報告書番号

381032

タイトル（和文）

セメント系改良地盤の耐震効果に関する研究－地震観測から見た改良地盤の制震効果（２）制震効果の力学特性とその予測－

タイトル（英文）

ASEISMIC EFFECT OF CEMENT-MIXED SOIL IMPROVEMENT -LOSS MECHANISM OF EARTHQUAKE MOTION ON IMPROVED GROUND (2)-

概要 （図表や脚注は「報告書全文」に掲載しております）

セメント系改良地盤の制震効果の力学特性を明らかにするため，第１報に引き続き，浅い部分のみを改良した改良Ｂ地盤（厚さ２ｍ，直径３０ｍ）に対し，その直径を約半分に縮小整形して地震観測を行い，直径の変更前後のデータを比較，検討した。（１）改良地盤と未改良地盤の間のスペクトル比は，直径を変化させても何等変化しないことが判明した。（２）重複反射理論と軸対象モデルＦＥＭ解析を比較した結果，この形状の改良地盤に対して前者は十分適用できることを確認し，これを用いて未改良地盤の波形から改良地盤の波形を予測すると，観測値と良く一致することを示した。（３）従って，こうした地盤改良の制震効果は主として改良地盤と未改良地盤間の波動インピーダンスの相違に基づく入射エネルギーの反射により生ずるものと考えられ，簡単な重複反射論を用いて基本的特性を予測できる。

概要 （英文）

IT HAS BEEN REPORTED IN THE PREVIOUS PAPER(PART(1))THAT THE CEMENT-MIXED SOIL IMPROVED GROUNDS,A AND B,SHOW THE REMARKABLE LOSS EFFECT FOR THE HORIZONTAL MOTION OF THE EARTHQUAKE WAVES.THIS TIME,TO EXAMINE THE LOSS MECHANISM OF IMPROVED GROUND MORE EXACTLY,THE FURTHER EARTHQUAKE OBSERVATION IS PERFORMED TO THE IMPROVED B GROUND OF WHICH DIAMETER IS REDUCED TO ABOUT A HALF. (1) ANY DIFFERENCE IS NOT AT ALL FOUNDED IN THE SPECTRAL RATIO BETWEEN THE GROUND B AND RIGHT UNDER UNIMPROVED GROUND,AND FROM THE INVESTIGATION ABOUT THE AMPLIFICATION CHARACTERISTICS OF EARTHQUAKE WAVE AT THESE GROUND SURFACES,IT IS COMFIRMED THE LOSS EFFECT OF B GROUND IS NOT EFFECTED BY THIS GEOMETRIC TRANSFORMATION IN THE DIAMETER. (2) IN A COMPARISON OF THE RESPONSE ANALYSES DUE TO THE MULTIPLE REFLECTION THEORY WITH AN AXI-SYMMETRIC STRUCTURE MODEL F.E.M.(CRAS),THE BOTH WELL AGREE WITH EACH OTHER,SO THE FORMER METHOD CAN BE ABLE TO USE FOR THE EXAMINATION OF THIS STUDY. (3) THESIMULATIONS OF EARTHQUAKE MOTION ON THE B GROUND ARE CARRIED OUT BY ABOVE METHOD USING THE RECORDS OBSERVED ON THE FREE SURFACE OF UNIMPROVEDGROUND.ACCORDING TO THESE EXAMINATIONS,IT CAN BE SAID THAT THE SIMULATED WAVES ARE WELL COINCIDENT WITH THE OBSERVED ONES IN THE WAVE FORM,MAXIMUM AMPLITUDE AND ACCELERATION RESPONSE SPECTRA. CONSEQUENTLY,THE LOSS MECHANISM OF IMPROVED GROUND IS MAINLY CAUSED BY THE REFLECTION EFFECT OF INPUT ENERGY AT THE BOUNDARY BETWEEN THE IMPROVED GROUND AND RIGHTUNDER SOFT GROUND BECAUSE OF THE GREAT DIFFERENCE IN BOTH ACOUSTIC IMPEADANCES,AND IT CAN BE SAID THAT THE LOSS EFFECTS OF THESE IMPROVED GROUNDS CAN BE ESSENTIALLY FORECASTED BY MEANS OF MULTIPLE REFLECTION THEORY WITHOUT CONSIDERING THE EFFECT DUE TO THE INPUT WAVE LOSS THEORY.

報告者

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