Geotechnical controls on a steep lateral moraine undergoing paraglacial slope adjustment
Geotechnical controls on a steep lateral moraine undergoing paraglacial slope adjustment
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冰坡调整中陡峭侧碛石的岩土控制
DOI：
10.1144/sp320.12
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
P. R. Porter
中科院分区：
文献类型：
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作者：
A. Curry;T. B. Sands;P. R. Porter
摘要瑞士瓦莱州Feegletscher的北方叶在“小冰期”后持续退缩，暴露出侧碛，显示出明显的上近端斜坡过陡，上斜坡段显示出高达约70°的角度。副冰川作用将冲沟侵蚀到上斜坡段，相关的碎屑流沉积物导致中斜坡和坡脚区的倾角较低，分别在34°和25°之间。为了评估允许准稳定，过陡的斜坡段的发展冰碛沉积物的岩土工程性质，一套标准的岩土工程措施被施加到Feegletscher冰碛沉积物的样品。剪切盒测试产生的摩擦角范围从松散样品的35°到致密样品的52°。尽管冰碛沉积物的非均质性质使得对现场沉积物的整个粒度范围进行实验室测试是不切实际的，但剪切盒试验结果表明，现场上边坡角超过冰碛沉积物的摩擦角26°-40°。我们无法复制剪切盒试验中的摩擦角，这些摩擦角对应于现场测量的上斜坡段的原位角。然而，我们认为，远倾云母片岩碎屑可能发挥重要作用，允许高角度边坡的稳定性。准稳定存储的冰川沉积物在高角度冰碛序列在十年的时间尺度上的影响，了解冰消期后，在该paraglacial改造和重新分配的沉积物可能会操作。
Abstract Sustained post ‘Little Ice Age’ retreat of the northern lobe of the Feegletscher, Valais, Switzerland, has exposed lateral moraines that show pronounced oversteepening on the upper proximal slopes, with upper-slope segments displaying angles of up to about 70°. Paraglacial processes have eroded gullies into the upper-slope segments, and associated debris-flow deposits result in lower angles of between 34° and 25° in the mid-slope and slope-foot zones, respectively. In order to assess the geotechnical properties of morainic sediments that permit development of quasi-stable, oversteepened slope segments, a standard suite of geotechnical measures was applied to samples of Feegletscher moraine sediments. Shear box testing yielded angles of friction ranging from 35° for loose samples to 52° for dense samples. Although the heterogeneous nature of moraine deposits makes laboratory testing of the whole size range of in situ sediments impractical, shear box test results imply that in situ upper-slope angles exceed the angles of friction of moraine sediments by 26°–40°. We are unable to replicate angles of friction in shear box tests that correspond to in situ angles of the upper-slope sections measured in the field. However, we suggest that distal dipping mica-schist clasts may play an important role in permitting high-angle slope stability. Quasi-stable storage of glacigenic sediments in high-angle moraine sequences over decadal timescales has implications for understanding the period following deglaciation over which paraglacial reworking and redistribution of sediments may operate.