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Reactivation of the old landslide caused by the land development—the case study
Abstract
Although landslides are a group of natural hazards, the factor causing their activation is often human activity. The construction of buildings and roads on slopes has an especially unfavourable impact on its stability. Additional load and disturbance of natural hydrological conditions are factors that may cause the reactivation of old landslides. This paper contains a case study of the activation of landslide processes, which was caused by human activity. In the area of the old and inactive landslide an educational complex was built. The complex consisted of four buildings located in one line across the slope. An additional, very unfavourable factor was the high level of groundwater, which was rising up to the ground surface temporarily. At the time of long-term rainfall activation of landslide processes in the substrate of the building occurred. These processes are characterized by slow changes, causing progressive destruction of buildings. The geological structure of the slope was determined by six core holes with a depth of about 20 m. On this basis, the geological layers, hydrological conditions and slide surface position were determined. Deformations of the slope and the building were monitored by using integrated survey techniques: precision leveling, electronic techeometry, traversing (angular-linear), static GNSS and laser scanning. The work includes the analysis of initial geological and hydrological conditions, the analy-sis of the causes and the course of deformation processes in the substructure, the results of the measurements and the analysis of the deformation of buildings caused by a landslide.
Terrain that has previously experienced a landslide is subject to the additional threat of reactivated landslides. The reactivated Wuwanchai landslide is located in Chiayi County in southern Taiwan at Expressway No. 18. The reactivated landslide has exhibited slow movement with continuing creek headwater erosion. The landslide comprises eight sliding blocks that are categorized as main slipping blocks, slow-moving blocks, and activated blocks in accordance with their deformation characteristics. The reactivated landslide’s deformation characteristics and failure mechanisms were monitored using field investigations, airborne LiDAR surveys, and unmanned aerial vehicle (UAV) photogrammetry; the results were compared with traditional inclinometer monitoring of the displacement and groundwater level measurements. The concave terrain tends to collect surface water, and the level of the groundwater table tends to fluctuate due to seasonal precipitation. Geologic structures and headward creek erosion increased the sliding of the deposited colluvium. An interaction mechanism for the sliding blocks is proposed on the basis of the deformation characteristics, activity of the sliding blocks, topography changes, sliding masses, and UAV images. Separation of the landslide area in accordance with the deformation characteristics of the composed sliding blocks best explained the reactivation mechanism of the large-scale landslide.
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