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.