抽气现场试验的土工膜下盲沟气阻数值模拟研究

Numerical simulation of air resistance of French drains beneath geomembrane in field vacuuming tests

膜下盲沟是水库土工膜防渗方案的重要工程措施,对膜下气体排出具有决定性作用。基于流量变化等效原则,提出了渗透系数与路径长度的平方成比例的变换关系。据此推断出水库面积巨大,排气路径太长,是盲沟气阻引发膜下气胀的主要原因。运用非饱和土固结简化计算方法模拟了抽气条件下膜下气压分布状态;对比现场试验实测值,验证了计算方法和参数的合理性。计算结果表明:无论有无盲沟,膜下沿水平向分为气压急变区和稳定区,气压急变区为抽气点沿水平向2.5 m范围,区内气压显著变化,反映了盲沟气阻的存在性;膜下气压梯度分布规律反映盲沟气阻的变化;影响盲沟气阻的主要因素是材料进气值和饱和度,进气值减小、饱和度降低均有利于减小盲沟气阻。研究成果可为合理评价库盘土工膜防渗方案设计提供科学理论依据。

The French drains beneath the geomembrane are an important engineering measurement for the geomembrane as anti-seepage structures of reservoirs, and have a decisive effect on the air exhaust beneath the geomembrane. The conversion relationship between the permeability coefficient and the square of path length is proposed on the basis of the principle of equivalent flow variation. It is deduced that the important reasons for the bulge of the geomembrane are the huge reservoir area and the long drain path because of the air resistance of French drains. The simplified method for consolidation of unsaturated soils is used to calculate and simulate the air pressure distribution beneath the geomembrane under the condition of vacuuming.The comparison between the measured and calculated values in the field tests has verified the rationality of the proposed method and parameters. The results reveal that a pressure changing zone and a stable zone exist along the horizontal direction whether there is a French drain or not. The pore-air pressure changes significantly in the zone of a range of 2.5 m along the horizontal direction from the vacuuming spot, which indicates the existence of the air resistance of French drain. The distribution of pressure gradient beneath the geomembrane reflects the change of the air resistance of French drain. The main influencing factors for the air resistance of French drain are the air intake value and the degree of saturation of materials.Reducing the air intake value and lowering the degree of saturation are beneficial to reducing the air resistance of French drain.The research results may provide a scientific theoretical basis for the evaluation of the design of anti-seepage scheme of the geomembrane.