西宁盆地黄土区典型草本植物单根抗拉力学特性试验

Experiment on single root tensile mechanical properties of typical herb species in loess region of Xining Basin

为进一步探讨西宁盆地黄土区草本植物根系固土护坡力学效应,该项研究以种植于西宁盆地自建试验区生长期为150 d的垂穗披碱草(Elymus nutans Griseb.)、细茎冰草(Agropyron trachycaulum Linn.Gaertn.)及紫花苜蓿(Medicago sativa L.)3种草本植物作为试验供试种,通过单根拉伸试验对比分析了3种草本植物在不同根径级别条件下,单根抗拉力、单根抗拉强度以及单根极限延伸率的差异性及其与根径之间的关系,同时进一步分析了3种草本植物单根在拉伸过程中表现出的应力-应变特征。试验结果表明:3种草本植物根径在(0.10,0.20]、(0.20,0.30]、(0.30,0.40]、(0.40,0.50]及(0.50,0.60]mm 5个根径级别条件下,紫花苜蓿单根抗拉力和单根抗拉强度较垂穗披碱草平均高1.32倍、1.30倍,较细茎冰草平均高1.26倍、1.31倍;垂穗披碱草单根极限延伸率较细茎冰草和紫花苜蓿平均高1.13倍和2.16倍。进一步研究表明,在根径为0.10~0.60 mm条件下,3种草本植物单根抗拉力和单根抗拉强度随着根径的增加,分别呈幂函数增长和幂函数降低关系;3种草本植物单根极限延伸率随着根径的增加呈逐渐增大变化趋势。单根拉伸试验过程中,3种草本植物单根应力-应变关系曲线表现出弹性变形、弹塑性变形、应变硬化及断裂破坏4个阶段,其中垂穗披碱草和细茎冰草的应力-应变关系曲线具有双峰值现象。研究结果表明,紫花苜蓿根系增强边坡土体抗剪强度的作用相对较为显著,其次为细茎冰草和垂穗披碱草。该项研究成果对于科学有效防治研究区高寒干旱环境条件下,坡面水土流失、浅层滑坡等地质灾害现象的发生,具有理论研究价值和实际指导意义。

To further explore the mechanical effects of roots of herb species on soil reinforcement and slope protection in loess region of Xining Basin,in this study,3 kinds of herbs i.e.Elymus nutans Griseb.,Agropyron trachycaulum Linn.Gaertn.and Medicago sativa L.,which were planted in the self-established testing area in Xining Basin,were selected as the research objects and the growth time was 150 d.Under the condition of different root diameter levels,single root tensile force,single root tensile strength and single root limit extensile rate of 3 kinds of herbs were assessed via single root tensile test.Furthermore,the stress-strain characteristics of 3 kinds of herbs during the tensile process were further analyzed.The test results are as follows:Under the 5 levels of root diameters i.e.(0.10,0.20],(0.20,0.30],(0.30,0.40],(0.40,0.50]and(0.50,0.60]mm,the single root tensile force of M.sativa,E.nutans and A.trachycaulum ranges from(2.28±0.67)to(12.00±3.89)N,from(1.75±0.43)to(7.66±0.72)N and from(1.82±0.46)to(7.95±0.47)N,respectively;the single root tensile force of M.sativa is averagely 1.32 times higher than E.nutans and 1.26 times higher than A.trachycaulum;the single root tensile strength of M.sativa,E.nutans and A.trachycaulum is from(49.21±17.06)to(124.88±46.63)MPa,from(35.33±1.76)to(84.87±15.93)MPa and from(35.96±2.46)to(73.32±19.56)MPa,respectively;the single root tensile strength of M.sativa is averagely 1.30 times higher than E.nutans and 1.31 times higher than A.trachycaulum;the single root limit extensile rate of E.nutans ranges from 50.36%±15.52%to 76.4%±3.05%,which is averagely 1.13 times higher than A.trachycaulum(from 45.84%±11.56%to 73.28%±10.82%)and 2.16 times higher than M.sativa(from 25.74%±8.05%to 36.09%±7.78%);in addition,when the root diameter is from 0.10 to 0.60 mm,the single root tensile force of the 3 kinds of herbs increases with the root diameter increasing,with a power relationship between single root tensile force and root diameter.Meanwhile,the single root tensile strength of the 3 kinds of herbs increases with the root diameter decreasing,and a power relationship exists between single root tensile strength and root diameter;moreover,the single root limit extensile rate of the 3 kinds of herbs increases with the increasing of the root diameter,but there is no significant functional relationship between them.The 3 kinds of herbs show 2 types of stress-strain curves(ⅠandⅡ)during the single root tensile test;both of 2 types of stress-strain curves for the 3 kinds of herbs can be divided into 4 stages:elastic deformation,elastic-plastic deformation,strain hardening and fracture failure;in addition,the stress-strain curves of TypeⅡhave the phenomenon of double peaks,which is due to the epidermis of root broken earlier than its internal tissue;the stress-strain curves of TypeⅡare found in the single root tensile process of E.nutans and A.trachycaulum,but not in M.sativa,which means the stress-strain process of root epidermis and its internal tissue of M.sativa has a relatively significant synchronism during the single root tensile test;it can also be concluded that,among the 3 kinds of herbs,M.sativa has the most significant effect on enhancing soil shear strength,followed by A.trachycaulum and E.nutans.These conclusions have a theoretical and practical significance in preventing soil erosion,shallow landslide and other geological hazards in cold and arid environment.