Rigidity Strengthening of Landslide Materials Measured by Seismic Interferometry

Keng-Hao Kang,Chih-Pin Lin,Wei-An Chao,Chun-Hung Lin,Yin-Jeh Ngui,Jui-Ming Chang,Ming-Chien Chung,Hsin-Chang Liu,Yu-Ting Kuo,Chien-Hsin Chen,Tung-Lin Tai,Chih-Hsiang Yeh,Che-Ming Yang,Jyh-Jong Liao

doi:10.3390/rs13142834

Abstract

Landslides have caused extensive infrastructure damage and caused human fatalities for centuries. Intense precipitation and large earthquakes are considered to be two major landslide triggers, particularly in the case of catastrophic landslides. The most widely accepted mechanistic explanation for landslides is the effective-stress dependent shear strength reduction due to increases in pore water pressure. The Chashan landslide site, selected for the present study, has been intensively studied from geological, geophysical, geodetic, geotechnical, hydrological, and seismological perspectives. Our seismic monitoring of daily relative velocity changes (dv/v) indicated that landslide material decreases coincided with the first half of the rainy period and increased during the latter half of the rainy period. The geodetic surveys before and after the rainy period identified vertical subsidence without horizontal movement. The results from the multidisciplinary investigation enabled us to draw a conceptual model of the landslide recovery process induced by water loading. Where all sliding materials were stable (safety factor > 1.0), unconsolidated landslide colluvium and impermeable sliding surfaces trapped the seepage water to form a water tank, provided that compact forces were acting on the materials below the sliding boundary. The vertical force of compaction facilitates an increase in the cohesion and strength of landslide materials, thereby increasing the landslide materials’ stability. We demonstrated that the recovery process periodically occurs only under the combined conditions of prolonged and intense precipitation and the related stability conditions.

Highlights

Landslides represent a major geohazard worldwide but the understanding of landslides remains limited
Most studies have demonstrated that the mechanism of weakening by fluid is an important trigger in landslides
The groundwater level (GWL) at different time steps was obtained by analyzing GeoStudio’s SEEP/W module, and these levels were compared with the actual observation data and adjusted repeatedly until the two exhibited the same trends

Summary

Introduction

Landslides represent a major geohazard worldwide but the understanding of landslides remains limited. With respect to fluid effects, water plays a crucial role in the mechanism of slope instability, decreasing soil cohesion and increasing pore water pressure on a sliding surface. To further our understanding of the mechanisms behind landslides, geophysical, geotechnical, and geodetic monitoring approaches, including electrical resistivity tomography (ERT) [8], active seismic exploration, borehole drilling [9,10], downhole monitoring of displacement and water level [11,12], and GPS-based surface movement [13,14], have been applied to clarify the geometry and geological structures involved and to ascertain the depth of the multiple sliding interfaces located beneath deep-seated landslides. A slow-moving, deep-seated landslide area (Landslide Inventory ID: DS160), was selected as the test site for investigating landslide behavior, especially fluid-related mechanisms. The Chashan landslide can be separated into the following three subdivisions and topographic features, which are delineated in Figure 1b: the tension crack zone, erosion gullies, and major/minor scarps

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Results

Conclusion