2004年新潟県中越地震における農業用ため池の被災状況
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概要
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平成16年(2004年)新潟県中越地震では、農業関連で多くの被害があった。本調査では、その中でも被災数、被災額ともにもっとも大きな被害を受けた農業用施設のうち農業用ため池の被災状況を調べた。対象は、被災が甚大であり、復旧事業費率が抜きん出ている新潟県長岡地域振興局管内とした。調査では、耐震を含めたため池の設計施工法の今後の進展に具体的に寄与できるように、個別事例の被災状況とそのメカニズム的な誘引に着目するようにした。調査は、2005年の9月から11月にかけて実施し、採取した土試料の土質試験は11月から翌1月にかけて行った。被災の状況や程度には、いまのところ、たとえば震央からの距離や堤体の規模などを指標としたパターン的な傾向が見られない。今回の調査を通して、土の締固めに対する理解とそれをいかに設計施工へ反映させていくかという点が、堤体の被災程度に重要に関与していると考えた。The Mid Niigata Prefecture Earthquake in 2004 brought serious damages to agricultural lands and facilities in mountain and hilly mountain areas in Chuetu, Niigata. This report summarizes results of field investigation conducted during September to November, 2005, to show some characteristics of the mechanical or structural damages of irrigation ponds which were caused by the Mid Niigata Prefecture Earthquake in 2004. Nagaoka and Ojiya, Niigata, were selected for the field investigation because these areas suffered most serious losses. Section, height and direction of embankment of the irrigation pond were surveyed, dry bulk density of surface soil of the embankment was measured by using RI counter, and some diagnoses of the mechanical or structural damage of the embankment were recorded based on simple observation. The distance of the embankment from seismic center of the first eruption of earthquake was determined from isoseismic map published by the Japan Meteorological Agency. Particle density and size of soil sampled from the embankment during the field investigation were measured in the laboratory. The degree of mechanical or structural damage was classified into level 0 to 3 by 1 based on the simple diagnoses recorded in the field investigation. Level 0 means no damage and 3 the most serious state of damage at which the embankment of irrigation pond never works. The degree of mechanical or structural damage was related to the distance from seismic center taking the embankment height into account. Any acceptable relationship between the degree of mechanical or structural damage and the distance from seismic center is not found. The dry bulk density of soil measured at no-damaged embankment was compared with that of the seriously damaged embankment to obtain some possible understand that a recognition of soil compaction during construction of the embankment may be an important key which determines the degree of mechanical or structural damage, or inversely, a resistance of the embankment against big earthquake. The investigation work is followed by a continuing effort.
- 新潟大学農学部の論文
- 2006-08-00
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