冻融循环作用下宽级配砾质土的渗透特性

摘要

针对西北地区特殊的气候条件和砾质土料源丰富的实际情况，提出采用宽级配砾质土代替黏土作为土工合成材料膨润土垫（GCls）的保护层共同构成垃圾填埋场复合防渗系统的构想。文中选取宁夏银川地区冲－洪积作用形成的天然砾质土料，经人工掺和制配成满足规范对 GCls 防渗垫保护层渗透系数要求的宽级配砾质土样，在实验室对该土样进行了冻融循环作用下的渗透性能试验研究。结果显示，随着冻融次数的逐渐增加，土样的冻胀率逐渐变大，渗透系数也相应增大，经过12次冻融循环后，渗透系数约增大1～2个数量级；冻融循环初期，冻融作用对土样的影响最为剧烈，随着冻融循环次数的增加以及时间的延续，土样性状逐渐趋于稳定。由于宽级配砾质土对冻融循环作用的敏感性小于粉质黏性土，故采用宽级配砾质土作为 Cls／GM的保护层共同组成填埋场复合防渗系统是值得期待的。%The design conception of composite liners is consisted of a geomembrane(GM),geosynthetic clay liners (GCls) and compacted gravel soils in landfills.This conception is presented on the basis of the climate characteristics,gravel soils material rich in nature,and GCls that have been exported all over the world for various applications.The artificially graded gravel soils are taken from natural sediment zone for flood alluvial at Yinchuan suburb in Ningxia.The gravel soil is figured out to meet the requirement of permeability coefficient through the compaction and penetration experiment.The frost-heaving ratio and hydraulic conductivity of gravel soil samples are tested under freeze-thaw cycling in this paper.The test results indicate that the frost-heaving ratio increases as the number of freeze-thaw increases.As the number of freeze-thaw increases,the permeability coefficient also increases. The permeability coefficient is increased by one to two orders of magnitude after 12 cycles of freezing-thawing.At the beginning of freeze-thaw cycle,it has an influence on the soil samples.The influence tends to be relatively stable state as the number of freeze-thaw cycles increases.The sensitivity of gravel soils under freeze-thaw cycling is less than that of the silt clay.It is acceptable to undertake the landfill composite liners which will be comprised of GCls/GMand compacted gravel soils together.