This paper presents the findings of an investigation on the prevention and mitigation of debris flow hazards by using steel open-type dams. First, the actual cases of trapping hazardous debris flow by steel open-type dams were surveyed. Through a field survey of actual cases, we classified them into four distinct scenarios based on the trapping type of debris flow: Scenario A (wooden debris + rocks + sediment), Scenario B (wooden debris + sediment), Scenario C (rocks + sediment) and Scenario D (wooden debris only). Second, recent trapping cases on protection and mitigation by various steel open dams were introduced. Third, trapping scenarios A, B, C and D were confirmed by performing physical model tests. Finally, a safety check of a steel open dam against a large rock was verified by two impact analyses, the finite element method (FEM) impact analysis using ANSYS Autodyn software, and the three dimensional (3-D) impact frame analysis.

This paper presents a failure analysis for a steel open-type Sabo dam (hereafter, steel open dam) against an extreme boulder debris flow load (hereafter, level II load) by a two-step analysis. The first step analysis is to estimate the level II load against the rigid wall by using the revised distinct element method (DEM). In the second step, the failure mechanism of a steel open dam is examined by using a dynamic elastic plastic analysis, in which the level II load-time relations obtained by the first analysis are multiplied by a reduction factor and then used. For the second step, the effects of the flange joint and dent deformation of the connection between column and beam are considered. Finally, a simple entire uniform load onto the steel open dam is proposed as a level II load model for the safety assessment.

Recently, steel pipe open type protective structures (steel open dams) have been damaged because of large-scale debris flow resulting from torrential rainfall based on abnormal climate. This article proposes a safety assessment method for the load-carrying capacity of a steel open dam against large-scale debris flow load (level II load) using the energy constant law. First, the safety assessment method of steel open dams is proposed that the ultimate strength must be larger than the required strength against the level II load, which is determined by using the energy constant law. Second, the load-carrying capacities of three types of steel open dams with different structural shapes against the front and eccentric debris flow loadings are investigated by a push-over analysis. Finally, the safety assessments on load-carrying capacities against the front and eccentric debris flow loading are confirmed and the strength reduction by the eccentric loading is examined for three steel open dams.

the Typhoon Morakot hit Taiwan and caused an extraordinary amount of rainfall. Due to the heavy rainfall, a large number of floods and sediment-related disasters occurred all over the island. In Shaolin Village, Kaohsiung County, a huge landslide occurred around 6 am August 9, destroyed the village completely and killed more than 500 people. After the landslide, authors visited the landslide site and investigated the landslide scour to collect information on factors affecting landslide occurrence such as exposed bedrock and soil layer conditions. GIS analysis using DEM data were also conducted to determine the sliding domain. According to the site investigation and GIS analysis, rainwater infiltration analysis and slope stability analysis were conducted. Results of the analysis suggested that the landslide domain, about 1,200 m long, 500 m wide and 80 m deep was collapsed by multi phased manner.Morakot 1 km I_721

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