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In this study, the c' - φ' diagram has been drawn up based on the stability analysis method, in which the residual factor is incorporated, concerning three landslides among which there are considerable variations in the cross section dimensions and soil strength. The characteristics of the c' - φ' diagram was extracted with an emphasis on the geometric elements and soil strength of the three landslides. Furthermore, the relationship between the c' - φ' diagram, the geometric elements of landslides and soil strength was clarified by means of various model landslides, which will be helpful in the creation and confirmation of the rationality of using the c' - φ' diagram in practice. Conclusions are drawn as follows :In the three landslides, the characteristics of the geometric elements and soil strength are reflected in the c'- φ' diagram having characteristic forms. The position of IP is decided by the movement of c'-tan φ' line controlled by the numerical value of Fs. The Influence of soil strength on the c'- φ' diagrams with the variation of groundwater level became obvious, and is reflected in the c'- φ' diagrams. The influence of length "L" is very minimal. Maximum thickness "D" has an effect on c' -intercept and inclination "B" of c'-tan φ' line, but has little impact on tan φ'-intercept whereas slope" α" has a significant impact on c' and tan φ' , but does not seem to have any effect on B. Influence of groundwater level appears as a large rightward shift of tan φ'. The soil strength at slip surface govern the cross section dimensions of landslide and has an influence on the c' - tan φ' diagram.

平成13年度～平成14年度科学研究費補助金(基盤研究(C)(2))研究成果報告書, 研究概要:本研究では,まず,安定解析に必要な強度定数c,φを得るために物理的・鉱物学的性質を異にする地すべり土について強度測定試験を行った.次に,残留係数を導入した三次元安定解析手法について検討し,提案した. 1.c-φ関係図において,c=37.5kN/m^2,φ=35.0°付近から正規圧密強度付近にまで及ぶ領域が強風化・破砕泥岩のピーク強度ゾーンとして設定された.正規圧密強度はc軸上のφ=23～30°の範囲にあり,残留強度はφ=9°～17°の範囲で与えられた.φ≦10°のような低い値は残留せん断面が鏡肌を呈するほどに発達した試料で得られた. 2.シルト・砂分が多く,粘土含有量が20％より少ない試料でもピークから残留への明瞭な強度逓減が認められた.強度逓減量は,配向性鉱物総量との関係において凸型変化を示した.地すべり土の応力～変位曲線は,含有される鉱物総量に基づいて4タイプに類別できた. 3.通常の地すべりの安定解析において、実験で得られるピーク強度,完全軟化強度(正規圧密強度)および残留強度の単独の適用は,安全率が過大または過小であると計算・評価してしまうため,すべり発生の事実が説明できない。提案された安定解析手法により,すべり面の平均強度定数が適切に算定され,二次元解析結果と比べてかなり小さいことが検証できた.また,本手法により,すべり時に動員されるピーク強度と残留強度の関与領域がすべり面全域で区分・表示できた., 要約(欧文):Strength measurement tests were carried out on landslide soils which showed a considerable variation in physical and mineralogical properties in order to obtain the their strength parameters c and φ for stability analysis. Then the three-dimensional stability analysis procedure, in which the residual factor was incorporated, was examined and proposed. The peak strength zone for strongly weathered and fractured mudstones was given by drawing the small area that reaches from the strength of c=37.5kN/m^2 and φ=35.0° close to the normally-consolidated strength in the c-φ figure. The parameters of normally-consolidated strength and residual strength were within the range of φ=23-30° and φ=9-17°, respectively. A fall in the strength from the peak to the residual state was clearly observed for the soil containing a large amount of silt and sand particles, and clay fraction below 20%. The variation of the strength reduction versus total contents of preferred-oriented clay minerals was expressed as a convex curve. Stress-displacement curves of landslide soils were classified into 4 types based on the total amount of minerals in soil. In the proposed analysis procedure, the average shear strength parameter acting along the slip surface was calculated precisely and was verified to be smaller than the parameter calculated by the two-dimensional analysis, and then each domain of both the peak and residual strengths mobilized at the slide could be expressed clearly on the whole slip surface area. This procedure will be helpful in rational and effective control works for landslide., 未公開：P.1以降(別刷論文のため)

整備事業の計画・実施に伴う波及効果により, 地域住民や市町村職員の意識の高揚などを含めた地域づくりが期待できる。現状の住民参加は行政主導の傾向が強く, 地域住民の形式的な参加に留まっているが, 市町村職員は住民参加や地域住民の主体的な参加の必要性を認識している。整備事業に伴う波及効果, 住民参加の必要性, 整備事業における市町村職員の役割および重要性についての職員の認識には差がある。今後, 整備事業を計画・実施していく上で, 市町村職員は, 自身が持つ役割の重要性を自覚し, 整備事業への取り組み姿勢に優劣が生じないように意識を高めていく必要がある。最後に, この研究を進めるに当たり, ヒアリング調査, アンケート調査に協力して頂いた市町村職員, 調査票作成に助言を下さった琉球大学生涯学習教育研究センターの大膳司教授および金城志保氏をはじめとする農学部農村農地整備及び防災学研究室の皆様に謝意を表する。, Local government officers' consciousness in the agricultural infrastructure improvement and rural development projects was investigated with questionnaire. Results of the investigation are as follows. Various repercussion effects including the consciousness exaltation of residents and local officers are expected in the project planning and implementation. But local government officers' recognitions are different in regarding repercussion effects of the project, need of resident participation and role of local government officers in the project. For future project planning and implementation, it is necessary that local officers should be conscious of their role and importance and their consciousness should not arise the difference of superiority for the success of the project.

伊豆味地区の農業用水確保に関しては, 地質的条件を考慮すると, 自然ブランケットを活かした取水堰と道路の水兼化による集水施設の建設が適切である。また, 樹園地の開畑・整備にあたっては, 土地環境保全型の畑面・園内作業道整備および防風林の整備が望まれる。崎山地区の排水不良問題に関しては, 排水路の底面は浸透性の地質層序を活かし, 側面のみをコンクリート張りにする。, Problems on the agricultural infrastructure improvement in model districts of rural revitalization, Izumi and Sakiyama of Okinawa prefecture, were considered, and suitable countermeasures were proposed. In Izumi district, according to the geological research results, the passable ditch and the diversion weir utilizing natural impervious blanket are effective measures for catching and storing of rain water. For the reclamation and improvement of orchard land, the preservation of land environment, the installation of a work road in the orchard and a wind break fence are desired. For the settlement of the poor drainage problem in Sakiyama district, the drainage canal had no concrete bottom was proposed considering a high permeability of the foundation geology.

整備事業の計画・実施に伴う波及効果により, 地域住民や市町村職員の意識の高揚などを含めた地域づくりが期待できる。現状の住民参加は行政主導の傾向が強く, 地域住民の形式的な参加に留まっているが, 市町村職員は住民参加や地域住民の主体的な参加の必要性を認識している。整備事業に伴う波及効果, 住民参加の必要性, 整備事業における市町村職員の役割および重要性についての職員の認識には差がある。今後, 整備事業を計画・実施していく上で, 市町村職員は, 自身が持つ役割の重要性を自覚し, 整備事業への取り組み姿勢に優劣が生じないように意識を高めていく必要がある。最後に, この研究を進めるに当たり, ヒアリング調査, アンケート調査に協力して頂いた市町村職員, 調査票作成に助言を下さった琉球大学生涯学習教育研究センターの大膳司教授および金城志保氏をはじめとする農学部農村農地整備及び防災学研究室の皆様に謝意を表する。, Local government officers' consciousness in the agricultural infrastructure improvement and rural development projects was investigated with questionnaire. Results of the investigation are as follows. Various repercussion effects including the consciousness exaltation of residents and local officers are expected in the project planning and implementation. But local government officers' recognitions are different in regarding repercussion effects of the project, need of resident participation and role of local government officers in the project. For future project planning and implementation, it is necessary that local officers should be conscious of their role and importance and their consciousness should not arise the difference of superiority for the success of the project.

黄土丘陵ガリ谷区のガリ谷密度, 地面破裂度, 傾斜度分布および段畑造成の可能土地量について検討した。結果は次の通りである。1) ガリ谷密度はモウ状丘陵ガリ谷亜区, 寛谷長梁ガリ谷亜区, 梁状丘陵ガリ谷亜区の順で, それぞれ4.16km/(km)^2,3.37km/(km)^2,2.97km/(km)^2である。ガリ谷密度と単位面積当たり年流出土砂量との間には正の相関がみられる。2) 地面破裂度は, 梁状丘陵ガリ谷亜区, モウ状丘陵ガリ谷亜区, 寛谷長梁ガリ谷亜区の順で, それぞれ45.7%, 29.8%, 25.1%である。3) 傾斜度分布は, モウ状丘陵ガリ谷亜区で15°以下の斜面が総面積の85.0%を占め, 梁状丘陵ガリ谷亜区では5∿25°の斜面が総面積の80.3%を占めている。寛谷長梁ガリ谷亜区は梁状丘陵ガリ谷亜区に類似している。4) モウ状丘陵ガリ谷亜区, 梁状丘陵ガリ谷亜区および寛谷長梁ガリ谷亜区における段畑造成可能土地量はそれぞれ総面積の73.7%, 71.6%, 76.2%に相当する。, Hilly-gullied loess area is the largest area of Loess Plateau in China, suffered most seriously soil erosion, and produce 90% of the sediments of Yellow River. According to the scientific research results and the experience in soil and water conservation in China, terraced field construction is one of most effectively measures for soil erosion controlling and sustainable development of local economy. But, in the planning process of terraced field, the topographical features are often neglected. In this paper, based on the analysis of topographical features of hilly-gullied loess area, the possible land area for terraced field construction for each sub-area was given out.

黄土高原は, 黄河の中流域に位置し, 総面積が中国陸地面積の6.63%を占め, 世界で最も土砂流出の激しい地域である。頻発する土壌侵食, 地すべり, 土石流などの土砂災害は, 黄土地域の社会的経済的発展の障害となっている。本研究では, 黄土地すべりの主要類型とその分布特性, および黄土地すべりの地形・比高などの地すべり発生要因を明確にした。さらに, 黄土地すべりの防止が黄土区域の社会・経済発展のキーになることを指摘した。, The area of loess covers 6.63 per cent of total land area of China and it is well known all over the world for its largeness and wide location. The frequent happening of natural disasters, such as soil and water erosion, landslide and mud-rock flow, is the major factor hindering the social and economic development of loess area. In this paper, the principal types of loess landslide and the distribution rules of loess landslide are pointed out, and the landform and relief characteristic of loess landslide influencing factors of loess landslide and its mechanism are analyzed. It emphasizes that the prevention and control of loess landslide is a key factor that will determine the sustainable development of local society and economy.

本研究では,植物の生理,生長状況,生物量,土壌への改善効果から,無小葉花棒と多小葉花棒との差異を検討した。得られた結果を要約すると,つぎのようになる。(1) 両生態型花棒の葉形態特徴,葉の解剖構造,葉の水分生理および根系の分布状況の分析によって,多小葉花棒に比して無小葉花棒はさらに乾燥環境に耐えられることが明らかになった。(2) 多小葉花棒の種子の品質は無小葉花棒より優り,種子の実用価値が無小葉花棒種子の2.24倍である。多小葉花棒の生枝・葉の粗蛋白質,粗脂肪含量および無窒素浸出物が無小葉花棒に比して多いので,飼料として高い価値を有する。(3) 流動砂地と比べて,無小葉花棒地および多小葉花棒地の土壌の理化学性は改善された。土壌の物理性の改善において,無小葉花棒は多小葉花棒に比して効果である。, In the previous paper, we have divided the H. scoparium into two ecotypes by use of the cluster analysis method, and named them as non-leaflet and poly-leaflet H. scoparium respectively. In order to serve the afforestation in desert area, we measured and analyzed some bioecological and physiological characteristics of these two ecotypes. As the results, it was revealed that, 1), the non-leaflet ecotype of H. scoparium is more obviously characterized with drought-against features in the aspects of leaf shape, leaf anatomical structure, physiological characteristics in water using, and root distribution; 2), the seed quality and of the non-leaflet ecotype is better than that of polyleaflet ecotype, but the fresh branch and leaves of poly-leaflet ecotype contains more gross protein, gross fat, non-nitrogen extractives than non-leaflet ecotype, and is more suitable to use as a kind of forage; 3), the soil physical property of non-leaflet ecotype is better than poly-leaflet ecotype.

天然・導入花棒の形態特徴を調査し,統計的な方法により花棒生態型の区分を定量的に行い,生態型別の花棒の形態区別,播種苗の形態変化過程を考察した。さらに,気候変遷に及ぼす花棒生態分化の要因と分化過程を検討した。得られた結果を要約すると次のようになる。1)天然花棒および導入花棒はともに,無小葉花棒と多小葉花棒の両生態型に分けられる。2)二種類生態型花棒の主な形態区別は,複葉,針状葉の数量及びそれぞれの割合が異なることに現れている。3)生態型別花棒苗の形態変化過程が異なる。4)花棒の生態分化は気候の変化,特に地域の乾燥度の変化により引き起こされたものである。, Hedysarum scoparium, one of posammophyte naturally distributed in the deserts of central Asia, are widely afforested in the desert or sandy land of northwestern china for combating desertification. As of vast distribution scope, the H. scoparium differs quietly in different areas. In this paper, firstly, we tried to divide the H. scoparium by the method of cluster analysis based on the morphological data set of branch and leaf sampled from both of its' natural distribution and introduced areas, then discussed it's dissociation process according to the observation to the seedling growth process and results of primary component analysis on the climatic characteristics across the whole area of distribution. It was founded that, 1), H. scoparium can be divided into two ecotypes, i.e. non-leaflet and poly-leafleat ecotypes; 2), these two ecotypes differs mainly in the amount and rate of compound leaf and needle-like leaf; 3), the morphological variation process differs from each other of these two ecotypes in the seedling stage; 4), the dissociation of H. scoparium could be due to the climatic change in ancient time.

雨水によるクラストの形成に伴う土壌表層の透水性と粒径組成の変化について検討し,以下の結果を得た。(1) 濁水の湛水に伴う土壌表層の透水係数(k)の変化については,150ppmにおいてk=1.33・(10)^<-3>cm/s,250ppmにおいてk=8.85・(10)^<-4>cm/sとなり,湛水前のk=3.61・(10)^<-3>cm/sよりも大幅に低下し,堆積クラストの形成が認められた。(2) 雨滴の衝撃に伴う土壌表層の透水係数(k)の変化については,降雨前のk=3.36・(10)^<-4>cm/sが,20分降雨後にk=1.23・(10)^<-4>cm/s,40分降雨後にk=3.09・(10)^<-5>cm/sとなり,構造クラストの形成が認められた。(3) また,土壌表層では雨滴の衝撃に伴って,粗砂・細砂の粗粒分の減少があり,飛散による影響が認められた。なお,雨水によるクラストの形成については,透水係数や粒径組成の変化による検証のみでは不充分であり,更に追究し,そのメカニズムを明らかにする予定である。, Approaches were made to examine the variation of infiltration capacity and particle size distribution of soil in the crusting process induced by rainfall in this paper. Following the accumulating of clouding water, the hydraulic conductivity (k) of soil surface greatly decreased from 1.33×(10)^<-3>cm/s before watering to 3.61×(10)^<-3>cm/s and 8.85×(10)^<-4>cm/s respectively for the cases watered with 150ppm and 250ppm clouding water. It reveals that a kind of accumulated crust had been formed. Furthermore, the hydraulic conductivity varied with the compaction of raindrops. Before the rainfall started, k was 3.36×(10)^<-4>cm/s, and then it declined to 1.23×(10)^<-4>cm/s and 3.09×(10)^<-5>cm/s at the times of 20 and 40 minute after raining. It could be confirmed that a kind of structural crust had been developed. Also, impacting of raindrops reduced the coarse and fine sand fraction on soil surface due to the influence of splashing.

黄土丘陵ガリ区は中国における侵食の激しい地域の一つである。激しい土壌侵食に半乾燥・乾燥気候,峻険な地形と悪化した生態環境に加えて,土地生産力は極めて低く,住民の生活も貧困である。このような自然・経済状況に鑑み適当な侵食防止策と農業開発技術を探討する為に,「黄土丘陵ガリ区における小流域の土壌侵食防止と農業開発技術に関する研究」を国家の指定研究課題とし,北京林業大学が寧夏回族自治区の西吉県の黄家二岔小流域において,1981年から一連の研究を行ってきた。採用された技術は該当地域の資源レベルと一致し,研究成果は類似な小流域にも適用・普及できる。黄家二岔小流域の侵食防止・農業開発の実際により,流域管理事業には連続的な資金・技術投入があれば,土砂流失は98%まで低減でき,食糧生産高と住民の年平均収入がそれぞれ526%と566%まで増加できるとされている。本研究は当該小流域の侵食防止措置と侵食防止事業の効果について検討するものである。, The loess gullied-hilly area of China is one of the most eroded areas. Soil erosion, along with semiarid to arid climate, dissected topography and fragile ecological environment, makes land productivity very low and the livelihood of rural people even hard. In order to promote appropriate strategies for soil erosion control and small watershed agricultural development techniques, long-term research has been carried out by Beijing Forestry University sponsored by the China government since 1981,in a small watershed, Huangjiaercha, of Xiji County in Ningxia Hui Nationality Autonomous Prefecture. These efforts have resulted in identifying appropriate technologies in relation to resource level, these strategies could be extended to similar agro-ecological situations. Soil and water conservation practices adopted in the watershed revealed that with investment level and continuous adjustment, soil losses of small watershed could be reduced by 98%, apart from increasing crop yield and per capita net income by 526% and 566% respectively. The impact of soil erosion control measures and its benefits will be discussed in this paper.

黄土丘陵ガリ区は中国における侵食の激しい地域の一つである。激しい土壌侵食に半乾燥・乾燥気候,峻険な地形と悪化した生態環境に加えて,土地生産力は極めて低く,住民の生活も貧困である。このような自然・経済状況に鑑み適当な侵食防止策と農業開発技術を探討する為に,「黄土丘陵ガリ区における小流域の土壌侵食防止と農業開発技術に関する研究」を国家の指定研究課題とし,北京林業大学が寧夏回族自治区の西吉県の黄家二岔小流域において,1981年から一連の研究を行ってきた。採用された技術は該当地域の資源レベルと一致し,研究成果は類似な小流域にも適用・普及できる。黄家二岔小流域の侵食防止・農業開発の実際により,流域管理事業には連続的な資金・技術投入があれば,土砂流失は98%まで低減でき,食糧生産高と住民の年平均収入がそれぞれ526%と566%まで増加できるとされている。本研究は当該小流域の侵食防止措置と侵食防止事業の効果について検討するものである。, The loess gullied-hilly area of China is one of the most eroded areas. Soil erosion, along with semiarid to arid climate, dissected topography and fragile ecological environment, makes land productivity very low and the livelihood of rural people even hard. In order to promote appropriate strategies for soil erosion control and small watershed agricultural development techniques, long-term research has been carried out by Beijing Forestry University sponsored by the China government since 1981,in a small watershed, Huangjiaercha, of Xiji County in Ningxia Hui Nationality Autonomous Prefecture. These efforts have resulted in identifying appropriate technologies in relation to resource level, these strategies could be extended to similar agro-ecological situations. Soil and water conservation practices adopted in the watershed revealed that with investment level and continuous adjustment, soil losses of small watershed could be reduced by 98%, apart from increasing crop yield and per capita net income by 526% and 566% respectively. The impact of soil erosion control measures and its benefits will be discussed in this paper.

本研究では,植物の生理,生長状況,生物量,土壌への改善効果から,無小葉花棒と多小葉花棒との差異を検討した。得られた結果を要約すると,つぎのようになる。(1) 両生態型花棒の葉形態特徴,葉の解剖構造,葉の水分生理および根系の分布状況の分析によって,多小葉花棒に比して無小葉花棒はさらに乾燥環境に耐えられることが明らかになった。(2) 多小葉花棒の種子の品質は無小葉花棒より優り,種子の実用価値が無小葉花棒種子の2.24倍である。多小葉花棒の生枝・葉の粗蛋白質,粗脂肪含量および無窒素浸出物が無小葉花棒に比して多いので,飼料として高い価値を有する。(3) 流動砂地と比べて,無小葉花棒地および多小葉花棒地の土壌の理化学性は改善された。土壌の物理性の改善において,無小葉花棒は多小葉花棒に比して効果である。, In the previous paper, we have divided the H. scoparium into two ecotypes by use of the cluster analysis method, and named them as non-leaflet and poly-leaflet H. scoparium respectively. In order to serve the afforestation in desert area, we measured and analyzed some bioecological and physiological characteristics of these two ecotypes. As the results, it was revealed that, 1), the non-leaflet ecotype of H. scoparium is more obviously characterized with drought-against features in the aspects of leaf shape, leaf anatomical structure, physiological characteristics in water using, and root distribution; 2), the seed quality and of the non-leaflet ecotype is better than that of polyleaflet ecotype, but the fresh branch and leaves of poly-leaflet ecotype contains more gross protein, gross fat, non-nitrogen extractives than non-leaflet ecotype, and is more suitable to use as a kind of forage; 3), the soil physical property of non-leaflet ecotype is better than poly-leaflet ecotype.

雨水によるクラストの形成に伴う土壌表層の透水性と粒径組成の変化について検討し,以下の結果を得た。(1) 濁水の湛水に伴う土壌表層の透水係数(k)の変化については,150ppmにおいてk=1.33・(10)^<-3>cm/s,250ppmにおいてk=8.85・(10)^<-4>cm/sとなり,湛水前のk=3.61・(10)^<-3>cm/sよりも大幅に低下し,堆積クラストの形成が認められた。(2) 雨滴の衝撃に伴う土壌表層の透水係数(k)の変化については,降雨前のk=3.36・(10)^<-4>cm/sが,20分降雨後にk=1.23・(10)^<-4>cm/s,40分降雨後にk=3.09・(10)^<-5>cm/sとなり,構造クラストの形成が認められた。(3) また,土壌表層では雨滴の衝撃に伴って,粗砂・細砂の粗粒分の減少があり,飛散による影響が認められた。なお,雨水によるクラストの形成については,透水係数や粒径組成の変化による検証のみでは不充分であり,更に追究し,そのメカニズムを明らかにする予定である。, Approaches were made to examine the variation of infiltration capacity and particle size distribution of soil in the crusting process induced by rainfall in this paper. Following the accumulating of clouding water, the hydraulic conductivity (k) of soil surface greatly decreased from 1.33×(10)^<-3>cm/s before watering to 3.61×(10)^<-3>cm/s and 8.85×(10)^<-4>cm/s respectively for the cases watered with 150ppm and 250ppm clouding water. It reveals that a kind of accumulated crust had been formed. Furthermore, the hydraulic conductivity varied with the compaction of raindrops. Before the rainfall started, k was 3.36×(10)^<-4>cm/s, and then it declined to 1.23×(10)^<-4>cm/s and 3.09×(10)^<-5>cm/s at the times of 20 and 40 minute after raining. It could be confirmed that a kind of structural crust had been developed. Also, impacting of raindrops reduced the coarse and fine sand fraction on soil surface due to the influence of splashing.

国頭マージ地帯の崩壊は流出土砂の生産源となっている。崩壊土砂の流出には, 谷地形における法面工事中に崩壊が発生し直接的に渓流に流出するもの, 整備後に側溝を介し流出するもの, 側溝閉塞が原因で起こる畑面ガリ侵食がもたらす二次的な土砂流出がある。崩壊には, 流れ盤性のすべり, 開口亀裂からなる弱化したレキ層のすべり, 細粒シルト層のすべりがある。崩壊の多くは層理や節理のような弱面とその走向に規制されている。弱面の強度は残留強度近くにまで低下し, 非弱面部ではピーク強度が発揮される。真喜屋の強風化岩および上新川の細粒シルトで示されたピーク強度定数はそれぞれc_f=16.1kPa・c_f=43.5°, c_f=12.0kPa・c_f=28.5°であり, 残留強度定数はそれぞれc_r=0kPa・φ_r=26.0&acd;33.3°, c_r=0kPa・φ_r=27.0°で, 地すべり土に比べて高値である。, In the Kunigami-Maaji (red) soil area in Okinawa, slope failures are one of the rise of soil loss which pollutes rivers. Most of slope failures occur controlled by the strike of geological weak planes. The shear strength along weak planes is lowered to the value close to residual strength. The peak strength is mobilized in shear zones where weak plane does not exist. Peak strength parameters for strongly weathered rock from Makiya and for weathered soil from Ue-arakawa were c_f=16.1kPa, φ_f=43.5°, and c_f=12.0kPa, φ_f=28.5°, respectively. Residual strength parameters were c_r=0kPa, φ_r=26.0&acd;33.3°for Makiya, and c_r=0kPa, φ_r=27.0°for Ue-arakawa, both higher than those for landslide soils.

地域特有のものを環境資源として評価し, 利活用することは, これからの農村整備に不可欠である。大里村を事例に資源の特性と利活用について検討した。自然環境では河川, 雑木林・斜面林, 御嶽の森があり, 御嶽の森は集落背後の深い森の一部に聖域として保全されている。社会環境では伝統的集落, 集落道, 湧水・井戸があり, 伝統的集落での屋根や石垣が沖縄独自のものなので地域性が高く, 湧水・井戸も沖縄の暮らしをささえてきた大切な場所としてその価値は高い。ダム・ため池, 圃場, 農道は生産環境資源である。農地の平野部や緩傾斜は, 農道の線形によって広がりのある美しい景観が得られる。地域資源を活用し, 特色ある景観やその背景となる自然や文化を理解することによって, 農村整備が望ましいものになると考える。, It is important to utilize regional resources for rural plannings. An intensive survey of the regional resources at the Ozato village reveals the following facts. Stream, homestead woods andUtaki(a shrine forest) are regional resources which represents the natural environmental resources.Utakiat the back of the settlement is well preserved as a holy place. Traditional settlements, community roads and springs-wells are social environmental resources. Traditional roofs and stone walls produce a calm atmosphere, and springs-wells are noble places that have been sustaining life from the old. Irrigation ponds, agricultural lands and roads are productive environmental resources. The environment surrounding ponds is important habitats for a variety of wildlifes. Flat areas and gentle slopes of agricultural lands at the Ozato village can be transfigured into extensive and beautiful scenery according to the alignment of farm roads.

平成6年度・平成7年度科学研究費補助金(一般研究(C))研究成果報告書, 研究概要:赤土(国頭マージ)地帯の崩壊は、層理や節理のような地質弱面とその走向に規制される。弱面の強度は残留強度の近くにまで低下し、非弱面部ではピーク強度が発揮される。ピーク強度の測定は、崩壊土の不攪乱試料について三軸圧縮試験装置を用いて行われた。完全軟化および残留強度の測定は、スラリー試料についてリングせん断試験装置を用いて行われた。ピーク強度については、地すべり性崩壊の不攪乱試料が微小レキの影響を受けてかなりのばらつき、C_f=3.0kPa～16.1kPa.φ_f=28.5°～43.5°を示した。完全軟化強度については、すべての試料がC_=35.0°～40.0°の範囲に納まった。残留強度については、バーミキュライトと粘土分を多く含む試料でC_r=0kPa.φ_r=16.5°～17.9°、石英が卓越している試料においてC_r=0kPa.φ_r=26.5°～31.0°、微小レキを含有する試料でC_r=0kPa.φ_r=19.8°～33.3°となり、地すべり土に比べて高値である。これは、赤土が配向性の鉱物粒子を含有していないこと、石英や微小レキの影響によって粒子の配向状況が良好でないことに起因したものである。赤土地帯の真喜屋地すべり性崩壊において、逆算解析によって得られる現場せん断強度(すべり面の平均強度)と試料のせん断強度の相互関係、および残留係数を導入した安定解析法の適用について検討した。真喜屋地すべり性崩壊の現場せん断強度は残留強度より大きいが、ピーク強度よりも小さい。対策のための設計強度定数は残留係数を導入した安定解析法を用いて計算でき、また逆算法と試料の強度定数を基にした図解法によっても決定できる。赤土に対する有機質資材の侵食抑制効果について人工降雨試験を行った。圃場容水量状態にした供試土において、流出土砂良は木炭土、有機土、チップ土および原土の順となり、10％木炭土において原土よりおよそ70％も侵食抑制効果が示された。, 要約(欧文):In the red soil (commonly called Kunigami Maaji) area in Okinawa, slope failures occur controled by the strike of weak planes such as bedding and joint plane. The shear strength along weak planes is lowered to the value close to residual strength. The peak strength is mobilized in shear zones where weak plane does not exist. The peak strength was measured for undisturbed samples from slope failures using a triaxial compression apparatus. The fully-softened strength and residual strength were measured for slurry of disturbed samples using a ring shear apparatus. Peak strength parameters were c_f=3.0kPa-16.1kPa, φ_f=28.5°-43.5°. Fully-softened strength parameters were c_=0kPa-7.9kPa, φ_=35.0°-40.0°. Residual strength parameters were c_r=0kPa, φ_r=16.5°-17.9° for soils containing vermiculite and high clay content, and c_r=0kPa, φ_r=19.8°-33.3° for quartz and small gravels-dominated soils, both higher than thosef or landslide soils. This is because clay particles in the red soil are poorly oriented, and, furthermore, the quartz and small gravels in the soils affected to make the residual strength high. The field shear strength (a average shear strength along the slip surface) and shear strength parameters of the soil from the slip surface were evaluated for the Makiya slope failure occurring in the red soil area based on the stability analysis method in which the residual factor was incorporated.A back-analysis of this slope failure showed that feild shear strengths are greater than residual strengths but smaller than peak strengths. The design strength parameters for control works were calculated by the proposed method and also by the graphic solution based on the back-analysis and shear strength parameters of the soil. The soil loss testing was performed by using a rainfall simulator in order to clear up that organic materials have the effect of erosion control on red soils. The quantity of runoff soil loss was small in the order of charcoal mixed soil

平成6年度・平成7年度科学研究費補助金(一般研究(C))研究成果報告書, 研究概要:赤土(国頭マージ)地帯の崩壊は、層理や節理のような地質弱面とその走向に規制される。弱面の強度は残留強度の近くにまで低下し、非弱面部ではピーク強度が発揮される。ピーク強度の測定は、崩壊土の不攪乱試料について三軸圧縮試験装置を用いて行われた。完全軟化および残留強度の測定は、スラリー試料についてリングせん断試験装置を用いて行われた。ピーク強度については、地すべり性崩壊の不攪乱試料が微小レキの影響を受けてかなりのばらつき、C_f=3.0kPa～16.1kPa.φ_f=28.5°～43.5°を示した。完全軟化強度については、すべての試料がC_=35.0°～40.0°の範囲に納まった。残留強度については、バーミキュライトと粘土分を多く含む試料でC_r=0kPa.φ_r=16.5°～17.9°、石英が卓越している試料においてC_r=0kPa.φ_r=26.5°～31.0°、微小レキを含有する試料でC_r=0kPa.φ_r=19.8°～33.3°となり、地すべり土に比べて高値である。これは、赤土が配向性の鉱物粒子を含有していないこと、石英や微小レキの影響によって粒子の配向状況が良好でないことに起因したものである。赤土地帯の真喜屋地すべり性崩壊において、逆算解析によって得られる現場せん断強度(すべり面の平均強度)と試料のせん断強度の相互関係、および残留係数を導入した安定解析法の適用について検討した。真喜屋地すべり性崩壊の現場せん断強度は残留強度より大きいが、ピーク強度よりも小さい。対策のための設計強度定数は残留係数を導入した安定解析法を用いて計算でき、また逆算法と試料の強度定数を基にした図解法によっても決定できる。赤土に対する有機質資材の侵食抑制効果について人工降雨試験を行った。圃場容水量状態にした供試土において、流出土砂良は木炭土、有機土、チップ土および原土の順となり、10％木炭土において原土よりおよそ70％も侵食抑制効果が示された。, 要約(欧文):In the red soil (commonly called Kunigami Maaji) area in Okinawa, slope failures occur controled by the strike of weak planes such as bedding and joint plane. The shear strength along weak planes is lowered to the value close to residual strength. The peak strength is mobilized in shear zones where weak plane does not exist. The peak strength was measured for undisturbed samples from slope failures using a triaxial compression apparatus. The fully-softened strength and residual strength were measured for slurry of disturbed samples using a ring shear apparatus. Peak strength parameters were c_f=3.0kPa-16.1kPa, φ_f=28.5°-43.5°. Fully-softened strength parameters were c_=0kPa-7.9kPa, φ_=35.0°-40.0°. Residual strength parameters were c_r=0kPa, φ_r=16.5°-17.9° for soils containing vermiculite and high clay content, and c_r=0kPa, φ_r=19.8°-33.3° for quartz and small gravels-dominated soils, both higher than thosef or landslide soils. This is because clay particles in the red soil are poorly oriented, and, furthermore, the quartz and small gravels in the soils affected to make the residual strength high. The field shear strength (a average shear strength along the slip surface) and shear strength parameters of the soil from the slip surface were evaluated for the Makiya slope failure occurring in the red soil area based on the stability analysis method in which the residual factor was incorporated.A back-analysis of this slope failure showed that feild shear strengths are greater than residual strengths but smaller than peak strengths. The design strength parameters for control works were calculated by the proposed method and also by the graphic solution based on the back-analysis and shear strength parameters of the soil. The soil loss testing was performed by using a rainfall simulator in order to clear up that organic materials have the effect of erosion control on red soils. The quantity of runoff soil loss was small in the order of charcoal mixed soil

平成元年度・平成2年度科学研究費補助金(一般研究(B))研究成果報告書, 研究概要:地すべり土の大変位せん断挙動についての検討結果によると、(1)残留状態に到達するまでの最小せん変位量は土粒子の性質や垂直応力に依存する。(2)最小せん変位量は泥岩試料で40～60cm、凝灰質れき質土では200～300cmとなり大変位である。(3)残留強度測定は、三軸や直接せん断試験では無理であり、リングせん断試験が望ましいが、排水条件を満たす必要があるので、長時間を要する。残留強度パラメータφrと2μm以下粘土分CF、塑性指数Ipおよびスメクタイト量Smの関係についての検討結果によると、(1)φr-CF関係および Shear mode区分は、すべり面土と非すべり面土の違いや残留せん断面における鏡肌形成を推し量るのに有効である。(2)φrとIpの間にはφr=35.9・Ip^<-0.368>関係式が成り立つ。(3)φr=13.8-0.092・Sm関係式が成り立つ。(4)上記関係および関係式によっておよそそのφr推定が可能である。提案された安定度評価法は、残留係数、逆算法、実験強度パラメータおよびモール・クーロン式を組み合わせたすべり面の平均強度パラメータ算定式に、残留係数と平均強度の関係を加味し安全率を予測しようとするものである。新潟の地すべりを事例としたせん断強度と安定度評価についての検討結果によると、(1) すべり面の状態は一様ではなく、鏡肌面や脆弱な破砕岩が混在しているので、強度パラメ-タを明確にする必要がある。(2)破砕泥岩のピ-ク強度は内在亀裂によって大きく支配される。(3)残留強度はスメクタイト粒子に依存し大幅に低下する。(4)残留係数とすべり面の平均強度の間には一次関係が成立つので、残留係数の推定が可能である。(5)推定残留係数に基づく安定度評価法は、地すべりブロックが多数分布し、その中のいくつかが地すべりを起こしているような地区において、小康を保っている地すべりブロックの危険度を判定する場合に有効である。, 要約(欧文):In evaluating the stability of landslide, it is important to clarify the characteristics of residual strength of materials in the slip surface zone. The residual strength is the minimal shear strength along the surface where clay particles are finally oriented. The magnitude of the minimal shear displacement that is needed to attain to the residual state depends on the clay particle property and the normal effective stress. The magnitude of displacement as long as 40-60 cm for mudstone and 200-300cm for gravelly tuffaceous soil were required. A ring shear test is an effective method to attain the residual state, although long time is required due to the large-displacement shearing and the drained conditions. Residual strength parameter is closely connected with the physical and mineralogical characteristics in landslide soils. It is concluded that clay fraction, plastisity index and amount of smectite appear to be a useful guide to estimate the residual strength parameter, and that further examination of the matter is warranted. Back-analyzed strength parameters were not capable of predicting stability of landslide-prone slopes. The proposed method that incorporates a combination of back-analysis, residual and peak strength parameters, residual factor, safety factor and the Mohr-Coulomb's equation makes it possible to conduct a large scale stability evaluation. The method for calculations of strength parameters are featured by the followings: (1) Laboratory strength parameters are incorporated into the evaluation for soil mechanical validity. (2) The standard slice method, a method used in back-analysis for safety factors, is introduced. (3) Two parameters of residual and peak strengths are incorporated into the expression after residual factors are introduced. (4)The type of slides and the condition of slip surfaces are taken into considerations. Calculations of safety factors through the estimated residual factor are believed to be effective in determining

平成元年度・平成2年度科学研究費補助金(一般研究(B))研究成果報告書, 研究概要:地すべり土の大変位せん断挙動についての検討結果によると、(1)残留状態に到達するまでの最小せん変位量は土粒子の性質や垂直応力に依存する。(2)最小せん変位量は泥岩試料で40～60cm、凝灰質れき質土では200～300cmとなり大変位である。(3)残留強度測定は、三軸や直接せん断試験では無理であり、リングせん断試験が望ましいが、排水条件を満たす必要があるので、長時間を要する。残留強度パラメータφrと2μm以下粘土分CF、塑性指数Ipおよびスメクタイト量Smの関係についての検討結果によると、(1)φr-CF関係および Shear mode区分は、すべり面土と非すべり面土の違いや残留せん断面における鏡肌形成を推し量るのに有効である。(2)φrとIpの間にはφr=35.9・Ip^<-0.368>関係式が成り立つ。(3)φr=13.8-0.092・Sm関係式が成り立つ。(4)上記関係および関係式によっておよそそのφr推定が可能である。提案された安定度評価法は、残留係数、逆算法、実験強度パラメータおよびモール・クーロン式を組み合わせたすべり面の平均強度パラメータ算定式に、残留係数と平均強度の関係を加味し安全率を予測しようとするものである。新潟の地すべりを事例としたせん断強度と安定度評価についての検討結果によると、(1) すべり面の状態は一様ではなく、鏡肌面や脆弱な破砕岩が混在しているので、強度パラメ-タを明確にする必要がある。(2)破砕泥岩のピ-ク強度は内在亀裂によって大きく支配される。(3)残留強度はスメクタイト粒子に依存し大幅に低下する。(4)残留係数とすべり面の平均強度の間には一次関係が成立つので、残留係数の推定が可能である。(5)推定残留係数に基づく安定度評価法は、地すべりブロックが多数分布し、その中のいくつかが地すべりを起こしているような地区において、小康を保っている地すべりブロックの危険度を判定する場合に有効である。, 要約(欧文):In evaluating the stability of landslide, it is important to clarify the characteristics of residual strength of materials in the slip surface zone. The residual strength is the minimal shear strength along the surface where clay particles are finally oriented. The magnitude of the minimal shear displacement that is needed to attain to the residual state depends on the clay particle property and the normal effective stress. The magnitude of displacement as long as 40-60 cm for mudstone and 200-300cm for gravelly tuffaceous soil were required. A ring shear test is an effective method to attain the residual state, although long time is required due to the large-displacement shearing and the drained conditions. Residual strength parameter is closely connected with the physical and mineralogical characteristics in landslide soils. It is concluded that clay fraction, plastisity index and amount of smectite appear to be a useful guide to estimate the residual strength parameter, and that further examination of the matter is warranted. Back-analyzed strength parameters were not capable of predicting stability of landslide-prone slopes. The proposed method that incorporates a combination of back-analysis, residual and peak strength parameters, residual factor, safety factor and the Mohr-Coulomb's equation makes it possible to conduct a large scale stability evaluation. The method for calculations of strength parameters are featured by the followings: (1) Laboratory strength parameters are incorporated into the evaluation for soil mechanical validity. (2) The standard slice method, a method used in back-analysis for safety factors, is introduced. (3) Two parameters of residual and peak strengths are incorporated into the expression after residual factors are introduced. (4)The type of slides and the condition of slip surfaces are taken into considerations. Calculations of safety factors through the estimated residual factor are believed to be effective in determining

一滴の連続的落下による土塊の破壊試験を行ない, 破壊率と含水比および水滴の運動エネルギーとの関係を調べた結果2,3の知見を得た。(1)水温が高いほど単位時間当りの水滴数は増加し, 水滴径は小さくなる。したがって, エネルギー的には水滴径を大きくすることによって落下高さの過不足を補うことができる。(2)破壊率と土塊の初期含水比および水滴数の関係を6つのタイプに分類することによって水滴の衝撃に対する土構造の安定度の判別が容易になる。(3)一滴の連続的落下試験は人工降雨による結果とよい一致をみた。(4)破壊率と水滴の運動エネルギーの間には相関関係がある。(5)水滴(4mm径)による土塊の破壊試験には2.5m前後の落下高さがよいようである。, Disintegration tests of small soil block using falling water drops were made in order to investigate the relation between percentage of disintegration and the change of moisture contents, the kinetic energy of water drops. The apparatus for producing drops is shown in Fig. 1 and the height of hypodermic needle from the testing soil were 6.5m, 2.5m, 1.0m and 0.5m respectively. Distilled water was employed and the three testing soils (YAGAZI-silty KIN-clayey, TOMIGUSUKU-clayey) were used in this investigation. The results of the investigation were as follows : 1. The higher the water temperature the more increase the number of drops per unit time. 2. The mass of a drop was influenced by water temperature and higher of the water temperature the smaller the mass of a drop. 3. By enlarging the size of drop, the lack of kinetic energy-falling height- was made up. 4. The relation between percentage of disintegration and number of drops can be classified into six types as sown in Fig. 4,and this makes easy the judgment of stability of soil against the impact of drops. 5. The test result by continuous falling of a water drop resembles by artificial rainfall closely. 6. There were correlation between the percentage of disintegration and the kinetic energy of water drops. 7. 2.5 meters high of falling water drops will fit in this investigation.

比較的密度の高い領域の作成供試土塊について乾燥・収縮特性を追求し, 次の結果を得た。(1)土塊の乾燥に伴なう含水比減少曲線の最大曲率の点は減率乾燥第1から第2段への転移点に相当する。(2)限界含水比や収縮限界はTable 3に示すとおり, コンシステンシー指数(Ic)や乾燥密度(γd)の影響をほとんど受けない。(3)土塊の収縮は限界点に達する相当以前に終了しており, 収縮限界と限界含水比は一致しない。(4)収縮率(Pc)とIcの間にはFig.5に示すような関係があり, 可塑性の大きな土程Pcが大きい。(5)体積変化係数CvcはIcやγdと無関係だが, 練返しの影響を多少受ける。各試料における。Cvc(W=0のCvc)の平均値はKinとYagajiで比較的大きく, Tomigusukuで小さい。(6)配列指数によって検討すると, 土粒子はIc=0.68&acd;1.15の範囲で等方配列を示し, 1.15以上では平行配列を示す。, Experimental studies were made on the drying and shrinkage characteristics of soil blocks. The results obtained are as follows; 1. The water content at the maximum curvature of the water content-time curve corresponds to that in the boundary from the first stage of drying in decreasing rate to the second stage of drying in decreasing rate. 2. The critical water content and shrinkage limit are not affected very much by the consistency index (I_c) and dry density (γd) as showed in Table 3. 3. The shrinkage behavior of the soil blocks finishes considerably before reaching the critical water content. 4. The percentages of cubical contraction (P_c) are related to I_c as showed in Fig. 5,the more plasticity of a soil the larger Pc. 5. The coefficients of volumetric changes (C_) of the soil blocks have not to do with I_c and γd, but there is some difference in the shrinkage behavior due to remoulding, the averages of _oC_-values (C_ at w=0) of each of the samples are relatively large in Kin and Yagaji, and very small in Tomigusuku, Okinawa Island. 6. On the basis of the coefficient of particle orientation, the particle arrangement during shrinking of the soil block of I_c in the range of 0.68-1.15 has a isotropic arrangement and that above 1.15 is parallel.

(1)国頭礫層土壌と泥灰岩土壌のスレーキングは乾燥過程によって著しく影響され, PF5.5&acd;PF6.5の水分状態で高い崩壊率を示し, その経時変化も顕著である。石灰岩土壌は耐水性であり乾燥過程の影響もほとんど受けない。(2)高含水領域からPF4.5まではスレーキング現象がほとんどみられない。(3)PF6.5&acd;PF7.0では外皮様薄層が形成されるため崩壊に幾分時間的遅れがあり, 量的にもやや少ない。(4)3試料は, その主要粘土鉱物組成や理化学的性質を反映し, スレーキングの形態を異にする。(5)島尻泥灰岩土壌は, 母岩(泥岩)の工学的性質(6,8)を反映し, 他2試料に比して膨張・収縮挙動が顕著である。以上のように, スレーキング試験は, 雨滴の衝撃作用による供試土崩壊試験(4)の場合と比較して, 低PFと高PF領域において量的に多少異なるものの, ほぼ同様な崩壊現象を示した。また国頭礫層土壌は, スレーキングの結果からも高い受食性土壌であることが明らかになった。なお本研究は昭和49年度文部省科学研究費の補助を受けたものの一部である。終りに, 実険にあたって終始協力して下さった専攻生の上運天英夫(現沖縄県土地調査局勤務)と又吉盛正(現沖縄県農林水産部勤務)の両氏に謝意を表したい。, This paper deals with the effect of drying upon slaking and the swelling and shrinking properties of the erosive soil from Kunigami gravels (sample : Hamada, Kin-son), the soil from Shimajiri mudstone (sample : Tomigusuku, Tomigusuku-son) and the soil from Ryukyu limestone (sample : Komesu, Itomancity) The experimental results are summarized as follows : 1. Hamada and Tomigusuku undergo to the influence of drying and show marked phenomena of slaking by drying in PF5.5-PF6.5 of the soil moisture. Komesu is the Water-stable soil, and the amount of its slaking is a little. 2. The three samples have their own phenomena of slaking according to the clay minerals and chemical composition of soil. 3. The behaviour of swelling and shrinkage of Tomigusuku is remarkable as compared with those of the other samples and seems to reflect the engineening properties of parent rock, Shimajiri mudstone.

In areas of SHIMAJIRI MAAJI-soil, runoff coefficient in raining and variation of soil moisture at a drought are different from those in other areas. It should seem that the main factor depends on permeability of each formation in this areas. In this investigation, field tests of permeability and infiltration capacity were run on SHIMAJIRI MAAJI-soils and RYUKYU limestones. The data showed that the coefficients of permeability were in the range of 10^<-5>&acd;10^<-4>cm/sec in SHIMAJIRI MAAJI-soils, and the order of 10^<-2>cm/sec in RYUKYU limestone. We have studied permeability in this areas, using those data and physical properties of soil.

ピーク強度(τ_f)は垂直応力(σ)の関数であるばかりでなく過圧密比(n_P)の関数でもある。すなわち次式が成り立つ。τ_f=b+T・σ^n・n_P上式においてnpを先行圧密荷重(P_0)で置き換えると, τ_f=b+T・σ^・P_0ここにb, T, nは土性によって決まる定数である。これはP_0の一次関数であると同時に, P_0を一定にした場合のτ_f&acd;σ関係すなわち過圧密領域のセン断強度特性を示す。したがって, 強度定数を求めるためには, 問題にしている過圧密領域のτ_f&acd;σ関係の湾曲部を直線で置き換えて限定包絡線とする。このように, 任意の粘土に対しある限られた範囲のτ_f&acd;n_P関係を実験的に求めることによってその定数が決まるので, P_0が変化した場合のτ_f&acd;σの特性と強度定数を推定できる。, The shear strength line of an overconsolidated clay has a curvature when the shear strengths are determined by undrained tests and plotted against total normal stresses (σ). The degree of the curvature increases regularly with increasing preconsolidation stress (P_0) and overconsolidation ratio (n_p). In this paper the mathematical relationships that exist between the shear strength envelopes and P_0 and n_p are developed. The results are summarized as follows : 1. The peak strength (τf) may be expressed in terms of σ and n_p : ^τf=b^^^- + T. σ^n. n_p where b^^^-, T and n are constants dependent on the degree of overconsolidation and a given soil. 2. Using P_0 as a replacement for n_p, the following expression is obtained : τf=b^^^- + T. σ^. P_0 It shows not only the fact that the value of τf is proportional to the value of P_0,but also the relationship between τf and σ for P_0=constant. 3. The constants b^^^-, T and n are therefore determined from τf&acd;n_p relationship in the limited stress range for a given soil, and then the shear strength curves for various preconsolidation stress can be illustrated.

実験結果から次の点が明らかになった。1)ピーク以後のτ&acd;D曲線の形状は解析的に次式で表わされる。[numerical formula]ここに, b, cは過圧密比や土性によって決まる定数, τ_f, D_fはピーク強度とそれに対応する変位を示す。2)過圧密状態におけるτ&acd;Dの挙動は試料の持つ応力履歴によって大きく影響される。すなわち過圧密の程度が高い土ほど, 固結化が進み, 強度の増加とピーク後の強度低下が顕著である。3)ピーク強度と変位の比(τ_f/D_f), ブリトル指数(I_B), 初期変形係数(E_i)等のτ&acd;D曲線の形状係数と過圧密比とは相関関係が極めて高い。, It is a well-known fact that if an overconsolidated clay is strained beyond failure, its strenght will decrease and finally reach a certain constant value, the ULTIMATE STRENGTH (it is referred to especially as the RESIDUAL STRENGTH under slow drained shear test), which will remain constant for further straining. For the overconsolidated plastic clays the drop in shear strength after failure is very significant. In order to investigate the relation between stress-displacement behaviour after passing the peak i. e. rate of progressive reduction in strength from the peak to the ULTIMATE (or RESIDUAL) condition and degree of overconsolidation, a series of direct shear test has been conducted under each different conditions of overconsolidation ratio (the ratio of preconsolidation stress to effective normal stress, n_p=P_0/σ) respectively for P_0=constant, σ=constant and n_p=constant. From the test results the following points were clarified. 1. The general shape of the stress-displacement curve (τ&acd;D curve) of the postpeak can be expressed analytically by [numerical formula] where b and c are constant on the overconsolidation ratio and the materials. 2. The stress-displacement behaviour of the state of overconsolidation is greatly dependent on the stress history of the sample-the higher the overconsolidation ratio, the stiffer the soil. 3. The shape factors of the stress-displacement curve, initial tangent modulus (Ei), ratio of stress to displacement at failure (τf/Df) and brittle index (I_B), seem to be well expressed as a function of the overconsolidation ratio.

残留強度を求めるには, セン断破壊を生じた後の大変位に対するセン断抵抗を測定できる試験が必要とされる。この範ちゅうに入る試験方法や装置がSkemptonやBishop等によって提唱されているが, 結果の解釈や装置になお多くの問題がある。それゆえ, 著者は今までの研究を基礎にして次の二つの手法を考えた。(1)完全に形成されたすべり面に沿ってセン断移動がおこるのであれば, 平衡状態のもとで発揮される応力はヒズミの大きさにかかわらずある一定値を示すはずである。この条件を満足する試験方法として, 予想セン断角で切り離された上下供試体と, 上部供試体の側方移動を可能にする圧縮セン断機構(BBピストン, 3-2-1参照)を用いて三軸圧縮試験を行ない, その破壊面における応力解析から残留強度を求める。(2)過圧密粘土では, 応力履歴によってτ&acd;ε曲線が種々変化し, 特にピークの位置とその後の曲線の形状が残留強度の大きさを左右していることに着眼して, τ&acd;ε曲線を式化し, その利用を試みる。なお, (2)においてはτ&acd;ε曲線が重要となってくるので, 過圧密比が変化する場合τ&acd;ε曲線が如何なる特性を示すかについて実験研究を行うと同時にτ&acd;σ特性についても考察を加えた。また沖縄における農地保全上, 重要な課題となる第三紀の島尻層泥岩(過圧密粘土)斜面の安定問題には未解明な点が多いため, 安定解析に進行性破壊や完全軟化の概念の導入を考え, Skempton法を用いて軟化泥岩の残留強度を求めた。そして実際の地すべり事例の安定解析に適用して, 地すべり機構解明の一助にした。まず, 一般的なSkemptonの試験法を用いて島尻層軟化泥岩の残留強度定数を求めた(2-2)。島尻層泥岩でみられる破壊面には鏡肌が形成されており, 残留強度に達していることがうかがえる。しかし泥岩について鏡肌が認められるほどの変位を与えるセン断試験はいままで行なわれておらず, 残留強度に関する知見は皆無である。したがって, すべり面付近の新鮮軟化泥岩と完全軟化粘土, 自然分離面, および作成分離面についてSkempton法による長期繰返しセン断試験を行ない, 残留強度やブリトル指数を求めた。新鮮軟化泥岩のピーク強度定数はC_=1.20&acd;1.55kg/cm^2, φ_=19&acd;22°, 同一の事前セン断面における残留強度定数はC_dr=0,φ_=17&acd;19°の範囲にある。さらにセン断破壊面が十分発達した自然分離面ではC_=0,φ_=17°, 作成分離面ではC_=0,φ_=15°となる。完全軟化粘土の場合, C_=C_=0は言うまでもないが, φ_=23°, φ_=19°は新鮮軟化泥岩や分離面のφ_よりも大きい。軟化泥岩のブリトル指数(I_B)は, σ'_n=1&acd;5kg/cm^2の応力範囲でI_B=80&acd;50%となる。またφ'_r&acd;粘土分の関係から島尻層泥岩はOxford Clay, Jari Jakfield, London Clayの過圧密粘土と類似していることが明らかになった。, つづいて, τ&acd;ε特性を用いて残留強度を求める著者の手法について述べた(2-3)。すなわち, 長期セン断試験結果を式化し, その最大値および最終値を, それぞれピーク強度, 残留強度とみなすものである。これには排水条件を満足する緩速なセン断強度が要求される。しかし, 急速セン断結果(非排水)から残留強度を推定する場合はτ&acd;ε曲線の最大値と最終値を時間効果で補正し求めることができる(2-3-3) これらの結果をSkempton法による試験と対比させた。すなわちτ&acd;ε曲線を利用する手法は, Skempton法よりσ=0.1&acd;0.7kg/cm^2の範囲において1&acd;17%程度大きめの残留強度が与えられるが, 作成分離面により求める場合と同様, 短時間に残留強度をえようとする場合有効な方法といえよう。一面セン断試験によるSkempton法に対し, 著者は三軸圧縮試験による残留強度決定法を提案した(3)。その試験における圧縮機構は, 圧縮時に上部供試体が作成セン断面に沿って滑動できるようにBBピストンを通じて負荷するものであり, 残留強度を計算するための式は破壊面の応力解析によって導びいた。すなわち[numerical formula](3-2-18)式のτ^^^-(η)は, BBピストンのもとで上下供試体が相対的なすべり変位を起こすときに軸圧が偏心荷重として作用することによって実際にすべり面に生じるセン断応力(3-2 -12)平均値で与えられ, 有効セン断面積(3-2-21)とゴムスリーブの拘束による軸差応力の増分(3-2-31)が考慮されている。そして完全に形成されたすべり面, すなわち作成セン断面に沿うセン断移動において, 定常状態に入った後に発揮される応力はヒズミの大きさにかかわらず一定値を示すので, τ^^^-(η)&acd;ε関係においてdτ^^^-(η)/dε=0になったときのτ^^^-(η)値を残留強度τ_rと考えればよい。この手法を鳥栖試料に適用した結果, C'_f=0.569kg/cm^2,φ'_f=23°50, This paper deals with the methods to determine the residual strength necessary for stability analysis of the slope and the application of the residual strength to practical problems. In order to obtain the residual strength, it is necessary to develop a simpler and reasonably satisfactory method to measure the shear resistance after large displacement. Test techniques and devices falling under this category of the method have been developed by Skempton, Bishop and others, but they still involve many problems in the interpretation of their test results and the mechanism of the devices. Based on his own studies and works done in foreign countries on the subject, the author proposes following two methods to evaluate the shear strength. (1) If a shearing of an overconsolidated clay occurs along a fully-formed slip plane, the shear stress mobilized after reaching the equilibrium state should be a fixed value, independently of the magnitude of the strain (displacement). The test method to satisfy this condition could be as follows : The residual strength is obtained using the specimen having the shear plane cut at an expected angle to the horizontal and the triaxial compression apparatus having a mechanism of compression and enable the top half of the specimen to move in lateral direction. (2) Noting the facts that the shear stress-strain (displacement) characteristics of an overconsolidated clay is affected by the stress history and that the residual value depends strongly on both the magnitude of the peak value and the shape of the curve after the post peak, the author tried to formularize a curve applicable to the determination of the residual strength. Since the shear stress-strain (displacement) curve is very important in the method (2) mentioned above, a few points have also been discussed on the shear stress-strain (displacement) characteristics in the case that the overconsolidation ratio changes and also on the τ&acd;σ characteristics., There are a number of unsolved points related to the stability of natural slopes in Shimajiri mudstone of an overconsolidated clay in Okinawa. In order to approach these problems the author, introducing the concept of the progressive failure and softening to the stability analysis of the slope, has obtained the residual strength of a softened mudstone by the reversal direct shear technique developed by Skempton. The results obtained were applied to stability analyses of actual landslides. The analyses are expected to be of much aid to make clear the mechanism of landslides. In the first place, the residual strength of softened Shimajiri mudstone has been determined with common procedure of the reversal shear test (2.2). From the slickenside observed on natural slip planes in Shimajiri mudstone, it is seen that the shear strength mobilized had fallen to the residual value. No reports, however, have been published concerning the residual strength of Shimajiri mudstone and no shear tests have been performed either for such large displacements as the surface of shear plane is polished to form the slickensides afterwards. Hence, the drained reversal shear tests were performed on intact softened mudstones, fully-softened clays, natural joints, and specimens with a pre-cut plane. The following results have been obtained : (1) After 5-cycle shear tests, no further reduction of strength occurred in the intact softened mudstone. Consequently, no further tests were carried out beyond 5-cycles. (2) The shear tests on intact softened mustone have shown the peak strength parameters of c_=1.20&acd;1.55kg/(cm)^2 and φ_=19&acd;22°, and the residual strength parameters of c_=0 and φ_=17&acd;19°. (3) The displacements necessary to reach the residual strength along the natural joint and pre-cut plane of specimens have been smaller than those of intact samples : a single cycle of reversal shear test has been sufficient to reduce the strength to a value very close to t

びょう打ち銃と山中式土壌硬度計を使用して泥岩切土ノリ面の風化状態と硬度の関係について調査し, 以下の結果を得た。(1)未風化泥岩のピン貫入量及び硬度指数はそれぞれP=4&acd;6cm, Y=34&acd;37mmとなり, 泥岩表土ではそれぞれP=30&acd;40cm, Y=5&acd;25mmとなる。(2)ガリ侵食面ではP=3&acd;8cmとなり, 表層風化部が絶えず雨水によって洗掘されて泥岩が露頭している。(3)切土面は乾燥・湿潤を繰返し, P=15&acd;20cmの風化層を早期に形成する。深度25cm付近では含水比変化も小さく, 風化速度も緩慢となる。(4)非植生ノリ面ではP=10&acd;37cmが得られ, 風化土の崩落や小規模崩壊によってノリ面が絶えず後退している。(5)植生ノリ面ではP=10&acd;17cmが得られ, 植生の被覆効果によって表層及び内部の泥岩の乾燥化が抑制され, 風化速度も緩慢となる。(6)地すべり多発斜面の軟化泥岩の硬度はP=25&acd;30cm, Y=24&acd;26mmを示し, かなり強度を低下させている。, Based on the idea that strength is the best index of weathering and implies a hardness when the degree of weathering is classified from the engineering point of view, this report deals with the relationship between the progressive state of weathering and hardness in the cutting slope of Shimajiri mudstone. Measurement of the hardness was conducted by using a pin penetration gun and a soil hardnessmeter of Yamanaka-shiki. Results obtained are as follows : 1. The pin penetration distance P is expressed in P=4-6cm, and the measured hardness Y in Y=34-37mm, respectively, in unweathered Shimajiri mudstone; and they have been P=30-40cm, and Y=5-25mm, respectively, in the soil layer from the mudstone. 2. P=3-8cm has been obtained in the face of a gully formed by erosion. 3. The cut plane in the mudstone repeats drying and wetting and forms soon a weathered layer with the hardness of P=15-20cm 4. In the slope without vegetation, P=10-37cm has been obtained, and the face of the slope keeps going back by falling of weathered soil in the mudstone and by small-scale collapse. 5. In the slope covered with vegtation P=10-17cm has been obtained. It is observed that drying of the mudstone is suppressed by the covering effect. 6. The softened mudstone has such hardness as P=25-30cm and Y=24-26mm, and its strength drops considerably in comparison with that of non-softened mudstone.

ピーク強度(τ_f)は垂直応力(σ)の関数であるばかりでなく過圧密比(n_P)の関数でもある。すなわち次式が成り立つ。τ_f=b+T・σ^n・n_P上式においてnpを先行圧密荷重(P_0)で置き換えると, τ_f=b+T・σ^・P_0ここにb, T, nは土性によって決まる定数である。これはP_0の一次関数であると同時に, P_0を一定にした場合のτ_f&acd;σ関係すなわち過圧密領域のセン断強度特性を示す。したがって, 強度定数を求めるためには, 問題にしている過圧密領域のτ_f&acd;σ関係の湾曲部を直線で置き換えて限定包絡線とする。このように, 任意の粘土に対しある限られた範囲のτ_f&acd;n_P関係を実験的に求めることによってその定数が決まるので, P_0が変化した場合のτ_f&acd;σの特性と強度定数を推定できる。, The shear strength line of an overconsolidated clay has a curvature when the shear strengths are determined by undrained tests and plotted against total normal stresses (σ). The degree of the curvature increases regularly with increasing preconsolidation stress (P_0) and overconsolidation ratio (n_p). In this paper the mathematical relationships that exist between the shear strength envelopes and P_0 and n_p are developed. The results are summarized as follows : 1. The peak strength (τf) may be expressed in terms of σ and n_p : ^τf=b^^^- + T. σ^n. n_p where b^^^-, T and n are constants dependent on the degree of overconsolidation and a given soil. 2. Using P_0 as a replacement for n_p, the following expression is obtained : τf=b^^^- + T. σ^. P_0 It shows not only the fact that the value of τf is proportional to the value of P_0,but also the relationship between τf and σ for P_0=constant. 3. The constants b^^^-, T and n are therefore determined from τf&acd;n_p relationship in the limited stress range for a given soil, and then the shear strength curves for various preconsolidation stress can be illustrated.

In areas of SHIMAJIRI MAAJI-soil, runoff coefficient in raining and variation of soil moisture at a drought are different from those in other areas. It should seem that the main factor depends on permeability of each formation in this areas. In this investigation, field tests of permeability and infiltration capacity were run on SHIMAJIRI MAAJI-soils and RYUKYU limestones. The data showed that the coefficients of permeability were in the range of 10^<-5>&acd;10^<-4>cm/sec in SHIMAJIRI MAAJI-soils, and the order of 10^<-2>cm/sec in RYUKYU limestone. We have studied permeability in this areas, using those data and physical properties of soil.

一滴の連続的落下による土塊の破壊試験を行ない, 破壊率と含水比および水滴の運動エネルギーとの関係を調べた結果2,3の知見を得た。(1)水温が高いほど単位時間当りの水滴数は増加し, 水滴径は小さくなる。したがって, エネルギー的には水滴径を大きくすることによって落下高さの過不足を補うことができる。(2)破壊率と土塊の初期含水比および水滴数の関係を6つのタイプに分類することによって水滴の衝撃に対する土構造の安定度の判別が容易になる。(3)一滴の連続的落下試験は人工降雨による結果とよい一致をみた。(4)破壊率と水滴の運動エネルギーの間には相関関係がある。(5)水滴(4mm径)による土塊の破壊試験には2.5m前後の落下高さがよいようである。, Disintegration tests of small soil block using falling water drops were made in order to investigate the relation between percentage of disintegration and the change of moisture contents, the kinetic energy of water drops. The apparatus for producing drops is shown in Fig. 1 and the height of hypodermic needle from the testing soil were 6.5m, 2.5m, 1.0m and 0.5m respectively. Distilled water was employed and the three testing soils (YAGAZI-silty KIN-clayey, TOMIGUSUKU-clayey) were used in this investigation. The results of the investigation were as follows : 1. The higher the water temperature the more increase the number of drops per unit time. 2. The mass of a drop was influenced by water temperature and higher of the water temperature the smaller the mass of a drop. 3. By enlarging the size of drop, the lack of kinetic energy-falling height- was made up. 4. The relation between percentage of disintegration and number of drops can be classified into six types as sown in Fig. 4,and this makes easy the judgment of stability of soil against the impact of drops. 5. The test result by continuous falling of a water drop resembles by artificial rainfall closely. 6. There were correlation between the percentage of disintegration and the kinetic energy of water drops. 7. 2.5 meters high of falling water drops will fit in this investigation.

比較的密度の高い領域の作成供試土塊について乾燥・収縮特性を追求し, 次の結果を得た。(1)土塊の乾燥に伴なう含水比減少曲線の最大曲率の点は減率乾燥第1から第2段への転移点に相当する。(2)限界含水比や収縮限界はTable 3に示すとおり, コンシステンシー指数(Ic)や乾燥密度(γd)の影響をほとんど受けない。(3)土塊の収縮は限界点に達する相当以前に終了しており, 収縮限界と限界含水比は一致しない。(4)収縮率(Pc)とIcの間にはFig.5に示すような関係があり, 可塑性の大きな土程Pcが大きい。(5)体積変化係数CvcはIcやγdと無関係だが, 練返しの影響を多少受ける。各試料における。Cvc(W=0のCvc)の平均値はKinとYagajiで比較的大きく, Tomigusukuで小さい。(6)配列指数によって検討すると, 土粒子はIc=0.68&acd;1.15の範囲で等方配列を示し, 1.15以上では平行配列を示す。, Experimental studies were made on the drying and shrinkage characteristics of soil blocks. The results obtained are as follows; 1. The water content at the maximum curvature of the water content-time curve corresponds to that in the boundary from the first stage of drying in decreasing rate to the second stage of drying in decreasing rate. 2. The critical water content and shrinkage limit are not affected very much by the consistency index (I_c) and dry density (γd) as showed in Table 3. 3. The shrinkage behavior of the soil blocks finishes considerably before reaching the critical water content. 4. The percentages of cubical contraction (P_c) are related to I_c as showed in Fig. 5,the more plasticity of a soil the larger Pc. 5. The coefficients of volumetric changes (C_) of the soil blocks have not to do with I_c and γd, but there is some difference in the shrinkage behavior due to remoulding, the averages of _oC_-values (C_ at w=0) of each of the samples are relatively large in Kin and Yagaji, and very small in Tomigusuku, Okinawa Island. 6. On the basis of the coefficient of particle orientation, the particle arrangement during shrinking of the soil block of I_c in the range of 0.68-1.15 has a isotropic arrangement and that above 1.15 is parallel.

一般に畑地や斜面において石灰岩風化土は乾燥しやすく, 泥岩風化土は保水力に富み, 受食性の国頭礫層土は両者の中間に位するといわれているが, 一連のガラスブロックによる水分測定試験結果から各試料の乾燥特性についての正しい認識のために役立つ2,3の解答が得られた。(1)恒率乾燥から減率乾燥への変位点(限界含水比)は30%前後にみられるが, その含水状態への到達時間は各試料・各深さによって著しく異なる。(2)土層の水分分布は時間の経過と共に, 表面から深さ7&acd;10cm位までの含水比差が大くなるが, 10cm以上の深部ではその差が小さい。(3)国頭礫層土の上表面にPF5以上の薄い乾燥膜が短期間(400cal/(cm)^2/dayとして連続7日間)に形成される。これは下層土の水分保持に寄与する反面, 水食にたいし弱点となる。(4)干ばつ性の石灰岩風化土は土層箱試験結果からすれば必ずしも乾燥速度の高い土とは言い難い。(その土の干ばつ性にたいしては地質学的な層序の影響が大だと考える)。(5)島尻泥岩風化土においてはキ裂の発達が著しく, 下層部分の乾燥を促進する。(6)PF-含水比曲線を作成し, Glass-beads block soil moisture instrumentと併用することによってPF値を知ることができる。例えば積算日射量9.5kcal/(cm)^2下における乾燥状態は国頭礫層土層でPF4.2&acd;5.0,石灰岩風化土層でPF3.6&acd;5.0,泥岩風化土層でPF3.8&acd;5.0となる。, In order to know the drying characteristics of the erosive soil from Kunigami gravels (sample : Yaka, Kin-son), the soil from Ryukyu limestone (sample : komesu, Itoman-city) and the soil from Shimajiri mudstone (sample : Tomigusuku, Tomigusuku-son), a glass-beads block soil moisture instrument was used. Before the instrument was put in practical use, fundamental experiments were carried out on the operation of the instrument and its calibration. The sample was packed uniformly in drying box, and was tested in two cases : the thermostatic drying and the out-door drying. The experimental results are summarized as follows : 1. The boundaries transiting from drying in constant rate to drying in decreasing rate of three samples are seen respectively in water constant of about thirty percents, and the drying time required to nearly reach this soil moisture differs greatly with each sample and each depth. 2. Water content profile in soil layer varies with time. In this profile, the difference in water content so far 7&acd;10cm depth from upper surface becomes very large with time, but there is not so much difference in water content in the parts deeper than 10cm depth. 3. Thin film of drying above PF 5 is formed on the upper surface of erosive soil from Kunigami gravels in the short period. 4. From the results of drying box tests, it doesn't always follow that drying velocity of soil from Ryukyu limestone droughting frequently is large. 5. Cracks developed in the soil from Shimajiri mudstone cause the evaporation of surface to increase markedly and accelerate drying of the lower parts of layer. 6. PF value is to be known by using the glass block soil moisture instrument along with the PF- water content curve. For instant, under the cumulative global radiation of 9.5kcal/(cm)^2 that the soil layers recived in the drying test period, soil from Kunigami gravels was dried up to the PF 4.2&acd;5.0 of soil moisture, soil from Ryukyu limestone up to the PF 3.6&acd;5.0,and soil fr

(1)国頭礫層土壌と泥灰岩土壌のスレーキングは乾燥過程によって著しく影響され, PF5.5&acd;PF6.5の水分状態で高い崩壊率を示し, その経時変化も顕著である。石灰岩土壌は耐水性であり乾燥過程の影響もほとんど受けない。(2)高含水領域からPF4.5まではスレーキング現象がほとんどみられない。(3)PF6.5&acd;PF7.0では外皮様薄層が形成されるため崩壊に幾分時間的遅れがあり, 量的にもやや少ない。(4)3試料は, その主要粘土鉱物組成や理化学的性質を反映し, スレーキングの形態を異にする。(5)島尻泥灰岩土壌は, 母岩(泥岩)の工学的性質(6,8)を反映し, 他2試料に比して膨張・収縮挙動が顕著である。以上のように, スレーキング試験は, 雨滴の衝撃作用による供試土崩壊試験(4)の場合と比較して, 低PFと高PF領域において量的に多少異なるものの, ほぼ同様な崩壊現象を示した。また国頭礫層土壌は, スレーキングの結果からも高い受食性土壌であることが明らかになった。なお本研究は昭和49年度文部省科学研究費の補助を受けたものの一部である。終りに, 実険にあたって終始協力して下さった専攻生の上運天英夫(現沖縄県土地調査局勤務)と又吉盛正(現沖縄県農林水産部勤務)の両氏に謝意を表したい。, This paper deals with the effect of drying upon slaking and the swelling and shrinking properties of the erosive soil from Kunigami gravels (sample : Hamada, Kin-son), the soil from Shimajiri mudstone (sample : Tomigusuku, Tomigusuku-son) and the soil from Ryukyu limestone (sample : Komesu, Itomancity) The experimental results are summarized as follows : 1. Hamada and Tomigusuku undergo to the influence of drying and show marked phenomena of slaking by drying in PF5.5-PF6.5 of the soil moisture. Komesu is the Water-stable soil, and the amount of its slaking is a little. 2. The three samples have their own phenomena of slaking according to the clay minerals and chemical composition of soil. 3. The behaviour of swelling and shrinkage of Tomigusuku is remarkable as compared with those of the other samples and seems to reflect the engineening properties of parent rock, Shimajiri mudstone.

(1)すべり面付近の新鮮軟化泥岩の圧密降伏応力はPy=10^/cm^2前後にある。(2)軟化泥岩の繰返しセン断試験結果からピーク強度定数はCdf=1.20&acd;1.55^/cm^2,φdf=19&acd;22°, 残留強度定数はCdr=0,φdr=17&acd;19°の範囲にある。(3)セン断破壊面が十分発達した自然分離面ではCdr=0,φdr=17°, 作成分離面ではCdr=0,φdr=15°となる。(4)軟化泥岩のブリトル指数は, σ_n=1&acd;5^/cm^2に対しおよそI_B=80&acd;50%となり, Py/σ_nとの関係ではI_B=44.2log Py/σ_n+32.5が成り立つ。(5)完全軟化粘土の正規圧密セン断から得られたφ_Nf=23°, φ_Nr=19°は分離面で求めたφdrよりも大きめである。, Drained shear tests were performed with shear box on intact softened mudstone, fully-softened clay, natural joint, and specimen with pre-cut plane. The following results have been obtained : 1. The consolidation yield stress of intact softened mudstone is about 10kg/(cm)^2. 2. Residual strength was determined with the common procedure of reversal shear tests. After 5-cycle shear tests no further reduction of strength occurred in the intact softened mudstone. Consequently the tests were not carried further than 5-cycles. 3. The shear tests on the intact softened mudstone show the peak strength parameters of Cdf=1.20-1.55kg/(cm)^2 and φdf=19-22°, and the residual strength parameters of Cdr=0 and φdr=17-19°. 4. The displacement necessary to reach the residual strength along natural joint and precut plane of specimen is smaller than that of intact sample : a single cycle of reversal shear test is sufficient to reduce the strength to a value very near to the residual one. 5. The shear tests on the natural joint and the specimen with pre-cut plane show the residual strength parameters of Cdr=0 and φdr=17°, and Cdr=0 and φdr=15°, respectively. 6. The brittleness index of the intact softened mudstone ranges from 0.8 to 0.5 as σ'_n changes from 1 to 5kg/(cm)^2,and the index is related to Py/σ'_n as follows : I_B=44.2log Py/σ'_n+32.5. 7. The friction angles of fully-softened clay are slightly larger than those along the joint and pre-cut plane.

びょう打ち銃と山中式土壌硬度計を使用して泥岩切土ノリ面の風化状態と硬度の関係について調査し, 以下の結果を得た。(1)未風化泥岩のピン貫入量及び硬度指数はそれぞれP=4&acd;6cm, Y=34&acd;37mmとなり, 泥岩表土ではそれぞれP=30&acd;40cm, Y=5&acd;25mmとなる。(2)ガリ侵食面ではP=3&acd;8cmとなり, 表層風化部が絶えず雨水によって洗掘されて泥岩が露頭している。(3)切土面は乾燥・湿潤を繰返し, P=15&acd;20cmの風化層を早期に形成する。深度25cm付近では含水比変化も小さく, 風化速度も緩慢となる。(4)非植生ノリ面ではP=10&acd;37cmが得られ, 風化土の崩落や小規模崩壊によってノリ面が絶えず後退している。(5)植生ノリ面ではP=10&acd;17cmが得られ, 植生の被覆効果によって表層及び内部の泥岩の乾燥化が抑制され, 風化速度も緩慢となる。(6)地すべり多発斜面の軟化泥岩の硬度はP=25&acd;30cm, Y=24&acd;26mmを示し, かなり強度を低下させている。, Based on the idea that strength is the best index of weathering and implies a hardness when the degree of weathering is classified from the engineering point of view, this report deals with the relationship between the progressive state of weathering and hardness in the cutting slope of Shimajiri mudstone. Measurement of the hardness was conducted by using a pin penetration gun and a soil hardnessmeter of Yamanaka-shiki. Results obtained are as follows : 1. The pin penetration distance P is expressed in P=4-6cm, and the measured hardness Y in Y=34-37mm, respectively, in unweathered Shimajiri mudstone; and they have been P=30-40cm, and Y=5-25mm, respectively, in the soil layer from the mudstone. 2. P=3-8cm has been obtained in the face of a gully formed by erosion. 3. The cut plane in the mudstone repeats drying and wetting and forms soon a weathered layer with the hardness of P=15-20cm 4. In the slope without vegetation, P=10-37cm has been obtained, and the face of the slope keeps going back by falling of weathered soil in the mudstone and by small-scale collapse. 5. In the slope covered with vegtation P=10-17cm has been obtained. It is observed that drying of the mudstone is suppressed by the covering effect. 6. The softened mudstone has such hardness as P=25-30cm and Y=24-26mm, and its strength drops considerably in comparison with that of non-softened mudstone.

排土方法がすべり面強度定数と密接な関係にありながら, 仮定に基づいた強度定数を使用することは安全率を不確実なものにするため, 設計が不鮮明になり, 適切な対策を行うことができない。したがって, セン断試験結果をc'-φ'図と関係づけて決定した強度定数c^^^-', φ^^^-'を排土工に適用して安全率の問題を論じることは意義あることである。検討結果を箇条書きにすると, 以下のようになる。(1)翁長地内の地すべりにおいてはすべり面の強度低下が著しく, 残留係数はR=0.966となる。(2)c'-φ'関係式とモール・クーロンの破壊規準に残留係数を導入することによって, 地すべり面の平均セン断強度定数c^^^-', φ^^^-'が一義的に決まる。(3)地すべり対策では, 信頼できる強度定数に基づいて設計がなされるべきであり, 翁長地内地すべりの場合c^^^-'=0.136kg/cm^2,φ^^^-'=14°27'を適用した結果, 良好である。(4)Benchingは, Flatteningに比べて排土効果が大であるが, 実際地すべりに適用するに際しては二次すべりの危険性や経済性も考慮した両者の有利な組合わせをButtress等の押え工と併用すべきである。, This report deals with the determination of the average shear strength parameters, ^^^- and <φ'>^^^-, mobilized on the slip surface at sliding. In general, it is difficult to explain the occurrence of a landslide with stability analysis based on the result of routine tests on an overconsolidated clay like Shimajiri mudstone, and a problem always arises in selecting the kind of strength parameters to be used. In order to approach the problem, the residual factor, R, is introduced into the c'-φ' relationship obtained by the back analysis and the failure criteria of Mohr-Coulomb, and this makes the determination of the parameters, ^^^- and <φ'>^^^-, possible. This report also considers the remedial excavation (flattening and benching cut) on the landslide and indicates, from the investigation into the relation between the quantity of excavation and satety factor resulting from stability analysis based on the parameters, ^^^- and <φ'>^^^-, that benching of the slope becomes clear to be more available than flattening. Benching work, however, has a close connection with the satety of a slope and a structure located to the upper part of the troubled area. Consequently, a method to effectively combine the both excavations should be used at the present time, together with buttress, counterweight fills and so on.