纤维纱加筋黄土力学变形特性及本构模型研究

MECHANICAL DEFORMATION CHARACTERISTICS AND CONSTITUTIVE MODEL OF FIBER YARN REINFORCED LOESS

将纺织坯布进行开松、分梳、切断形成纤维纱,将纤维纱按照一定掺加比例与素黄土拌合制备成纤维纱加筋黄土。利用伺服液压加载双室高压三轴仪对纤维纱加筋黄土进行等向压缩试验及三轴剪切试验,系统分析纤维纱加筋黄土的压缩变形及应力-应变特性。试验结果表明:在等向压缩试验中,随着素黄土中纤维纱掺加比例的增大,其压缩变形量减小;确定出纤维纱加筋黄土的屈服压力,屈服压力随素黄土中纤维纱掺加比例的增大而提高。根据纤维纱加筋黄土三轴剪切试验应力-应变关系发现,在相同的固结压力作用下,随着素黄土中纤维纱掺加比例的增大,反映出的剪应力也随之增大;在相同的纤维纱掺加比例条件下,随着固结压力的增大,反映出的剪应力也随之增大。构建一个可以综合反映纤维纱加筋黄土实际加固效果的指标——纤维加筋指数Ir,通过三轴剪切试验数据分析得到纤维加筋指数Ir随着轴向应变的增大而逐渐减小;黏聚力随着纤维加筋指数Ir的增大呈双曲线增大的变化趋势,内摩擦角随着纤维加筋指数Ir的增大基本保持不变。基于修正剑桥模型的理论基础,根据纤维加筋指数Ir的不同,确定出随着纤维加筋指数Ir变化而变化的等向压缩球应力以及临界状态线,以塑性体积应变为硬化参量,推导出纤维纱加筋黄土弹塑性本构模型。通过试验验证,证明了本构模型可以较为合理地描述纤维纱加筋黄土的力学变形特性。

Fibre yarn is formed by loosening,carding and cutting waste synthetic textile polyester fabric.A certain proportion of fibre yarn was added to plain loess,which formed fibre yarn reinforced loess.The uniaxial compression test and triaxial shear test of fiber reinforced loess were carried out using servo hydraulic loading double chamber high pressure triaxial apparatus.The compressive deformation and stress-strain characteristics of fiber yarn reinforced loess were systematically analyzed.The results showed that with the increase of fiber yarn proportion in plain loess,the compressive deformation decreases.The yield pressure of fiber yarn reinforced loess was determined.The yield pressure increased with the increase of fiber yarn proportion in plain loess.According to the stress-strain relationship of fiber yarn reinforced loess in triaxial shear test,it was found that under the same consolidation pressure,with the increase of fiber yarn proportion in plain loess,the reflected shear stress also increased.With the increase of consolidation pressure,the shear stress increased with the increase of fiber yarn blending ratio.According to the stress-strain relationship of fiber yarn reinforced loess in triaxial shear test,a comprehensive index—fiber reinforced index I r was constructed.The index I r could reflect the actual reinforcement effect of liber yan reinforced loess.The cohesive force was hyperbolic with the increase of the index I r.The internal friction angle kept constant with the increase of the index I r.Based on modified Cambridge model,according to the difference of the index I r,the isotropic compressive ball stress and critical state line with the change of fiber reinforced index I r was determined.Taking plastic volume strain as hardening parameter,the elastoplastic constitutive model of fiber yarn reinforced loess was derived.After testing validation,it was proved that the constitutive model can reasonably describe the mechanical deformation characteristics of fiber yarn reinforced loess.