木质素纤维改性季冻区膨胀土强度特性与微观结构研究

Study on strength characteristics and microstructure of expansive soil treated with lignin fibers in seasonal frozen area

为了充分利用资源,采用木质素纤维对季冻区膨胀土加以改性,提高其抗剪强度的可行性与效果。通过固结不排水三轴剪切试验对掺入不同木质素纤维质量分数的膨胀土及其经历冻融循环后的强度特性进行研究,并通过电镜扫描试验观察其微观结构,从微观层面揭示木质素纤维改善经历冻融循环前后膨胀土强度特性的机理。研究结果表明:将木质素纤维掺入膨胀土后,膨胀土自身抗拉能力能够限制其周围接触土体的变形,从而有效提高了膨胀土的“准黏聚力”,且随着纤维掺量增多,膨胀土的“准黏聚力”增幅越明显;膨胀土本身存在着一些天然微裂缝、贯通裂缝和孔隙,经历冻融循环后,土体内微小裂隙会发展成为大裂隙,同时,土颗粒间的错动与重排会产生更多的孔隙,从而导致其抗剪强度降低;木质素纤维掺入后被周围土体包裹,纤维与土体形成的空间网络结构能够发挥“桥联增韧”作用,延缓微小裂隙的形成与发展,阻止土颗粒间的错动与重排,从而提高膨胀土抗冻融循环作用的能力,且随着木质素纤维质量分数增大,膨胀土抗冻融能力增强。

To explore the strength characteristics and micro mechanism of expansive soil treated by different mass fractions of lignin fibers before and after freeze-thaw cycles,a series of undrained triaxial shear tests and scanning electron microscope tests were conducted.The results show that the tensile capacity of lignin fiber can limit the deformation of the surrounding soils,and thus effectively improve the cohesion of the expansive soil.With the increase of the fiber mass fraction,the effect of enhancing the cohesion of expansive soil is more obvious.After freeze-thaw cycles,the microcracks in the expansive soil develop into large cracks,and at the same time,the rearrangement and dislocation of the soil particles produce more pores,which leads to the reduction of its shear strength.The lignin fiber added in the expansive soils is wrapped by the soils and a spatial network structure formed by fiber and soil.The structure can delay the formation and development of microcracks,prevent the dislocation and rearrangement of soil particles,and thus improve the anti-freezing and thawing ability of the soil.With the increase of fiber mass fraction,the anti-freezing and thawing ability of expansive soil becomes stronger.