In a large-scale landslide, two or more slip surfaces might often occur according to activity of second order landslides. For this case, it is difficult to observe the deeper slip surface for a long term by using a conventional wired sensor so that a shallower slip surface may break the cable or the observation borehole. For the solution of the above issue, we developed the wireless sensors that combined the radio equipment with the underground displacement sensor and the pore water pressure sensor and installed those sensors in the bore holes. In this paper, we show the observation data for five years or more, and clarify the site applicability and the effectiveness of these sensors.

  The Hai Van landslide area in central Vietnam is geologically composed of fractured and deeply weathered granitic rocks. Under the geological and weather condition, the Hai Van landslide has repeatedly activated during the monsoon rainy season. It is significant to clarify the relation between the hydrogeological structure of weathered and unweathered rocks and landslide activity, and subsequently to assess the risks of landslide disaster.

  Here we provide new information about the distinctive hydrogeological structure of the landslide in relation to landslide movement by investigating various data derived from the literature of precedence researches, a drilling survey, water quality analyses of samples from springs and boreholes, and also quantitative measurements of landslide movement. As a result, the hydrogeological structure clearly indicates that the landslide response is sensitive to water pressure exerted through groundwater channels in the fractured and deeply weathered granitic rocks in the Hai Van landslide area.

  This research was carried out as a part of the Japan－Vietnam joint research project “Development of Landslide Risk Assessment Technology along Transport Arteries in Vietnam.

  As a case of landslide with increased load of ground anchors, applicability of 2D elasto-plastic finite element method (FEM) was examined for load prediction of ground anchors after additional countermeasures. In the finite element analysis (FEA), we set the parameters of the ground based on inverse analysis, and then obtained the load of the ground anchors after the unloading work and adding the ground anchors. As a result, the load of the ground anchors after the additional countermeasures by the FEA showed values in the range of －17 to 5％ with respect to the measured value. This result suggests that the FEM model calibrated by inverse analysis using the load measurement value of the ground anchors may be used for rough estimation of load after additional countermeasures.

  Mixed reality (MR) is the technology for merging real and virtual worlds seamlessly, and the users recognize virtual objects through the MR device in real space. This advanced device is supposed to be useful for disaster prevention fields such as education and inspection of facilities. This paper introduces visualized contents we developed using the MR device.

  A slope failure at Taigang, Taiwan, triggered by rainfall on 1 October 2016, was followed by episodic rockfall events over several months. This study reports on the basic geological causes of the slope failure, to clarify its mechanisms of failure to inform landslide mitigation measures and risk management. Cumulative rainfall in the region reached 488.5 mm in about five days, and the slope failure occurred four days after the peak in rainfall intensity. The slope failure occurred in an old landslide scar at the lower part of a gravitationally deformed slope. The bed rock of this slope consists of argillite and alternating beds of sandstone and shale with a steeply dipping foliation. The beds are 300 m thick and show flexural toppling down-slope, which has led to the formation of many open fractures. The flexural toppling is expressed as a depression at the ridge top and a convex slope at lower levels, which indicate that the slope deformation must have already taken place long before. This deformation was the fundamental cause of the slope failure. The occurrence of new scarplets and tension cracks behind the landslide scar suggests the landslide is active and should be monitored.