基于微观结构的青藏高原风积沙导热系数变化机理研究

doi:10.7522/j.issn.1000-0240.2014.0146

摘要/Abstract

摘要：

风积沙作为青藏高原一种重要的局地因素, 改变了多年冻土的赋存条件. 风积沙的导热系数特征对预报分析其对冻土赋存有利或者不利具有重要作用. 采用非稳态法对青藏高原红梁河风积沙进行了导热系数测试, 并结合电镜扫描/能谱分析, 从微观结构的角度探讨了风积沙的导热系数变化机理. 结果表明: 研究区风积沙平均粒度为242.427 μm; 标准偏差值为0.125, 分选极好; 偏度为0.359, 接近对称; 峰度值为1.086, 峰态中等; 颗粒粒径主要分布在75～500 μm之间, 沙粒均匀, 不含黏土及砾石成分, 自然堆积状态下其孔隙率为0.391. 天然状态下的风积沙颗粒呈类球形, 颗粒磨圆度高, 点与点接触, 颗粒间孔隙较大; 表面有明显撞击坑和擦痕, 这导致颗粒的比表面积增大, 连通性增强, 孔隙率增加. 干燥状态下风积沙颗粒的相互接触面积较小, 孔隙由空气填充, 导热系数较低; 而在湿润状态下, 正温时孔隙中的水间接增大了风积沙的接触面积, 导致其导热系数增大; 负温时, 孔隙内的水变成冰, 从而导致导热系数进一步增大. 天然状态下, 暖季地表风积沙含水量较低, 导热系数较低, 而冷季地表风积沙含水量较大, 导热系数较大. 此外, 风积沙为颗粒物质, 表面光滑, 颗粒之间粘性小, 孔隙未被填堵, 结构松散, 这些因素导致自然堆积状态下其渗透系数较一般细砂大, 透水性良好, 保水性差, 是防冻胀较好的换填材料.

关键词: 风积沙, 多年冻土, 导热系数, 微观结构

Abstract:

Aeolian sand is one of the most important factors that are able to change the permafrost environment in the Tibetan Plateau. Thermal conductivity is the key parameter for predicting the effects of sand sediments on ground temperature of permafrost. The variation mechanisms of thermal conductivity of aeolian sand were studied with scanning electron microscope/energy dispersive X-ray. The granulometric analysis of grain shows that the grain size is in between 75-500 μm, well-distributed, without clay and gravel. The aeolian sand always forms sand dune without any regular shape in natural state, with large porosity, high grain roundness and good sorting. The grain surface has obvious impact craters, which noticeably increase the specific surface area and porosity. There is less mutual contact area between the dry aeolian sand grains and more pores filled by air, resulting in decrease of thermal conductivity. While the thermal conductivity will increase gradually when the pores are filled with water; the corresponding conductivity will go up continuously when temperature decreases below 0 ℃ and the water in the pores will be frozen gradually. The natural water content and thermal conductivity of aeolian sand are low in warm season, but they are high in cold season. Additionally, the aeolian sand is the granular matter with even and smooth surface and few cohesive soil, and has a loose clastic structure with lager porosity, all of which result in high permeability, good drainage, and poor ability of water retention, indicating that aeolian sand is a good filling material for mitigating frost-heave of infrastructure.

Key words: aeolian sand, permafrost, thermal conductivity, microstructure

中图分类号:

P642.14

陈琳, 喻文兵, 杨成松, 易鑫, 刘伟博. 基于微观结构的青藏高原风积沙导热系数变化机理研究[J]. 冰川冻土, 2014, 36(5): 1220-1226.

CHEN Lin, YU Wenbing, YANG Chengsong, YI Xin, LIU Weibo. Conductivity of aeolian sand on the Tibetan Plateau based on microstructure[J]. JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY, 2014, 36(5): 1220-1226.

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