報告書番号

380047

タイトル（和文）

セメント系地盤改良の耐震効果に関する研究─起振実験からみた地震改良効果─

タイトル（英文）

ASEISMIC EFFECTS OF A GROUND IMPROVED BY CEMENT MIXTURE -EXAMINATION ON ASEISMIC EFFECTS OF IMPROVED GROUND BY THE IN-SITU VIBRATION TEST-

概要 （図表や脚注は「報告書全文」に掲載しております）

地盤とセメントを原位置で攪拌して改良された２種の地盤〔（１）直径約３０ｍ、厚さ２ｍの改良地盤Ｂ、（２）改良地盤Ｂの中央部分を約１０ｍ角で深さ２３ｍにある支持地盤まで改良した地盤Ａ〕の耐震効果について、それぞれの地盤上および未改良地盤Ｃ上に設けた模型基礎の起振実験時挙動を比較することにより検討し、以下の結果を得た。（１）水平加振に対する基礎・地盤系共振振動数の比較から、ＡＢ地盤はＣ地盤に比べ、８倍以上と３倍程度のＳ波速度増加が認められた。ただし、上下加振に対しては、Ｂ地盤についての改良効果は、顕著ではなかった。（２）基礎を支える地盤をばねとダッシュポットでモデル化し、それぞれのモデル定数の特性を検討した結果、Ａ地盤のばね係数はＣ地盤に比べ著しく大きく改良効果は顕著であるが、Ｂ地盤は複雑な特性を示すこと、Ａ、Ｂ地盤とも減衰係数はＣ地盤に比べて大きく、かつ、Ａ、Ｂ地盤でその値がほぼ等しいことが

概要 （英文）

THIS PAPER DESCRIBES THE RESULTS OF THE IN-SITU VIBRATION TEST WITH A MECHANICAL VIBRATOR TO TWO KINDS OF IMPROVED GROUNDS,WHICH ARE DESIGNATED IMPROVED GROUND A AND IMPROVED GROUND B,RESPECTIVELY. B IS THE GROUND WITH THE SURFACE IMPROVED ABOUT 30M IN DIAMETER AND 2M IN DEPTH. A IS THE GROUND WHOSE SURFACE IS IMPROVED THESAME AS B AND,MOREOVER,ITS CENTER PART OF SURFACE IS IMPROVED TO 23MIN DEPTH IN THE SHAPE OF THE COLUMN 10MX10M IN PLANE.THE MODEL FOUNDATION MADE OF CONCRETE BLOCK(3.5MX3.5M IN PLANE,1M IN HIGHT)IS INSTALLED AT THE CENTER OF A, B AND THE NATURAL SOFT GROUND C,RESPECTIVELY.EACH FOUNDATION IS VIBRATED BY THE MECHANICAL VIBRATOR AND ITS DYNAMIC BEHAVIOR IS MEASURED.THE RESULTS OBTAINED ARE AS FOLLOWS. (1)BY THE HORIZONTAL VIBRATION TEST,THE RESONANT FREQUENCIES OF THE FOUNDATION-GROUND SYSTEM ARE RECOGNIZED TO BE OVER 25HZ IN CASE OF A,ABOUT 9HZ IN CASE OF B AND ABOUT 3HZ IN CASE OF C.AND THE RESPONSE VALUE OF FOUNDATION ON A ANDB IS INDICATED TO BE MUCH SMALLER THAN THAT ON C.THUS,IT IS SUPPOSED THAT THE SEISMIC EFFECT OF THE IMPROVED GROUND CAN BE EXPECTED BOTH ON THE RIGIDITY AND ON THE DAMPING.(2)THE VIBRATION SYSTEM IS FOUND OUT TO BE FORMED BETWEEN THE IMPROVED RIGID GROUND AND THE NATURAL SOFT GROUNDBORDED ON THE IMPROVED GROUND.THESE RESONANT FREQUENCIES ARE ESTIMATEDTO BE UNDER 3HZ IN BOTH IMPROVED GROUND(A AND B).AND THE VIBRATION PROPERTY OF A AND B IS NOT SIMPLE SUCH AS THE RIGID BODY,THOUGH THE RIGIDITY OF THE IMPROVED PART IS 100 TIMES THE ONE OF THE NATURAL GROUND.SO,IN ORDER TO JUDGE THE ASEISMIC EFFECTS OF A GROUND IMPROVED THE PART OF THE NATURAL SOFT GROUND BY THE CEMENT MIXTURE AND SOON ,THE ROLES OF THIS DYNAMIC PROPERTIES UNDER THE EARTHQUAKE MUST BE EXAMINED BY ANALYSISAND EXPERIMENT INCLUDING EARTHQUAKE OBSEARVATION,SYNTHETICALLY.

報告者

キーワード