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The vulnerability of the Nan-Shi-Keng landslide area in Taiwan is investigated via single-station horizontal-to-vertical spectral ratio analysis. The measurement stations in the area are arranged as follows: (1) a transverse arrangement through the landslide site along Highway No. 175 (Case 1) and (2) two longitudinal arrangements down the slope (Case 2). In Case 1, the distribution of the vulnerability index along the highway indicates that the risk of surface deformation is high on sections of the highway located outside the potential sliding zone. The low vulnerability index of highway sections within areas where the protection measures have been taken indicates that they successfully stabilize the highway and the upper slope area. In Case 2, the deformation-prone directions (i.e., the directions with the maximum vulnerability index) evaluated at various stations using anisotropic microtremor measurements of the landslide site correlate strongly with the local sliding directions obtained using conventional inclinometer measurements and telemetry monitoring. The value of the vulnerability index is related to the highway damage and soil movement behavior. Therefore, the vulnerability index serves as a useful warning parameter to locate sites with a high probability of slope failure. • Microtremor detection was applied to locate a landslide and the cracks along a highway. • Kg-based direction of the microtremor strongly corresponds to the local sliding direction. • Vulnerability index and HVSR peak amplitude are good index to show the local hazard of the landslide. • An on-site investigation in August 2022 found numerous cracks on the highway. [ABSTRACT FROM AUTHOR]

Slope failure is a widely observed phenomenon in the mountainous areas in Taiwan due to rainy climatic and fragile geological conditions. Landslides easily occur after intense rainfall, especially from typhoons, and, accordingly, cause a great loss of human life and property. At the northern end of the Western Foothill belt in northern Taiwan, Huafan University is founded on a dip-slope about 20° toward the southwest composed of early Miocene alternations of sandstone and shale. Data from continuous monitoring using inclinometers and groundwater gauges reveal that 6-10 mm/month of slope creeping occurs, and a potential sliding surface is then detected about 10-40 m beneath the slope surface. To understand the potential runout process of the dip-slope failure at the campus, particle flow code 3D models based on a discrete element method are applied in this study. Results of the simulation reveal a critical value of the friction coefficient to be 0.13 and that more than 90% of the campus buildings will slide down in 100 s when the friction coefficient is reduced to half the critical value. The weakening of the shear zone due to the rise of groundwater during rainstorms is assumed to be the main factor. Some suggestions for preventing landslide disasters are to construct catchpits to drain runoff and lower the groundwater table and to install a sufficient number of ground anchors and retaining walls to stabilize the slope. [ABSTRACT FROM AUTHOR]

• Deep-seated gravitational slope deformation (DSGSD) in Lushan was investigated. • Transformation from cleavage- to weakened rockmass-controlled DSGSD observed. • Drilling cores, acoustic borehole televiewing, P-wave logging, inclinometers, GPS utilized. • Five geometrical styles and geotechnical zones of deformed rockmasses identified. • Empirical model for Taiwan slate proposed: V = 0.6 × log Q c + 4.0. The northern slope in Lushan (NSL) in central Taiwan is recognized as a large deep-seated gravitational slope deformation (DSGSD) in anisotropic slate and is often activated by typhoons and heavy rainfall. However, a recent southward movement of the DSGSD was apparently not caused by translational sliding along the eastward-dipping cleavage in the NSL. Because the regional attitudes of the cleavages in the NSL moderately vary and no major fault has been observed in the field, the deformed cleavages with their random dips indicate that the deformation of the rockmass was caused by older mass movements. In addition, ancient progressive erosion of the NSL toe by the Talowan River, which passes through the eastern side of the slope, induced deep, large-scale mass movement toward the east. Based on detailed core recognition measurements including the cleavage dips, log Q values, and inclinometer measurements, we identified five geometrical styles and geotechnical zones of the deformed rockmasses for characterization of the evolution of the NSL DSGSD with regard to the spatial distributions of old mass movements and recent transformations. Curves obtained from recent inclinometer measurements suggested two deformation behaviors, namely, specific sliding and progressive deformation. The underlying rockmass with overturned and flexural folding in cleavages at the slope toe have baffled a recent southward advancement of the DSGSD. Consequently, the deep specific sliding surface close to the basal disintegrated rockmass at the center of the NSL was transformed into progressive deformation, which mostly occurred in the overturned rockmass at the toe. Based on our observations, we propose the following relationship between the P-wave velocity (V p , km/s) and log Q c (where Q c is a normalized Q) as an empirical model for slate in Taiwan: V p = 0.6 × log Q c + 4.0. This empirical model might be suitable for the low-uniaxial compressive strength slate in the Lushan area and could be used for the quantitative evaluation of the geotechnical zone of the DSGSD of the NSL. [ABSTRACT FROM AUTHOR]

• A comprehensive framework consists of TDR installation, data acquisition, post-processing, and warning index. • The old colluvium slope at Lushan was characterized by TDR as a buckling fold. • Creep found by TDR contributed to the large surface displacement at Lushan. • Rebounded deformation was captured by TDR's high temporal and spatial resolution at Jufen. • Simplified index for early warning was substantiated by field implementation. Due to the climate change and hazardous geological environment in Taiwan, real-time landslide monitoring for safety of adjacent tribes or infrastructures is much conspicuous. Time domain reflectometry (TDR) is considered as valuable technology for continuously capturing dynamics and locations of shear deformations with high temporal and spatial coverages. In this study, a comprehensive framework was proposed by integrating up-to-date procedure of installation guide, data acquisition, sliding deformation identification, and early warning processing. The advantages of the proposed framework were then examined and substantiated via field cases. The first case is at a large colluvium slope in Lushan, central Taiwan. The colluvium is still active after heavy rainfall events, but limited evidence of sliding characteristic was collected previously by manual inclinometer logging. Therefore, the TDR framework was deployed and multiple landslide surfaces at great depths were timely observed. Movement of colluvium mass was thereby interpreted as a buckling fold. Additionally, creep occurred among the colluvium layer during the monsoon season because of strength weakening influenced by pore pressure fluctuations. Monitoring results of the second landslide case in Jufan, northern Taiwan, reported the dynamics of a thin sliding plane captured with TDR high temporal resolution. This unique behavior was further applied for devising of a novel early-warning strategy in terms of time-variation of TDR response, validating that the comprehensive framework of TDR landslide can effectively contribute to early warning. [ABSTRACT FROM AUTHOR]