根直径及干湿循环对根土复合体抗剪强度影响的试验研究

Experimental investigation into the influence of root diameter anddry-wet cycle on the shear strength of root-soil composite

探究植被根系对土体的加固效应及干湿循环对根土复合体强度的劣化机制,为边坡生态治理及灾害防治提供帮助。开展了不同根直径及干湿循环的根土复合体三轴试验,利用电子显微镜对根土复合体的微观结构进行分析。研究结果表明:新鲜根、饱和根和干燥根的抗拉强度随直径的增大呈幂律减小。干燥根的抗拉强度最大,其次是新鲜根和饱和根。根土复合体的应力—应变曲线表现为持续硬化。随着应变的增大,偏应力先迅速增大后缓慢增加,最终保持稳定。随着根直径的增大,根土复合体的抗剪强度先增大后减小。根直径过小或过大,根对土壤的加固效果减弱。根系显著改变土壤黏聚力,对内摩擦角影响较小。抗剪强度随围压的增加而增大,随干湿循环的增加而减小。随着干湿循环次数的增加,抗剪强度和黏聚力呈线性下降,土颗粒团聚体分解,土体裂缝和孔隙面积呈指数增长。根土复合体的破坏形式为剪胀破坏。考虑干湿循环,修正的根土复合体强度预测模型是有效的,预测结果与试验数据吻合较好。

This study investigates the reinforcing effect of the roots of vegetation on the soil,and the mechanism of weakening of the root-soil composite when subjected to wet-dry cycles,with the aim of providing suggestions for the ecological management of slopes for disaster prevention.We conducted triaxial tests on root-soil composite samples featuring roots with varying diameters that were subjected to wet-dry cycles.The microstructure of the composites was analyzed by using electron microscopy.The results showed that the tensile strength of fresh,saturated,and dry roots decreased according to the power law with increasing root diameter.Dry roots exhibited the highest tensile strength,followed by fresh and saturated roots.The stress-strain curve of the root-soil composite reflected continuous hardening behavior.As the strain increased,the deviatoric stress initially increased rapidly and then slowly,and eventually stabilized.The shear strength of the root-soil composite first increased and then decreased as the diameter of the roots increased.However,when the root diameter was too small or too large,the reinforcement effect of the roots on the soil weakened.The root system significantly altered the cohesion of the soil but had little impact on the internal angle of friction.Its shear strength increased with the confining pressure but decreased with an increase in the number of dry-wet cycles.As the latter increased,the shear strength and cohesion decreased linearly,the soil aggregates were decomposed,and the area occupied by cracks and pores increased exponentially.The root-soil composite exhibited a shear dilation-based pattern of failure.The results showed that considering the influence of dry-wet cycles can enhance the accuracy of the model for predicting the strength of the root-soil.The predictions of our model were in good agreement with experimental data.