青藏高原冰碛土在冻融循环下的强度劣化对冰碛堤稳定性的影响

Impact of Strength Deterioration of Moraine Soil in Qinghai-Xizang Plateau Under Freeze-Thaw Cycles on Stability of Moraine Dam

摘要

为探究冰碛土在冻融循环作用下物理力学特征参数劣化对冰湖冰碛堤稳定性的影响,本研究以青藏高原山南市努确沟为研究区,对高溃决风险冰湖及冰碛堤进行野外详查.首先在现场采集冰碛砂土和冰碛粉土两种土样,采用层次分析法选取8个因子,对努确沟流域18个冰湖进行危险性分析;然后在室内对不同冻融循环次数下的冰碛砂土和冰碛粉土开展静三轴试验及变水头渗透试验,分析冰碛堤稳定性的变化规律;最后采用Massflow数值仿真软件推演冰碛堤失稳-冰湖溃决-洪水-泥石流的动力学灾变演进全过程.结果表明:1)冻融循环前期(冻融0~5次),冰碛砂土和冰碛粉土的黏聚力劣化趋势明显,劣化率分别为12.21%和7.89%,内摩擦角随冻融循环次数增加呈小幅波动态势,渗透系数持续增大,冻融循环对土体结构和孔隙分布的影响具有持续效应;2)冰碛堤稳定性系数在冻融循环前期衰减率最大,为-0.0222,衰减规律与冰碛土强度特征参数的劣化规律一致,表明冰碛土的强度特性是影响冰碛堤稳定性的重要因素;3)BH06冰碛堤在完全失稳的最不利条件下,导致冰湖溃决,进而引发山洪并演化为泥石流,最大流速达5.1m/s,最终堆积厚度为4.5m,堆积面积为4220m²,堵塞了流域部分主沟道.综上,冻融循环前期冰碛土强度劣化显著,导致冰碛堤稳定性快速下降,并可能引发冰湖溃决及链式灾害.

Abstract

To investigate how the degradation of physical and mechanical parameters of moraine soils under freeze-thaw cycles affects the stability of glacial lake moraine dams, this study focused on Nuquegou in Shannan City on Qinghai-Xizang Plateau. Field investigations were first conducted on high-outburst-risk glacial lakes and moraine dams, during which moraine sandy soil and moraine silty soil samples were collected on-site. Subsequently, eight evaluation factors were selected using the analytic hierarchy process (AHP) to assess the hazard risk of 18 glacial lakes in the Nuquegou watershed. Laboratory standard triaxial tests and falling-head permeability tests were then performed on both soil types subjected to varying numbers of freeze-thaw cycles to analyze the evolution patterns of moraine dam stability. Finally, the Massflow numerical simulation software was employed to reconstruct the complete dynamic disaster chain process, spanning moraine dam failure, glacial lake outburst, flooding, and subsequent debris flow. The results indicate the following: 1) In the early stages of freeze-thaw cycles (0-5 cycles), the cohesion of both moraine sandy and silty soils exhibited a pronounced degradation trend, with degradation rates of 12.21% and 7.89%, respectively. Meanwhile, the internal friction angle fluctuated slightly as the number of cycles increased, whereas the permeability coefficient increased continuously, indicating that freeze-thaw cycles exert a sustained effect on soil microstructure and pore distribution. 2) The stability coefficient of the moraine dam experienced its maximum attenuation rate (-0.0222) during the early stages of freeze-thaw cycles. This attenuation pattern aligned with the degradation of the strength parameters of the moraine soils, confirming that soil strength characteristics are a critical factor governing moraine dam stability. 3) Under the worst-case scenario of complete failure of the BH06 moraine dam, the simulated glacial lake outburst triggered a flash flood that subsequently transformed into a debris flow. The maximum flow velocity reached 5.1 m/s, resulting in a final debris flow deposition thickness of 4.5 m and an accumulation area of 4220 m², which partially blocked the main channel of the watershed. In summary, the significant strength degradation of moraine soils during the early stages of freeze-thaw cycles drives a rapid decline in moraine dam stability, potentially triggering glacial lake outbursts and cascading disaster chains.

关键词

冻融循环 / 冰碛土 / 冰碛堤 / 失稳 / 冰湖溃决 / 灾变演进 / 青藏高原

Key words

freeze-thaw cycle / moraine soil / moraine dam / instability / glacier lake outburst / catastrophic evolution / Qinghai-Xizang Plateau

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基金资助

四川省科技计划项目(2025YFNH0008)

珠峰大科学计划项目2.0(20250101)