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A catastrophic flowslide that overrides a liquefied substrate: the 1983 Saleshan landslide in China
Author(s) -
Zhang Fanyu,
Peng Jianbing,
Wu Xiugang,
Pan Fazhen,
Jiang Yao,
Kang Chao,
Wu Weijiang,
Ma Wenguo
Publication year - 2021
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.5144
Subject(s) - landslide , geology , liquefaction , geotechnical engineering , pore water pressure , alluvium , hydrogeology , water table , geomorphology , alluvial fan , loess , debris , debris flow , groundwater , hydrology (agriculture) , structural basin , oceanography
Flowslides that override a liquefied substrate can vastly enhance a disaster after failure initiation. These effects may result from the rapid velocity and long runout distance from slides mobilized into flows. It is thus crucial to provide an improved understanding of the transformation mechanisms of catastrophic flowslides for hazard evaluation. This study examines the Saleshan landslide in Gansu, China, which occurred in 1983 and killed more than 200 people. The Saleshan landslide travelled for approximately 1 km due to pore water pressure generation resulting from overrunning and liquefication of the alluvial sands in the river valley below. We used geomorphologic and topographic maps to determine its dynamic features and mobilization behaviors on the landslide body, and placemarks and seismic signals to identify its approximate velocity at different sites. Electrical resistivity tomography (ERT) surveys also revealed the hydrogeological conditions post‐landslide, showing a clear groundwater table along with the liquefied alluvial sand and gravel layers. Particle size distributions and triaxial shear behaviors confirmed more ready liquefaction of superficial loess and underlying alluvial sand in comparison with the red soil above and below them. Novel loading impact triaxial testing was also performed on the alluvial sand to elucidate its liquefaction potential in undrained and drained conditions. The alluvial sand was found to be markedly prone to liquefaction in undrained conditions due to impact‐induced increased pore water pressure. The results further demonstrated that the Saleshan landslide underwent a transformation from a slowing slide on a steep slope, where it originated, to flow on a nearly flat terrace with abundant groundwater that it overrode. The transformation mechanism involved the liquefied alluvium sand substrate, which greatly enhanced the landslide mobility. Along with recent, similar findings from landslides globally, substrate liquefaction may result in a widespread, significant increase in landslide mobility and thus hazard, and the present study identifies the requisite conditions for this phenomenon to occur.