含非饱和导排层的毛细阻滞覆盖层长期性能分析

Analysis on long-term performance of capillary-barrier cover with unsaturated drainage layer

为了验证含非饱和导排层(UDL)毛细阻滞覆盖层的防渗性能,采用模型试验在中国东部湿润气候区自然气候条件下进行2年的长期监测.覆盖层模型尺寸为2.0 m×1.0 m×0.55 m(长×宽×厚),坡度为18.4°(坡率为1∶3).结构剖面从上至下依次为植被生长层(15 cm)、粉土层(20 cm)、砂层(10 cm)和碎石层(10 cm).长期监测试验结果表明:监测期累计降雨量为3 448.4 mm;渗漏量为2.62 mm,显著低于北美湿润气候区土质覆盖层的防渗标准.非饱和导排砂层(UDL)侧向导排量为581.77 mm,占降雨量的16.87%,导排作用明显.在一个典型的水文年中,4～11月自然降雨、气温和腾发作用三者高峰期重合;雨热同期的有利气候条件以及UDL层的侧向导排作用,有效控制了渗漏量. 6～9月的连续强降雨为覆盖层易发生渗漏的极端气象段,是防渗设计的控制性气象条件.冬季12月至次年3月气温低但降雨量较少,增设的非饱和砂层导排作用明显;避免了因腾发作用弱不能及时蒸散水分而发生渗漏的问题.含非饱和导排层(UDL)的毛细阻滞覆盖层由粉土、砂和碎石等非胀缩性土构成;湿胀干缩和开裂现象不明显.

Outdoor model test was carried out for two years in humid area of China in order to study the long-term performance of the capillary-barrier cover with an unsaturated drainage layer (UDL). The size of model was 2.0 m (length)×1.0 m (width)×0.55 m (thickness);meanwhile, the slope rate and gradient were 1∶3 and 18.4°, respectively. From top to bottom, the structural profiles were vegetation growth layer (15 cm), silt layer (20 cm), sand layer (10 cm) and gravel layer (10 cm).The monitoring results show that: with the annual rainfall of 3 448.4 mm, the percolation is 2.62 mm, which is in line with the impervious standard of soil cover layer in humid climate zone of North America. Lateral diversion is 581.77 mm, which accounts for 16.87% of the cumulative rainfall and the lateral diversion effect is obvious. From April to November in humid area of China, the three peaks of temperature, rainfall and evapotranspiration coincide every year. The favorable climatic conditions in the same period of rain and heat, and the lateral diversion of UDL, effectively control the percolation. The continuous heavy rainfall from June to September is high risk to percolation meteorological event which is a controlled meteorological condition for seepage prevention design. From December to March of next year with scarce rainfall and weak evapotranspiration, the lateral diversion effect is obvious and avoid to percolation. The capillary barrier cover with unsaturated drainage layer is made up of silt, sand and gravel. Swelling, shrinkage and cracking are not obvious.