Elevated Pore‐Water Pressure Regulating Dynamic Liquefaction of a Flow‐Like Landslide in Loess
Ruijun Wang, Shun Wang, Dianqing Li, Xuan Kang, Peng Xin
Abstract
Abstract At 23:59 (UTC + 8) on 18 December 2023, an earthquake of Ms 6.2 struck Jishishan County in Gansu Province, China, and triggered a large‐scale, flow‐like loess landslide in Zhongchuan Town, resulting in some 20 deaths. Originated from relatively gentle terrain, the loess flow displayed high mobility with a run‐out distance of 3,200 m, suggesting that pore‐water may play a critical role in the mobility of Zhongchuan flowslide. Following onsite investigations and soil sampling, we replicated the initiation process of the flowslide through dynamic back pressure direct shear tests under a constant shear stress condition. Two types of tests were conducted on saturated loess samples: elevated back pressure tests to simulate instability induced by high pore‐water pressure, and dynamic loading tests to examine the evolution of pore‐water pressure under seismic loading conditions. The experimental results, supported by microscopic analysis, indicate that elevated pore‐water pressure is the key factor driving the progressive transformation of shear displacement from accelerated motion to instantaneous runaway. Meanwhile, dynamic loading substantially amplifies the generation of excess pore‐water pressure. Moreover, the initial pore‐water pressure was found to be a critical factor in both the initiation and high mobility of the Zhongchuan flowslide. These experiments quantitatively capture the in situ evolution of pore‐water pressure throughout the liquefaction process, providing a physically based framework for understanding the mechanisms of loess landslides.