報告書番号

U91001

タイトル（和文）

軟岩上の重力式係留基礎の地震時滑動に関する基礎的検討

タイトル（英文）

SLIDING OF GRAVITY MOORING FOUNDATIONS ON SOFT ROCK DURING EARTHQUAKES

概要 （図表や脚注は「報告書全文」に掲載しております）

浮揚式原子力発電所の浮体を係留する重力式係留基礎を海底の軟岩地盤上に建設する場合，地震時における係留基礎の滑動が重要な検討項目のひとつになると考えられる。本報告では，基礎地盤が泥岩で構成されている場合を想定し，係留基礎の地震時滑動に関する基礎的検討を行った結果について述べており，主な成果は以下の通りである。（１）滑動により，構造物の応答加速度，動水圧は低下する。（２）泥岩とコンクリートの接触面での摩擦特性を調べるため，繰返し一面せん断試験を実施し，すべり速度が速いほど動摩擦係数が低下することを確認するとともに，実験結果に基づいた摩擦特性の定式化を行った。（３）地震時滑動を考慮した数値解析手法を開発し，振動台実験のシミュレーションによってその妥当性を確認した。（４）静止摩擦係数が大きくかつ静止摩擦係数と動摩擦係数の差が小さいほど，地震時滑動量が小さくなることを解析的に検討した。

概要 （英文）

IN-SHORE FLOATING NUCLEAR POWER PLANTS HAVE BEEN PROPOSED AS ONE ADVANCED SITING TECHNOLOGY BUT THERE ARE SOME PROBLEMS TO INVESTIGATE REGARDING THE STABILITY OF PLANTS AGAINST EARTHQUAKES,WAVES AND WIND. THIS REPORT DESCRIBES THE RESULTS OF STUDIES ON SLIDING OF A GRAVITY MOORING STRUCTURE DURING EARTHQUAKES. THE FOLLOWING RESTS GAVE THE FOLLOWING CONCLUSIONS. 1. SHAKING-TABLE TESTS ON SLIDING DURING EXCITATION OF SMALL-SCALE MODEL (1) THE RESPONSE ACCELERATION OF THE MODEL AND THE DYNAMIC WATER PRESSURE ACTING ON THE MODEL ARE REMARKABLY REDUCED WHEN SLIDING OCCURS. (2) THE SLIDING DISPLACEMENT IS PROPORTIONAL TO THE INPUT ACCELERATION AT A CONSTANT EXCITATION FREQUENCY. (3) THE EFFECT OF FREQUENCY ON THE SLIDING DISPLACEMENT IS VERY LARGE AND IS INVERSELY PROPORTIONAL TO THE SECOND POWER OF THE FREQUENCY. (4) THE SLOPE OF THE SEABED HAS AN EFFECT ON THE AMPLITUDE AND THE RESIDUAL SLIDING DISPLACEMENT.2. DIRECT SHEAR TESTS ON FRICTION AT CONTACT SURFACE (1) THE COEFFICIENT OF STATIC FRICTION AT THE SURFACE BETWEEN THE CONCRETE AND MUD STONE IS 0.7. BUT THE COEFFICIENT OF DYNAMIC FRICTION DEPENDS ON THE SLIDING VELOCITY AND IS SMALLER AT HIGHER SLIDING VELOCITIES. (2) THE COEFFICIENT OF DYNAMIC FRICTION WAS CALCULATED FROM THE EXPERIMENTAL RESULTS. (3) THE COEFFICIENT OF FRICTION DEPENDS ON THE TYPE OF SOFT ROCK. WHEN THE SOFT ROCK HAS A VERY ROUGH SURFACE(TUFF),THE COEFFICIENT OF DYNAMIC FRICTION IS HARDLY REDUCED EVEN AT HIGH SLIDING VELOCITIES. 3. NUMERICAL INVESTIGATION OF SLIDING DURING EARTHQUAKES (1) NUMERICAL SIMULATIONS INCORPORATING A NEWLY-PROPOSED CONSTITUTIVE RELATONSHIP AT THE CONTACT SURFACE WERE PERFORMED ON THE SHAKING-TABLE TESTS.THE RELIABILITY OF THIS NUMERICAL METHOD FOR PREDICTING SLIDING DISPLACEMENT WAS VERIFIED. (2) THE COEFFICIENT OF STATIC FRICTION AND THE DIFFERENCE BETWEEN THE COEFFICIENTS OF STATIC AND DYNAMIC FRICTION HAVE A LARGE EFFECT ON THE SLIDING DISPLACEMENT.

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