JITOUSONO, Takashi

SHIMOKAWA, Etsuro

TERAMOTO, Yukiyoshi

THOYA, Yuki

In order to clarify the nature and scale of the damage caused by typhoon Nabi in September 2005 to the slopes borderingthe forest road through the Takakuma Experimental Forest at Kagoshima University，thirty five slopes bordering the road，damaged by typhoon Nabi，were investigated. Characteristic results were as follows:   (1) The geological composition of the study area is a sandstone and shale base，overlaid with pyroclastic fall and pyroclastic flow deposits，volcanic ash and volcanic pumice originating from eruptions of the Sakurajima Volcano. Several types of erosion and slope failure were observed within the study area.: slope failure occurring on the downhill side of the forest road，as a result of the combined effect of groundwater from between the bedrock and the pyroclastic fall deposits being augmented by an influx of rain water; shallow landslide resulting from the infiltration and concentration of rain water into surface soil in the cutting and natural slope; deep-seated landslide resulting from groundwater between the bedrock and pyroclastic fall deposits combining with an influx of rain water; failure of the subbase and subgrade bearing body of the forest road itself，as a result of groundwater between the bedrock and pyroclastic fall deposits together with an influx of rain water; and the clogging of conduits and partial failure of the forest roads themselves，as a result of inundation by sediments due to debris flow.   (2) Areas of slope failure and sediment yields resulting from slope failure within the study area were investigated. The area of slope failure ranged from 16㎡ to 400㎡ (average 133㎡) and the sediment yield due to slope failure ranged　from 10㎥ to 1,600㎥ (average 223㎥). The following figures obtained in one particular area of slope failure and sediment yield were obtained slope failure occurring on the downhill side of the forest road; deep-seated landslide; and failure of the subbase and subgrade bearing body of the forest road itself showed a big value comparing with types of other erosion and slope failure within the study area.2005年9月の台風14号による鹿児島大学農学部附属高隈演習林の林道法面の被害状況を明らかにするため，高隈演習林内の35箇所の林道法面を対象として侵食・斜面崩壊に関する調査を実施した。得られた結果は以下の通りである。 (1)調査地は砂岩・頁岩が基盤岩となり，それを姶良カルデラおよび阿多カルデラから噴出した降下火砕物や桜島火山から噴出した火山灰・軽石が被覆した地質構造となっている。調査地でみられたおもな侵食・斜面崩壊の形態として，基盤岩とその上部を覆う大隅降下軽石層の聞に集中した雨水および地下水に起因して発生した林道の谷側斜面の崩壊，自然および切り取り斜面への雨水の浸透に起因した表層崩壊，基盤岩とその上部を覆う大隅降下軽石層の聞に集中した雨水および地下水に起因して発生した深層崩壊，基盤岩とその上部を覆う大隅降下軽石層の聞に集中した雨水および地下水に起因して発生した路体を支持する路盤の決壊，土石流による土砂氾濫に伴う林道の破壊および暗渠の閉塞が挙げられる。  (2) 調査地において，斜面崩壊の面積および斜面崩壊による生産土砂量の測定を行った。その結果，斜面崩壊の面積は16～400㎡の範囲（平均133㎡) ，斜面崩壊による生産土砂量は10～1,600㎥ の範聞（平均223㎥）であった。林道の谷側斜面の崩壊，深層崩壊，および路体を支持する路盤の決壊は，調査地においてみられた他の侵食・斜面崩壊の形態に比べ規模が大きかった

寺本, 行芳

下川, 悦郎

地頭薗, 隆

遠矢, 有希

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Damage caused by typhoon Nabi to slopes bordering forest roads in the Takakuma Experimental Forest，Kagoshima University，in September 2005

Damage caused by typhoon Nabi to slopes bordering forest roads in the Takakuma Experimental Forest，Kagoshima University，in September 2005

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