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令和元年（2019 年）東日本台風による斜面変動に関して，宮城県丸森町とその周辺に発生した斜面崩壊地の岩石と土層の諸物性，および岩手県重茂半島と普代村の斜面崩壊地付近の岩石物性について調査した．その結果，表層崩壊が多発した花崗閃緑岩斜面では，土層は，主に原位置風化により，表層に向かって物理的・化学的風化が進行していた．すべり面は，風化程度の小さな高透水性の粗粒土からなり，ハロイサイト（10 Å）が含まれていた．凝灰岩斜面では，すべり面の斜面勾配が小さい（5º ～10º）崩壊が発生しており，土層は粘性土であり，すべり面は低透水性であり，一部にはスメクタイトとハロイサイトが含まれていた．堆積岩斜面では表層崩壊が発生しており，すべり面には泥質岩起源のスメクタイトを多く含む低透水性の粘性土と硬質な砂礫質岩が露出していた．重茂半島・普代村と丸森町の花崗閃緑岩の鉱物組成は類似していた．また，重茂半島の溶結凝灰岩は，花崗閃緑岩と比較すると，風化を受けやすい黒雲母を欠く細粒の岩石であった．We investigated rock and soil properties for the slope failures induced by Typhoon Hagibis on October 2019 near Marumori Town, Miyagi Prefecture, and the Omoe Peninsula and Fudai Village in Sanriku coastal area, Iwate Prefecture. The soil layer was physically and chemically weathered toward the ground surface mainly due to in-situ weathering in the granodiorite slope where shallow slope failure occurred frequently. The slip plane consisted of weakly weathered, highly permeable, coarse-grained soil and contained halloysite (10 Å). Cohesive soil layer was formed in the tuff slope where some slope failures occurred along the gentle slip plane (5º to 10º). Soil in the slip plane was low permeability, and smectite and halloysite are contained. Some shallow slope failures occurred on the sedimentary rock slopes, and harder gravelly rock and low-permeable cohesive soil containing a large amount of smectite derived from muddy rock were exposed on the slip plane. The mineral compositions of granodiorite were similar each in the Omoe Peninsula, Fudai Village and Marumori Town. Compared to granodiorite, the welded tuff in the Omoe Peninsula was fine-grained rock lacking biotite which is easily weathered.

令和元年（2019 年）東日本台風によって宮城県丸森町周辺と岩手県三陸海岸沿いでは，多数の斜面変動（斜面崩壊や土石流）が発生した．土砂移動分布図の作成や現地調査により，斜面変動の分布を調査し，それらと雨量・地質との比較を行った．斜面変動は，火山岩類や付加体などの堆積岩類の分布域と比べて，花崗岩類の分布域に多く発生した．花崗岩類の分布域では，概ね6 時間雨量と24 時間雨量がそれぞれ約180 mm，約300 mm を超えると斜面変動が増え始め，特に，6 時間雨量が約250 mm かつ24時間雨量が約400 mm を超える場所では斜面変動が密集する傾向がある．斜面変動の発生頻度や個々の斜面変動の規模・流出土砂量は，各地域の雨量差を反映して，丸森町付近が最も大きく，次いで重茂・船越半島が大きくて，普代村はそれより小さいと考えられる．Serious slope disasters were induced by Typhoon Hagibis on October 2019 near Marumori Town, Miyagi Prefecture and Sanriku coastal area, Iwate Prefecture. The distribution of slope movement (e.g. slope failure, debris flow) was investigated by developing a trace map of sediment movements by air photo interpretation and field survey, and the rainfall distribution and geology were compared. Slope movements occurred more frequently in the area of granites than in the areas of volcanic rocks and sedimentary rocks such as accretionary prisms. In the area of granites, slope movements began to increase when the 6-hour rainfall and the 24-hour rainfall exceed about 180 mm and 300 mm, respectively. The slope movements concentrated in slopes where 6-hour rainfall exceeds 250 mm and 24- hour rainfall exceeds 400 mm. The occurrence frequency, size and amount of sediments of slope movements were the largest near Marumori Town, followed by the Omoe and Funakoshi Peninsulas, and smaller in Fudai Village, reflecting the differences in rainfall in each region.

2021年2月福島県沖の地震によって被害が生じた福島県，宮城県において，被害状況の特徴を把握するべく，現地調査を実施した．本調査では，2つの目的を設定した．1つは，今回の地震の被害推定の被害実態との誤差検証，もう1点は，新型コロナ感染症下の行政（避難所）対応状況についての調査である．調査は車内からと徒歩とで行い，撮影した写真は随時「令和3年2月福島県沖地震：災害調査写真マップ」で公開した．今回の地震の被害推定と被害実態との誤差については，調査した区域に限定した結果ではあるが，推定された家屋倒壊数ほどの被害は発生していなかったことが確認できた．宮城県山元町坂元地区に比べて地震動の影響は相対的に小さいと推定されていた福島県新地町の住宅地域では，軽微な被害ではあるが家屋の屋根損壊棟数が多く，坂元地区に次ぐ破損棟数の地域であったことがわかった．なお，現地での被害項目としては，ブロック塀の倒壊なども一部では確認できたが，大部分が屋根の破損であった．また，新型コロナ感染症下の避難所の受付はアクリル板で区切られ，消毒，検温が実施されていたが，今回はフェースシールド，防御服までは使われていなかった．今回の避難所で特筆すべきは，これまで避難所内では見ることのなかったテントが，感染防止とプライバシー保護のために用意されたことである．We conducted a field survey in Fukushima and Miyagi Prefectures, which were damaged by the 2021 Fukushima Offshore Earthquake, in order to understand the characteristics of the damage. In this survey, we set two objectives: one was to verify the error in the estimation of the damage caused by the earthquake compared with the actual damage, and the other was to investigate the status of administrative (evacuation center) response under the COVID-19 infection countermeasures. The survey was conducted both from the car and on foot, and the photos taken were published on the “2021 Fukushima Offshore Earthquake: Disaster Survey Photo Map” as needed. As for the error between the estimated damage of the earthquake and the actual damage, it was confirmed that the damage was not as great as the estimated number of collapsed houses, although the results were limited to the surveyed area. In the residential area of Shinchi Town, Fukushima Prefecture, which was estimated to be relatively less affected by seismic motion than the Sakamoto area of Yamamoto Town, Miyagi Prefecture, the number of damaged roofs of houses was large, although the damage was minor, and the area was found to have the second largest number of damaged houses after the Sakamoto area. Some block walls were found to have collapsed, but most of the damage was to roofs. The reception area of the evacuation center for the new coronary disaster was separated by an acrylic panel, and disinfection and temperature checks were conducted, but face shields and protective clothing were not used this time. What is noteworthy about this evacuation center is that tents, which have never been seen in evacuation centers before, were prepared to prevent infection and protect privacy.

紀伊半島の白亜系付加体である日高川層群の分布域で，平成23年の台風12号によって発生した斜面崩壊と土石流の特性を分析した．日高川層群は，沈み込む海洋プレートによって付加体深部に押し込まれたため，破壊により細片化した岩石からなるので，風化によって最終的には細粒物質を中心とする厚い風化層ができる．しかし，地下深くの高圧で強く再固結した岩石でもあるので，風化・侵食に強く高い山を形成しており，山腹斜面の河床からの比高は四万十帯の中で最も大きい．山腹斜面に生成された細粒の風化物質は，山腹斜面の全面で一斉に崩壊を起こす場合と，分割して崩壊する場合とがある．前者の場合は，先行河川である緩傾斜の本流の河床に崩落することが多く，その場所に厚く堆積して天然ダムを形成することも多い．後者の場合は，山地の隆起ととともに形成された急傾斜の渓流に崩落することが多く，土石流に転化して渓流沿いに長距離流下する．他の地質帯と異なり，このような２つのタイプの斜面崩壊/土石流が発生する日高川層群地帯では，これらを認識できるような防災教育が必要で，そのための地域住民向けの教育素材も考案した．, I analyzed the characteristics of slope failures and debris flows caused by typhoon No. 12 in 2011 in the distribution zone of the Hidakagawa Group, which is a Cretaceous accretionary prism on the Kii Peninsula. Since the Hidaka River Group is pushed into the deep accretionary prism by the subducting oceanic plate, it is composed of rocks that have been fragmented by fracture, weathering eventually results in a thick weathered layer centered on finegrained material. However, since it is also a rock that has been strongly reconsolidated at high pressure deep underground, it forms a high mountain that is resistant to weathering and erosion, and the relative height from the riverbed on the hillside slope is the highest in the Shimanto geologic belt. The fine-grained weathered material generated on the hillside slope may collapse all at once on the entire surface of the hillside slope, or it may collapse separately. In the former case, it often collapses on the riverbed of the gently sloping mainstream, which is the preceding river, and often accumulates thickly at that location to form a landslide dam. In the former case, it often collapses on the riverbed of the gently sloping mainstream, which is the preceding river, and often accumulates thickly at that location to form a landslide dam. In the latter case, it often collapses into a steep mountain stream formed with the uplift of the mountains, and it is converted into a debris flow and flows down a long distance along the mountain stream. Unlike other geological zones, in the Hidaka River Group where these two types of slope failures / debris flows occur, disaster prevention education that can recognize these is necessary, and educational materials for residents have been devised for that purpose.

変位計測による斜面崩壊の危険度評価手法を最前線で活動する消防の立場で用いる場合，計測機器の設置の手間や，設置時に専門知識を要するなど，実装には現状としての課題が多い．そこで，現場での救助活動に対する即応性，設置の容易さ，広範囲の安全監視，専門知識が不要な計測手法を念頭に考慮し，非接触の距離計測をリアルタイムに行うことができるデプスカメラに着目した．本研究では，模型斜面の崩壊実験の過程をデプスカメラで計測し，その有効性を検証した．その結果，精度においては分解能の限界や計測値のばらつき等の課題はあるものの，近距離での計測においては，降雨時という悪条件下においても微小な変位の計測が可能であった．そのため，より高精度のデプスカメラを用いれば，遠距離計測でも微小な変位の検知が可能となるため，既往の変位計測による斜面崩壊予測への適用や消防活動時の安全監視の補助ツールとしても適用が期待できる．This study investigates the effectiveness of using a depth camera to detect the risk of slope failure. There are many challenges to be met when applying methods for evaluating the risk of slope failure to safety monitoring during rescue activities at a disaster site, because setting the instruments requires a considerable amount of time and technical knowledge. We therefore focused on a depth camera because it is easy to use, easy to set and can monitor a wide area. In this study, we conducted a model slope failure test to verify the effectiveness of deformation measurement with a depth camera. The results indicated that a depth camera can detect a minute slope deformation over a short distance even under rainy conditions. However, greater depth resolution and a stable measurement depth are required for accurate long distance measurements. Therefore, a minute slope deformation over a long distance could be detected by using a high-precision depth camera, which could also be applied to a slope failure prediction method and as a tool to support safety monitoring during firefighting (rescue operations).

Geohazards have occurred almost every year and their mechanisms have been still being newly found. The physical principles that control landslides are rather simple and mostly already known, but the diversity in geological conditions beneath the ground surface makes it difficult to make models and to do quantitative analysis for their prediction and mitigation. Here, various cases of landslides induced by rainstorms and earthquakes are reviewed and new mechanisms found from them are introduced.

平成29年7月5~6日に生じた平成29年7月九州北部豪雨によって, 福岡県朝倉市から大分県日田市にかけて斜面崩壊・土石流・河川氾濫などの被害が発生した. 被災地域の山地・丘陵地は, 花崗岩・変成岩・石英安山岩質火山岩などからなり, 地質によって流出土砂の様相が異なっていた. 河川流路の攻撃斜面での洗堀に伴う被害が顕著であるほか, 流木の集積箇所からの流路側方への氾濫が顕著に認められた.

2018 Eastern Iburi Earthquake induced over 8000 landslides in an area of 400 km2 with the seismic intensities of 7 and 6+. Most of the landslides were of pyroclastic fall deposits and highly mobile. Those deposits were of Ta-d pumice of 9 ka and En-a pumice of 20 ka, and their sliding surfaces were made within specific beds, which were the bottom of Ta-d, reworked Ta-d in its base or reworked En-a beneath Ta-d, or volcanic soil with pumice grains beneath the Ta-d or volcanic soil beneath En-a. The materials that accommodated the sliding surfaces were heavily weathered to be rich in halloysite, which mineral has been found from the sliding surface materials of previous earthquake-induced landslides of pyroclastic fall deposits and is supposed to be very weak to earthquake shaking. The depths of the landslides varied from 2 to 3 m. Most of the beds that slid were undercut at the lower portion of the slopes, because of man-made cutting or convex slope breaks of which origin is in dispute.

2017 年九州北部豪雨では，氾濫，土石流，斜面崩壊による被害が多く生じた。北野平野の氾濫は，自然堤防は非浸水か浅い浸水，後背湿地と旧河道は深さ1 m を越す浸水となった。氾濫時の水深は氾濫原の微地形を反映し教科書的な被害となった。三郡山地南端部では，表層崩壊や地すべり性崩壊起源の土砂が土石流化し，家屋，河川施設に多くの被害が生じ，また複数の学校が被災した。被災した各学校は周囲に比べ小高い豪雨災害には比較的安全とみなされる地形に設置されていた。しかし地形判読の結果，各学校は，未離水の地形では堆積，離水した地形では河川の側方侵食に伴う被害を直接受けており，また学校周辺の通学路も氾濫被害や土砂災害を被った。それら被害も学校の災害対応を困難にした。各学校での聞き取り結果から，山地に近い方が警戒対応は早いが，全児童・生徒下校に要する時間は，経路被災の影響で時間を要したことが分かった。また未離水の地形に注意する施設配置の重要性も分かった。したがって学校安全には，校地周囲の詳細な地形区分に加えて，通学路を含んだ包括的な地形区分の双方を必要とし，学校に止まらず校区全体を見据えた災害対応計画が求められる。

The 2017 Northern Kyushu Rainstorm induced numerous numbers of landslides, which heavily damaged forest, roads, rivers, and houses with 37 fatalities and 4 missing. We investigated landslides using air photographs and high-resolution digital elevation models. Landslides occurred mainly in areas with over 200 mm/3 hr of rainfall. Landslide densities were higher in granodiorite and pelitic schist areas than in areas of volcanic rocks. Landslides were mostly shallow but large landslides occurred in at least two locations, where landslide dams were made. Huge volume of tree logs yielded with rock debris and soil, enlarging the disaster.

The 2016 Kumamoto Earthquake, which occurred on 16th April 2016 with a moment magnitude of 7.0, induced many landslides in the western part of the Aso caldera. The bedrocks of the survey area consists of lava flows and pyroclastic rocks with a wide range of chemistry from basalt to rhyolite. They are thickly covered by tephra, of which volcanic soil can be classified from color tone; we classified the volcanic soil into brown volcanic soil, black volcanic soil, and blackish brown volcanic soil. One of the most devastating types of landslides induced by this earthquake was of tephra slopes, because they occurred on rather gentle slopes and ran out long distances. The landslides had sliding surfaces in three types of tephra; these were Kusasenrigahama pumice layer 30, 000 years ago (Kpfa), black or blackish brown volcanic soil layer and brown volcanic soil layers that contained felsic lava blocks. These layers that accommodated sliding surfaces had high water content and rich in a clay mineral halloysite, which was formed by the weathering of the buried tephra. Many of the landslides of the tephra layers occurred on slopes where the sliding surface horizon had been undercut beforehand.

研究成果の概要 (和文) : （１）1995年兵庫県南部地震，2004年新潟県中越地震，2014年長野県神城断層地震，2016年熊本地震における斜面崩壊被害と道路防災点検データ等をもとに，地震時の斜面崩壊確率算定式を提案した．また，斜面崩壊確率と崩土流動域との関係を示した．さらに，崩壊確率算定式を和歌山県南部と長野県北部地域への適用を試み，孤立地域推定に対する有用性を示した．（２）岩手・宮城内陸地震で国内最大級の地すべりを起こした荒砥沢地すべり地の現地調査ならびに土質資料の採取，室内試験等を行い，その荒砥沢地すべり地の3次元SPH解析を行った．SPH解析の減衰や時間積分法を改良することで解の安定性，精度を改善した．, 研究成果の概要 (英文) : (1)We proposed some equations of probability on slope collapse during strong earthquake based on the slope damages during the 1995 Kobe, the 2004 Chuetsu, the 2014 Kamishiro fault and the 2016 Kumamoto earthquakes, as well as the road disaster prevention check data. We indicated the validation for the isolated areas assessment in the southern Wakayama and the northern Nagano by using the results of statistical analysis for the relationship between the slope damage probability and the road damage.(2)We conducted twice field surveys at Aratozawa where one of the largest landslide in Japan occurred during the 2008 Iwate-Miyagi inland earthquake, and laboratory tests of the soil and the rock samples. Based on the test results, we performed three dimensional Smoothed Particle Hydrodynamics analyses for the landslide. We also improved the methodologies of time integration and damping calculation for analytical stability and accuracy.

2016年熊本地震における地盤被害として, 熊本市, 益城町, 大津町, 南阿蘇村, 阿蘇市における液状化被害, 斜面崩壊, 地震断層変形について報告する。

The Kumamoto earthquake(Mj7.3) on April 16, 2016 triggered numerous landslides in and around Minamiaso Village, which is located at the western part of Aso caldera, southwestern Japan. The landslides were divided into two types:landslides occurring at steep caldera walls and landslides generated on the slopes of post-caldera central cones of Aso Volcano. Several landslides occurred on slopes steeper than 25°at the northwestern to western caldera walls, which comprise pre-Aso volcanic rocks (lavas and pyroclastics). The largest landslide (ca. 300m high, 130-200m wide) occurred on the western caldera wall, damaging National Route 57 and the Hohi line of the Japan Railway. Because a clear rupture surface could not be observed, unstable blocks which had been divided by cracks, were likely to collapse due to the intense earthquake on April 16. At the post-caldera central cones of Aso Volcano, earthquake-induced landslides were generated not only on steep slopes but also on slopes gentler than 10°. They occurred in unconsolidated superficial tephra deposits overlying lavas and agglutinates, and the thickness of the slides usually ranged from 4 to 8 m. The sliding masses traveled long distances (

Multiple small-scale hazards such as road submergence, poor visibility, slope failure, flood, and inundation can obstruct evacuation from sediment disaster and may enlarge human damage caused by large-scale of sediment movement. To clarify the process of small-scale hazards during sediment disaster, a numerical simulation model integrating models of sediment production caused by landslides, sediment supply and sediment transport in a watershed has applied to the sediment disaster event caused in Sakiyama river basin located in Hyogo prefecture, Japan. Based on the calculated results, we proposed indexes of 3 groups of hazard related to the landslide occurrence, water level in the channel, and rainfall intensity. The temporal change of indexes showed different characteristics according to the property of precipitation such as total amount of rainfall and maximum intensity.

2011年3月11日，東北太平洋沖地震が発生，地震に伴い発生した津波により，東北太平洋側地域に甚大な被害をもたらした。また，福島県白河市葉ノ木平地区等では，人的な被害を伴う土砂災害が発生した。被害は決して小さなものばかりではなかったが，全体的に見ると，地震の規模や記録された地震動の加速度の大きさにもかかわらず，山地部における斜面崩壊等の土砂災害は少数であり，規模も小さかった。また，人的被害を伴う土砂災害は，福島・栃木県に限定されていた。この原因について検討するために，地震発生時の土壌水分状態と地震の加速度を考慮した静的な斜面安定解析を行い，土壌水分状態が斜面安定性に与える影響を検討した。その結果，地震発生時期の先行降雨が少なかったことで，斜面安定性は大きく低下しなかったことが判明，仮に夏季の降雨イベント後に地震が発生していたら，実際よりも大きな被害がもたらされたと結論付けられた。, The pacific side of Tohoku region, Japan was suffered by a devastating earthquake on 11th March, 2011. Several hillside slopes were collapsed due to the earthquake in inland region, and a number of people were also killed by the sediment related disaster. Contrasting with the devastating earthquake which suffered wide area, the landslides were limited in its number, area, and size. To understand the reasons of this limited landslide occurrences, distribution of the maximum earthquake acceleration was investigated. The effects of the slope topographical properties such as slope gradient, direction, and bedrock geomorphology were also investigated by the field observation. Numerical experiments were also conducted to demonstrate the effects of the slope topographical properties and soil moisture conditions on the landslide occurrences. From the field investigations and numerical simulations, it is elucidated that the reasons of the limited landslide occurrences are 1) limited suffering area of strong acceleration by the earthquake and 2) relatively dry soil moisture condition of slopes at the earthquake occurrence.

Intense rainfall on 11-12 July 2012（ maximum total 572 mm; maximum 4-hour rainfall 385mm） triggered numerous landslides and associated lahars in Aso caldera, central Kyushu, southwesternJapan. Most of the landslides were concentrated in the eastern part of Asodani Valley,at the northern part of Aso caldera. The landslides were divided into three types: landslidesoccurring at steep caldera walls, landslides generated on the slopes of the post-caldera centralcones of Aso Volcano and landslides occurring on steep slopes of Nekodake Volcano. Most of thelandslides were shallow （about 1-2 m thick） soil slips in unconsolidated fallout tephra layersoverlying lava and welded Aso pyroclastic-flow deposits, and mobilized completely into lahars.The lahars eroded talus slopes and/or channel side slopes and transported boulders, which damagedhouses and caused fatalities at some sites. Similar landslide and associated lahar disastersoccurred at Aso Volcano in June 1953, July 1990 and June 2001. The characteristics of landslidesand lahars provide important information for preventing or mitigating future similar disastersin the Aso caldera region.

斜面崩壊の予測は一般的に降雨データに基づいて行われる。ある地域内で斜面崩壊の発生を判定する手法として，たとえば時間降雨量と積算雨量の平面上に崩壊発生限界線を決め，降雨量がその線を越えるか否かで判定する方法が使われるが，先行降雨量によって限界雨量は異なるし，その地域内に崩壊が発生するか否かだけの情報しか得られない。気候変動に伴い継続時間が長く，積算雨量の大きな豪雨の発生が増加すると，限界雨量を超えた後の連続する斜面崩壊のプロセスの情報が警戒避難システムに重要である。本研究では，実斜面を対象にして，様々な地形条件，降雨条件のもとに斜面崩壊シミュレーションを行い，個々の斜面の土層内水分量がその斜面の崩壊発生を判定する指標として適切であることや崩壊規模と降雨特性の関係を示したうえで，この指標や解析結果を重要な情報とした斜面崩壊プロセスについて，気候変動による将来の降雨条件を想定して検討する。, Slope failure is predicted based on rainfall data. For example, a critical line for slope failure in an area is drawn on coordinates of hourly and cumulative precipitations, and we can predict that slope failure occur somewhere in the area when rainfall condition crosses the critical line. However, it is important to provide information on successive slope failure process if an extreme rainfall event occurs frequently with climate change. In this paper slope failure was simulated under different geographical and rainfall conditions and the simulation results indicate that water content in an individual slope-soil layer is an adequate index for predicting slope failure. The characteristics of sediment disaster such as the relationship between slope failure magnitude and rainfall condition is discussed and an idea for an evaluation system for successively occurrence of slope failure is presented considering a prospective rainfall event due to climate change.

The Mikabu and Chichibu belts in the Anabukigawa arre were studied with respect to their composition， boundaries and the relation with landslides. The main body of the Mikabu Greenstones is composed of the MORB-type tholeiite, and the Hawaiian and Polynesian-type alkaline basalts. The greenstones are dominated by dolerite intrusions into bedded-cherts. The coincidence of the chemical composition attributes the Taigo and Nakano greenstone bodies to the Mikabu Greenstones. The limestone phyllite of the Mt. Tsurugi was dated by the occurrence of Late Carboniferous conodonts. The co-occurrence of conodonts and crinoids suggests that the limestone originates from the tropical reef settings.The Fujinoike-dani Valley and the southern slope along the Anabukigawa River are characterized by the frequent occurrence of landslides and collupse of forest road-cuts. Because the faults，that cut the North Chichibu Belt，an d bounds from the Mikabu Greenstone Belt as well as the Kaminirogawa-Akuigawa Fault that obliquely cut them later，are concentrated in the Fujinoike-dani Valley and the southern slope along the Anabukigawa Riiver.The landslides are concentrated along the valley walls of the Anabukigawa River where Mikabu Greenstones and the Sanbagawa green and pelitic schists occur. The distribution of landslides in the area is controlled by the lithology (distribution of greenstone and schists)，the coincidence of their dipping with valley wall, the contents of swelling clay minerals in the weathered materials， and the changes in rock properties of pelitic schists due to weathering.

本稿は，21世紀COEプログラムの中で「山地・河川・海岸系における物質動態に関する研究」の成果を一昨年および昨年度に引き続き第3報として取りまとめたものである。穂高砂防観測所をはじめとする隔地観測所・実験所で実施されている観測・実験を通して、山地から河川、さらに海岸・海域に至るまでの物質動態、とくに土砂動態を中心に取りまとめている。山地部では、裸地斜面からの長期的な土砂生産量を観測し、凍上・融解による土砂生産と粒度分特性が明らかになってきた。また、模型斜面を用いた豪雨時表層斜面崩壊の実験と予測モデルの検証並びに山地部での降雨・土砂流モデルの構築と観測データによる検証が行われている。水害調査にもとづく谷底平野および沖積平野における水害地形と河道変動に関する検討や、没水時の水制による局所洗掘に関する3次元流と河床変動解析法の開発も行われ、その概要が示されている。また、暴風時の沿岸流の特性や海浜風や降雨に与える黒潮などの暖流の影響などが現地観測やシミュレーションを通して明らかにされている。, This manuscript describes some of the recent research results obtained under the 21st COE project on long-term observation of sediment yields in the mountain regions, development of numerical simulation model on riverbed evolution, characteristics of flood plains and its formation by the flood, and fluvial sedimentary features in flood-stricken areas. Moreover, temporal variation of observed longshore current velocity and the relationship between the current velocity and external forces (winds and waves) is discussed, especially under storm conditions. And also, effects of Kuroshio warm current sea surface temperature on coastal wind and precipitation fields are simulated by meso-scale meteorological model MM5.

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.

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.

1972 年に発生した天草豪雨災害では，100mm/h を越える豪雨により，天草上島南東部一帯において斜面崩壊が多発した。地質調査と空中写真判読の結果，砂岩と泥岩との地質境界直下の泥岩の風化部で崩壊が多く発生し，砂岩の急崖における崩壊の発生は少ないことが分かった。砂岩との地質境界直下の泥岩で斜面崩壊が多発した地質的要因としては，(1) 泥岩は砂岩より初生的に軟質であり，風化による強度低下が著しいこと，(2) 高透水性と推定される砂岩の直下に難透水性の泥岩が分布し，両者の地質境界付近で地下水の浸透が遮断され，泥岩最上部における間隙水圧が上昇したこと，が挙げられる。, Many slope failures occurred in Amakusa Island, Japan, triggered by heavy rainfall on Jury 6th, 1972. Slope failures concentrated in mudstone based on the results of aerial photograph interpretationand field survey. Field evidence suggests that rainwater penetrated into permeable coarse sandstone withsystematic joints superposed on poor permeable massive mudstone. Many slope failures occurred at poorpermeable mudstone because of a rise in the groundwater level. The occurrences of slope failures ofmudstone were controlled by hydrogeological structure of mountain slope.

We carried out investigation of soil temperature at one-meter depth and water quality (water temperature and electric conductivity) to make clear relationship between slope failure and groundwater flow at source area of debris flow in the Tobinosu-dani-A stream, Zentoku, Tokushima, Japan. Furthermore, we investigated water temperature and electric conductivity of springs, at Tobinosu-dani-C stream, boreholes and underflow at Z6 block of Zentoku landslide to grasp the origin of groundwater. The results of our investigations are as follow. The groundwater flows at the source area of Tobinosu-dani-A stream are under flow type, which is flowing from outside of basin. Direction of these flows are Northeast to Southwest, which may be controlled to relative high permeability structure in the bedrock. The slope failure at source area of debris flow in this stream is caused by underflow from North to South.

Many debris flows caused by heavy rainfall have occurred at mountains in crystalline schist area, Shikoku Island, Southwestern Japan. The typical movement form of debris flow caused by heavy rainfall in mountainous area is fluidizing of soil mass from source area of debris flow to down slope (Stream). The debris flow at Tobinosu-dani stream in Zentoku, Nishiiyayama village on 29 June 1999 is this type of movement form. Therefore, it is important to make clear about occurrence mechanism of slope failures at source area of debris flow. Then, we carried out investigations of soil temperature at one-meter depth, water temperature and electric conductivity of springs and boreholes at the source area in the Tobinosu-dani stream and the Zentoku landslide. The results of our investigations are as follow. 1) There are two types of groundwater flows at the source areas of debris flows in the Tobinosu-dani stream that cause slope failure. One type is underflow changed by groundwater flow in deep layers with low value of electric conductivity. The other type is fissure water like groundwater vein-streams from deep layer with one digit higher value of electric conductivity than the underflow. 2) It is presumed that different of value of electric conductivity between underflow and fissure water is based on the different storage time (groundwater pass). Depth of the fissure water supply, especially, is corresponding to the approximate depth of the sliding surface (or bed rock) in the Zentoku landslide.

Ground information databases have been of increasing interest in recent years. Due to the complexity of these databases, labor saving are of importance in their preparation. Also, due to the various applications that ground information databases can be utilized for, data must be easy to manipulate. Furthermore, analytical results must be easily discernible when they are put in diagram form for display purposes. Based on these considerations, Visual Basic is selected for developing the system in this project. The data for a ground information database which appeared to be correlated with primary causes of slope failures could be made in 50 m mesh unit. Simultaneously, slope failure histories were analyzed using Quantification Method Type II and slope failure risk evaluation points for every category were determined. Slope failure risk prediction for every mesh in the database was then evaluated using the slope failure risk evaluation point method.

地質弱面がすべり面に転化した斜面崩壊について, 残留係数を導入して安定解析を行った。得られた知見は以下に示すとおりである。(1) すべり面全域で破砕ピーク強度または残留強度のいずれかが動員されたと想定して, それぞれF_s=3.27,F_s=0.16を得たが, これらの数値では崩壊の状況を説明できない。(2) 崩壊は, その直前(F_s=1.01)から発生時(F_s=0.98)への移行過程で残留係数Rが0.727から0.737へと微増していることから, 進行性破壊に因るものと説明できる。(3) 地質弱面を内在する不安定斜面において, 弱面の内在状況を把握して残留係数Rを想定し, 弱面付近試料の強度定数を活用することにより安定度評価が可能になる。, The occurrence mechanism of the slope failure generated along the geological weak plane was considered using the stability analysis in which the residual factor R was incorporated. Assuming that either peak strength or the residual strength was mobilized on the slip surface, F_s=3.27 for the former and F_s=0.16 for the latter were obtained. However, the situation of the failure could not be explained in these values. The failure can be explained in the progressive failure, because residual factor R slightly increases from 0.727 to 0.737 with the change from F_s=1.01 to F_s=0.98. The evaluation of the stability of the unstable slope with the geological weak plane becomes possible by utilizing shear strength of the sample near the weak plane and assumed the residual factor R., 紀要論文

Many slope failures were occurred by a heavy rainfall 476mm/day on 29 June 1999 at the Zentoku landslide area in the central Shikoku Island, Japan. It is necessary to investigate the distribution and behavior of groundwater in the slopes, because the occurrences of slope failures and landslides are caused by increase of pore water pressure on the sliding surface. We determined soil temperatures in one-meter depth at Taishido and water temperatures in non-strainer boreholes along the line of extensometers at the Z6 block in the Zentoku landslide, in order to find groundwater vein-Streams. Here we give a summary of our investigation as follows. 1) Two types of groundwater vein-streams are distinguished by the distribution of soil and water temperatures and are respectively derived from shallow and deep layers in the landslide mass. 2) The largest vein-stream of groundwater from deep layers is found from the north to east part of the study area, and probably flows toward the southeast direction. The lowest soil temperature in one-meter depth along the vein-stream shows 12.32℃ and is close to water temperature at the bottom of boreholes in the upper slope. There are also two or three local groundwater vein-streams from deep layers in the study area. 3) Another large groundwater vein-stream is distributed from the west part of the study area to a large slope failure nearby Taishido and probably flows toward the east direction. The soil temperatures in one-meter depth along this vein-stream and the water temperature at a spring in the head scarp of the large slope failure are significantly higher than the soil temperatures along the above largest vein-stream from deep layers. This vein-stream flowing toward the east direction, therefore, is the shallow groundwater in origin. 4) The large slope failure nearby Taishido and a surface subsidence might be caused by groundwater from shallow layers, on the basis of the distribution of the vein-streams and slope failures. The slope failures located in the northeast part of the study area were influenced by groundwater from deep layers.

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.