172線48K崩塌機制及治理對策之研究

Abstract

172線48K崩塌坡地位於嘉義縣中埔鄉三層村及東興村，2009年莫拉克風災及2010年凡那比颱風時，因豪雨而造成邊坡坍滑，為恐再次降雨發生而二度崩塌，造成嚴重土砂災害或土石流，危及區內住戶生命財產安全及上游172縣道、研究區內農業用地約30公頃、15棟屋舍、6座橋梁及道路等公共設施損壞，故本研究展開調查穩定分析及整治對策。 本研究調查崩塌地基本資料、地質鑽探、崩塌地現況等工作做出穩定性分析來發展出治理對策，另外增加邊坡傾度管及地下水監測工作，傾度管監測為傾度管裝設完成後及暴雨後各量測1次，地下水監測為自動化量測，期程為2011年6月至2011年12月止。 經調查結果，本研究區出露之地層由上游至下游由老而新依序為鳥嘴層、沄水溪層、六重溪層及崁下寮層岩性分佈，其地層走向約為北偏東30度至50度，向西北傾斜約25度至70度以上；依據地質鑽探結果，可發現各孔皆有厚度達30至40公尺之軟弱泥質角礫岩分佈，推測為古老崩塌殘存之古崩積地層。 根據本研究現場地質調查成果，研究區邊坡主要破壞型態為覆蓋於坡面上之崩積層產生滑動破壞。研究區冠部之172線邊坡滑動型式屬崩積土層與岩層界面間之複合型滑動，故本研究依據探測結果所得之地層剖面、地下水位資料、土層力學參數等資訊，進行邊坡穩定性分析，並藉由分析成果得到最可能發生之邊坡破壞面與安全係數值，提供爾後工程設計參考。

The collapse and landslide area of county NO. 172, 48k is located at San Tseng Village and Dong Xing Village in Zhongpu Township of Chiayi County. During the rainfall of Typhoon Morakot in 2009 and Typhoon Fanapi in 2010, the rain caused the collapse of the slide slope. To prevent further collapse that may lead to serious soil and sand hazard or debris flood that may jeopardize the lives and properties of residents living in that area, as well damage to the infrastructure such as the upstream #172 county road, the 30 hectares of agricultural land in the planned area, 15 houses, 6 bridges and relevant roads, This study is developed to execute investigation and dredging. The activities to be executed for this study include the basic information of the collapsed land, geological exploratory drilling, current situation of the collapsed land and the engineering planning of the dredging work, etc. Further, the side slope inclinometer and the groundwater monitoring work was also implemented. The inclinometer was measured for once after the installation and the storm respectively; whereas, the groundwater monitoring was conducted automatically from June 2011 to December 2011. The investigation result indicated that the strata exposed in the Planned Area were presenting the following lithological distribution, sequentially from upstream to downstream and from old and to new, of Wutsui Formation, Yungshuishi Formation, Liuchungshi Formation and Kanxialiau Formation, which run north by east for 30 to 50 degrees and inclining to the northwest for 25 to 70 degrees and above. According to the result of geological exploratory drilling, we can see that each hole contains 30 to 40 meters of soft muddy breccia rock, which is considered as the ancient colluvial stratum remaining from the older collapse action. It is considered that the collapse and destructive stratum exposed at the side slope is the progressive erosion effect of the creek from the old colluvial layer. Therefore, a short-term dredging program is developed for the above-said collapsed land for which, the improvement will be taken to eliminate the water outside the surface and to protect the slope face in the progressive erosion area. Further, retaining wall piles will also be planted along Jia-#172-route to penetrate the potential sliding surface and enhance the sliding resistant capacity. As for medium and long term program, two sand-checking weirs will be erected at the middle stream in the branch of the Touchien River for achieving siltation and protect the side slope toe from being washed away. Aiming to the natural eroded trench inside the side slope, a series of consolidation facilities should also be constructed to inhibit the slope face eroding effect.