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山間部峡谷に堆積した土砂地盤の流出特性を知るため、原位置浸潤試験により地盤の透水性を調べた。調査サイトは、斜面崩壊土が流下し、峡谷の河川敷に堆積した地盤で、大きな礫の問に小礫まじりの砂が分布する。試験にはゲルフ式プレッシャーインフィルトロメータ(GPI)法を用いた。簡便で迅速な原位置試験法であることから、比較的多くの測定データが得られ、調査地盤の透水性を適切に評価することができた。礫を含む地盤の透水係数の評価法を提示し、堆棟地盤からの流出特性に及ぼす礫の影響を検討した。, Permeability of sand sediment soil was measured by using itl-situ infiltration test to predict amount of runoff from the soil subject to heavy rainfall. The debris flow had sedimented onto river bed to form the soil between narrow valley. The soil was sand mixed with small to large gravel. A Guelph pressure infiltrometer (GPI) was employed to measure field-saturated hydraulic conductivity of the soil. The GPI method was effectively applied to measure the hydraulic conductivity of the soil quickly and easily. A physical model to determine of hydraulic conductivity of soil taken account of gravel content was proposed. Effect of gravel conteilt Oll the runoff amount from the soil was examined by using saturated-unsaturated seepage analysis.