含根量对秋枫根-土复合体抗剪强度的影响

为研究含根量对秋枫(Bischofia javanica)根-土复合体抗剪强度的影响,利用纵剖面法探究了秋枫根面积比沿土层深度的分布规律,基于根面积比的分布范围,分别对7级不同根面积比梯度的重塑垂直根-土复合体试样在4级正应力下进行了改进的大盒直剪试验,定量探究了不同含根量对土体抗剪强度的影响,分析了根-土复合体黏聚力和内摩擦角的变化规律。结果表明:相比于素土,秋枫根-土复合体抗剪强度的增幅为1%～25%;在相同根面积比情况下,根-土复合体抗剪强度随正应力的增大而增高,但其增长幅度却相应减小;随着根面积比的增大,根-土复合体抗剪强度呈现先增高后降低的趋势,存在最优含根量使根-土复合体抗剪强度达到最大值。4级正应力下的峰值抗剪强度值分别为100,121,136,142 kPa,对应的根面积比均为0.20%;当根系含量超过最优含根量时,根-土复合体抗剪强度出现了较大幅度的衰减,衰减率与正应力有关,正应力越大,衰减幅度越小;根面积比对根-土复合体抗剪强度指标的影响主要体现为黏聚力的改善,而对内摩擦角的影响较小。研究结果可为秋枫根系固土稳坡提供一定的理论依据,对进一步认识乔木根土相互作用具有积极意义。

Effects of the Influence of Root Content on the Shear Strength of Root-Soil Composite of Bischofia javanica

In order to quantitatively evaluate the effect of different root contents on the shear strength of the root-soil composite, the distribution characteristics of the root area ratio of the Bischofia javanica with the increase of buried depth were analyzed. An improved large-box direct shear experiment was carried out on the remolded vertical root-soil composite with seven different root area ratios and four different normal stress levels. The changing rules of the soil cohesion and internal friction angle under different root area ratios were studied. The results showed that the shear strength of the root-soil composite of the Bischofia javanica was increased by 1%~25% compared with the soil without roots. Under the same root area ratio, the shear strength of the root-soil composite increased when the normal stress increased, but with a decreased growth rate. With the increases of the root area ratio, the shear strength of the root-soil composite increased first and then decreased. There was an optimal root content to maximize the shear strength of the root-soil composite. The peak shear strengths under four different normal stress levels are 100, 121, 136, 142 kPa respectively, and the corresponding root area ratios were all 0.20%. When the root content exceeded the optimal value, the attenuation rate of the shear strength was related to the normal stress. The larger the normal stress, the smaller the attenuation. The effect of the root area ratio on enhancing the shear strength of root-soil composite was mainly reflected in the soil cohesion, while its influence on the internal friction angle was small. The results of this study could provide some theoretical bases for stabilizing slopes using Bischofia javanica roots and have positive significance for further understanding the interaction between the arbor roots and soil.