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飽和砂地盤上の盛土の動的変形挙動を調べるため，遠心模型実験，および多重せん断ばねモデルによる有限要素解析（FLIP）を行った．本研究で対象とした盛土は，堤体高さ3ｍ，天端と下端の長さが4ｍと11.5ｍ（実物スケール）である．また下部地盤の層厚は5ｍである．緩詰地盤を対象とした数値解析では地盤のN値=1に対応するパラメータを用いた場合に，天端の沈下量が実験結果と良く一致した．数値解析の結果，入力加速度が大きいほど，盛土下部の非液状化領域が大きくなり，それがくさびとなって周辺の液状化地盤を押しのけるため沈下量が大きくなるという，一見すると直感的ではない変形メカニズムが推察された．, Dynamic behavior of an embankment (3 m height) made of dry sand underlain by saturated sand deposit with 5 m depth are studied. Firstly, centrifuge experiments under 50 G are conducted. The relative density of saturated sand deposit is approximately either 30 % or 70 %. Sinusoidal input motions with various levels of peak acceleration amplitude are employed. Test results show that the maximum settlement was 1.4 m and 0.09 m, respectively, for loose and dense deposit. The amount of settlements for dense deposit are found to be proportional to the peak amplitude of input acceleration, while it may have a plateau for the case of loose deposit with increase of input acceleration amplitude. Following the centrifuge experiments, an effective stress analysis is carried out with the same prototype dimension of the experiments. The numerical analysis simulates well deformations and transient motions of the experimental counterparts. It is found that, in the analysis for loose deposit, when input acceleration increased, non-liquefied area underneath the embankment became large, causing larger non-liquefied wedge pushing liquefied soils aside.

杭―地盤相互作用に伴って生じる水平断面内での杭周辺地盤の変位・変形性状を詳細にとらえることを目的として模型実験を行った。実験した断面について，数値シミュレーションも実施し，模型実験から得られた結果の一般化を図った。数値シミュレーションにおいて用いた砂の力学モデルは，多重せん断機構に基づくモデルである。乾燥排水条件では，杭周辺の地盤変位ベクトルは杭前面では杭変位と同じ方向に，また，杭の側面では杭表面からの距離に応じて急速に変位が小さくなる傾向を示した。飽和非排水条件では，杭側面で渦状の変位形態が見られ，杭の前後では，それぞれ押出し，引込みの変位形態を示した。杭間の変位は，杭表面付近にひずみが集中する傾向が見られた。, Two dimensional model tests are performed on a horizontal cross section of a soil-pile system in a pile foundation. The objective of the model tests is to evaluate local soil displacement field in the vicinity of the piles associated with a global displacement of soil around the pile foundation. Two dimensional effective stress analyses in horizontal plane are also performed to generalize the findings from the model tests. An effective stress model based on multiple shear mechanism is used through a computer code FLIP. In dry condition, displacement vectors are directed away from pile front, and displacement at pile side rapidly decreases with an increasing distance from soil pile interface. In undrained condition, displacement field shows vortexes at pile side associated with push-out/pull-in pattern of displacements in front of and behind the pile. Distribution of local soil displacement between piles shows high strain concentration at soil-pile interface.

本研究の目的は，地盤内間隙水圧の波浪応答に関する数値計算の結果と，防波堤での現地観測によって得られたデータとを比較することによって，高波浪時における地盤内間隙水圧の波浪応答を明らかにすることである。本研究では，波と構造物，地盤の動的挙動を同時に解析することができるVOF-FEM 法を改良し，地盤部の弾塑性解析を可能にした。土の塑性に起因して生じる残留ひずみを表すことができたが，土の繰り返し塑性に起因して生じる残留間隙水圧を再現するには到らなかった。, The present study investigates the response properties of pore water pressures in the seabed beneath a composite breakwater armored by concrete blocks. In order to compute residual pore water pressures, the VOF-FEM model is modified by introducing the elasto-plastic constitutive model which involves the rotation of principal stress axes. It has been revealed that the motions of the coastal structures due to wave loads strongly affect the response properties of pore water pressures in the seabed beneath the coastal structures like the caissons and the concrete blocks.

高波浪時における海底砂質地盤の応答を調べるため，海底地盤上の水圧と地盤内間隙水圧を系統的に観測した．また，VOF-FEM による数値計算を実施し，間隙水圧の波浪応答について観測結果と比較した．現地観測の結果，残留間隙水圧の長周期変動成分は，来襲波浪の波群特性に関係していることがわかった．また，上載構造物下の地盤内における間隙水圧の位相差を含んだ時系列変動は，波浪作用によって生じる構造物の運動に起因していることを数値計算で明らかにした．液状化については，構造物による上載圧の増加を考慮すると，法先自由地盤を除いて，発生する可能性は極めて低いという結論に達した．, The purpose of this study is to clarify the response properties of pore water pressures in the seabed beneath a composite breakwater. The build-up of residual pore water pressures was found in the sandy seabed during the storm waves. It has been revealed that the response properties of residual pore water pressures are closely related to the wave grouping characteristics of the specific wave periods. It was clarified that the possibility of liquefaction occurrence was extremely small except the free seabed at the toe of foot protection considering the loading stress of the structures.

大阪港では更新統砂礫層が厚く、十分な透水性を有しており、k=10^-3cm/s以上の透水係数であれば、その透水性は更新統粘土地盤の沈下性状にほとんど影響しないことがわかった。埋立初期からの更新統全層の沈下実測結果との比較から，更新統砂礫層の剛性はかなり大きく，地下水位低下に伴う有効応力変化によって生じる更新統砂礫層の圧縮量から算定する大倉らの手法で求めた値がパラメータとして妥当であることがわかった。, A series of elasto-viscoplastic finite element analyses is carried out to investigate the effect of the permeability and compressibility of the Pleistocene gravelly sand layers on the stress-deformation characteristics of the Pleistocene deposits in Osaka Port. The relevant procedure to evaluate the rigidity of the Pleistocene gravelly sand layers is also introduced. It is found that the estimation of the elastic shear modulus, G0 as well as permeability of the Pleistocene gravelly sand layers plays a significant role for the settlement prediction of the reclaimed islands in Osaka Port.

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

土層中のパイプおよび風化基岩に発達したクラックを通した選択流が斜面安定性に及ぼす影響を検討するため，土層と大孔隙内の水流に関する水理モデルを用いて数値シミュレーションを行なった。数値シミュレーションにおいて，表土層と風化基岩層からなる斜面を想定し，それぞれに水理特性値を与え，土層および風化基岩層に関する浸透流計算を行なった。結果より，斜面表層に降った雨水が選択流路を通して迅速に基岩深部に輸送され，選択流路が風化基岩内部で閉塞している場合は，その閉塞点近傍の圧力水頭値の急激な上昇をもたらすことが確認された。この圧力水頭上昇によって，斜面が不安定化し，斜面崩壊の危険性が高まることが示された。, Numerical experiments were conducted to assess the effect of preferential flow through pipes and cracks within weathered bedrock on slope stability, using hydrological model in which water flows within both the matrix and macropores. The hillslope consists of soil and weathered bedrock layers. Hydraulic properties were assigned to the weathered bedrock as well as the soil layer, and the regolith flow calculations were conducted within the slopes. Results demonstrated that the preferential flow pathway rapidly transported rainwater to the deeper layer of the slope, and if the outlets of the preferential flow pathway remained within the slope, the pressure head increased around these points. This increase in pressure head caused a decrease in the factor of safety at the deeper layer of the slope.

大阪湾海成粘土の地盤物性の評価は、今後のベイエリア開発において基本的に重要な課題である。ここでは、海底地盤の物性を鉱物学的視点から解明することを目指し、海底粘土地盤中の粘土鉱物の同定・定量をX線回折分析によって行い、大阪湾海底地盤の水平・垂直方向の粘土鉱物の分布を推定する。それとともに、従来の地盤パラメーターを収蔵している大阪湾海底地盤情報データベースを活用することによって、粘土鉱物組成と地盤物性との相関について広域的に検討し、堆積環境や地域特性について明らかにする。, The objective of this study is to evaluate the relationship between the composition and distribution of clay minerals andphysical and/orengineering properties of seabeddeposits in Osaka basin. Despite of similarity of theirchemical composition, clay minerals show the different physical and/orengineering properties. As the clay minerals are considered to cbfine the engineering characteristics of the clayey soils, special attention was focused on the clay minerals, and identification or quantitative analysis of clay minerals were conducted.Some of them aredependingon the distribution of clay mineral contents.The physical and engineering properties of the soil were obtained by using the Osaka Bay seabed database (SBDB).

This paper concerns with the applicability of cone penetration tests and measurement of shear wave velocities for assessing the liquefaction resistance of sandy deposits. The miniature cone penetration tests and the measurement of shear wave velocities were carried out before and after the shaking table tests of the silicone oil-saturated horizontal layer under 50-g centrifugal condition. The cone tip resistance (qc) and the shear wave velocity (V) were well correlated to the void ratio of the ground. Judging from the very limited number of experimental results, qc and V could be good indeces of the in-situ liquefaction potential.

RI cone penetrometer tests are carried out at four different sites. The foundation grounds discussed here mainly consist of clayey materials. The measured results by RI cone penetrometers are shown for Kyobashi, Hachirougata, Kurihama and Kinkai Bay site. According to comparison of water content and density profiles by RI cone measurement with the conventional testing results, RI cone penetrometers are proved to be versatile tools for site investigation. Settlement assessment by RI cone penetrometer is also discussed by exemplifying the embankment at Kinkai Bay site. Elasto-viscoplastic finite element analysis correspondingly performed strongly supports the RI cone based assessment. Repeated use of RI cone penetrometer with the advance of construction enables us to assess the consolidation process of the clay foundation.

A more comprehensive collection of site conditions at various locations where some typeof liquefaction or no liquefaction was used to determine the relationship between liquefactionresistance ratio, standard penetration resistance and effective overburden pressure. Theresults are shown in Fig. 5, and the field value of cyclic stress ratio separating liquefiablefrom non-liquefiable conditions can be determined with acceptable accuracy from Eq. (7).Furthermore, the background of support for these Fig. 5 and Eq. (7) was considered andthe comparisons of author's proposal with previous methods, H. B. Seed (1976) or Iwasaki-Tatsuoka (1978), were made.

A review of field performance of sandy soil deposits during past earthquakes is conducted withemphasis being placed on CPT qc-values and soil gradation. The empirical relationship separatingliquefiable and non-liquefiable conditions is presented in terms of dynamic shear stress ratio, normalized qc1-values, and fines content or mean grain size. The proposed CPT correlations arecompared with those presented by Robertson & Campanella (1985). The proposed CPTcorrelations are also evaluated using field data and laboratory test results from Canada and Japan.

In this report, the dynamic response of horizontally layered soil is numerically analyzed, usingthe stress-strain relation of sand and the equation of motion of two phase mixture. The saturatedsoil with water is treated as a two phase mixture. As the pore water and the soil particle is assumedto be incompressible, the effective stress analysis becomes useful. In the case of horizontally lay-ered soil deposit, the lateral deformation is considered to be confined during the earthquakes.Then, in this study, the laterally confined condition is taken into consideration.

This paper is concerned with the predicted performance of an offshore airportfill to be built on the bed of soft alluvial clay underlain by very thick strata of ple-istocene clays. Coupled stress-flow analysis using the method of finite elements areperformed, with emphasis on predicting the behaviour of the seawall and the nearbyabutment for the access bridge. Elastoplastic and creep properties of the Quaternaryclays is considered in the analysis procedure in a consistent way, through the im-plementation of a plane-strain elasto-viscoplastic constitutive model. The predictedperformance emphasizes the importance of the long-term consolidation of the pleisto-cene clays, in terms of post-construction deformation, as compared with the behavi-our of the overlying soft alluvial clay that is treated partly with columns of denselycompacted sand (SCP) and more extensively with vertical sand drains (SD). It isshown that the vertical stress tends to concentrate into the SCP-treated region ad-joining the more compressible SD-treated region, and that such stress concentrationaccounts for the peak occurring in the profile of compression of the pleistoceneclays along the axis of the access bridge. It is also shown that the initially over-consolidated pleistocene clays undergo yielding in their upper part, along with thegradual dissipation of excess porewater pressures, and that the front of yielding pro-gresses downwards with time. Such delayed yielding is shown to be predominantwell after the end of construction and is accompanied by the delayed, laterally out-ward deformation of the pleistocene clays. This behaviour of the undersea clays iscontrasted with the behaviour of the crest of the sea wall and the abutment footing, both of which exhibit the inward lateral movements with time, in general accord-ance with the settlement profile of the undersea soils along the axis of the accessbridge.

The mechanical behavior of a rock mass with clayey seams was investigated by conducting aseries of triaxial compression tests. In the tests, a rock mass was modeled by a specimen made bysandwiching an alluvial clay seam between two pieces of Ohya stone. From the experimentalresults, it has been found that even if the thickness of the clayey seam is so thin, the shearstrength of a rock mass is almost governed by that of the clayey seam.

This paper starts with reviewing basic patterns of deformation of the soft clay foundationsloaded by embankments, along with suggestions for obtaining the integrated information onlateral soil movements from field measurements. In this respect, a new procedure for back-analyzing the strain path of any soil element below the center of embankment is proposed andis successfully applied to three cases of well instrumented test embankments(Kanda A, B andCubzac-les-Ponts B). Furthermore, effects of vertical sand drains on the correlation between late-ral deformation and consolidation settlement are discussed by comparing the performance of theKanda A test embankment on untreated soft foundations with the performance of the Kanda Btest embankment with vertical sand drains, in the light of the corresponding predictions fromcoupled elasto-viscoplastic consolidation analyses in terms of finite elements.

This study deals with experiments on the liquefaction of soft surface layers and the settle-ments of a rigid structural foundation and the surface layers caused by the liquefaction, underhorizontal and vertical shakings. Two directional motion has been achieved by making use ofa shaking table and a small vibration generator.It is shown that under two directional shaking the liquefaction and the settlement of thestructural foundation are not always caused in proportion to the excess pore water pressure, notwithstanding the excess pore water pressure under two directional shaking is greater thanthat under horizontal shaking. However, in some cases there are test data which mean thesettlement under two directional shaking is greater than that under horizontal shaking.On the basis of these results, the phase lag and the excitation frequency ratio are alsodiscussed between the horizontal and the vertical motions of two directional shaking.