植被根系含量对膨胀土持水和渗透特性的影响

Effect of Vegetation Root Content on Water Holding and Permeability Characteristics of Expansive Soil

为探究植被根系含量对膨胀土持水和渗透特性的影响规律,选取南宁市膨胀土地区的膨胀土,掺入狗牙根根系制备不同含根率的试样,进行室内压力板仪试验和变水头渗透试验,采用Van Genuchten-Mualem模型预测不同含根率的膨胀土非饱和渗透系数。结果表明:掺入根系后,膨胀土持水能力减弱,根系掺入增加膨胀土内部大孔隙的比例,含根率越高,大孔隙体积占总孔隙体积比例越大,持水能力相较于纯土下降的幅度越大;饱和状态下,膨胀土渗透系数随含根率增大而增大;非饱和状态下,低吸力阶段(0~25 kPa)的膨胀土渗透性随含根率的增大而增大,随着基质吸力增加到高吸力阶段(200~1 000 kPa),根系优势流效果减弱,含根膨胀土渗透性逐渐趋近低于纯土;细观结果表明根系的掺入使膨胀土内部产生贯通裂缝,是影响膨胀土持水和渗透能力的关键因素。研究进一步揭示了植被根系对膨胀土增渗作用的机理和规律,为综合评价植被防护膨胀土边坡效果提供参考。

In order to explore the influence of vegetation root content on the water holding and permeability characteristics of expansive soil,samples with different root content were prepared by mixing bermudagrass roots with expansive soil from Nanning expansive soil area,and indoor pressure plate test and variable head permeability test were conducted,the Van Genuchten-Mualem model was used to predict the unsaturated permeability coefficient of expansive soil with different root contents.The results show that the water holding capacity of expansive soil decreases after the addition of roots,and the addition of roots increases the proportion of large and medium pores in the expansive soil.The higher the root content,the greater the proportion of large pore volume to total pore volume,and the greater the decrease in water holding capacity compared to pure soil.In saturated state,the permeability coefficient of expansive soil increases with the increase of root content.In unsaturated state,the permeability of expansive soil at low suction stage(0~25 kPa) increases with the increase of root content.As the matrix suction increases to high suction stage(200~1 000 kPa),the effect of root dominant flow decreases,and the permeability of expansive soil with roots gradually tends to be lower than that of pure soil.The mesoscopic results indicate that the incorporation of root system causes through cracks in the expansive soil,which is a key factor affecting the water holding and permeability of the expansive soil.This study further reveals the mechanism and regularity of the infiltration enhancement effect of vegetation roots on expansive soil,providing a reference for comprehensive evaluation of the effect of vegetation protection on expansive soil slopes.