植被作用下土质覆盖层渗透特性的现场试验

通过现场试验监测了3种不同覆盖层的内部水分运移过程，研究了不同植被对覆盖层防渗性能的影响。首先在室外自然环境中修建了3种覆盖层场地，分别是无植被裸土覆盖层、狗牙根草覆盖层（须根系植被）、香根草覆盖层（直根系植被）。在亚热带潮湿气候条件下培育一年，选择降雨量和蒸发量较大的7~9月份实时监测了3种覆盖层内部不同深度处的体积含水率和基质吸力。研究发现，香根草的存在使得覆盖层的渗透系数增大，从而减弱了覆盖层的防渗性能；相反，狗牙根草降低了覆盖层的渗透系数，从而增强了覆盖层的防渗性能。这主要是因为须根类根系（狗牙根草根系）和直根系（香根草根系）对土体中水分运移的影响不同。监测结果显示，在覆盖层较浅的位置（如5 cm深度处）土体内的含水率主要受降雨和蒸发的影响，有无根系对此处的含水率变化影响较小。在覆盖层深处（如50 cm处），只有香根草覆盖层还受降雨和蒸发的影响，而狗牙根草覆盖层和裸土覆盖层深处含水率基本没有变化，这说明了香根草覆盖层根系影响了覆盖层深处，而狗牙根草根系只对覆盖层浅处有影响。

Field test on seepage performance of soil cover with different types of vegetation

The aim of study is to investigate anti-seepage performance of landfill covers with different types of vegetation. First, three field test sites were built with different types of vegetation conditions, i.e. no vegetation, Bermuda grass (fibrous root) and vetiver grass (tap root). During one year of vegetation growing under the subtropical climate, the real-time responses of volumetric water content (VWC) and matric suction were monitored at different depths of the covers from July to September when the rainfall and evaporation were the largest. Results show that the vetiver grass enhances the coefficient of permeability and reduces the integrity of the cover. The Bermuda grass decreases the coefficient of permeability and improves the performance of the cover. The reason is that the effects of different plant roots on the moisture flow path in cover are different. The monitoring results indicate that the effect of vegetation on the water content changes at 5 cm depth can be ignored. The changes of VWC and matric suction at this depth are mainly controlled by the rainfall and evaporation. The water content at 50 cm depth changes only in cover with vetiver grass. This indicates that the vetiver grass results in preferential flow in deep soils. The Bermuda grass mainly changes the moisture flow within small depth.