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In port and harbour areas, soft soils such as dredged soil can be solidified by mixing them with cement and other solidifiers in a pumping pipe. This method is known as pneumatic flow mixing. In this method, the soil and solidifiers are stirred and mixed using the turbulence effect of the plug flow generated in the pipe. The authors investigate the long-term durability of the treated soil on the artificial island where this method was first fully introduced. This paper summarises the results of five investigations on the island immediately after construction and 4, 10, 15, and 20 years after construction. No reduction in the unconfined compressive strength or needle penetration gradient was observed in the treated soil. Some degradation was observed at the top and bottom exposed surfaces of the treated soil, similar to that of soil subjected to other treatments. In addition to needle penetration and chemical tests, elemental mapping using an electron beam microanalysis was performed to determine the degree of degradation. The depth of degradation 20 years after construction was 18–25 mm. Although the amount of cement added in the pneumatic flow mixing method was relatively small, this value was within the range of degradation depths over time investigated in previous studies and did not represent a significant degradation.

During the Great East Japan Earthquake and Tsunami of 2011, enormous coastal levees collapsed as a result of tsunami overflows. Concrete-covered levees, where concrete blocks are used to protect levees made of soil, showed a specific failure mode in which back slope blocks and internal soils were dislodged. Although several hydraulic experiments have been conducted in an attempt to understand the failure mechanism, the complexity of the failure requires that both hydro-dynamical and geotechnical points of view be taken into account for a deeper understanding. This study uses a centrifuge to identify the failure behavior of levees from those points of view. The centrifuge can reproduce the stress, water pressure, and overflow velocity of the prototype-scale ground. Overflowing at sufficient time periods was produced in the centrifuge by generating differences in water height for seaside and landside areas. The test results showed that the levees collapsed due to a combination of the effect of water flow on the back slope and seepage inside the levees. In addition, the effectiveness of several proposed countermeasures for preventing collapse was confirmed.

Seashore ground stability is a crucial issue in the composite problems of hydraulics and geotechnics. Many studies have been conducted on covering materials and sediment transport. However, very few studies have examined this issue from a geotechnical viewpoint. This is because the ground displays complicated responses against breaking waves, and because it is difficult to examine ground behaviours through a prototype-scale model test. The physical modelling of breaking wind waves and seashore ground helps explain ground stability. This study examined the efficacy of centrifuge modelling with regard to this issue. The authors showed the similarity laws, including fluid behaviours and developed a new wave generator. The centrifuge model efficacy was verified mainly by way of the modelling of model tests on waveform, wave height and water pressure on and in the ground. Additional tests indicated that excess pore-water pressure was generated due to wave set-up. Increasing the wave height and/or wave frequency caused a seepage force, which could decrease ground stability.

Rotavirus infections have been reported to account for 40–50% of all hospitalized acute gastroenteritis cases in young children (

Cellulose nanofibre (CNF), a material composed of ultrafine fibres of wood cellulose fibrillated to nano-order level, is expected to be widely used because of its excellent properties. However, in the field of geotechnical engineering, almost no progress has been made in the development of techniques for using CNFs. The authors have focused on the use of CNF as an additive in cement treatment for soft ground, where cement is added to solidify the ground, because CNF can reduce the problems associated with cement-treated soil. This paper presents the results of a study on the method of mixing CNF, the strength and its variation obtained by adding CNF, and the change in permeability. CNF had the effect of mixing the cement evenly and reducing the variation in the strength of the treated soil. The CNF mixture increased the strength at the initial age but reduced the strength development in the long term. The addition of CNF also increased the flexural strength, although it hardly changed the permeability.

In this study, a new tsunami overflow-seepage-coupled centrifuge experimental system was developed and applied to investigate the concurrent processes, and to elucidate the mechanism, of the instability involving the scour of the mound/sandy seabed, bearing capacity failure and flow of the foundation, and the failure of caisson breakwaters, with high-resolution image analysis. A series of experiments were conducted with and without the effects of the seepage by keeping the same overflow conditions (water volume, overflow velocity, fall height and water depth), and with different mound cross-sections. All of the experiments were conducted under 50 gravities and comprised of 3 series. The first series of experiments targeted the instability of the mounds themselves by constraining the caisson movement (sliding and overturning). The second series of experiments then allowed the caisson movement and clarified how the mound scour would affect the overall stability of the caissons. The third series of experiments examined the effect of a countermeasure on the basis of the results from the two series of experiments. The experimental results first demonstrated that the coupled overflow-seepage actions promoted the development of the mound scour significantly. Notably, the scour front developed in the form of progressive slip failure at the vicinity of caissons, regardless of the mound thickness. This stems from the fact that the development of the mound scour shortened the seepage path around the shoulder area of the mound, enhancing the coupling effect of the overflow and seepage. Indeed, the scour stopped far from the caisson toe in the absence of seepage without affecting the stability of the caissons. By contrast, the scour development due to the coupled overflow-seepage approached the caisson toe and brought about bearing capacity failure of the mound, resulting in the total failure of the caisson breakwater, which otherwise remained stable without the coupling effect. The velocity vectors obtained from the high-resolution image analysis illustrated the series of such concurrent scour/bearing-capacity-failure/flow processes leading to the instability of the breakwater. The influence of placing an embankment as a countermeasure was also examined by employing different bank thickness. It is shown that the stability of the breakwaters was significantly improved with decreasing hydraulic gradient that manifested underneath the caissons due to the embankment effect. These findings will facilitate better assessment and improvement of the stability of caisson breakwaters with rubble mound foundations.

Liquefied ground loses its stiffness and strength, and it flows laterally in sloping areas and backfill areas behind collapsed quay walls. A method of installing piles such as cement-treated ones into the ground to prevent the lateral flow has been proposed and studied. The authors are investigating the most effective arrangement of piles to optimise cost-effectiveness. It is proposed to irregularly displace the piles to prevent lateral flow in various directions. In the present study, centrifuge model tests were conducted to verify the efficacy of piles against the lateral flow of liquefied ground and the effect of the pile arrangement in detail. This study first demonstrated the similarity law for the lateral flow of liquefied ground in a centrifuge, where both the Froude and Reynolds numbers can be satisfied. Numerical analyses assuming the flow of liquefied ground to be fluid-like were conducted to consider the improvement mechanism and the effect of the pile arrangement. The results of the model tests and numerical analyses indicated that the improvement by piles dramatically reduced the lateral displacement and that the average total flow velocity was small in the irregular arrangement case.

The improvement rate of countermeasures adopted in constructing a second track on an embankment on soft ground is determined empirically due to unknown factors such as the deformation properties of soft ground. In this study, centrifuge model tests were performed to grasp the deformation properties of soft ground for such construction cases. Based on the test result, a new countermeasure was proposed, which has high horizontal support performance and combines deep mixing wall-type ground improvements and cement-mixed gravel. The proposed method having the same improvement rate as deep mixing was confirmed as being able to reduce the deformation of the embankment and the surrounding ground.

A tsunami-induced difference between the water levels of the seaward and the landward sides of breakwaters generates one-way seepage in the rubble foundation under the breakwaters. Such seepage may decrease the bearing capacity of the rubble foundation, trigger the piping and/or boiling of the foundation, and cause the scouring of the sandy seabed. In this paper, we describe the stability of a breakwater foundation under the action of seepage based on the results of model tests and FEM analyses. The main feature of our study is the application of the centrifuge technique to such composite hydrodynamic and geotechnical problems. The centrifuge technique can be used to produce high-water pressure and ground stress corresponding to those of prototype-scale breakwaters. The experimental results show that seepage-induced scouring and boiling occur, and that the seepage force decreases the bearing capacity of the rubble foundation. The results of the numerical analyses also reveal the effect of the reduction in bearing capacity in the presence of seepage.

Itching and infiltration of immune cells are important hallmarks of atopic dermatitis (AD). Although various studies have focused on peripheral mediator–mediated mechanisms, systemic mediator–mediated mechanisms are also important in the pathogenesis and development of AD. Herein, we found that intradermal injection of lysophosphatidic acid (LPA), a bioactive phospholipid, induces scratching responses by Institute of Cancer Research mice through LPA 1 receptor– and opioid μ receptor–mediating mechanisms, indicating its potential as a pruritogen. The circulating level of LPA in Naruto Research Institute Otsuka Atrichia mice, a systemic AD model, with severe scratching was found to be higher than that of control BALB/c mice, probably because of the increased lysophospholipase D activity of autotaxin (ATX) in the blood (mainly membrane associated) rather than in plasma (soluble). Heparan sulfate proteoglycan was shown to be involved in the association of ATX with blood cells. The sequestration of ATX protein on the blood cells by heparan sulfate proteoglycan may accelerate the transport of LPA to the local apical surface of vascular endothelium with LPA receptors, promoting the hyperpermeability of venules and the pathological uptake of immune cells, aggravating lesion progression and itching in Naruto Research Institute Otsuka Atrichia mice.

Water level difference induced by tsunami generates seepage flow in a mound of caisson-type breakwaters. It has been pointed out that the seepage force weakens a bearing capacity of a mound. The present paper describes bearing capacity properties of a mound under seepage flow, by using centrifuge model tests and finite element method analyses. Two types of model tests were conducted in the study: horizontal load tests and combined tests with horizontal load and seepage flow. According to the model tests, seepage force resulted in decrease of a bearing capacity. In addition, it was confirmed that finite element method analyses could simulate the model tests, and the suitable hypothetical adhesion was shown to simulate the effect of seepage force.

The dynamic and non-dynamic interactions between a gravity-type quay wall and a backfill ground were investigated by centrifuge model testing, considering cases in which a rigidly cement-stabilised ground existed at varying distances from the quay wall. In conducting the centrifuge tests, the performance of the instrumentation applied to measure the pressure from granular soils was critically assessed. At non-dynamic states, the backfill confined between the quay wall and the rigidly stabilised soil block exerted smaller earth pressure at deeper locations, at both apparently active and transient states. The calculation, based on perfect plasticity and considering friction arching, was useful in explaining these results. A similar feature was also observed during the steady-state oscillations, in the case of dry sand backfill, and was associated with the system’s increased seismic stability. In underwater cases, the pore water fluctuations in the backfill dominated the total earth pressure behaviour, with the active pressure being smaller again from a confined fill than from a fully extending one. Despite the reduced active pressure, placing the stabilised soil in the proximity of the quay wall increased the wall’s permanent seaward movement, unless the two bodies were in direct contact. This ostensible association of smaller active pressure with greater instability in the underwater cases cannot be explained by the conventional, simplified conception of the active earth pressure as a unilateral cause of instability. The evaluation of such unconventional backfill conditions seems to require rigorous consideration of the simultaneous soil–water-structure interactions.

ケーソン等の重力式構造物構築時の軟弱粘性土に対する代表的な対策工法であるサンドコンパクションパイル工法（SCP工法）は，その中詰め材料として一般的に良質な天然砂を用いる。本研究では，代替材として固結特性を有する鉄鋼スラグを用いた場合における地震時の改良地盤の変形挙動について検討した。実験的検討として，中空ねじりせん断試験機を用いて粘土と改良杭からなる複合地盤の繰返し載荷実験を行った結果，改良部にダイレイタンシー特性が顕著に現れることが分かった。また，遠心場での模型振動実験を行った結果，鉄鋼スラグと砂を用いた場合で変形挙動は同様であるが，改良エリアにおける残留変形量は鉄鋼スラグの方が小さい結果となった。さらに，模型振動実験の有効応力法による再現解析では，鉄鋼スラグ改良地盤のダイレイタンシー特性の評価が重要であることが分かった。

In-situ static compaction by grouting is routinely used as a countermeasure against liquefaction in loose sandy ground. The surrounding ground's stress changes induced by grout injection are considered to be an important cause for the stabilisation effects, along with some densification of the ground in the bulb's vicinity. The present study investigates characteristics of the stress changes by simulating compaction grouting processes in a geotechnical centrifuge. Detailed descriptions are given of apparatus and experimental techniques specifically developed for conducting miniature injection tests. The observed increases in the horizontal stresses, evaluated in terms of the earth pressure coefficient, K, reflected the influence of grout pile spacing, and were found to be consistent with field measurements except near the surface. The centrifuge tests also allowed the changes in the dominant stress direction within the horizontal planes at the stabilised domain's centre to be evaluated, with the results indicating the dependency of the stress changes upon depth and interactions between neighboring grout piles. The significance of the stress changes in increasing the liquefaction resistance is demonstrated by mapping liquefaction curves against initial stress states through a series of cyclic hollow cylinder simple shear tests.

Cement Treat Granulate Soil (CTGS), a new artificial granular material, has been developed recently by mixing the dredged marine clay with appropriate amounts of cement and polymer. The CTGS particles are crushable and deformable, thus forming a compressible material. Besides being a lightweight material, CTGS is a granular material, and is therefore expected to be applied in reclamations or as a back fill or subsoil materials. This study investigates the deformation and crushing of the CTGS particles and their effects on the stress-strain behaviors. The comprehensive investigation of the principle of treatment, the micro-structure of particles, triaxial stress-strain behaviors, induced particle crushing and particle deformation are first presented via the experimental work done on two types CTGS produced from a lean-mixture design of cement and polymer. Subsequently, the results of X-ray Computer Topography (CT) scanners along with triaxial CD tests on CTGS and conventional gravel having rigid particles are presented. The test results reveal local failure mechanisms between the individual particles of the CTGS and gravel, from which the failure models of the granular materials formed by deformable and crushable grains and non-crushable grains are interpreted.

軟弱粘土層上に重力式岸壁を整備する場合，安定性向上ために締固め砂杭工法（SCP工法）が多く利用されている。本研究では，改良材として天然の砂質土の代わりに固結特性を有する鉄鋼スラグを用いた地盤の安定性について，遠心模型実験および円弧滑り計算によって検討した。模型実験では，比較対象として鉄鋼スラグ以外に砂質土等で改良した粘土層に対しても遠心力場で埋立載荷した。その結果，砂質土および鉄鋼スラグによる改良地盤が破壊に至る変形モードは一致した。また，砂質土よりも鉄鋼スラグで改良を施した地盤の方が載荷によって生じる変形量が小さく，安定性も高いことが分かった。

含水比が高い軟弱な粘土・シルト系の土を改良して比較的高強度な粒状体（造粒固化土）を作製する技術がある。一般的な地盤材料に比べて造粒固化土は軽量であり，例えば重力式ケーソン岸壁背後の埋立材に適用すれば，地震時におけるケーソンの水平変位量を低減できる。本研究では，岸壁の振動特性を詳細に調べ変位低減のメカニズムを明らかにすることを目的として，動的変形特性試験および動的遠心模型実験を実施した。模型実験では，ケーソンへ作用する土圧を計測し，その土圧と振動特性の関係を調べた。その結果，造粒固化土で形成された地盤からケーソンへ作用する地震時土圧は小さく，これを主要因として変位量が低減されることを確認した。

軟弱粘土層の安定性向上を目的として，SCP工法は多くの地盤改良工事に用いられているが，経済性の追求や施工上の問題から改良率の低減や改良範囲の縮小が求められている。しかしながら，特に改良範囲を縮小したSCP改良地盤の破壊挙動に関しては，研究が進んでいないのが現状である。本研究では，遠心模型実験および数値解析手法を用いて，鉛直荷重を受ける杭式SCP改良地盤の破壊挙動の検討および改良範囲の縮小化の破壊挙動への影響評価を行った。その結果，改良地盤の破壊時に基礎直下にいわゆる主働くさびが形成され，周辺部の砂杭は湾曲する現象が観察された。数値解析によって，この破壊メカニズムを解明するとともに，改良範囲縮小化において適切な範囲が存在することを明らかにした。

The consolidation characteristics of clay, based on the isotache concept in which the strain rate effect is considered, have been studied by many researchers. Most of these studies are aimed at calculating the secondary consolidation with high accuracy in order to evaluate the long-term settlement of large structures. In this study, as the first step toward improving the accuracy of the evaluation of long-term settlement at the Kansai International Airport, the consolidation characteristics of Osaka Bay clay are examined and organized based on the isotache concept. This study proposes a simplified model based on the isotache concept by using a compression curve and the relationship between the consolidation yield stress and the strain rate. The former and the latter are obtained from the constant rate of strain consolidation (CRS) tests and long term consolidation (LT) tests, respectively. The latter is expressed by an equation with three isotache parameters. This model is very practical because it requires a minimum of only one CRS test and one LT test. It is widely applicable to the Osaka Bay clay. The isotache parameters used in this model can be commonly determined for the Osaka Bay clays retrieved from various depths at the Kansai International Airport.

閉塞した中間砂層を含む粘土地盤上に盛土を築造する際，粘土層に発生した過剰間隙水圧は中間砂層を介して周辺部へ伝播すると考えられ，地盤内の過剰間隙水圧の伝播特性および圧密沈下特性は複雑になる．本研究では，粘土層内に閉塞した中間砂層を有する過圧密粘土地盤に対して載荷実験を行い，過剰間隙水圧の伝播特性や圧密沈下挙動について検討した．その結果，過剰間隙水圧が中間砂層を介して周辺部へ伝播することによって，他の盛土載荷による周辺部での圧密沈下を遅らせるだけでなく，条件によっては砂層から粘土層内に過剰間隙水圧が伝播し地盤が膨張することを観察した．さらに，盛土載荷時期や砂層数が圧密沈下挙動に与える影響を実験的に調べた．