Geo-disaster Prevention Engineering Laboratory

​Liquefaction can cause substantial damage to buildings in the form of ground subsidence and bearing capacity failure of the soil after an earthquake. In Japan, numerous low-rise structures and traditional houses suffered severe damage caused by liquefaction. To consider remediation measures on vulnerable housing in liquefaction prone regions, it is necessary to adopt appropriate remediation measures in geotechnical engineering practice. To address this issue, a new liquefaction mitigation technique of a grid form with a horizontal slab ground improvement method is developed. Different from the conventional grid type improved methods, a small grid spacing ratio of 0.2 is utilized to suppress excess porewater pressure ratio during an earthquake. Moreover, the additional horizontal slab is enhanced expect from the vertical grid wall, to provide sufficient reinforcement to liquefiable soil in both vertical and horizontal directions. A series of experimental modeling and numerical modeling were studied to evaluate the effectiveness of the newly proposed method.

Highway embankments are very important and strategical infrastructures that play a crucial role in resilience to natural disasters and providing road transport services in disaster relief after an extreme event. Many highway embankments were damaged at Kumamoto Prefecture, Japan due to the 2016 Kumamoto earthquakes. Many road embankments in this region are founded on liquefiable loose soil which raises the need for the development of new applicable and cost-effective deformation countermeasure technique for new and existing highway embankments. The hybrid pile system which includes vertical piles, slanted piles and geo-grid is introduced in this study. Several 1g shaking table tests which were produced aim to investigate the performance of hybrid pile system supported road embankment in liquefaction resistance and settlement reduction during seismic loadings.

Development of material constitutive model has been turned to challenging task for researchers. Linear and non-linear viscoelastic models which is being used to predict behavior of soil materials cannot precisely reflect complexity of reinforced materials and Advanced models based on the concepts of plasticity require the definition of large number of parameters which would be difficult to determine. In order to overcome aforementioned issues, this study aims to propose a constitutive reinforced soil model which is capable of capturing stress-strain behaviour with high degree of performance. To this end, a series of element tests are being conducted to identify important parameters affecting static and dynamic behaviour of reinforced soil, then data mining method will be used to enrich the data and implemented to capture stress-strain behaviour of reinforced soil.

Landslide triggered by the 2016 Kumamoto earthquake results huge damage in properties and loss of lives. This research aims to determine the failure mechanism of those slopes and elucidate the effect of cyclic loading on strength characteristics of volcanic soil. In this research, especially the failure mechanism of volcanic slope is mainly investigated by a series of undrained static and cyclic triaxial test. Also, for further understanding of volcanic soil material strength, X-ray powder diffraction analysis (XRD), X-ray fluorescence analysis (XRF), and Scanning electron microscope analysis (SEM) were performed.

Retaining walls, which are used to promote deep excavations, deep embankments, and basements, etc., is one of the essential components of different infrastructural projects. In deciding the cross-sectional dimensions of the retaining wall, the earth pressure has an important role. Therefore, this research aims to assess the change of magnitude and distribution of earth pressure as well as its point of application and total thrust from at rest to an active case on the wall rotation about base and translation. Also, to evaluate the effect of surcharge load location that; the surcharge load within the Rankin’s active failure zone. In this study, an experimental method was used to determine the magnitude and distribution of earth pressures caused by a strip surcharge load on the retaining wall backfill using a small-scale laboratory model, which is shown in the Figure.

Gabion Retaining walls is one of the important geotechnical structures, it is used in every place and corner of the world. most used on shallow foundation structures, in mountainous areas, Bridge protection, slope protection, Roads, railways, prevent floods, Coastal protection, river banks protection, earthquake, embankment, and dam structures. On the other hand, in deciding the cross-section dimensions of the gabion retaining wall, the earth pressure has an important role. we can use the gabion structure in retaining wall and strength of slope, to keep the soil from the devastating effects. so the purpose of this study is to investigate the performance of gabion retaining wall is under Successive impact load (rock fall) with according to the different weight and heights, and also my more focus will be on this part.

平成28年（2016年）熊本地震では4月14日と16日に最大震度7を観測し，人的被害とともに建物・道路等インフラおよび住宅に多数の被害が出た．また，布田川断層帯と日奈久断層帯では推定位置の近傍に主に横ずれを示す地表地震断層が出現した．さらに，この地震による被害は熊本平野およびその周辺に及んでおり、阿蘇火山周辺では多数の斜面災害が発生した。
発生した斜面災害数は約700箇所以上もあり、その崩壊形態やメカニズムは、火山地質地帯の複雑な地質構造も相まって、完全に明らかにされていない。また、この地域は過去（平成24年）に、豪雨災害に見舞われた地域でもあり、当地においては、地震並びに豪雨の両誘因を考慮した減災・防災対策が必要である。
本研究では、今回の地震により発生した複雑な斜面崩壊メカニズムを明らかにする。その上で、降雨災害との差別化を図り、将来的な地域防災計画の方向性を明確にする。

2016年4月14日、16日に熊本地方を中心に最大震度7を観測する大きな地震が相次いで発生し、中部九州を中心とした広い地域で強い揺れが観測されました。この地震により熊本平野や八代地方において広く液状化の被害が発生しましたが、その被害状況は地震のマグニチュード・震源距離などに比してそれほど大規模ではありませんでした。噴砂の分布は広範囲に面的に広がるのではなく、特定の地質等に集中して見られたのが特徴的です。過去の地震においても、震度5強以上において液状化被害は観測されてきましたが、古い埋立地や自然地盤での被害は限定的でした。また、今回の液状化の特徴として、火山灰質砂が噴砂として多く観測されたことが挙げられます。これらの点から、この地域の火山灰質砂の力学的性質や地質状況に着目し、熊本平野の地盤の液状化特性を明らかにすることを目的としています。

Research on the breakwater against earthquake and tsunami. People usually separate earthquake and tsunami to study the breakwater. For the breakwater, not only the tsunami may cause great damage to the breakwater, but also the earthquake may do harm to the breakwater. Because the earthquake may cause the breakwater foundation loosing and liquefying, thus causes the breakwater sliding or collapsing. So the combination of earthquake and tsunami can be close to the actual situation.

  Test different resilient breakwaters with sheet piles, gabions and wave-dissipating blocks. It’s to find the best model. With previous researches, some measures have effectively improved the stability of the breakwater. Now wave-dissipating blocks and some other changes will be done in the breakwater to find more stable breakwater models.

2011年3月に発生した東日本大震災では，強い地震動とそれに伴う巨大な津波により防波堤などの海岸保全施設は甚大な被害を受けました。これを受けて，近い将来発生率が高いと予測されている南海トラフ巨大地震の際に，設計津波高を越える津波が来襲した場合でも被害を最小限に抑えられる構造の防波堤が必要と考えられています。本研究では，その中でも特に津波による防波堤の破壊形態に関して着目して研究しています。

本研究では，水理模型実験を行い，津波に対して効果的な防波堤の補強構造の開発を目指すことを目的としています。また，解析ソフトを用いて，防波堤の破壊形態のメカニズムや，最適な補強構造についてのメカニズムを解明することも目的としています。