報告書番号

385001

タイトル（和文）

海底土質地盤の特性と波力に対する安定性評価に関する現状

タイトル（英文）

A STATE OF THE ART REPORT ON PROPERTIES OF MARINE SOIL DEPOSITS AND ITS STABILITY EVALUATION FOR WAVE LOADING.

概要 （図表や脚注は「報告書全文」に掲載しております）

原子力発電所等の大型重要海洋構造物を支持する基礎地盤の海洋で想定される諸外力に対する安定性を確証することは重要である。そこで，土質工学の立場からこの問題に対処するために，海底土質地盤の諸特性と海洋特有の外力である波力に対する地盤の安定性について既往の研究を取りまとめた。その結果，海底地盤は，未圧密状態や擬似過圧密状態にある場合もあり，それらは地盤の安定性に影響を及ぼすこと。台風時などには，波力によって海底砂地盤が液状化する危険性があること。海の波は周期が長いため地盤の排水性を考慮しなければ安定性を過小評価する可能性があることなどが判明した。今後は，海底地盤の物性をより詳細に検討するとともに，地盤－構造物の耐震安定性評価と同様，耐波浪安定性評価の手法を確立していくことが課題であると言えよう。

概要 （英文）

IT IS IMPORTANT TO PROVE THE STABILITY OF FOUNDATION GROUND WHICH SUPPORTS THE LARGE-IMPORTANT OCEAN STRUCTURES SUCH AS NUCLEAR POWER PLANTS,OCEAN PLATFORMS AND UNDERWATER LARGE PIPELINES ETC..TO DEAL WITH THIS PROBLEM FROM THE GEOTECHNICAL ENGINEERING POINT OF VIEW,ARE REVIEWED THE PREVIOUS INVESTIGATIONS ABOUT THE PROPERTIESOF MARINE SOIL DEPOSITS AND THE STABILITY OF UNDERWATER SOIL GROUND FOR WAVE LOADING WHICH IS THE PECULIAR EXTERNAL FORCE ON THE OCEAN.CONSEQUENTLY THE FOLLOWINGS ARE UNDERSTOOD.(1)THERE IS A POSSIBILITY OF MARINE SOIL DEPOSITS EXISTING UNDER UNDERCONSOLIDATION OR QUASI-OVERCONSOLIDATION CONDITION AND THESE CONDITIONS HAVING AN EFFECT ON THE GROUND STABILITY.(2)THE CYCLIC CHANGE OF SHEAR STRESS BY A HARMONIC WAVE LOADING MOVING ON ELASTIC HALF-SPACE GROUND IS CHARACTERIZED BY A CONTINUOUS ROTATION OF THE PRINCIPAL STRESS DIRECTION WITH THE DEVIATOR STRESS(MAXIMUM SHEAR STRESS) BEING ALWAYS MAINTAINED CONSTANT.(3)IN CASE OF THE TYPHOON ETC., UNDERWATER SANDY GROUND IS IN DANGER OF LIQUEFYING BY LARGE CYCLIC WAVE LOADINGS.(4)AS THE PERIODS OF OCEAN WAVES ARE SO LONG,NOT CONSIDERING THE DRAINAGE OF GROUND,IT LEADS TO THE UNDERESTIMATION OF ITS STABILITY.RESULTED FROM THIS INVESTIGATION ,AS THE FUTURE PROBLEMS AWAITING TO BE SOLVED,IT WILL BE NECESSARY (1)TO DEVELOP THE NEW IN-SITU TESTING PROCEDURES FOR UNDERWATER GROUND WITH LARGE DEPTH,(2)TO EXAMINEIN DETAIL THE MECHANICAL,PHYSICAL AND CHEMICAL PROPERTIES OF MARINE SOILS UNDER VARIOUS CONSOLIDATION CONDITIONS,AND(3)IN CONSIDERATION OF THOSE PROPERTIES TO ESTABLISH THE METHOD OF ESTIMATING THE STABILITY OF UNDERWATER GROUND FOR THE WAVES AS THAT FOR THE EARTHQUAKES.

報告者

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