沙柳直根抗拉特性对循环荷载的响应

Straight root tensile properties of Salix psammophila in response to cyclic loading

为揭示风力侵蚀区植物长期遭受大风使其根系反复受力后的固土性能,以神东矿区广泛分布的水土保持植物种沙柳(Salix psammophila)为研究对象,采用TY8000伺服式强力机对1~5 mm径级沙柳直根进行轴向循环荷载试验,探究直根抗拉特性对模拟大风拉拔产生的反复加载-卸载作用的响应。结果表明:(1)承受循环荷载后直根极限抗拉力与根径呈幂函数正相关,抗拉强度与根径呈幂函数负相关,与单次荷载下直根抗拉力、抗拉强度-根径关系相似。(2)承受循环荷载后各径级直根抗拉力、抗拉强度较单次荷载均有所增强且差异显著(P<0.05),1~2 mm、2.5~3.5 mm、4~5 mm直根抗拉力、抗拉强度分别增长了60%、60%,48%、50%,31%、32%。(3)直根力-位移曲线在循环过程中表现出明显的周期循环特征,随循环次数增加,滞回环间距逐渐闭合,由加载段-卸载段曲线组成的滞回环面积随之减小,抵抗塑性变形能力越来越差,最后趋之稳定。直根累计伸长率随循环次数的增加而增长,分为快速增长阶段和缓慢增长阶段。(4)承受单次荷载和循环荷载后,直根弹性应力、极限应力、弹性模量与根径呈负相关,累计弹性应变、极限应变与根径无关系;承受循环荷载后,直根弹性应力、极限应力、累计弹性应变明显增大,极限应变则表现为:单次荷载>循环荷载,弹性模量在不同荷载下无规律性。综上所述,沙柳根系在承受一定程度的营力低周循环荷载后,能够更加适应外界环境,增强对侵蚀营力的抵抗能力,更有利于植物根系发挥固土效能。

To clarify mechanical properties of straight roots in response to repeated loading and unloading induced by simulated high wind drawing,an axial cyclic load test was applied to straight roots of Salix psammophila.These roots had a diameter of 1-5 mm in the Shendong mining area and a TY8000 servo-type strong force was used to reveal the soil-fixing ability of plants in wind-eroded areas after their roots were repeatedly stressed by strong long-term winds.Results show the following:(1)the tensile force of straight roots after cyclic loading was positively correlated with the diameter based on a power function;the tensile strength after cyclic loading was negatively correlated with root diameter based on a power function,which was similar to the relationship between tensile force,tensile strength,and root diameter under a monotonic load.(2)Compared with the monotonic load,the tensile force and tensile strength after cyclic loading of straight roots of all diameters were significantly enhanced(P<0.05),and the tensile force and tensile strength of 1-2 mm,2.5-3.5 mm,and 4-5 mm roots increased by 60%,60%,48%,50%,and 31%,32%,respectively.(3)In the cycle process,the force-displacement curve of straight roots showed obvious cycle characteristics with increasing cycle number;the hysteresis loop spacing is gradually close to closing;and as the area decreases,the capacity of resistance to plastic deformation becomes worse,which tends to be stable.The accumulated elongation of straight roots increases with increasing cycle number,which can be divided into a rapid growth stage and a slow growth stage.(4)The elastic stress,ultimate stress,and elasticity modulus of straight roots was negatively correlated with root diameter after monotonic load and cyclic load,and the accumulated elastic strain and ultimate strain have no relationship with root diameter.The elastic stress,ultimate stress,and accumulated elastic strain after cyclic loading of all diameters was enhanced,the ultimate strain was monotonic load>cyclic load,and the elastic modulus has no relationship under different loads.