The mountainous highway, Route 7 and 9 in rainy northeastern area of Taiwan, is frequently influenced by landslides and rockfalls which have induced casualties, road closure, and infrasture damages. In this study, we propose an assessment procedure to evaluate the hazard susceptibility by integrating micro-topography interpretation and numerical simulation. The high resolution raster data acquired from both airborne and terrestrial LiDAR scanning is systematically enhanced for interpreting microrelief structures in advance. For the purpose of identifying the possible zone of geo-hazard, hill-shading, slope gradient, sky view factor, and openness map are overlaped to visualize the significant landslide feature and weathering lineation on rock mass. The identification of these morphological characteristic shows the location with high hazardous susceptibility, so one can identify the corresponding scarp, landslide mass, surface joint, and discontinuity pattern on the DTM. Considering the volume of the sediment hazard, 2-D slope stability analysis and joint measurement are applied to provide the approximate sliding depth for landslide and rockfall, respectively. Once all the initial conditions are given, the numerical simulation for specific scenario can be performed based on the geo-technical and field investigation.

The visualization mapping of DTM indicates a visible morphological feature of deep-seated landslide at the station of 88K+150 in Route 7, some gullies characterized by headward erosion triggers slope failure at the landslide toe. The RAMMS simulation result shows that the landslide may transform into gully-type debris flow and even form a typical alluvial fan covering the highway. The numerical result shows a detailed hazardous degree map and influence area can be obtained based on the spatial resolution of DTM. Consider the landslide susceptibility, the renewal of this deep-seated landslide seems to be inactive as a result of remote sensing interpretation in the recently years. In addition, the rockfall susceptibility analysis from high resolution terrain is also explored in Route 9. The stability of rock slope is dominated by surface of discontinuity and fissure distribution. In fact, the density and orientation of fissure are most influence factors to govern the evolution of weathering rock slope. This work selects a vulnerable road section where the rockfalls frequently occur in the study area. The kernel density estimation has further validated from lineament interpretation along the rock slope near the coastal highway, so that the corresponding weathering rock size on steep source zone could be exactly determined. RAMMS:ROCKFALL simulation demonstrates the hotspot of rockfall deposition is situated on the talus cone and railway station adjacent to the highway. The preliminary result shows that based on this propose procedure, it is possible to identify the location of catastrophic landslide and rockfall and to assess the hazard susceptibility around the mountain area.