原状黄土冻融过程抗剪强度劣化机理试验分析

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1、原状黄土冻融过程抗剪强度劣化机理试验分析　　摘要：通过对西安Q3原状黄土在封闭系统冻融作用下的电镜扫描和直剪试验，研究了冻融作用对原状黄土微观结构和强度的影响。试验表明：冻融过程中原状黄土微观结构发生显著变化，大颗粒集粒数量明显减少，小粒径土颗粒所占比重增加，孔隙面积比增加。进一步基于损伤力学理论，得到微观结构冻融损伤度随冻融次数增加呈指数增加趋势，反映出冻融作用一定程度上破坏黄土体的结构强度，但多次冻融后黄土体结构强度趋于稳定的残余强度。冻融过程土样表面结构发生破坏，且含水率越高，土体表面特征破坏越严重。粘聚力随冻融次数增加呈指数衰减趋势，且含水率越高，粘聚力衰减幅值和速率越小；粘

2、聚力随含水率增加表现出线性衰减特征，且冻融后粘聚力与含水率的变化规律近似重合；内摩擦角无明显规律性变化。粘聚强度冻融损伤系数随冻融次数增加呈指数增加趋势，随含水率升高有增大趋势。基于试验数据规律性，进一步提出了原状黄土粘聚强度劣化模型，该模型经试验验证可较好描述原状黄土粘聚强度劣化规律。　　关键词：原状黄土；冻融作用；电镜扫描；微观结构；抗剪强度　　中图分类号：TU444　　文献标志码：A文章编号：1674-4764（2016）05-0090-09　　Abstract：SEManddirectsheartestswereconductedtostudytheinfluenceoffr

3、eeze-thawactiononthemicrostructureandstrengthofxi’anQ3undisturbedloessundertheclosedsystem.The16experimentalresultsshowedthatthemicrostructureofloesschangessignificantlyduringthefreeze-thawprocess，withthenumberoflargeparticlesaggregatedecreasing，theproportionofsmallparticlesizeincreasing，andthe

4、ratioofporeincreasing.Basedonthedamagemechanicstheory，thefreezing-thawingdamagedegreeversusfreezing-thawingtimeswasestablished.Analysisindicatedthatthefreezing-thawingdamagedegreeexponentiallyincreasedwiththeincreaseoffreezing-thawingtimes，representingthatthestructuralstrengthofloesscanbedestro

5、yedbyfreezing-thawing.However，thestructuralstrengtheventuallyreachedaresidualstrengthvalueafterrepeatedfreezingandthawing.Freezing-thawingmadethesurfacestructureofsoildestroyed，andhadabiggerinfluencewiththeincreaceofwatercontent.Thecohesionexponentiallydecreasedwithfreezingandthawingtimesincrea

6、sing，andhadasmallerattenuationamplitudeandratewiththeincreaseofwatercontent.Withtheincreaseofwatercontent，thecohesionlinearlydecreased，andhadanapproximatelysamevariationafterfreezingandthawing.Theinternalfrictionanglehadnoobviousvariationduringthewholefreezing-thawingprocess.Thefreezing-thawing

7、damagecoefficientofcohesionexponentiallyincreasedwiththeincreaseoffreezing-thawingtimes，andalsoincreasedwithwater16contentincreasing.Acohesionstrengthdeteriorationmodelwasdevelopedbasedonthelaboratorytestresults，andthemodelcanbeus