纤维和细粒含量对秸秆纤维土抗冻融性能的影响

Effect of Fiber and Fine Particle Content on Freeze⁃thaw Resistance of Straw Fiber Soil

为了增强秸秆纤维土的抗冻融性能,分别将长9 mm的玉米秸秆和芦苇秸秆纤维掺入到淤泥质土中,经历不同冻融循环次数后进行无侧限抗压强度试验和直剪试验,同时开展细粒含量对纤维土强度影响的常规试验和冻融试验,通过电镜扫描深入分析其内部变化。试验结果表明:冻融对土体强度和黏聚力影响显著,对内摩擦角影响较小。随着冻融循环次数增加,土体受到冻胀效应的影响,土颗粒重新排列,土体结构受到破坏,产生裂缝,导致强度和黏聚力降低,经历5次冻融循环后,土体结构达到稳定,强度和黏聚力也趋于稳定。适量的纤维可以明显提高土体抗冻性,冻融后对比两种纤维土的力学性能,玉米秸秆纤维土强度更高,芦苇秸秆纤维土韧性更好。除此之外,细粒含量对土体冻胀敏感性有较大的影响,细粒含量越高,土体冻胀效应越明显,从而导致土体强度的大幅衰减;但在未冻融时,细粒含量的增加反而能提高土体的抗压强度。

In order to enhance the freeze-thaw resistance of straw fiber soils,corn straw and reed straw fiber with a length of 9 mm were mixed into muddy soil respectively.After different freeze-thaw cycles,unconfined compressive strength test and direct shear test were carried out.At the same time,the conventional test and freeze-thaw test on the influence of fine particle content on the strength of fiber soil were carried out,and the internal changes were deeply analyzed by electron microscope scanning.The test results show that freezing and thawing have significant influence on soil strength and cohesion,but little influence on internal friction angle.With the increase of freeze-thaw cycles,the soil is affected by frost heave effect,the soil particles are rearranged,the soil structure is destroyed,cracks are produced,and the strength and cohesion are reduced.After five freeze-thaw cycles,the soil structure is stable,and the strength and cohesion are also stable.Appropriate amount of fiber can obviously improve the frost resistance of soil.After freezing and thawing,comparing the mechanical properties of the two kinds of fiber soil,the strength of corn straw fiber soil is higher and the toughness of reed straw fiber soil is better.In addition to this,the fine particle content has a greater effect on the soil freezing and swelling sensitivity(frost heave properties),the higher the fine particle content is,the more pronounced the effect of freezing and swelling of the soil is,which leads to a substantial attenuation of the strength of the soil body.However,in the absence of freezing and thawing,the increase in fine particle content can instead improve the compressive strength of the soil.