The Study on Initial Machanism of Earth Disasters at Hillslope of Conglomerate Formation

在礫石層地層發育之溪谷，長期侵蝕作用在上游邊坡形成崩塌後退現象，而崩落的礫石停積於邊坡趾部與堆積於溪谷源頭中，為豪雨來臨時產生土石流之材料來源。加上溪谷兩岸之側蝕，亦形成陡峭之邊坡，並將土石崩落至溪谷中，隨逕流以土石流或其他流態搬運至下游堆積；而下游堆積區除了具巨礫集中於前端部、自然堤等土石流流動經過之特徵以外，更可因其堆積規模之龐大，而形成有助於土石流發生之地形環境，使得礫石層之邊坡發育不斷重複發生崩塌、土石流、細粒.蝕等土砂災害。本研究擬以礫石層土砂災害發生區為主要研究對象，以瞭解地形、地質及土石材料特性對災害發生、流動與堆積型態之影響，並藉由理論分析、配合室內模擬試驗與野外調查，以掌握不同坡度、土砂組成、水分條件所可能形成之流態、與影響範圍，以提供災害調查、防災規劃與設計之參考。研究項目如下所述：1.蒐集國內外有關礫石層地質、材料特性，崩塌、流動與堆積發生機制之相關文獻。2.根據相關理論，推導礫石層邊坡破壞之理論公式。3.進行火炎山溝谷內土砂災害範圍調查，探討坡面破壞之型式與機制。5.模擬礫石層土體之粒徑組成，於室內進行土砂災害之發生試驗，分析在不同坡度、孔隙度、水分條件下，可能發生坡面破壞的形式。6.探討礫石層邊坡發生土砂災害之機制。In the conglomerate formation valley, the long term corrosion forms the slopefailure with going backward phenomenon to slope surface in the upstream, causesthe falling cobble and gravel stay in the toe region of hill slope and the originregion of valley, which becomes to the source of debris flow material when thetorrential rain happened. In addition, lateral corrosion of the ravine generatessteeply slopeland, intends the colluviums bring to valley, debris flow and other fluidstate along with runoff transporting to the downstream deposition. The depositionareas at the downstream of the conglomerate formation except to have the boulderconcentrating to the front, levees with huge amount of depositions are helpful forthe environment to generate debris flow in downstream area, make the valley ofconglomerate formation to grow unceasingly process of landslide, debris flow andfine grain particle erosion.This research take the conglomerate formation as the main research object,analysis the topographic, geological and the debris materials behavior to influentthe earth disasters flowing and deposing state, according to the theoretical analysis,the laboratory flume test and the field investigation, analysis under different slope,debris composition, water content condition possibly forms the fluid state and theinfluence area, provides helpfully the disaster control work of investigation, planand design.The research project as follows states:1. Collecting the domestic and foreign related literature about conglomerateformation geology, the materials behavior, landslide and debris flowmechanism of occurrence.2. Derive the theory formula of the slope failure at conglomerate formation.3. The investigation for earth disasters area at Ho-yan hill.4. The simulation of particle size of composition for conglomerate formationby laboratory flume test carries on occurrence process of earth disasters,analysis, possibly type of slope failure under different slope, the porosity,water content condition.5. The analysis on occurrence mechanism of earth disasters