpose of this paper is to present briefly the results of experiment on thecharacteristics of mud-flow. In this experiment, the velocity distribution and fric-tion coefficient are measured and the effect of the concentration on the streamflow si discussed.

The authors carried out some observations on tlse runofl sediment yield and transport ina small mountain watershed, called Hirudani Experimental Watershed, which is a tributary of theJintsu River in Gifu Prefecture, Japan. This paper presents some results of the observations onrunoff characteristics, rate of sediment yield and transport on each classification of rocks in thesediment and transport, and changes in water qualities during floods. By using these results, the authors consider as follows:-1) The conductance of flood water is an indicator of the component of runoff.2) The quantity of sediment yields and transport discharge are limited during the period ofthe observed runoff.3) The characteristics of transport materials reflect the runoff processes over the sedimentsource areas.

Upheaval phenomenon at the tip part of landslide is not so rare. But the upheavalat the opposite side of the river which runs at the tip part of landslide seems to suggestthe factore of cause of the landslide.Accordingly, for the purpose of making clear the phenomenon, the study was carriedout.In beginning, the electric survey was carried Out atsome landslide areas which hadthe specific upheaval phenomenon.As the result of the investigation, the next facts were revealed:(1) The difference of the apparent resistivity between the upheaval area and thenon upheaval area was caused by the occurrence time of the upheaval phenomenon.(2) The difference of the apparent resistivity between the upheaval area and thenon upheaval area was caused by the geological factor.

Along the Gamata River basin, there exists numerous landslide. Knowledge of con-ditions under the landslide area is both useful and important for understanding the mechanismof the occurrence of the landslide in this area.For investigation of geochemical features in this area, the authors determined thedistribution and the change with time in the chemical composition of ground waters.This is, from August 1968 to November 1968, ground water Samples were taken at intervalsof two weeks and the composition was determined.Temperature, pH and conductivity values were measured in the field and chemicalconstituents such as Na+, K+, Ca2+ + Mg2+ and Soluble Si02 were determined in thelaboratory.It was found that general tendencies were as follows:(1) The concentrations of Soluble Si02 increased after a rainy term.(2) The concentrations of Ca2+ + Mg2+ decreased after a rainy term.(3) The reverse relation of concentration was observed between the soluble Si02and the Ca2+ + Mg2+. (4) The variation of the concentrations of Ca2+ + Mg2+ and Soluble Si02 in aftera rainy term, were large in the landslide area.

In this paper, Non-Newtonian character of the mud-flow is discussed upon the baseof the experimental data, and the mean velocity of the mud-flow is calculated as non-Newtonian liquid. The mud flow of the prototype in the mountainous region is con-cluded as the same character as the experimental flow. The boundary shearing stressin a trapezoid section of the mud flow, and the pseudoplastic viscosity of the mud isestimated in order to caluculate the velocity of the mud flow.

In this paper, the author discussed a turbulent flow of a non-Newtonian liquid. Fro, ii th~experimental results of the resistance law to a smooth pipes, the author thought that the w ixinglength theory make clear the Reynolds stress and drived a velocity distribution and a resistancelaw to a turbulent flow of a non-Newtonian liquid from the mixingth length theory. Theauthor showed that the universal constant K is function of x~/x~ that the coeffient of eq. (1.10)of the redistance law is constant. The value of K was showed in Fig. 3. In the next, , , heauthor discussed the kinetic similitude in a Bingham flow. The kinetic similitude of a Binghamflow established when the Reynolds number of eq. (3.11) is equal for the plototype and themodel.

Most observations on the sediment flows have been performed in plain rivers, butthese in the mountainous region are little in Japan. The authors carried out someobservations on the sediment yield and transport in a small mountain watershed, calledthe Hirudani Experimental Watershed, which is a tributary of the Jintsu River in GifuPrefecture, Japan. - This paper presents some informations on the watershed and someresults of the observations on soil characteristics, run-off characteristics, rate of sedimentyield and transport, and changes in water qualities during floods. Some considerations onthe sediment yield and transport in a mountain basin are made and methods of theobservation are discussed.

In studying mechanics of transportation of sediments by stream, it is desirable to know fallvelocity frequency distribution rather than size frequency distribution of sediments. Usual methodsfor observing characteristics of sediments are mainly for size frequency analysis of granularparticles as minute as Stokes' law applicable. Differential pressure gages are already utilized forthe sedimentation test, but its applicability is limited within granular particles and is not completelyclarified yet. The authors performed some experiments on the applicability of this method toconsiderable coarse particles as gravels in a mountain stream and the limit of applicability isclarified based on the experimental results.

Water samples have been collected from the landslide areas of Tertiary and fractured zones toinvestigate the water quality of geologically different landslide areas. The authors have examinedthe relationships among the chemical species contents of the waters and the following have beenobtained: In general, the concentrations of calcium and bicarbonate ions show high value amongdissolved ions in the natural waters of the two landslide areas, the concentration of soluble silica inthe natural waters of landslide areas of fractured zone is low value, calcium to sodium ratio and tomagnesium of dissolved elements can draw a fairly clear between two landslide areas, montmorillonit-es and kaolinite are in equilibrium with the waters of the Kuraisbi, Maruyama, Kozuehiyama andMinamikaminaka landslide areas, and equilibrium between kaolinite and montmorillonite isattained at the concentrations of bicarbonate ions over about 80 mg/I in the natural waters oftheir investigated fields.

Ground water flow may be generated in sloping soil layer laid on semi-pervious rock surfacewhen the infiltration of rain water I throughout the soil layer exceeds in the downward leakage ofwater L Out of bed rock surface. The author investigated theoretically the development of sucha flow due to the infiltration under semi-infinite region of rainfall in the ease where the bed rocksurface is fiat with a inclination b≡tan β to horizontal plane and the soil layer has a porosity a, permeability k and an uniform vertical thickness D and found an uniform flow which is coveredby two free surfaces; the one stretching downstream from upper limit of leak surface with a constantinclination cm tanr to horizontal surface and the other growing upwardly at a constant rate(I-L)/ σ in parallel with the bed rock surface. This flow exists within the limit of conditions1 -I>(1-I) (1 -tan2β/2) and I>l, where I≡l/k and l≡L/k may be called the specific infiltrationand leakage, respectively. In the case where 1-I= 1 -tan2β/2, then r =β/2. The frontalline of steady free surface will seep at the position in the distance S= UD sec β/(I-L) (U: horizontalDarcy's velocity of flow) downwardly along sloping soil surface from the fringe of rain-fall regionat the time T= σ D/(I-L) after the wetting front of the infiltration reached the bed rock surface.

In this paper, the author had studied thr relationship between variation of tiltineter andlandslide movement observing bulb type tiltmeters~ in the creep type landslides. From the resultsof them, the variation of tiltmeter in landslide is related with the landslide movement of creep type.When we make judge the landslide movement from variation of inclination on the soil surface, it is usefull to confer the standard curves that was maked by observational facts.The critical inclination for soil movement, is assumed about 4"/day as N-S and E-W com-ponent respectivelly.

This paper deals with the critical tractive force for gravels in a mud stream. Whether thestream is a mu& or clear flow, the mechanism of initial movement of gravels is similar. But, it is hard to analyze theoretically the mechanism in a mudstream because the fluid characteristicsare not clarified yet.In this paper the author presents an arrangement of the experimental results on the criticaltractive force in a mud stream using a Reynolds number derived from the kinetic similitude ofmovement of gravels. The Reynolds number is expressed as a function of the Reynolds numberof critical tractive force proposed by Shields and the ratio of yield stresses of fluid to boundaryshear. It was concluded from the treatment that the critical tractive force for gravels in amud stream is expressed by the same relation as that in a clear stream, and that the relationshipis in good agreement with the experimental results.

On the Tono region in Gifu pref., central Japan, there are many landslides with the phe-nomenon of the subsidence about the ground. Genesally, the subsidence was divided by thefaulty line or the vertical faulty plane. These phenomena of the ground transformation wererecognized the landslide of a peculiar sort when made study of it’s a problem on the ground bythe geophysical method.In this paper, the authors argued as a prediction for study of the landslides with anotherform.

The relation between stress and strain for the mixture consisted of clay and water wasexamined as the fundamental step for the approach to the physical character of mud flow.Two types of rotational viscometer, the cap rotation type and the bob rotation type, were usedin the mesurement.Through the experiment, it was disclosed that the relation between stress and strain forthe mixture follows to the power law or Biogham's law. Although the conditions goveringthese laws are not yet clear, it seems to be due to the construction of micelle.

The Makiuchi landslide and the Gongenyama landslide had occurred at Matsushirotown, Nagano city, in Sept. 17 and Oct. 9, 1966 respectivelly. These areas where thelandslides occurred are situated at the middle part of the Matsushiro earthquake swamwhich effect on the faults, cracks, spring discharges and upheaval of crustal block.These landslides are very rare one for its clasifications, therefore we are studying naturalradioactivity survey and chemical analysis were carried out to explain the mechanismsof these landslide occurrence.Natural radioactivity of near cracks and faults from 2.5 x 10'm7/h to 6.2 x 10'm7/himplys being of active faults and hotspring activity. Farther more we continue this su-rvey to explain that the faults and cracks and hot spring activity are increasing or notby the natural radioactivity variations.Chemical analysis of the water samples from the springs which recently gushed outwas carried Out in relation to pH, Na~, Ca", Mg'~, HCO, , C1, SO4~, and solubleSiOz. The wide variation of the content of each ion from 10mg/I to 3, 000mg/I suggeststhat these water samples contain the highly mineralized water from the great depths.The concentration of ions in the spring water increased several times from Septemberto October but the increasing rate varies with the kind of ions. Therefore thevariation of the concentration of each ion can not be explained solely by the dilutionof the mineratized water by the surface water.

The author has walked for survey of the geology and geomerphology on some areas which arenotorious for their landslide in the Mikabu terrain of Shikoku.The results obtained are summerized as follows:1 ) The deposits of landslide areas consist of angular and subangular detrital materialswith small quantity of clay and subrounded graveles.2) The deposits have been deposited into the brooks of landslide areas, and the thicknessof those deposits is rather thin in contrast to the length of landsliding slope.

大和川が奈良盆地の小流を集めながら西流し, 一本となり生駒山脈を横断して大阪平野にぬける付近は, 通称"亀の瀬"と呼ばれ, 峡谷をなしている。この左岸は奈良県北葛城郡王寺町で, 明神山・二上山と続き急峻な地形となっており, この裾を関西本線・国道25号線が走り, 関西交通網の幹線となっている。また, 右岸は大阪府柏原市峠町で, はるか北の方に信貴・生駒の山並みを望み, 付近一帯は緩やかな丘陵地帯となっており, 肥沃な土壌と南の日ざしをうける傾斜地は果樹の生育に適し, 古くからぶどう・桃・みかん等の産地として有名である。このような, 一見のどかな丘陵地帯も宿命的な地すべり地で, 昔から度重なる地すべりによる被害を受けており, 中でも1931年年末から起った地すべりは, 峠部落を中心に32haの土地がすべり, 当時穐の瀬地すべり"と呼ばれてニュース面をにぎわした。この地すべり地域の西側の清水谷地域(Photo.1参照)における地すべりが最近活発化するにおよび, 建設省においては, 地すべり防止工事を実施することになり, 昭和38年度を初年度とする5カ年計画で総土量60万m3の排土が行なわれつつある。筆者らは・この排土工事に関する諸資料を得るため・昭和37年以来当地域一帯で, 地質学的・地球物理学的・土木工学的な諸調査を実施してきたが, 以下筆者の行なった地球物理学的な調査に関する地震探査・地表面の伸縮や傾斜変化などについて述べる。, At Kamenose Landslide zone located in Toge, Kashiwara City, Osaka Prefecture, the geophysical investigation to establish the perfect stabilization plan has begun at 1962.First of all, seismic prospecting along 9 traverse lines were carried out in this areaand the fractured zone distributed NW-SE, dividing this area into two blocks wascaught.The observations of ground-strain are being carried out by 74 wire type extensometersset up along 8 survey lines. Considering the distribution of strains, also the landslideblock in this area was divided in two by fractured zone and the change of strain wasthe largest near the fractured zone.In the case of landslide due to soil mass removal, the peculiar variations of ground-strain and ground-tilt were found which seemed to be the forerunning phenomena to thelandslide.

The authors resumed the geophysical observations of soil mass movement in the Kushibayashilandslide area located in Ogoto town, by internal strain meters, extensometers and tiltmeters fromJuly, 1971. Particularly, we were interested in detailed surveies of features of the distributions oftilting and extention of the ground surface, and investigated the relationship between the state ofmovement of the ground surface and the form of the slip plane by finite element method in elastictheory of plane strain. Then, we presumed the form of the slip plane from the distributions oftilting and extention, as shown in Fig. 7.

アジアモンスーン地域に位置する日本列島では,毎年,豪雨に伴う斜面崩壊・土石流が発生し,土砂災害として社会・経済に大きな損害を与えている。2013 年～2014 年にかけては,2013 年台風第26 号による伊豆大島(東京都大島町)での土砂災害,2014 年7 月長野県木曽郡南木曽町での土砂災害,2014 年8 月豪雨による広島県広島市での土砂災害が発生し,甚大な被害が生じた。本研究では,これらの土砂災害を事例に,斜面崩壊の発生と降雨の再現期間,および2 種類の降雨パターン(短時間集中(SH)型と長時間継続(LL)型)との関係を分析し,今後の防災情報への応用を考察した。その結果,伊豆大島での土砂災害は再現期間100 年以上の降雨により発生し,SH 型として斜面崩壊が発生しやすい降雨パターンであった。南木曽町の土砂災害は,引き金となった豪雨の再現期間は30 年程度であり,LL 型の降雨パターンとして先行降雨も影響していた。また,2014年8 月豪雨による広島県広島市での土砂災害事例は,2 時間～3 時間雨量がこの地域において非常に大きな値であり,加えてLL 型の降雨パターンとして先行降雨も影響していた。これらの事例について,降雨の再現期間と2 種類の降雨パターンを分析することで,事前に斜面崩壊が発生しやすい降雨パターンの特徴を把握可能であったと考えられる。今後,地形・地質情報を含めて,より多数の事例を分析することが課題である。