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In the Izusan district of Atami City, Shizuoka Prefecture, a debris flow occurred at an altitude of about 390 m on the Aizen River at around 10：30 on July 3, 2021 due to heavy rain. However, the cause of the damage has not yet been clarified.Therefore, in this paper, we analyzed the cause of the collapse as to the reason why the debris flow occurred on the embankment slope. As a result, high embankment slopes filled with steeper slopes were very dangerous, but no drainage treatment or erosion control was installed. Construction of a residential area on the north side of the col-lapsed embankment slope changed the traditional basin boundary, revealing that a very large amount of rainwater in-filtrated the embankment and collapsed. The signs of this collapse may have begun in 2019.In the future, a joint project between the Sabo Department of the Water and Disaster Management Bureau and the Urban Safety Division of the City Bureau will be launched within the Ministry of Land, Infrastructure, Transport and Tourism, and a comprehensive survey will be conducted on high embankments with a height of 5 m or more to identify dangerous areas. It is necessary to extract and take immediate measures.

We had a deluge in July 2012 in the northern Kyushu district with intense rainfall of 800mm and 108mm/hr. This intensity yielded countless traces of debris flow and slope failures that induced tremendous damage and causalities in the area. Hence, several field investigations and reconnaissance tasks were conducted by the society to delve into this sediment-related disaster. The various results and the information obtained through this investigation were reported as the primary report, mentioning the damage, geologic-geomorphologic features and hydraulic characteristics of the debris flows, vegetation effects, and the efficiency of Sabo facilities in other scenes of this disaster.

低平地を中心として急速に周辺丘陵地へと拡大する都市域では，地震時液状化，宅地造成地盤崩壊，人工・自然斜面崩壊など，地盤災害の危険性が増している。本研究は，これらの地盤災害に対する都市域の脆弱性診断技術と危険度評価技術の高度化，地盤基礎構造物の性能向上技術の開発を目的とする。平成17年度のとりまとめとして，本論文では，都市域の地盤情報データベースの地盤ハザード評価への適用，地質・地形的前兆現象による大規模崩壊の発生場所予測の可能性，都市周辺の巨大古墳に記録された地震による地すべり災害についてとりまとめた。, Urban development rapidly expanding from lowland to surrounding hills and mountains poses increasing risks in geo-hazards, including liquefaction during earthquakes, and failure of artificial and natural slopes. Objective of this study is to develop methodologies for assessing vulnerability to these hazards, and technologies for improving the performance of geotechnical works in urban areas. This paper summarizes the results of the study with respect to (1) the use of geotechnical data base for urban areas for assessing vulnerability to liquefaction hazards and identifying priority areas for improvement, (2) prediction of large landslides for hazard mapping, and (3) landslides induced historical earthquake in ancient tomb mound.

本稿は、2004年新潟県中越地震により発生した斜面災害、地震前の降雨条件及び災害後の復興を紹介すると共に、地すべりダムを形成した東竹沢地すべり及び寺野地すべりを対象に、現地調査及びリングせん断試験を実施し、再活動地すべりにおける地震時高速地すべり発生・運動機構を研究したものである。また、リングせん断試験結果を用いて、崩壊後東竹沢地すべりの運動過程についてシミュレーションを行った。, During the 2004 Mid-Niigata Prefecture earthquake, thousands of landslides were triggered. Among them five catastrophic landslides were introduced in this paper. In addition, the influence of rainfalls in prior to the earthquake and the urgent response to prevent disastrous failure of landslide dams were also discussed and presented. Higashi Takezawa and Terano landslides occurred within past landslide masses and dammed the river at the toe of the landslides, causing great damages to the properties. Detailed field investigation was performed on these two landslides. To examine the triggering and movement mechanisms, samples were taken from these landslides. By using a ring shear apparatus, real earthquake wave loading test and cyclic loading tests were performed on these samples. The test results revealed that those sand samples from both landslides can suffer from sliding surface liquefaction phenomenon with very lower final apparent friction angles, while the silt sample from Terano landslide showed no liquefaction failure, indicating that landsliding during this earthquake time was triggered within the sand layer above the silt layer in the past landslide masses. Finally, the movement of Higashi Takezawa landslide was simulated.

本研究は，地震時液状化，宅地造成地盤崩壊，人工・自然斜面崩壊などの地盤災害に対する都市域の脆弱性診断技術と危険度評価技術の高度化, 発生場の時空的予測技術の開発，地盤基礎構造物の性能向上技術の開発を目的とする。平成16年度のとりまとめとして，本論文では，河川堤防の耐震性能，風化花崗岩斜面内での地下水浸透挙動，表層土のクリープ挙動，2004年中越地震によって発生した斜面移動現象の発生場についてとりまとめた．, Urban development rapidly expanding from lowlands to surrounding hills and mountains poses increasing risks for geo-hazards, including liquefaction during earthquakes, and failure of artificial and natural slopes. In order to develop methodologies for assessing vulnerability to these hazards and for making spatial and temporal predictions, and to develop technologies for improving the performance of geotechnical works in urban areas, we studied: (1) seismic performance of river embankments; (2) water infiltration behavior and creep movement of decomposed granite slopes; and (3) landslides triggered in residential areas in valley fills and hills by the 2004 Chuetsu earthquake.

本研究では、非排水条件における飽和土塊の液状化崩壊に必要な間隙水圧の変化予測モデルを評価した。モール・クーロン破壊基準おける土のせん断抵抗が、これと等しくなる時に発揮されるしきい間隙水圧が液状化崩壊した試料で示された。崩壊性地すべり地の滑落崖の試料を用いて様々な条件下で試験し、崩壊後に示される数秒間のせん断抵抗が土の密度を発達させた。しきい間隙水圧によりせん断開始直後に液状化した試料は、崩壊以前にもダイレタンシー傾向の強度が得られた。, A theoretical model predicting the pore pressure change necessary for liquefaction failure of saturated soil masses in undrained condition is assessed. It is shown that a threshold pore pressure, uc, derived from the Mohr Coulomb failure criterion when pore pressure at failure is equal to the corresponding shear resistance is enough to initiate liquefaction type of failure in sandy masses. Loading tests to failure on source-area sandy soils from a catastrophic landslide location, undertaken to verify the model, show that under definite conditions of loading, a threshold state, characterized by the equality and subsequent constancy of pore pressure and shear resistance from a few seconds after the commencement of shearing until failure, develops in the sands at a given density. Samples in which the threshold pore pressure was exceeded readily liquefied while those in which the pore pressure built-up was below the limit gained strength by tendencies to dilate. This paper demonstrates that while the stability of a slope founded on sandy soils may be breached when the pore pressure exceeds a certain limit, it is possible to make estimates of the limit. It is shown that where such estimates are accompanied with adequate field measurements of pore pressure, the efficiency of landslide prevention projects may be enhanced because only slopes whose stability is proven to constitute a real public threat are reinforced and reinforced adequately.

ここでは日本で起きた 2 種類の再活動地すべりの研究結果を示す。対応策の設計および地すべり活動の阻止のため、現地および実験室にて調査を行った。得られた結果より、すべり面の残留強度が地すべり活動に大きく寄与することが示され、土の残留強度時における粘土含有率や粘土鉱物について研究した。これにより、粘土含有率の増加はモンモリロナイト含有時と同様に、残留強度を十分に減少させることが示された, This article presents the results of two case studies of reactivated landslides which occurred in Japan. Field and laboratory investigations, including a series of drained ring-shear tests, were conducted in order to design a set of countermeasures and prevent further landslide movement. The obtained results indicated that residual shear strength of soil from the sliding surface contributed greatly to the behavior of landslide; and for this reason, a special effort was made to study the effect of clay content and clay mineralogy on the residual shear strength of soils. It was found that an increase in clay content as well as the presence of montmorillonite significantly reduced residual shear strength.

2004 年は多くの台風が日本に上陸し，各地に甚大な土砂災害を引き起こした。ここでは，その中から台風10 号による徳島県木沢村および台風21 号による三重県宮川村（現大台町）での斜面崩壊等の土砂移動現象に着目して，それらの発生メカニズム，土砂移動現象の特性などについての調査結果と解析結果について述べる。とくに，現地で観測された段階的崩壊プロセス，地下の集水構造と土砂移動の関係，崩壊過程の違いによる天然ダムの規模の違いについて焦点を当てて報告する。, In 2004 a lot of typhoons attacked the Japanese Islands and they caused a lot of sediment related disasters. Among them, we have investigated the sediment disasters in Miyagawa Village by Typhoon 21 and in Kisawa Village by Typhoon 10 and collected the information on the process of some slope failures and the characteristics of bedrock feature. In this paper, we analyzed the water movement in the slopes and its role on the slope failure, the phased failure process observed in Kotaki, the influence of the phased failure on the formation of landslide dam. As a result, a numerical simulation could explain the phased slope failure in Kotaki, and a hybrid-debris flow model could show such a slope failure process produce the difference of height, width and length of landslide dam.

平成16 年7 月25 日に発生した台風10 号に伴って, 徳島県南部地域では7 月30 日から8 月2 日までの4日間で連続降雨量が2, 000mm を超過する記録的な豪雨が発生した。この豪雨により，徳島県木沢村の大用知, 加州, 阿津江及び釜ケ谷地区で大規模な斜面崩壊が発生した。現地調査, 計測を行った結果, これらの斜面崩壊が高速長距離運動となったと考えられる。また, 阿津江地区の崩壊により崩壊地の背後に再滑動を始めた大規模な地すべりが生じたことが判明された。さらに, リングせん断試験機を用い, 阿津江と釜ケ谷崩壊地から採取した試料に対して降雨による斜面崩壊の再現実験を実施した。その結果, 地下水位が降雨により一定の値まで上昇することによって, 崩壊が発生し, その後せん断に伴って水圧が急速に増加し, せん断抵抗が低い値まで低下したことが分かった。, During Typhoon Namtheun, heavy rainstorm fell on Shikoku area, and triggered numerous landslides in Nakagawa basin of Tokushima Prefecture, Japan in August 1, 2004. Among them four large landslides were triggered in Kisawa village, causing great damage to properties and leading the missing of two persons. Preliminary investigation on them revealed that these landslides experienced rapid long runout movement. Ring shear tests on the samples from different landslides showed that shear resistance could be reduced greatly due to the build-up of high excess pore-water pressure after the shear failure was triggered by the increase in ground water table during the rain.

本研究では、三重県宮川ダム流域において、空中写真判読、ダム堆砂量の解析、現地調査等を行い、土砂生産と土砂流出の量的・時間的な関係、およびその関係に影響を及ぼす要因を検討した。ダム湖周辺における土砂流出のタイミングは大きな降雨流出イベントのあった年と一致する。また、土砂生産の影響は土砂流出に数年以上継続する。これらの特性は、崩壊・土石流による堆積土砂の堆積位置に影響を受けていると考えられる。, Because sediment supply affects sediment yield, knowledge of the relationship between sediment supply and transport are needed to estimate catchment-scale sediment yield. This study investigates timing and volume of sediment supply and transport based on aerial photo interpretation and volume of sediment deposits behind the dam in Miyagawa Dam catchment. We discuss the factors that affect the relationship between sediment supply and transport processes. Timing of sediment transport around the dam lake corresponds to large rainfall-runoff events. Sediment supply affects sediment yields for more than several years; this influence depends on the position of landslide/debris flow deposits in the catchment.

中国三峡地域では、ダム貯水による斜面変動が活発になっている。本研究では，貯水による斜面安定性への影響を解明するために，活発的に変動している樹坪地すべりにおいて，伸縮計を用いて斜面変動の連続観測を行なった。地下水存在状態を解明するために，1m深地温探査を行った。その結果、斜面内部の地下水の分布は斜面変位に直接関係していることは分かり、また、計13台の伸縮計の観測結果より，斜面変動の様子が概ね把握できた。, The Three Gorges Dam construction on the Yangtze River in China is the largest hydro-electricity project in the world. After the first impoundment in June 2003, many landslides occurred or reactivated. Shuping landslide is one of the most active landslides among them. In this paper, the deformation of the Shuping landslide monitored by GPS, extensometers, and crack measurements are summarized. Also, for the investigation of the groundwater situation, 1m-depth ground temperature measurement was conducted, and the groundwater veins were estimated. Based on the monitoring data and exploration results, a deformation model of the landslide caused by impoundment of reservoir was proposed.

この研究では，ゆるい砂質土等で構成される緩斜面で地震時における大規模地すべりの発生を評価する方法を提案する。この手法は，すべり面においてせん断力の反転が起きない条件での地震による非排水性の地すべり変位を評価した「修正Newmark 法」に基づいている。この方法は，非排水単調載荷リングせん断試験によって得られるせん断抵抗―変位関係を用いて，降伏加速度を変化させた場合に計算される変位の感度をシミュレーションモデルに組み込んだものである。この研究では，修正Newmark 法をベースに最大加速度が異なる様々な横揺れ地震波の下での非排水条件の斜面の挙動を考慮する。そして適用例として，恒久的な地震変位のもとでどのような基準により緩斜面での地震による大規模地すべりの危険度（大・中・小）が設定できるかを示す。, This paper outlines a methodology for evaluating the likelihood of catastrophic landslide occurrence on gentle slopes in liquefiable soils during earthquake. The approach is based on a modified Newmark sliding block model of assessing the earthquake-induced undrained landslide displacements for conditions of no shear stress reversals on the sliding surface. By employing the shear resistance-displacement relationship from undrained monotonic ring shear tests, the simulation model incorporates the sensitivity of computed displacements to variations in yield acceleration. The proposed approach involves an examination of undrained seismic slope performance under various horizontal seismic waveforms scaled to different specific values of the peak earthquake acceleration. An example problem illustrates how the proposed methodology may be used to demarcate, based on the magnitude of permanent seismic displacement, the levels of low, moderate and high risk of catastrophic landslide on a gentle slope in a saturated cohesionless soil susceptible to liquefaction during earthquake.

都市域の住宅密集地における地震時高速長距離地すべりの危険度評価は世界中の地すべり危険地帯のどこにおいても現在もっとも重要な災害軽減における課題となっている。本報では佐々が代表を務める地震豪雨時の高速長距離土砂流動現象の解明(APERIF)プロジェクトのうち、重要な成果をとりあげ紹介する。具体的には、(1)空中レーザースキャンによる地すべり危険地形の抽出、(2)人工降雨装置を用いた実規模斜面模型による実験、(3)自然斜面における人工降雨による地すべり発生実験、(4)都市化域における地すべり危険度評価と災害危険地区予測、の4課題について紹介する。(4)の試験地は東京近郊の多摩地区の住宅密集地2カ所に設定され、現地調査、地質ボーリング、レーザースキャン型高度計による測量、リングせん断試験など室内実験の結果をあわせたところ、両試験地においてすべり面液状化の可能性があることを示した。本研究において得られた定量的なデータを用いた地盤工学的地すべり運動シミュレーション(RAPID/LS)により、都市域における地すべり危険値予測を街区単位で実現することができた。, Risk evaluation for earthquake induced rapid and long-travel landslides in densely populated urban areas is currently the most important disaster mitigation task in landslide-threatened areas throughout the world. The major research achievements of the Aerial Prediction of Earthquake and Rain Induced Rapid and Long-Travelling Flow Phenomena (APERITIF) project which was coordinated by Sassa, is introduced in this paper; (1) Detection of landslide prone slope using airborne laser scanner, (2) Full-scale landslide flume test using artificial rainfall instrument, (3) Landslide triggering experiment on natural slope by artificial rainfall, (4) Landslide risk evaluation and hazard zoning in urban development areas. Test site of (4) is the Tama residential area near Tokyo. A set of field and laboratory investigations including laser scanner, geological drilling and ring shear tests showed that there was a risk of sliding surface liquefaction for both sites. A geotechnical computer simulation (Rapid/LS) using the quantitative data obtained in the study allowed urban landslide hazard zoning to be made, at individual street level.

本稿は，豪雨時を対象とした表層斜面崩壊のモデリングについて示したものである。斜面の安定性は土層内の水分の消長に大きく依存するため、これを精度よく表現し得るリチャーズ式を導入している。降雨実験により、モデルの適用性を検討した後、無限長斜面を仮定した3層からなる斜面の安定性を、リチャーズ式によって評価される土壌水分の消長を考慮して検討している。この斜面安定性の解析法を木津川上流域のタコラ谷に適用し、実際の豪雨時斜面崩壊箇所との比較検討により、本モデルの適用性が確認された。さらに、透水係数、土層厚、安息角、土粒子密度など、モデル中のパラメータが崩壊発生個数に与える影響について感度分析を行い、斜面安定解析において重要なパラメータを特定している。, A landslide simulation model based on the Richards equation for the ground water flow and with assumptions of soil matrixes comprising three horizontal layers was prepared to simulate rainfall induced shallow landslides. The model is capable to explicitly calculate the change in pore pressure in response to transient rainfall. Infinite slope failure was assumed for the slope stability module. The numerical solution of the unsteady pore-water pressure was experimentally verified by the physical experiment. The model was used to reproduce the landslides occurred in 1973/10/26 at the Takora basin located upstream of Kizu river basin. Comparison of the result of transient rainfall model and steady state model was done by applying both models to simulate the landslide produced by the same rainfall. Performance of the transient response model is better compared to steady state model as the latter highly over-predicted the instability. Sensitivity analyses of some of the model parameter were also done which indicates that depth of the layers, soil angle of repose and soil density have great influence on the stability of the soil domain. Correct representation of their values and their proper spatial distribution are vital to enhance the performance of the model output.

1999年12月にベネズエラ北部のカリブ海沿岸で発生した洪水・土砂災害は, 災害原因となった自然現象ではわが国で起こったものからかけ離れて大規模であったとは言えず, また, 災害の起こり方においても, 規模の差はあるものの, わが国で生じているものと同様であった。犠牲者数でわが国の災害と大差が生じた原因は, 無秩序な土地利用と防災対策の立ち遅れであり, とくに都市流入人口によるスラムが危険地域に立地することが災害を激しいものにしている。本文では, 災害発生の自然的・社会的条件の分析と, 日本の状況との比較を通して上記の問題点を明らかにし, 今後の対応策についても言及している。, A severe rainfall in December 1999 caused numerous landslides, debris flows and flash floods on the Caribbean coast of Venezuela, and it killed 25, 000 to 50, 000 people.The natural phenomena themselves were as large and severe as the ones used to occur in Japan, and the types of hazards were also similar.Thereason for the far larger number of casualties than the Japanese cases is attributable to the lawless land utilization and the lagging of the countermeasures.The most important and difficult problem among othersis how to cope with the slums that locate on the most dangerous areas

岡山県中央部の高梁市にある備中松山城の大手門岩盤においては落石, クラックの進行, クリープ挙動が現れ, 対策工の必要性が指摘されている.この岩盤斜面について崩壊誘因と崩壊メカニズムについて検討した.風化の進行, 斜面末端の地すべり運動, および風によるクラックに貫入した樹根による揺さぶり等の諸要因による影響を解決するために離散要素法(DEM), 特にUDECプログラムを用い, 節理面に沿ったせん断変位に注目してシミュレーションを行った.さらに現在設置中の監視システムの最適化のための岩盤斜面の今後の挙動予測を行った., In this paper a rock slope failure of Bitchu -Matsuyama castle rock located near Takahashi city in the central part of Okayama prefecture is presented. Rock mass creep movement, which mechanism and triggering factors are studied here, endangers the castle, which walls are suffering damage and need to be repaired.In order to find the reason of the damage various triggering factors such as weathering progress, slope -toe erosion (toe sliding) and a special phenomena for this site - wind tree action are simulated using distinct element method (DEM), namely UDEC (Universal Distinct Element Code) as one of the numerical modeling codes.The joint shear displacements of several points are observed in the model as key factors for result comparison. Further a failure analysis of rock slope is carried out in order to find out the future behavior of the rock slope and optimize the design of monitoring system, which is in process of installation.

1999年12月14-16日にかけて南米ベネズエラで900mmを超える記録的な豪雨が発生し, カリブ海に面したバルガス州の多くの河川流域で土砂災害が発生した。本研究では, その中でカムリグランデ川流域を対象として, 流量ハイドログラフの見積もり, 土砂氾濫・堆積過程の再現計算, および砂防ダムと流路工による砂防施設配置効果を検討している。従来, 砂防ダムや流路工といった砂防施設の機能や効果を評価する場合, 水理模型実験を行うことが多かった。これは, 数値計算精度や基礎方程式の不確かさとともに, 複雑な構造物に対しては数値計算の境界条件が与えにくいといったことも原因していると思われる。しかしながら, 比較的単純な構造の施設であれば, 数値シミュレーションによる施設の評価はある程度可能であり, 経費的にも節約が図れるなど有効な手段と考えられる。, A disastrous debris flow occurred in the Camuri Grande River basin due to a heavy rainfall on December 16, 1999 in Venezuela. This paper shows the estimated debris flow hydrographs of the Camuri Grande River and its tributary by using one-dimensional simulation model, in which the grain size distribution of the riverbed materials is taken into account. Moreover, flooding and deposition processes on the fan of the river are reproduced using two-dimensional model, where calculated results obtained by one-dimensional model such as flow discharge, sediment discharge, and sediment diameters are used as inflow boundary conditions on to the fan area. In this model, the unstructured meshes are adopted to express the shape of the rivers, buildings, roads, and etc. in accurate on the fan. Calculated sediment deposited area and thickness of deposits correspond fairly well with the actual ones. The effects of countermeasures by Sabo dams and channel works against debris flow disasters are investigated by using one- and two-dimensional numerical model. The numerical simulation method is found to be very useful to evaluate the effectiveness of countermeasures such as Sabo dams and channel works.

近年, 平常時或いは中小出水時の土砂を通過させ, 土石流発生時の危険な土砂は捕捉する目的で透過性砂防ダムが設置されてきているが, その機能を定量的に評価できているとは言い難い。そこで, 昨年度開発した透過性砂防ダムの閉塞モデルをベースとして、本研究では, 透過性砂防ダムによる土石流堆積過程に着目し, 水路実験及び数値シミュレーションを行い, 透過性砂防ダムの土石流拝止機能を解明しようとしている。, Recently, many open-type sabo dams have been constructed. These dams have functions to pass through the sediment transported during normal floods downstream and store hazardous big boulders transported by a debris flow. In this study, we pay attention to the sedimentation processes of debris flow by a open-type Sabo dam, and flume experiments and numerical simulations are carried out to clarify the function of the open-type Sabo dam.

Preliminary discussion on the geomorphological conditions of characteristic ground surface movements induced by the 1999 Chichi Earthquake is presented on the basis of the field reconnaissance study in December, 1999.The displacement of the soft ground by the earthquake‐inducing fault was dominated by the horizontal movement and induced damage of structures. Two gigantic landslides visited in this study suggest that the dip of the intercalated mudstone and sandstone of the Neogene and the groundwater conditions determined the occurrence of large‐scale landslides.Extensive occurrence of surficial landslides suggests the importance of the weathering characteristics of coarse sedimentary formation of weak cohesion.

これまで, 格子型砂防ダムによる土石流捕捉モデルは種々開発されてきたが, ほとんどの場合は「確定的」に土石流捕捉率などが決定されている。本研究では格子型砂防ダムで巨礫が捕捉される過程は確率過程であるという概念に基づき, まず, 水路実験で格子型砂防ダムの閉塞パターンを明らかにすることで, この考え方の妥当性を検証するとともに, 石礫濃度と流速を種々変化させて土石流を発生させ, その時の瞬間閉塞確率を求めることによって, 確率的な格子型砂防ダム閉塞モデルを開発する。また, このモデルを用いて格子ダムの閉塞過程の再現計算を行う。, Debris flow disaster can be reduced by a grid-type dam, which traps large boulders but passes small size sediments in a debris flow through it. Various models have been developed to predict the trap rate of sediments by a grid-type dam using the characteristics of a debris flow and a grid-type dam. Experimental results show that a little difference of arrival time of a large boulder at a grid-type dam markedly affects the blocking mechanism even though the other conditions are the same. In this research, the blocking phenomenon is regarded as a stochastic process and a new stochastic model of blocking for a gird-type dam by large boulders in a debris flow is proposed.

本報では急傾斜都市における土砂動態を考慮した氾濫解析法を提示した。上流部の山地部では流出流量と土砂濃度のハイドログラフを求め, それより下流域の都市部に対する境界条件とした。都市部では全領域を河川, 道路, 堤内地に属性分けすることによって都市の諸要素を考慮に入れた非構造格子法を用いて, 土砂を含んだ二次元氾濫解析を行った。本モデルを神戸市の生田川流域に適用し, 土砂流出を考慮した場合としない場合の解析結果を比較し, 土砂を考慮した場合では考慮しない場合に比べて, 浸水深, 氾濫規模はともに大きく, より危険であるという知見が得られた。したがって土砂生産の盛んな河川流域の都市では, 土砂の影響を考慮した氾濫解析の必要性が確認できた。, This paper treats the inundation flow analysis in steep slope cities considering the effects of sediment.A computational river basin is divided into mountainous area and urban area. The hydrographs of discharge and sediment concentration in mountainous area are imposed as the boundary conditions of upstream end in urban area. The above model is applied to Ikuta River basin in Kobe. The results show that the extent of inundation is much severer than that of the case without considering sediment. So it has been found out that sediment influences inundation flow behavior considerably in the river basin with much sediment.

流れの全流動深にわたって高濃度に石礫が分散して流れている石礫型土石流, 石礫が流れているのは全流動深の内の下層部に限られ, 上層部は微細砂を浮遊しているだけの掃流状集合流動, 構成粒子が比較的細かく, 下層部は掃流状集合流動の場合と同様に粒子群が互いにほぼ平行に層流状に移動しているが, 上層部では水流の乱れによって粒子が高濃度で浮遊している中間型土石流, さらには, 中間型土石流の内, 下層部の厚さが非常に薄く, ほぼ全体が乱流状態である泥流状土石流(泥流)では, 粒子および水の運動に対して慣性の影響が強く働いており, 総括して慣性土石流と分類できる。本論文は, 粒状体の慣性流動に関する構成則と乱れによる粒子浮遊の式を基本として, 慣性土石流に関する統一モデルを提案するものである。モデルは実験によって検証されている。また, 以前に高橋によって, 各土石流のタイプに対して個別に与えられている理論が, 今回の理論と同様に適合性のよいものであることも示されている。, This paper gives a unified theory of the inertial debris flows applicable for all the subclassifications I.e., the stony, immature, hybrid and muddy debris flows. The stony debris flow is defined as the flow whose entire depth is composed of mixture of coarse particles. In the immature debris flow the coarse particle mixture layer occupies only a lower part of the depth and beyond that virtually no coarse particle are contained. In contrast to the stony and immature debris flows, the hybrid debris flow appears when the comprising particles are small and it is composed of lower particle colliding and jostling layer and the upper particle suspension layer. Of the hybrid flows that has only a thin particle colliding layer is called as the muddy debris flow. The unified theory is based on the constitutive equations for an inertial granular flow and the turbulent suspension equation. The experimental data confirm the theory. The theory also revealed that the previous Takahashi's simplified theory can predict the solids concentrations in the stony and in the immature debris flows equally well.

豪雨災害時の死亡原因の多くは崖崩れであり、福島県白河市周辺で多発していた。代表例が西郷村「からまつ荘」の土砂崩れであり、最上流部の谷頭2カ所で崩落した土砂が勾配10度程度の谷を高速地滑りを起こして流下した。郡山市での避難行動の調査により、ハザードマップは住民及び対策担当者双方にとって有効であること、避難行動手段として自動車の利用は地域の交通網状況、災害弱者救援などを考え有効に活用または規制する必要がある。, Landslide caused by the heavy rain around Shirakawa City, Fukushima, Japan, claimed large human loss. The land mass at Karamatsu slided at two places in the upper valley would flow on a mild slope down to the building, killing5persons.The field investigation inKoriyama reveals the efficiency of hazards map for people as well as city officers and importance of appropriate utilization of vehicles taking into account of traffic condition and flood area.

本研究では, MOS-1/MESSR, マルチバンド画像データと, 多時期のJE:RS-1/SAR画像データを用い, 土地被覆分類を行う手法を検討する。さらに, セル分布型土砂流出モデルを構築し, インドネシア・ジャワ島東部のブランタス川流域に適用し, 火山噴出土砂の流出解析を行なう。MOS-1/MESSR画像データのみを用いて土地被覆分類を行なったところ, 雲がかかっていて分類できない地域や不正確な分類となっている地域が存在した。そこで, 多時期のJERS4/SAR画像データによる土地被覆分類データを統合し, マルチバンド画像データのみによるものよりも正確な土地被覆分類を行なうことができた。次に, 1990年2月のクルー山の噴火によって大量に堆積した土砂の流出を解析することを目的とし, セル分布型土砂流出モデルを構築した。このモデルは, 流域を多数のセル(250m四方の正方形領域)の集まりとする分布型モデルで, 各セルにおいてkinematicwave法により降雨流出計算を行なう。土砂の流出は雨水流量に従い, 斜面のセルでは, 地表面流の発生に伴って土砂が生産され, 河道のセルでは, 流砂量式により決定される流砂量が流下するとしたモデルである。このモデルを主要な支川の一つであるプティー川およびそれを含むクルー山南西斜面域に適用し, 土砂堆積厚の空間的および時間的変化, ブランタス川への土砂の横流入をシミュレートすることが可能となった。, This paper describes (1) a method of land cover classification that uses both multi-spectral band images of MOS- 1/MESSR and multi-temporal images of JERS- 1/SAR and (2) a grid-cell based distributed runoff model that can estimate sediment runoff from volcanic mountain slopes in the Brantas River basin, East Java, Indonesia.As for (1), this paper indicates that the use of multi-spectral band images only does not produce very good land cover map, and the combination of MOS-l/MSSR and JERS-1/SAR can obtain more accurate land cover conditions of the basin. As for (2), the runoff model, which uses land cover information as well as a 250-in digital elevation models, can evaluate transition of spatial distribution of volcanic ash on the slopes.This paper illustrates the results of computer simulation with this model on temporal and spatial distribution change of sediment yield in the Putih River basin, a tributary of the Brantas and the basins on the south slope of Mt. Kelud, which erupted on February 10, 1990.

中間流・地表面流統合型kinematicwaveモデル, 表層崩壊予測モデル, 石礫型土石流モデルを結合することによって、山地流域を対象とした水・土砂動態モデルを構築する。本モデルは水の流れと土砂の移動を一次元的に解析し、連続的かつ一体的にモデル化するところに大きな特徴がある。本モデルを馬門川流域に適用し、従来用いられてきた二次元型のモデルの計算結果と比較したところ、表層崩壊の予測についてはほぼ同様の結果を得た。さらに、本モデルを単一の斜面素片に適用して土石流の計算を行なった。上流から土石流を流入させた場合には合理的な結果を得たが、上流から洪水流を流入させた場合には、土石流の運動方程式が切り替わるところで土石流流量が不自然に変動する結果となった。, A water and sediment flow model for a mountainous area is developed by combining a rainfall-runoff model, a slope failure model, and a debris flow model. The distinctive feature of this model is to calculate the water and sediment flow with one dimensional flow analysis.The model was applied to the Umakado river basin and the results were compared to those of the two dimensional model, which has been often used to predict the sediment yield from a mountainous area, and it was shown that the two models gave almost similar results. Then the model was applied to single slope unit to conduct debris flow simulations. When a debris flow hydrograph was given as the upstream boundary condition, the results were reasonable. However when a water flow hydrograph was given from the upstream boundary, the output debris flow hydrograph fluctuated unnaturally at which the equation of motion of the debris flow was replaced according as the density of the particles decreased.

Distribution of woody debris and sediment was examined in a mountain stream, northern Kyushu, southwestern Japan. A densely-welded pyroclastic flow deposit dominates the study basin, and forms steep sideslopes and a flat valley floor. The watershed was disturbed by a powerful typhoon in 1991, which leveled many trees on the hillslopes. Subsequent storm-triggered shallow slope failures deposited timber along streambeds. Channel morphology (gradient, channel width and sinuosity), location and volume of woody debris, and streambed sediment characteristics were investigated three and half years after the typhoon. Log jams of various sizes occurred in the channel ; the largest log jam was 100m long, had a volume of 3, 100m3, and was located along the middle reach of the research section. Principal component analysis of channel morphology and volume of woody debris and sediment suggests that sediment deposition is controlled by tractive force decrease owing to broad channel width and gentle gradient. The analysis demonstrates that there is no conspicuous relationship between volume of woody debris and geomorphic factors such as gradient and sinuosity. Field observations reveal that most log jams occur behind large boulders in the research section. Our results indicate that accumulation of woody debris is influenced more by topographic barriers such as large boulders than by channel morphology. We believe that the supply of boulders from sideslopes greatly influences the storage of woody debris in the investigated stream.

西南日本の大地震の活動をプレート聞及びプレート内地震の間の力学的な相互作用を考慮したモデルによりシミュレートすることを試みた.このモデルでは, それぞれの断層で測地データのインバージョンにより推定されたバック・スリップに応じて応力が蓄積し, それがしきい値を越えると地震が起き, 応力が再配分される.シミュレーションの結果, 相互作用によりカスケードや移動現象などの複雑なパターンが生じることが明らかになった.断層によって, 繰り返し間隔がある平均の周りにばらつくものと, 2-3の繰り返し間隔を持つものに分かれ, 後者は紀伊半島の周辺に多いことが示された.また, 初期値の小さな誤差により数百年後の地震活動に大きな差が生じることも示された., Activity of large earthquakes in southwest Japan is simulated with a model incorporating mechanical interactions between inter- and intraplate faults. In this model, stress on each fault accumulate by constant back-slip derived from inversion of geodetic data and, when cumulative stress of a fault is larger than assumed thresholds, that fault slips forward and stress is redistributed.The results of simulations show that interaction causes complex patterns (e.g. cascade, migration etc.). Recurrence intervals of events at some faults fluctuate around an average.Other group of faults, especially around the Kii peninsula, have more than two discrete recurrence intervals. Simulations indicate that small errors in parameters may produce large difference in seismicity after hundreds of years.

すべり面液状化現象は砂質土地すべり高速運動の原因の一つとなる。佐々らは「すべり面液状化現象」, すなわち非排水条件下でのせん断ゾーンにおける粒子破砕に伴う過剰間隙水圧の発生によるせん断抵抗が低下するというメカニズムを提案した。本研究では, リングせん断試験機を用いて, 三種類の砂質試料について, a)定圧定速度排水せん断試験, b)定圧定速度非排水せん断試験, および, c)設定した斜面条件での一定振幅の繰り返し載荷試験を行い, 砂質土斜面のすべり面液状化の発生過程, 特に粒子破砕の起こり易さと過剰間隙水圧比の関係を調べた。その結果, 以下の結論が得られた:(1)砂質土のすべり面液状化現象は土粒子破砕の起こり易さと密接な関係がある。粒子破砕の起こりやすい材料ほどすべり面液状化を起こし易い;(2)砂質土のすべり面液状化の指標となる過剰間隙水圧比は, 速度制御や繰り返し載荷に関わらず, 試料の特性とせん断距離に関連する;(3)砂質土のすべり面液状化の発生は排水せん断試験中の沈下量より推定できる;(4)繰り返し載荷の周波数, 初期応力状態、及び初期密度は過剰間隙水圧の発生に影響する。, To study the mechanism of rapid landslide, especially, the factors affecting high-mobility, three series of ring shear tests (drained speed-controlled test, undrained speed-controlled test and undrained cyclic-loading test) were conducted by ring-shear system.The employed samples were Toyoura standard sand, silica sand and Osaka group coarse, sandy soil. Excess pore pressure ratio, expressed as excess pore pressure with respect to the initial effective normal stress, was used as an evaluation index for the degree of mobility.The test results showed that, in the soil susceptible to grain crushing in drained tests, the pore pressure generate easily both in undrained speed-controlled test and undrained cyclic-loading tests.Parametric studies, involving initial stress state, initial relative density, and frequency of cyclic-loading were also performed.

平成9年7月10日午前1時頃, 鹿児島県出水市針原地区で発生した土石流によって, 死者21名, 負傷者13名がでる災害となった。本研究では, 洪水流出解析を行って針原川の洪水流出特性を検討するとともに, 深層斜面崩壊を模擬して土石流を発生させた数値解析を行い, その氾濫・堆積過程の再現を試みる。さらに, この計算結果をもとに, 計画を上回るような土石流に対して今後どのように取り組めばよいかについて言及する。, A severe debris flow disaster occurred at the Harahara River, Izumu City, Kagoshima Prefecture, Japan at the midnight of June 10, 1997.Twenty‐one persons were killed and 18 houses were destroyed by the debris flow. The debris flow was caused by a big slope failure with sediment volume of 160, 000 cubic meters due to heavy rainfall.In this paper, a numerical simulation was performed to explain the behavior and the depositional processes of the debris flow.The actua phenomena such as a sediment depositional area. And a thickness of deposits are fairly well explained by the the calculation.

仙台湾の海底や仙台平野を構成する土砂の主要な供給源の一つとして阿武隈川がある。近年、阿武隈川の河口に隣接する海岸の沿岸漂砂下手側海岸が侵食する傾向にあり、土砂供給源としての阿武隈川の特性が変化していることを示している。そこで、阿武隈川河口の周辺で実施されている、さまざまな機関の観測結果を収集してそれらを解析し、阿武隈川が海域に排出する土砂の、短期的および長期的な輸送速度を推定した。, The Abukuma River was one of the major sources to supply sediment constituting the bed of the Sendai Bay and Sendai Plain.However the north coast neighboring on the river mouth, which is the lee side for the long shore drift, has been eroded since about twenty years ago. It means that the role of the Abukuma River on the sedimentary source has been changed.sedimentary source has been changed. This paper evaluates the efflux rate of sediment in long and short time scale, by collecting data observed around the river mouth and by analyzing these data.

空中写真判読から検出したリニアメントを、山地の地形発達史の過程で現出する各種のスケール、プロセスをもつ変形構造の空間的実態、広域テクトニクスとの関連のもとに考察し、地塊山地の山体崩壊の潜在的発生とその位置の特定を試みた。潜在大規模崩壊の発生、位置、規模、形状は急速に隆起する山地の変動地形学的位置条件や山体を構成する花筒岩と堆積岩との岩質差と構造に規定されながら進行していることを明らかにした。, The aim of this paper is to describe lineaments pattern, and forecast the site and type of potential-large slope movement in Hira Range.The results of research are summarized as follow:1) Main lineaments which interpreted from aerial-photographs, in the range is shown Fig.3. The author classified them into 5 types, as A, B, C, D, and E-type.2) A, B, and C-type of lineaments are controlled by tectonic movement, formed under compression stress in up-building process of the range.3) From examined with the drainage pattern, extent, locality, active fault, slope type and direction, he obtain a understand, D and E-type lineaments have close relations to sagging, derive from release of stress in basement rock which compose the surface of the range. It seems a sign of large slopemovement.4) Saggings are recognized on both side slopes of the range, and it makes progress difference in type and size. Numerous Toppling-type of deformations are dominant in the east half of the range , composed granite. Sliding type deformations progress in the west-half of the range, composed the Paleo-Mesozoic Sedimentary rocks.The influence of bedding structure of rock is clear.5) Tectonic displacements are very dominant in Hira Range and its surroundings and the influence to large slope movement is very close.

土中を流れる浸透流が地震時の斜面崩壊にどのような影響を与えるのかを明らかにすることを目的として、浸透流を有する斜面模型に種々の地震外力を与える実験を行った。土中の加速度、間隙水圧、および斜面の変形に関するデータを計測することにより、土中の間隙水圧の変化と崩壊発生との関係を検討している。, In order to clarify the effects of the seepage flow on the slope failure due to earthquake, . Physical experiments were done by using shaking table under the several conditions of seismic force, depth of seepage water, shaking direction and so on.The relationships between pore pressure and the occurrence of slope failure are discussed form experimental data.

避難計画を立てる場合, 最適な避難地や避難経路を行政側だけでなく地域住民が周知しておくことが重要である。本研究では, GISのネットワークデータを利用した住民の避難行動の解析方法を示すとともに, 実流域を対象として老人や子供歩行速度を考慮した避難行動の解析を行って避難所要時間を求めている。さらに, これに基づいて新たな避難施設を設置した場合の効果についても検討している。, Non‐structural countermeasures, such as residents living in the hazard area taking refuge before the onslaught of a debris flow, is effective for saving lives.A simulation method for evacuation is presented that is based on a refuge network, built using the GIS (Geographic Information Systems, ARC/INFO).Visual display of the act of evacuation is very useful for both the administrators and residents of the basin.

粘性土石流が頻繁に発生する渓流で, 土石流の観測と地形変動の調査行って, 次の成果を得た。チベットの古郷溝では, 1950年代に活発な土砂生産のため谷の開析が急激に進行したが, 最近では, 侵食速度が当時の1/10以下に低下している。雲南省の蒋家溝では粘性土石流が頻発して, つぎのような河床変動が進行している。侵食域における一年あたりの侵食深と, 堆積域における堆積深はともに最大2-3mに達するほど河床変動が活発である。土石流通過域における堆積は, 主として間欠流の繰り返しの過程で進行するのに対し, 侵食は, 間欠流に後続する連続流の出現中に進行するという特徴がある。, Among the various types of debris flow in China, viscous debris flow distributes vastly, and the hazards caused by it is a big problem. According to the data of debris-flow hazard, the hazards caused by viscous debris-flow amounts to 65 % of whole debris-flow hazards in recent 100 years. It mainly distributed in Yunnan, Sichuan and Tibet. The change in the elevation of the stream channel due to scouring and deposition is significant, the speed of the change is very fast. Any hyperconcentrated stream flow does not induce such a large change. The change in viscous debris-flow channel is mainly controlled by erosion and deposition by debris flows, which are affected by the conditions of gully topography, longitudinal slope gradient, geologic property, drainage scale and the dynamic action of debris flow.This article emphasizes the change in ravines of viscous debris-flow over several years, as well as in one year and by one event of debris flow.

中国雲南省の蒋家溝で典型的な形態が見られる粘性土石流を, 同様の粒度分布を持つ材料による水路実験によって再現した。これにより, 慣用とは相違して, 粘性土石流をニュートン流体としてモデル化するのが適切であることや, 流れの粘性係数, 粒子支持機構, 堆積および侵食の機構, 間欠性の発生原因, 抵抗則等の解明への道筋が明らかになった。, The viscous type debris flow, that typically arises at the Jiangjia gully, Yunnan Province, China, is generated in an experimental flume using the sediment mixture material similar to that in the Jiangjia gully. Different from so far many modellings, the experiments showed that the flow can be well modeled as a Newtonian fluid with very high viscosity. By discussion on the interpretation of the experimental results, the near future approach to the quantitative estimations of the viscosity, the particle supporting mechanism in a laminar flow, depositon and erosion processes, cause of intermittency, resistance law, and so on is made clear.

本論文は、地表踏査, 既存試料から地質解析を行い、華清池地すべりの地すべりブロックを区分し、運動履歴の多いIブロックについてその規模を特定し、安定解析および対策工の検討を行ったものである。対策工の選定においては、我が国で信頼性, 実績が豊富な深礎杭工+アンカー工法の採用が望まれるが、中国という地域的特徴を考慮し、今回新たに、多段鉄筋コンクリート(RC)杭の「竪坑方式」と「横坑方式」を提案した。, Many faults were developed at Lishan, a hill at the back of the Huaqing Palace. And landslide topography and creep topography restricted by these faults were recognized. Because of these, the existing geology was analyzed this time, landslide blocks were divided by the reconnais-sance of site, the scale of BlockI having significant kinetic hysteresis was specifically designated, and stability analysis and landslide prevention measures were investigated. In the slope stability analysis, investigations were made not only for ordinary times but also for the time of earthquake.Also, in selecting the prevention measures, milti-stage vertical RC piles and horizontal RC piles were proposed by considering the regional characteristics in China.

中国華清池(驪山)地すべりの発生機構の一つとして, 岩盤のクリープ運動が考えられている。有力なすべり面と考えられている断層を挟む2種の片麻岩(上盤をLGNA, 下盤をLGNBと呼ぶ)が採取され, 室温で封圧40MPaまでの, 圧縮強度と残留強度が測定された。両者の強度およびその封圧依存性は等しいことが判明した。LGNAは異方的な結状構造が発達し, これに沿った巨視的なクラックが形成されている。一方, LGNBは巨視的には等方的である。これらの結果から, LGNAの方が空隙率が大きいことを考慮すると, 2種の岩盤境界の間隙水圧が大きくなる可能性があり, この境界のすべりが予期されると考えられる。, Two gneisses from the Lishan landslide slope were studied experimentally, for understanding the mechanism of Lishan landslide.These two rocks are situated faced to a possible potential sliding surface, upper bedrock LGNA and lower one LGNB.LGNA has an extensive anisotropic structure of mylonitized foliation, while LGNB is isotropic.The compressive strength and the residual strength of these rocks were measured at room temperature under a confining pressure up to 40 Mpa.Both rocks have the same compressive and residual strengths and the same pressure dependencies.The compressive strength for the LGNA sample with foliation oriented at 30°to the compressive stress direction is close to the residual strength.LGNA has higher porosity thanLGNB.These results suggest that a high pore pressure could be possibly formed in the boundary between these bedrocks and the boundary could form a potential sliding surface.

中国雲南省の蒋家溝を対象に, 粘性土石流のメカニズムと土石流対策に関する観測調査を行って, 土石流が降雨の発生時刻からかなり遅れて発生すること。土石流が, 多数のサージが間欠的に流下するという一連のイベントからなっていて, その間欠性は, 降伏応力を用いたモデル, 天然ダムの決壊モデル, 流れの不安定性に基づくモデルを用いて説明が試みられていること。砂礫の濃度が著しく大きいにもかかわらず, 土石流が流れ易いこと。流動中の土石流には栓流が存在しないこと。さらに, 蒋家溝の中下流域での, 土石流発生に伴う地形変化が災害発生ポテンシャルを高めていること。禿げ山化した山地の緑化が進められた結果, 土石流発生などの土砂流出抑制効果が認められたが, そのメカニズムの検討が課題であることを述べた。, The observational study on the viscous debris flows at Jiang-jia Creek in Yunnan Province, China clarified the following points. The time delay of one to five hours from the beginning of rainfall to the onset of debris flow may be ascribed to an accumulating process of slurry from tributary gullies to the main channel bottom at the source reach of the debris flow. The intermittence of debris-flow surge may be explained through the mechanism either of or a complex of an yield strength model, a model of a series of breaching of small natural dams, or a model of an instability of the flow itself. The absence of plug-flow phenomena in the viscous debris flow indicates the yield strength of the flow is unexpectedly small, and a new alternative model is necessary to explain the mechanism of viscous debris flow. The field survey of the countermeasures against debris flows in Dongchuan County over five years showed the tree-planting project at mountain slopes in these several years may have been effective in increasing the slope stability, suppressing sediment discharge and debris flows. Further study is needed to evaluate this effect of countermeasure quantitatively.

1991年に開始した中国西安市驪山地すべりの予測のための日中共同研究の成果を概観する。華清池後背斜面は大規模潜在地すべりである可能性があり、この斜面が崩壊した場合、宮殿のみならず臨憧県の中心部の住宅密集地を直撃し大災害になる。斜面変形の観測とボーリング、調査トンネルによる地質調査により、この斜面が現在大規模岩盤すべりの前兆である岩盤クリープの段階にあることがわかった。リングせん断試験等の土質試験の結果、この驪山の岩盤すべりは1903年のカナダ・フランク地すべりや1983年中国・Sale山地すべりのように飽和沖積層への非排水載荷のメカニズムによって長距離運動するであろうことを示している。将来起こるであろうこの地すべり災害を防ぐためには、以下の2通りの災害の危険への備え、すなわち1)斜面運動の自動観測システムの設置、2)クリープ中の岩盤斜面の安定化工法、を遅すぎることのないよう早急に実施することが必要である。, Results of the Japan-China joint Research on Assessment of Landslide Hazard in Lishan, Xian, China which have been carried out since 1991 were summarized. The slope behind the Huaqing Palace had been suspected to have a potential large-scale landslide which may fail the Palace and the center of Lintong county.Monitoring of slope deformation and geological investigation by boring and investigation tunnel during this joint research exposed that this slope is now in the rock creep process of large scale rockslide. The geotechnical test proved that this rock slide mass must travel long like the 1903 Frank Slide in Canada and the 1983 Sale landslide in China in the undrained loading mechanism onto the saturated alluvial deposit in Lishan. To prevent or mitigate the coming disaster, two ways of landslide risk preparedness should be taken without delay. 1) to install automatic monitoring system of slope movement, and 2) to stabilize the creeping rock slope.

本報では1995年兵庫県南部地震により六甲山系で発生した山腹斜面崩壊の特徴を発生位置, 分布, 面積および土量, 方位および局所地形条件等からまとめた。次いでこれらの特徴および崩壊発生後の現地踏査結果より, 地震時において出現したと考えられる崩壊機構をトップリング型と推定し, HoekとBrayが提案している階段基盤上に生じるトップリングの極限平衡解析モデルを用いて地震動を外力として作用させ, そのとき得られる極限内部摩擦角φLを用いて, 地震時に働いたであろう震度の推定を試みた。

In mountainous rivers, huge rocks are scattered on river bed which have been supplied by debris flows or side slope failure caused by heavy rainfalls or earthquakes.The rocks can not be transpoted by medium or small floods, and affect stream channels variation and sediment runoff.In this paper, flume tests are conducted to investigate the process of channel variation where gravels are set along the banks of the stream channels in order to clarify the relationship between arrangement of rocks and stream channel variation.Numerical simulation model is also proposed to calculate the channel variation, and the results of the calculation are compared with the data obtained from the flume tests.

A theory for the mechanics of the Merapi type pyroclastic flow is presented, in which the self-excited fluidization of the bed due to upward movement of the gas emitted from the pyroclastic material itself plays an essential role.The main body of the flow comprises the base layer and the fluidized layer on it. In the base layer particles are sustained by the contact force between the particles and the energy is consumed mainly by friction, whereas in the fluidized layer particles are sustained by the up-lifting force of the upward gas flow and the large scale turbulent mixing of the mixture of particles and the gas is the main cause of consumption of energy. The solids concentration in the main body is nearly uniform and the formulae to predict the thicknesses of the base as well as the fluidized layers, velocity distributions in the base as well as the fluidized layers and the resistance to flow of the main body are obtained. The laboratory flume experiments prove the theory is valid and that theory well predicts the velocity of the real pyroclastic flow observed at Unzen and Semeru volcanos.The solids concentration and the velocity distribution in the hot ash cloud layer which exists above the main body are also discussed.The process of deposition downstream of the change in slope is observed and some important characteristics are made clear.

A magnetically shielded room (MSR) for paleomagnetic and rock magnetic experiments was constructed at Sakurajima Volcanological Observatory. The remaining dc magnetic field is less than 50 nT, one thousand of shielding factor with regard to the geomagnetic field, at inside the MSR. The MSR is surrounded by two layers of permalloy plate, and has no tight door and maze-like walls. Instruments for paleomagnetic measurements were installed in the MSR with taking special care for the disturbing magnetic field created by the instruments themselves. This MSR and instruments may produce very low noise environment for paleomagnetic experiments.

Sand pocket is used to store the harmful sediment discharge, and reduce the peak of sediment discharge.It has a wide dam at the downstream end, and the width of river is made larger than the ordinary channel width.In this paper, flume tests are performed to investigate the processes of sediment deposition in sand pockets, in terms of the parameters; the initial bed slope and the length of the depositional area.One dimensional simulation method was applied to the deposition processes in sand pocket.In the model, the effect of the transverse variation of a stream channel is considered, and also the permeation of the flow was included. The results of numerical simulation were tested by flume data.

Sediment yield is characterized by various regional factors including geology, topography, weather and vegetation. So many factors are relevant to the phenomena of sediment yield that prediction is rather formidable task and it needs untiring observation of the realities of the phenomena. The present research has been carried out considering that sediment yield depends mainly on the gradient of slope, and the real situation of sediment yield was clarified through observation and survey of actual slopes in the field.

The equations for describing the particle sustaining pressure and the shearing stress in a viscous debris flow are proposed under the assumption that the micro-flow structure of the interstitial fluid induced by approaching and receding of the lined up particles in the adjacent upper and lower layers plays major role. The two such fundamental equations give the vertical particle concentration distribution and the equilibrium particle concentration with which the flow continues to run down neither deposition nor erosion. The viscous debris flows on a rigid bed are classified into five categories by the relationship among the supplied particle concentration, the equilibrium particle concentration and the critical particle concentration to guarantee the particle sustainment by the action of micro-flow structure of the interstitial fluid. The vertical distribution of the first approximation of the mean velocity is obtained by assuming uniform particle concentration in the particle mixture layer which appears in the lower part or in the entire depth depending on the flow category it belongs.The theoretical considerations are proved valid by the laboratory experiments and the parameters included in the discussion are assessed. In general, the apparent viscosity of the debris flow is far larger than that of the interstitial fluid by both the effects of decrease in the shearing area and micro flow structure in the interstitial fluid.The experiments revealed that the ratio of the two effects is different depending on the viscosity of the interstitial fluid.The equilibrium concentration of the particle in the experiments is not much different from that of the stony type debris flow. Therefore, the mechanism of the viscous debris flow freighting much more particles than the experimental debris flow and still flows on gentle slope with fantastic speed that mainly appears in China needs further discussions and experiments using nonuniform materials.

The flow characteristics of fine sands and water mixture is discussed in terms of experimented results concerning the flow resistance, sediment concentration profiles and sediment diffusion. (1) Flow resistance does not change so much in the range of sediment concentration less than 10 percent by volume, but increases gradually and then rapidly with increase of the sediment fraction. (2) The profiles of sediment concentration can be evaluated well by Rouse's formula in the low range of sediment fraction. These tend to be uniform when the sediment fraction increases. (3) Turbulent diffusion coefficients of tracer particles decrease almost linearly with increase of sediment fraction.These facts indicate that some stresses except Reynolds ones dominate above the range of general open channel flows with suspended loads.

Observational studies on the runoff, sediment yield and the sediment transport have been carried out in an experimental basin, the Ashiaraidani creek (6.5 km^2), which is a tributary of the Jintsu River.(1) The relation between sediment yield and rainfall, slope grade are examined, to clarify the processes of sediment yield in various slopes, taking seasonal variations as well as site conditions into accounts. (2) The relation between sediment runoff and sediment storage in the steep channel with pools were investigated in the Hirudani creek (0.85 km^2). (3) The occurrence of debris flow were investigated with attention forcused on rainfall intensity in the Shiramizudani creek (2.1 km^2).

A big landslide of 3.5 × 10^7m^3 ccurred at the Saleshan mountain, Gansu Province, China on 7 th March 1983. It moved at a high speed (13-14 m, sec at average) and killed 227 persons and destroyed 585 houses.The landslide mass slid down from a steep slope and rode on the quaternary alluvium and moved over about 800 m until the Baxie river.Sassa, 1989 has developed a new high-speed high-sress ring shear apparatus to estimate the friction angle during the motion of large-scale landslides. We took the sample from the quaternary alluvium on which the Saleshan landslide moved. In use of this sample, the authors performed tests to estimate the shear strength during mation under rapid loading using the high-speed high-sress ring shear apparatus. This rapid loading tests presented a small apparent friction angle during motion in the Saleshan landslids.Sassa, 1988 proposed a new computer simulation model for the motion of landslides. This method was applied fur this Saleshan landslide using this measured apparent friction angle. The result almost reproduced the real motion of the Saleshan landslide.