雅鲁藏布江色东普沟冰崩机理试验研究

Mechanism of ice avalanche in the Sedongpu sag,Yarlung Zangbo River basin-an experimental study

近年来青藏高原地区冰崩灾害事件频发,冰崩成因机理问题备受关注。本文根据色东普沟多期影像数据分析了冰崩灾害演化过程与影响因素,并通过开展不同温度下冰介质剪切试验研究揭示了色东普沟冰崩成因机理。研究结果表明:(1)地形坡度超过30°时易发生冰崩灾害,地震加剧了冰川变形破裂,气候变暖是导致色东普沟冰崩频发的主要原因;(2)重塑多晶冰与冰-岩嵌固体的剪切应力-剪切位移曲线均成“脆性变形型”,在较低的温度条件下重塑多晶冰的剪切应力-剪切变形曲线会出现“二次峰值”;(3)随温度上升,多晶冰样和冰-岩嵌固体的黏聚力与内摩擦角呈直线下降甚至呈加速下降趋势,在相同温度下冰-岩嵌固体的黏聚力小于多晶冰样的黏聚力,而冰-岩嵌固体内摩擦角普遍大于多晶冰样的内摩擦角;(4)温度上升会导致冰川冰或冰-岩嵌固体剪切滑动带的强度衰减,抗滑力下降,从而触发冰崩。

In recent years ice avalanche disasters occur frequently in the Tibetan Plateau and the mechanism of ice avalanche has attracted much attention.In this paper,the evolutionary process and controlling factors of ice avalanche in the Sedongpu sag were investigated via multi-stage imaging analysis.In the mechanistic study,shear strength tests were carried out at different temperatures on two types of ice materials:crystalline ice and ice-rock mixture.The crystalline ice sample was prepared by pressing crushed ices into a mold,and the ice-rock mixture was prepared by pressing crushed ices and slate.Imaging analysis results showed that glaciers with 30°or steeper terrain slopes were prone to ice avalanche while strong near-field earthquakes aggravated glacier deformation/fracture,and climate warming was the main reason for the frequent occurrence of ice avalanches in the Sedongpu sag.In the shear test,the shear stress-shear displacement curves for both materials revealed brittle deformation type,while for polycrystalline ice a“secondary peak”appeared under low temperature conditions,indicating refreezing phenomenon.With increasing temperature,the cohesive strength and internal friction angle of both materials decreased linearly,even at an accelerated pace;whilst at the same temperature,the cohesive strength was less and the internal friction angle was greater for ice-rock mixture than for polycrystalline ice.Thus the likely genetic mechanism of ice avalanche is that the rise of temperature leads to decrease of shear strength of the ice/rock shear sliding zone thus its anti-sliding force to trigger an ice avalanche.