川西地区季节冻土渗透系数的时空变化特性

Temporal and Spatial Variation of Permeability Coefficient of Seasonal Frozen Soil in Western Sichuan

冻融循环作用引起的边坡体内部水分迁移是川西地区季节冻土边坡失稳的主要原因,研究边坡土体渗透系数时间、空间变化特征是掌握水分迁移规律的重要手段.针对冻融循环作用下季节性冻土坡面渗透系数时空变化问题,选取川西新都桥地区某边坡粗颗粒土为测试土样,设计冻土渗透系数试验装置,以30%乙二醇溶液为试验渗透溶液,分别制备不同初始含水率、细颗粒含量、干密度测试土柱;添加30%乙二醇放至低恒温箱中进行12 h以上冷冻处理,开展不同冻融循环次数作用下冻土渗透系数试验,并分析其渗透系数变化规律;在此基础上结合边坡冻融期含水率现场监测数据,分析渗透系数时空变化规律.试验结果表明:初始含水量及干密度不断增加时,冻土非闭合孔隙度和渗透系数均呈减小趋势;冻土渗透系数随细颗粒含量的增加而减小,当细颗粒含量大于20%时,冻土渗透系数减小的幅度较小;冻融循环次数对冻土渗透性能起到抑制作用,当循环次数超过3次时,冻融作用对渗透性能影响不大;季节性冻土边坡1 m冻结深度以内,渗透系数随深度增加减小;11月—1月冻深范围内冻土渗透系数减小,1月—3月渗透系数开始增大.

The moisture migration caused by freeze-thaw cycle is the main reason for the instability of seasonal frozen soil slope in western Sichuan Province.It is an important means to master the rule of water migration by studying the spatiotemporal variation characteristics of permeability coefficient of slope soil.In view of the spatiotemporal variation of permeability coefficient of seasonal frozen soil slope under the action of freeze-thaw cycle,permafrost permeability coefficient tests were conducted on a self-developed device using the coarsegrained soil sample from a slope in Xinduqiao area of western Sichuan Province.The test soil columns with different initial moisture contents,fine particle contents and dry densities were prepared with the osmotic solution of 30%ethylene glycol,and then placed into the low constant temperature box for more than 12 h freezing treatment.The permafrost permeability coefficient tests under different freeze-thaw cycles were then carried out and variations of the permafrost permeability coefficient was analyzed.On this basis,combined with the on-site monitoring data of water content of slope in freeze-thaw period,the spatiotemporal variations of permeability coefficient were analyzed.Experimental results show as follows:with the increase of initial water content and dry density,the open porosity and permeability coefficient of frozen soil decrease.The permeability coefficient of frozen soil decreases with an increase in the fine particle content.When the content of fine particle content is more than 20%,the permeability coefficient of frozen soil decreases slightly.The number of freeze-thaw cycles has an inhibitory effect on the permafrost permeability;however,when the number of cycles is more than 3,the effect of freeze-thaw on the permeability of frozen soil is not significant.Within 1 m frozen depth of seasonal frozen soil slope,the permeability coefficient decreases with the increase of depth;in addition,the permafrost permeability coefficient decreases from November to January,and increases from January to March.