報告書番号

U93061

タイトル（和文）

波と水中放水流による洗掘対策Ｉ法の提案その２ＳＰＡＣ（ＳｐｒｅａｄｉｎｇＡｒｍｏｒＣｏａｔ）工法の平面設計法

タイトル（英文）

COUNTERMEASURES TO SEABED SCOURDUE TO SUBMERGED DISCHARGE AND WAVES PART2 PLAN DESIGN OF SPAC(SPREADING ARMOR COAT)

概要 （図表や脚注は「報告書全文」に掲載しております）

前報では外洋に面した砂浜海岸における水中放水口前面の海底洗掘対策工法ＳＰＡＣ（ＳｐｒｅａｄｉｎｇＡｒｍｏｒＣｏａｔ）を考案し、その断面設計法を明らかにした。ＳＰＡＣは放水口前面の砂質海底を浚渫して捨石層で置換する工法であり、波と放水流の作用によって捨石が洗掘斜面に展開し、アーマコートを形成させるものである。本研究では、水理模型実験により波と流れによる洗掘の平面形状を把握するとともに、捨石の展開幅に沿岸流による放水流のドリフトを加味してＳＰＡＣの所要幅を決定する平面設計法を確立した。なお、捨石の展開幅は放水流野は場報告の広がり方から評価できた。また、放水流のドリフトは、まず一様勾配海岸に波が斜めに入射する場合の式から沿岸流速を求め、これを流れに直角に放水された噴流の式に適用して評価できた。さらに、実験結果と現地観測結果を比較し、洗掘深さと洗掘幅についての実験結果の妥当性を明らかにした。

概要 （英文）

THIS REPORT DISCUSSES THE STABILITY OF SUBMERGED OUTLET STRUCTURES OF THERMAL POWER PLANTS SITED ON SANDY OCEAN BEACHES. LARGE WAVES ACCELERATE SCOURING OF STRUCTURE TOES, IN AND LARGE CURRENT VELOCITIES OCCUR AT DISCHARGES FROM OUTLETS NEAR THE SEABED. WE CONCEIVED A NEW SCOURING PROTECTION CALLED SPAC (SPREADING ARMOR COAT) ANALOGOUS TO THE ARMOR COAT FORMED IN NATURAL RIVERS WITH A STABLE BED COVERED BY LARGE PEBBLES. SPAC IS CONSTRUCTED BY DREDGING AND RIPRAPPING OF THE SEABED JUST IN FRONT OF THE OUTLET. RIPRAP ROCKS ARE SPREAD OVER THE SAND SLOPE SCOURED BY WAVES AND CURRENT, AND THUS FORM ANAR,ARMOR COAT NATUALLY. A VERTICAL-SECTION TWO-DIMENSIONAL EXPERIMENT WASPERFORMED ON SPAC AND OFFSHORE SEABED SCOURING. THIS STUDY INVESTIGATES THE PLANE DESIGN OF SPAC BY MEANS OF 1/25 SCALE MODEL SIMULATING THE SEA AREA IN FRONT OF NOSHIRO POWER STATION. FIRST, WE COMPARED SEABED SCOUR DUE TO SUBMERGED DISCHARGE, SUBMERGED DISCHARGE WITH MULTI-DIRECTIONAL WAVES, AND SUBMERGED DISCHARGE WITH MONOCHROMATIC WAVES. SECOND, WE INVESTIGATED SPREADING OF SPAC, AND CLARIFIED THE NECESSARY WIDTH OF SPAC. WE ALSO TRIED TO REPRODUCE THE SCOUR OBSERVED ON THE OFFSHORE SIDE OF SPAC AT NOSHIRO POWER STATION ON THIS PHYSICAL MODEL. THE FOLLOWING CONCLUSIONS WERE REACHED. (1)THE WIDTH OF SPAC IS DETERMINED BY BOTH THE SPREADING WIDTH OF RIPRAP ROCKS AND THE DRIFT OF THE DISCHARGE FLOWDUE TO LONGSHORE CURRENT. (2)THE SPREADING WIDTH OF THE RIPRAP ROCKS IS DETERMINED BY ASSUMING THE HALF-VALUE-WIDTH OF DISCHARGED CURRENT VELOCITY DISTRIBUTION AS THE WIDTH OF SCOURING AND BY TURNING THE 20. SLOPE OF THE SPREAD SPAC AROUND ITS TOE. (3)THE VELOCITY OF THE LONGSHORE CURRENT IN FRONT OF THE OUTLET IS DETERMINED BY THE FORMULAE FOR LONGSHORE CURRENT DISTRIBUTION DUE TO OBLIQUE INCIDENT WAVES. (4)THE DRIFT OF THE DISCHARGE FLOW DUE TO THE LONGSHORE CURRENT IS DETERMINED BY THE TRAJECTORY FORMULAE FOR A JET ....

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