Effect of NaCl solution as pore water on the residual shear strength and
index properties of soil from mudstone areas
Gyanu Ratna TULADHARａ）＊, Hideaki MARUIｂ）, Naoki WATANABEｂ） and Binod TIWARIｃ） |
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Abstract
NaCl solution has significant effect on the residual shear strength of soil from mudstone areas. Soil samples were collected from the intact rock（unsheared zone）and sliding surface（sheared zone）of five mudstone landslide areas. Mixtures of distilled water and the intact rock possessed higher electric conductivity than those of distilled water and the sliding surface soil. When these samples were leached with distilled water for five times, they showed a substantial decrease in the electric conductivity. The residual shear strength varies according to the NaCl concentration in the pore water. Ring shear tests were also carried out in the commercial standard clays as bentonite and kaoline to understand the shear strength characteristics of the mudstone soils. When bentonite was treated with NaCl solution as pore water, it showed about three times increase in residual shear strength and decrease to one quarter in liquid limit. The effect of NaCl solution as pore water in kaoline was comparatively low. The residual shear strength of soil from mudstone area also increased when it was treated with NaCl solution as pore water. The result of the X‐ray diffraction analysis showed that the proportion of smectite is higher than that of kaolinite in the residual soil from mudstone. These smectite minerals were found to be highly sensitive to NaCl solution. Because of the sensitive changing character of smectite minerals to NaCl solution, soil samples with NaCl rich water showed lower value in consistency limits and higher value in the residual shear strength compared to soil samples with distilled water. The findings suggest that the residual shear strength and index properties should be considered as variable properties as a result of the change in the pore water. Such properties are useful to understand frequent re‐activation of the landslide occurring in the mudstone areas.
Key words:residual shear strength, index properties, NaCl solution, clay minerals |
すべり面の最大深さを用いた強度定数の推定法
Estimation of strength parameters based on maximum thickness of sliding mass in a failed slope
蒋 景彩ａ）＊・山上拓男ａ）・神田幸正ｂ）
Jing‐Cai JIANG, Takuo YAMAGAMI and Yukimasa KANDA |
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Abstract
This paper first shows that in a uniform slope with a given pore water pressure distribution the location of the critical slip surface for a particular method of slices is dependent only upon the c’/ tan φ’ ratio of that slope. Then, two representative types of slope profiles with a rotational sliding mode are presented to model actual slope failures, and two dimensionless parameters are introduced for each of the two slope models. Charts showing the relationship between these two parameters are obtained for typical slope inclinations and three different values of the pore pressure ratio. Using the charts and the safety factor equation of a method of slices, a unique pair of（c’，φ’）values can be rapidly determined based on the failure surface in a uniform slope. The proposed method is demonstrated on the results back calculated from two well‐documented failed slopes.
Key words:back analysis, failed slopes, strength parameters, limit equilibrium method, critical slip surface, graφc methods
和文要旨
まず間隙水圧分布が与えられた均質斜面において，極限平衡法の安全率算定理論による臨界すべり面の位置はその斜面の粘着力c’と内部摩擦角tan φ’との比（c’/ tan φ’）にのみ依存することを示した。この事実は，すべり面の最大深さと対応するのは，慣行法が示唆する粘着力ではなく，c’/ tan φ’の値であることを意味する。
次いで地山強度の新奇な逆算法を構築すべく，斜面を二つのタイプにモデル化した後，二つの無次元パラメータを導入して，これらパラメータと斜面勾配および間隙水圧係数の関係を規定する図表を作成した。この図表と安全率算定式を活用すれば，すべり面の最大深さに基づいてすべり面に沿う強度定数（c’，φ’）を唯一かつ簡便に逆算することができる。
構築した逆算法を幾つかの事例に適用したところ，精度的に十分満足できる解が得られた。ただし，ここでは斜面形状を理想化しているため，複雑な形状の斜面の場合，解の精度が幾分低下することは否めない。従って，この方法は何よりも簡便で迅速に強度定数を逆算できる点にその意義を見出すべきである。
キーワード：逆解析，破壊斜面，強度定数，極限平衡法，臨界すべり面，計算図表 |
地すべり地の堆積物の諸相とシーケンス―山形県朝日町八ツ沼地すべりを例として―
Some facies and its sequence for the sediments of landslide :As an example
of the Yatsunuma Landslide in Yamagata Prefecture, Northeast Japan
山野井徹ａ）＊
Tohru YAMANOI |
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Abstract
Some sediments of the head of landslide blocks were observed, which appeared by road construction. Some sediments of this area were described geologically and classified into three facies according to the forming mechanism. The facies have a sequence of sedimentation as one cycle of landslide erosion. Namely,（１）Occurred of landslide event as a mass movement on the slope（forming of the“event facies”）. In this time, sliding area is turned into a low land with a rough surface, which becomes a sedimentary field.（２）The rough surface of the lowland changes into a flat surface by mainly of an inflow water action caused rapid sedimentation and erosion（forming of the“repairing facies”）.（３）After weak supply of eroded material, eolian deposits become dominant sedimentation, which cover slowly on the surface（forming of the“covering facies”）.
By the clarification of the sequence or multiple sequence of a landslide area, it is possible to recognize a detail history of landslide.
Key words:sequence of sediments, sediment of landslide, event facies, repairing facies, covering facies, history of a landslide
和文要旨
道路開設によって地すべり地の頭部に良好な露頭が現れ，この露頭の観察を行った。この区域での堆積物の地質学的記載を行い，成因的に３つの相に区分した。それらの相は地すべり侵食の１サイクルとしての堆積シーケンスである。すなわち，(１)斜面にマスムーブメントとしての地すべり事件が発生する（「事件相」の形成）。この際，凹凸のある低地ができて堆積の場が生ずる。(２)低地の凹凸は，そこに流入する水の作用が主体となって，侵食と埋め立てが速やかに進行して平滑化が進む（「修復相」の形成）。(３)やがて侵食物質の供給が弱まると風成層の堆積が卓越し，ゆっくりとした堆積により表層が覆われていく（「被覆相」の形成）。
地すべり地のシーケンスや多重シーケンスを解析することにより地すべり地の詳細な履歴を知ることができる。
キーワード：堆積物のシーケンス，地すべり堆積物，事件相，修復相，被覆相，地すべりの歴史 |
地すべり形態に及ぼすボトルネック構造の影響
The Influence of bottle neck structure on the behavior of landslide
佐々木慶三ａ）・宜保清一ｂ）＊・中村真也ｂ）・周 亜明ｃ）
Keizo SASAKI, Seiichi GIBO, Shinya NAKAMURA and Yaming ZHOU |
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Abstract
The number of sliding units in a landslide has greatly affected on the generation mechanism of the landslide. Bottle neck structure is one of the controlling factors of the landslide behavior, however, roles of the bottle neck structure are still not well known due to the limited number of published researches. The bottle neck structure is considered to provide controlling effects the development and direction of movement of the sliding unit. The mutual interaction between multiple bottle neck structures can develop to a single sliding unit which can ultimately cause a large‐scale landslide.
Key words:huge landslide, geologic structure, sliding unit, bottle neck structure
和文要旨
地すべりが単独の移動体からなるか，二つ以上の移動体の集合からなるかは，地すべりの発生機構と深くかかわる。地すべり形態を規制する要因の一つにボトルネック構造があるが，公表事例が少なく，その役割は不明であった。ボトルネックは，地すべり移動体の分化と移動方向を規制する効果がある。また，複数のボトルネックの相互関連によって，単一の移動体からなる長大地すべりを形成することがある。
キーワード：長大地すべり，地質構造，地すべり移動体，ボトルネック構造 |
崩壊面から湧出する地下水の赤外画像による遠隔観測
Remote sensing of discharge of groundwater in collapsed slope by means
of infrared thermal imaging
新井場公徳ａ）＊
Kiminori ARAIBA |
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Abstract
This study shows the posibility to quantitatively observe the discharge of groundwater from collapsed slope by remote sensing. In order to remotely observe the discharge situations of groundwater, the temperature of collapsed slope was observed by means of infrared thermal imaging. A slope had been artificially failed by artificial rainfall then a series of thermal images was taken from a distance. Since the collapse occurred at time when the underground temperature was higher than that of ground surface and air, the temperature of collapsed surface immediately after the failure was relatively higher than that of the original ground surface. The collapsed surface then began to be cooled by convection of the air but the temperatures were found to fall down at different rate. Slow rate was observed in some areas and it is considered to be due to the heat transfer from the deep ground to the surface in such areas. According to the observation in this experiment, temperature around one of such areas formed an one‐meter‐width peak after failure and, the width became to be about ０．５ m at ３６ minutes after the failure.
Key words:slope failure, spring water, remote sensing, groundwater, temperature, thermal image
和文要旨
本研究は崩壊面からの地下水の湧出状況を遠隔で定量的に監視することの可能性を示したものである。地下水湧出状況を遠隔で観測するために，人工降雨による自然斜面崩壊実験において，崩壊後の地盤温度を赤外画像装置で計測した。崩壊は地表・大気より地下の温度が高い時期に発生したため，崩壊時に高温の地盤が露出した。その後冷却されたが，温度低下の遅い部分がみられた。地下水による深部からの熱の移流によるものと考えられた。その点の周辺温度を見ると，崩壊直後に幅約１mでピークが発達し，３６分後には幅約５０cmとなった。
キーワード：斜面崩壊，湧水，リモートセンシング，地下水，温度，熱画像 |
秋田県東成瀬地域における大規模地すべり地形形成の地質的素因
Geological origin of large‐scale landslide topography in the Higashinaruse
region of Akita Prefecture, northeast Japan
森屋 洋ａ）＊・羽沢大樹ａ）・阿部真郎ａ）・佐藤康彦ｂ）
Hiroshi MORIYA, Daiki HAZAWA, Shinro ABE and Yasuhiko SATO |
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Abstract
Mountain slopes of landslide origin are distributed under the ２５km２ in the Higashinaruse regeon, Akita Prefecture,northeast Japan, where the Neogene siliceous mudstone are dominant. We have studied the formative process of such landslides through investigating geological structures and rock fractures in the siliceous mudstone in the field. As a result, it has been clarified that such large‐scale landslide topography was not formed by a single block movement but has been formed in multi blocks. The topography of these landslide blocks have been formed under control of the fractures of siliceous mudstone and the inclination direction of the stratum. These results are expected to clarify the mechanisms of landslide formation in the Neogene siliceous mudstone beds that are widely distributed in northeast Japan.
Key words:rock slide, dip slope, landslide topography, fracture
和文要旨
秋田県東成瀬地域の新第三系珪質泥岩の分布域には，面積２５km２にもおよぶ大規模な地すべり地形が存在する。本稿では，地域全体の踏査結果より，地質構造と岩盤内の亀裂系を分析して地すべりとの関連性を検討した。その結果，これらの地すべり地形は全体が同一のブロックとして変動して形成されたものではなく，珪質泥岩の亀裂や，地層の傾斜方向に規制された複数の地すべりブロックによって形成されていることが明らかになった。本結果は東北地方に多発する他の珪質泥岩層地すべりの発生機構解明に役立つものと考えられる。
キーワード：岩盤地すべり，ディップスロープ，地すべり地形，亀裂 |
大規模地すべり地の地下水流動特性に関する考察〜東北地方の第三紀層地すべりを例として〜
Characteristics of groundwater flow in large scale landslide areas−On
Tertiary landslides in Tohoku region−
相楽 渉ａ）＊・丸井英明ｂ）・吉松弘行ａ）
Wataru SAGARA, Hideaki MARUI and Hiroyuki YOSHIMATSU |
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Abstract
The authors have analized comprehensively the mechanism of the groundwater flow in large scale landslide areas based on the results obtained from groundwater quality analyses in two large scale landslide areas in Tertiary system in Tohoku region. A comprehensive analysis of groundwater flow is effective and credible by executing comparisons of the results of groundwater quality analyses, groundwater level observation, and groundwater tracing in addition to analyses of surveying of geological structure.
In Takisaka landslide the flowing behavior of groundwater was comprehended by the analyses combined with groundwater quality and groundwater tracing with due consideration of variations of groundwater levels in each geological formation and sliding block. Furthermore it is suggested by the analysis of the distribution of Cl− ion concentration in groundwater that the deep groundwater through granite rock mass has a certain influence for raise up of groundwater level during snow melting period.
In Hirane landslide the flowing behavior of groundwater was comprehended by the interpretation of mixing of groundwater from Tertiary system and groundwater from deep zone. The flowing behavior of the groundwater estimated by the groundwater quality analyses is coincident with the results of groundwater tracing.
As a result a holistic method to analyze behavior of groundwater flow in large scale landslide areas is newly proposed. It is appropriate and effective to carry out the following steps, namely groundwater quality analysis, comparison with groundwater tracing, identification of groundwater level variation, estimation of groundwater flow pass and lastly holistic analysis of characteristics groundwater flow in whole landslide area.
Key words:large scale landslide, Tertiary landslide, groundwater, water quality
和文要旨
本論文では，東北地方の第三紀層地すべり地における水質調査結果に基づき，大規模地すべり地における地下水流動機構に関する総合的考察を行った。水質調査結果を地下水位調査結果，地下水追跡調査，更には地質構造と対比し，総合的な地下水解析を行うことが有効であることを示した。
滝坂地すべり地を対象とした解析では，地下水位の変動タイプを地質・地すべりブロック別に考慮し，地下水水質並びに地下水追跡調査結果を組み合わせることで地下水の流動状況を把握した。更に，地すべり地内における地下水のCl−イオン濃度分布の調査結果に基づいて，融雪期の地下水位の上昇に花崗岩体を通過してくる深層地下水が関与している可能性が高いことを示した。
平根地すべり地を対象とした解析では，新第三紀層中から流入する地下水と，地下深部から上昇してくる地下水の混合状況から，各地すべりブロックにおける地下水流動状況を把握した。水質解析結果から推定された地下水流動状況は地下水追跡試験結果と合致している。
以上の考察結果を総合して，大規模地すべり地における総合的な地下水流動特性の解析手法を提案した。
キーワード：大規模地すべり，第三紀層地すべり，地下水，水質 |
理想化されたすべり土塊を用いた三次元斜面安定解析法の精度検証：ホフランド法と三次元簡易ヤンブ法の比較
Examination of preciseness of ３D slope stability analysis methods using
several idealized sliding masses : comparisons of Hovland method and ３D
simplified Janbu method
鵜飼恵三ａ）＊・若井明彦ａ）・蔡 飛ａ）
Keizo UGAI, Akihiko WAKAI and Fei CAI |
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Abstract
Three‐dimensional safety factors of idealized slopes composed of plane sliding surfaces are calculated and compared based on the exact solution method, Hovland method and the ３D simplified Janbu method. Conclusions are as follows;（１）Hovland method gives smaller safety factor values compared to the exact solutions, especially in cases of narrow failure width and high water pressure along sliding surfaces.（２）the ３D simplified Janbu method gives the same safety factor values as the exact solutions.
Key words:safety factor, three‐dimensional, slope stability analysis method, Hovland method, ３D simplified Janbu method
和文要旨
すべり面がいくつかの平面から構成される理想化された三次元すべり土塊を想定し，厳密解法，ホフランド法，および三次元簡易ヤンブ法により安全率を計算し比較した。ホフランド法は，一般に小さ目の安全率を与え，特に破壊幅が狭く，すべり面上の水圧が高い場合にそれが顕著になることを説明した。三次元簡易ヤンブ法の安全率は厳密解法の安全率と一致し，精度の高い方法であることが示された。
キーワード：安全率，三次元，斜面安定解析法，ホフランド法，三次元簡易ヤンブ法 |
Chlorite exhibits a little swelling property formed in green rock distributed
in the Nishinotani landslide area, Ehime, SW Japan
Masaaki MIYAHARAａ）＊, Yohei UNOａ），ｂ）, Ryuji KITAGAWAａ） and Ryuichi YATABEｃ） |
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Abstract
Green rocks that have originated from basalt and tuff are distributed in the Nishinotani landslide area. Chlorite is the major constituent mineral of green rocks, and it is formed in the phenocrysts found in these rocks. The chlorite in these rocks exhibits a little swelling property because it includes several smectite components. Thus, it is proposed that the landslide activity is induced not only by smectite, but also by chlorite, which exhibits a little swelling property.
Key words:chlorite, clay mineral, landslide, smectite, swelling property
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