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The background and mechanism of the Gamahara Torrent debris flow of 6 December, 1996 is reported. It is very unusual that the debris flow occurred at the beginning of December in terms of the necessary water supply. Clearly the debris flow was triggered by landslide which occurred at the geological formation boundary at an elevation of about 1,300m. The soil layer above the formation boundary probably contained very much water due to antecedent rainfall before the occurrence of the landslide. Chemical analysis of the water contained in the debris flow deposit should provide an effective measure of identifying the origin of this water. Chemical analysis results showed that the water in the debris flow deposit did not originate directly from rainfall and snow melt but came from stored groundwater. This report interprets also the physical and mechanical properties of the unstable debris deposits in the various areas of the Gamahara torrent basin. Various geotechnical investigations were performed in order to analyze the mechanism and the process of the debris flow. The shear strength parameters of debris flow deposits on the torrent floor in the lower part of the watershed and slope failure deposits in the landslide scar which triggered the debris flow were determined by using a ring shear apparatus.

This report interprets the physical and mechanical properties of the unstable debris deposits in the Urakawa river basin. The Urakawa river basin locates along the great tectonic line (Fossa Magna) in Nagano prefecture in Japan and is well known by frequent occurrence of debris flows initiated by slope failures in the upper part of the basin area. Also in April 1992 a relatively large debris flow with the volume of 1 million m^3 has occurred. Various geotechnical investigations were performed in order to analyse the mechanism and the process of debris flows. Especially the shear strength parameters of debris flow deposits on the river bed were determined by using a ring shear apparatus.

The routine works of shearing tests are carried on normal stress range 50 to 100kPa. This normal stress range is correspondent to overburden of 3.0 to 6.0 m. Most slipes of embankment filles occure at or after rainfalles and the thickness of most slipes are smaller than 1.0 to 2.0 m. Using the strength parameters c and φ obtained with routine works for stability analysis, these parameters are extrapolated from results of routine works but the appropriateness of this method is scarcely examined. In this paper, using the spesimen of compacted clay which D-value is in the range of 95% to 85%, the direct shear tests with constant pressure of the range from 10 to 350 kPa are performed under the conditions of intact and inundation. Assuming as low pressure range to be 10-100 kPa and ordinary pressure range 50-350 kPa, there is a considerable difference between the strength parameters c and φ of low pressure range and ordinary one at the intact condition but the difference becomes less at the inundation condition. The applicability of non-linear equation for wide range of pressure is better than MohrCoulomb equation.

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, organic material mixed soil, wood shavings mixed soil and original soil. 10%charcoal mixed soil showed the more effective erosion control than original soil by 70%.

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^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 safety factors of those landslide-prone slopes in dormant state, particularly of those found in areas where many landslide blocks are being spread out, some of which are actually undergoing slides.

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 ^^^-, 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 ^^^-, 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 ^^^-, 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., 紀要論文

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∿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∿ε曲線を式化し, その利用を試みる。なお, (2)においてはτ∿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∿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∿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∿1.55kg/cm^2, φ_=19∿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∿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∿5kg/cm^2の応力範囲でI_B=80∿50%となる。またφ'_r∿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∿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∿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∿ε曲線を利用する手法は, Skempton法よりσ=0.1∿0.7kg/cm^2の範囲において1∿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)∿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∿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∿1.55kg/(cm)^2 and φ_=19∿22°, and the residual strength parameters of c_=0 and φ_=17∿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, 紀要論文

(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∿1.55^/cm^2,φdf=19∿22°, 残留強度定数はCdr=0,φdr=17∿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∿5^/cm^2に対しおよそI_B=80∿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., 紀要論文

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∿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∿33.3°for Makiya, and c_r=0kPa, φ_r=27.0°for Ue-arakawa, both higher than those for landslide soils., 紀要論文

移動量の大きい浅層すべりと深層すべりの再発生時安定解析に残留強度および回復強度を適用し, 以下の知見を得た。(1)薛城鎮の三次すべりは層厚が8m∿10mの浅層すべりである。再発生時の安定解析に残留強度のみを適用した場合, 安全率がF_s=0.91となり, 斜面の安定度が過小に評価された。残留強度に加え, すべり面の低い土かぶり圧領域に回復強度を適用することによって安定度が合理的に評価できた。(2)亀の瀬地すべりの峠地区は峠ブロックと稲葉ブロックからなり,層厚が40m∿70mの深層すべりである。安定解析では, 高い土かぶり圧領域の全体に占める割合が極端に大きいため, 高い土かぶり圧領域の全体に占める割合が極端に大きいため, 残留強度のみによる安定解析を行い,合理的な結果を得た。峠ブロックは安全率はF_s=0.84となり, 稲葉ブロックによる抑止効果が約16%の安全率に相当していることが明らかになった。, The large moved landslides are usually analysed assuming that the strength along the entire length of a slip surface droped to the residual value. However, in most cases, the safety factor is underestimated. The test of large displacement shear-re-consolidation-re-shear in the present experiment indicated the recovery from the residual strength after re-consolidation under the low normal stress such as 30kPa∿100kPa. The residual and recovered strength parameters were applied in the stability analysis for the shallow slide and deep slide of the large movement. The tertiary slide of the Xuechengzhen landslide is shallow, about 8m to 10m deep. Application of the residual strength to the stability analysis gave the safety factor of 0.91,which was underestimated. Higher reasonable strength parameters were obtained by using the recovered strength in the shallow slipsurface zone having low overburden pressure, and the residual strength in the deep slip-surface zone having high overburden pressure. The Toge unit in the Kamenose landeslide is deep, whilst, the thickness of the slide is 40m to 70m. Most part of the slip-surface zone is subjected to high overburden pressure. Thus, the stability analysis based on only the residual strength led to a result which was quite satisfactory., 紀要論文

本研究は,身体機能と抑うつとの間にどのような関連があるのかを明らかにするために,宮城県S町に在住する75歳以上の在宅高齢者281人を対象に,面接調査と体力測定を実施した.握力,10M最速歩行時間,UP&GO,開眼片足立,長座位体前屈の体力測定項目や老健式活動能力指標の得点といった身体機能と老年うつ病スケール(Geriatric Depression Scale)の得点に着目し,分析をおこなった結果,抑うつ症状と関連している身体機能は歩行機能であり,また生活機能の低い群は高い群に比べうつ傾向が高いことが明かとなった.また,身体機能の状態を良好に保つことが抑うつ傾向を予防することにつながると考えられた., The present study aims to clarify the relationship between physical function and depression, and to ascertain whether state of physical function can be used to screen for early depression and depressive symptoms in healthy elderly individuals. Elderly individuals (n=281) 75 years of age or older and living at home in a city in Miyagi Prefecture were interviewed and underwent a physical strength test. Physical function was assessed in terms of elderly activity indexes and physical strength parameters (i.e., grip strength, 10 m fastest walking time, Timed Up and Go Test, balancing on one leg with eyes open, and seated trunk flexibility test). Depression was assessed using the geriatric depression scale. Results showed that among the various physical functions, walking was correlated to depressive symptoms. In addition, elderly individuals with low physical function tended to be more depressed than elderly individuals with high physical function. Thus, the present study suggests that maintaining favorable physical function can prevent depression in community-dwelling elderly.

Slope failures have frequently occurred along discontinuous planes during a small amount of rainfall. The discontinuous planes were chosen as following: 1) the boundary plane between talus cone and ground, 2) the fractured clay in landslide area, 3) the joint developed in slate, 4) the thin glossy black soil adhered to joint or schist of metamorphic rock, 5) the boundary plane between granite and decomposed granite, 6) the boundary plane between decomposed granite and clay vein, 7) the boundary plane between schist of pelitic schist and the decomposed soil, 8) boundary plane between schist of pelitic schist-hornfels and the decomposed soil. Field and box shear tests were performed on the specimen having the discontinuous planes. These test results suggest that the strength parameters should be used in the stability analysis of cut slopes having the discontinuous planes.

廃棄発泡プラスチック破砕片を軽量地盤材料として有効利用することを目的に,これを用いた軽量混合土を作製し,圧密非排水三軸圧縮試験を行うことによりその基本的な力学特性を検討した。その結果,強度特性については,有対応力で考える限り,両者のせん断挙動にはほとんど差が見られず,内部摩擦角などの強度定数も同じであることがわかった。その一方で,変形特性については,混合土の方が土よりもかなり圧縮されやすいことが確認され,その差は,同一荷重による圧密量および間隙水圧が最大値に達するまでの圧縮量で比較すると約2.5倍程度であることがわかった。従って,有効応力のみで考える限りは両者の強度特性に差はないものの,変形量やひずみで破壊を定義する場合には混合土の方がより小さな応力で破壊に達する可能性があるため,実際の設計や施工においては応力とひずみの双方から安定性を検討する必要があることが明らかになった。, It was intend to make research into the efficient utilization of crushed expanded plastic wastes, by way of light-weight geomaterials. In this study, light-weight mixed soils were made using plastic waste, and a series of consohdated-undrained triaxial compression tests were conducted to investigate the mechanical properties of the soils. As a result, it was clarified that the strength properties such as internal friction angle and effective stress path were almost the same between these soils. On the other hand, deformation properties were quite different from each other. The compressibility under the same consolidation pressure and the axial strain until pore water pressure reaches maximum of the mixed soil was about 2.5 times larger than that of soil alone. Consequently, it was found that the stability should be examined from the both criteria of stress and strain conditions, under actual designing and construction. Because it is possible for the mixed soil to fail more small stress state when the failure is defined from deformation and strain conditions, though the strength parameters obtained from effective stress relation are almost the same between mixed soil and soil alone.

Natural slopes consisting of weathered granite rocks (Masado) have frequently failed during heavy rainfalls. In Yamaguchi prefecture, it is necessary to determine the strength of Masado using slope stability analysis. In order to obtain the in-situ strength parameters of undisturbed Masados, field shear tests using a field shear test apparatus were carried out at 9 sites in Yamaguchi and Hiroshima prefectures. The effect of the side friction and maximum grain size of the soils on the test results was investigates. Furthermore, constant volume shear tests were performed to remove the effect of the side friction.

From the viewpoints of soil engineering, geology, and slope disaster prevention engineering, field investigations were made of 109 failures of slopes with countermeasures such as sodding, retaining walls, and rock-fall prevention walls. Furthermore, physical properties and strength parameters of the surface soils were examined.The conclusions obtained are as follows: 1) In regard to the geology of Yamaguchi prefecture, the most slope failures occurred in the granite rock region. 2) Owing to the catchment topography, relatively small-scale failures occurred in slopes existing at the upper parts of the countermeasure works.

A new field shear test apparatus was developed in order to obtain the strength parameters of solpe soils. From the test result obtained on soils at 9 sites, the following conclusions were shown. (1) the shear strengths of undisturbed soil samples with an original grain size distribution could be determined using this apparatus. (2) The field shear behaviors of the soil samples were affected by heterogeneity. (3) The field shear tests gave smaller internal friction angle were and larger cohesion than the box shear tests.

The background and the process of the Hachimantai debris flows of 11 May 1997 are reported. At first a big landslide occurred in the upper slope of the Sumikawa hot spring. Clearly the landslide was triggered mainly by snow melt and additionally by 110mm rainfall. The total volume of the slid soil mass was estimated to be 594,000,000m^3. From the toe area of the landslide a soil mass of 116,000,000m^3 flowed downward several times as debris flows along the Sumikawa torrent. Chemical analysis of the water contained in the debris deposit in the landslide area should provide an effective measure of identifying the origin of the water. Chemical analysis results showed that the water in the debris deposit did not originate directly from rainfall and snow melt but came from stored groundwater. This report interprets also the physical and mechanical properties of the unstable debris deposits in the landslide area as a source material of the debris flows. Various geotechnical investigations were performed in order to analyze the mechanism and the process of the debris flows. The shear strength parameters of debris deposits in the upper part and the toe part of the landslide area were determined by using a ring shear apparatus.

Strength parameters of isotropic high-density graphite are thought to be strongly correlated to pore structure of the graphite from experimental results on fracture toughness. In this paper, we present quantitative analysis of pore structure in the isotropic graphites by means of an image processing of a polarizing microscope image of the material. Power spectra of the polarizing microscopic images of the isotropic graphite are obtained by the 2-dimensional fast Fourier transform. These results indicate that the structure of the pores and the other solid parts of the graphite are almost isotropic. Distribution of the area, the number, the circularity, and the fractal dimension of cross-section of the pores are measured, and the pore structure is analyzed quantitatively.

The consolidated undraind triaxial compression tests were performed with the compacted tuff used for semipermeable material of a filldam and the effects of compaction moisture content w and dry density ρ_d on shearing properties were experimented. The following results were obtained from these test.(1) Pore pressure at failure △u_f is decreased with increment of w and ρ_d and △u_f comes to negative value. (2) The compressive strength and strength parameters c' and φ' are increased with dry density. (3) The failure criterion for noncohesive sandy soil is approximated with bi-linear envelope passed to origin.

The consolidated undrained triaxial compression tests were performed for the specimen cut from vertical (V), parallel (H) and diagonal (D) by compacted plane． From these experiments, thereis no variance in stress-strain relations, pore pressure coefficient, compressive strength and strength parameters c^'and φ^'or c_ and φ_ among V, H and D specimen. From these results there is no anisotropy in the shearing properties of compacted soil mixed with tuff and volcanic clay. But, c^' and φ_ are decreased considerably in the case of adsorption of specimen.

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)

Slopes of sandy soil such as decomposed granite soil are susceptible to be suffered from damages when they are inundated by rainfalls. One of causes of such shallow slips is attributed to the decreasing of shear strength of the soil due to submergence. Another noteworthy characteristic of this soil is that the particles are easily crushed under a relatively low stress. In order to discuss the shallow slips of decomposed granite soil, it is necessary to investigate the chang in shear characteristics owing to the variation of the water content at low normal stresses. The commonnest strength parameters in use for the stability analyses of the slope are generally obtained from the test at higer normal stresses than the actual stress which applys to the slope. This paper shows the effect of water content on the shear strength characteristics of decomposed granite soil at a very low normal stress in detail on the basis of the direct shear test result, and its comparison with the results of triaxial compression test. As the results of this experiment, we found the uniqe relationship between the shear strength and the degree of saturation at a low normal stress.

締固めた泥質れき状土について三軸圧縮試験を行い, 強度・変形特性に及ぼす締固め含水比, 乾燥密度(締固め仕事量), 締固め方法及び水浸作用の影響を明らかにした。その結果を要約すると, 次のようになる。(1)側圧一定のUU試験による非水浸状態の応力∿ひずみ関係は締固め密度と含水比の影響を受けるが, 水浸状態ではすべてひずみ硬化型であり, これらは締固め方法の影響を受けない。また, 水浸状態の応力∿ひずみ関係にはKondnerの双曲線式が適用できる。(2)非水浸強度は含水比一定のとき密度とともに増大し, 強度(対数)と密度の関係は線形関係にあり, 自然含水比より乾燥側では締固め方法の影響を受けないが, 湿潤側では静的締固めによる強度が動的締固めよりも大きい。一方, 水浸状態の強度は締固め含水比に関係なく, 水浸後の乾燥密度とともに増大し, 強度(対数)と乾燥密度の関係は線形で, しかも零空積曲線上の強度分布を表示している。(3)以上の結果を含水比ω, 乾燥密度γ_d, 強度(対数)log(σ_1-σ_3)fを軸とする座標空間に表示すると, ω∿γ_d∿log(σ_1-σ_3)f関係は, 非水浸状態では側圧によって変動する曲面で, 水浸状態では側圧に一定な曲線で示される。(4)非水浸状態に対する側圧を変えたUU試験では, 応力∿ひずみ関係は締固め含水比, 密度, 側圧の影響を受ける。また, 強度定数cu, φuは, 含水比一定の場合, 密度とともにcuの増加とφuの減少傾向にあるが, 密度一定の場合, 含水比に対しcuはほぼ一定で, φuは自然含水比の乾燥側で大きい。(5)水浸飽和後のCU試験では, 水浸により吸水現象を示すにもかかわらず, 圧密過程では低密度の締固めは体積圧縮, 高密度の締固めは吸水膨張を示し, その中間の締固めでは圧密圧力に伴って吸水膨張から体積圧縮へと変化する。これらの応力∿ひずみ関係はひずみ硬化型である場合が多いが, 湿潤側あるいは自然含水比での高密度の締固めではひずみ硬化∿軟化型である。また, これらの含水比∿圧密圧力∿強度関係を正規圧密粘土のそれと比較すると, 水浸作用を受けても, その挙動は過圧密的である。(6)標準的な締固め仕事量による締固めの場合, 有効応力にもとづく強度定数c', φ'は締固め含水比の影響を受けず, そのうちのφ'に注目すると, 正規圧密粘土に対するφ'=26°(c'=0)よりも大きく, 高密度の締固めに対する値よりは小さい。, In this paper the influence of soaking on shearing properties of compacted nondurable mudstone aggregate are investigated by triaxial tests with the specimens compacted with dynamic or static compaction methods at various molding water content and dry density. The shape of stress-strain relation in unsoaked specimens at constant confining pressure turned from strain-hardening to strain-hardening-softening type with the decrease of molding water content and the increase of dry density. On the other hand, those of specimens subjected to wetting were found to be strain-hardening type, regardless the compaction methods. Compacted strength (σ_1-σ_3)_f increased with dry density γ_d at constant molding water content, and log (σ_1-σ_3)_f-γ_d relations were liniarity. This liniarity was recognized in soaked specimens which were situated on zero air void curves. In the case of soaked specimens compacted with standard Procter compaction efforts, the influence of the molding water content on the effective stress strength parameters c' and φ' were relatively small. One of these parameters, the internal angle of friction, φ', were found to be higher value more than in remoulded normally consolidated, but lower than in soaked specimens compacted in densely with heavy efforts at natural water content., 紀要論文

築堤から43年の年月を経た宜野座ダムの堤体盛土とその縮固め土では力学性状が異なり,堤体盛土の方が締固め土よりも体積圧縮係数土圧密降伏応力,せん断強度等が大きく,弾性変形領域が広く,間隙水圧の発生量が低い傾向がみられた.このような差違は年代効果によると考えられる.終わりに,試料採取においては沖縄県北部農林土木事務所にご協力を頂き,小那覇安通氏には宜野座ダムに関する資料を提供して頂いた.記してお礼申し上げる., This study was conducted to investigate the aging effects on mechanical properties of compacted soil. The consolidation and shear strength parameters were measured on the undisturbed soil sample collected from 7.8m depth in Ginoza earth dam passed through 43 years and its compacted soil. Volumetric compressibility, consolidation yield stress, shear strength of the dam soil were bigger than those of its compacted soil, and the elastic deformation region of dam soil was wider than that of its compacted soil and the generation rate of pore water pressure tended to be low with the passage of the time. It seemed that these differences were caused by the aging effects., 紀要論文