平原水库库盘防渗土工膜下气压分布及排气计算

Pressure Distribution and Exhaust Calculation under Impervious Geomembrane of Plains Reservoir Basin

针对平原水库库盘防渗土工膜膜下气压分布及排气沟设计中的关键技术问题,基于膜下非饱和土中孔隙气体的运移模型,借助于热传导模型的求解方法得到了膜下孔隙气体运移模型的解答,利用已有的膜下孔隙气压计算的理论公式法,验证了数值模拟法的合理性,模拟计算了地下水位不同上升高度时膜下非饱和土中的孔隙气压,分析了孔压分布规律,探讨了排气沟间距对孔隙气压的影响。研究结果表明:采用土工膜库盘防渗的平原水库,当入渗水与地下水相接触时会形成封闭气体的空间,地下水位上升会引起土工膜气胀。地下水位上升的幅度影响库盘土工膜膜下土体中气压分布的大小,且膜下气压随地下水位上升幅度呈非线性增长。当地下水位上升引起膜下气压增加时,设置了30~175 m八种不同间距的排气沟,并进行了膜下气压对比分析,发现设置排气沟可有效减缓地下水上升过程中的气压增加,加速膜下气体运移;同时,排气沟间距影响排气效果,排气间距越大,气压降幅越小,越不利于气压的消散,对于典型实例推荐采用75 m间距的排气沟。

Based on the transport model of pore gas in unsaturated soil under the membrane,the solution of the transport model of pore gas under membrane is obtained by means of the solution method of heat conduction model.The rationality of the numerical simulation method is verified by using the theoretical formula method of pore pressure calculation under the membrane.The pore pressure in the unsaturated soil under the membrane is simulated and calculated when groundwater levels different rise of heights,and the pore pressure distribution law is analyzed.The influence of exhaust ditch spacing on pore pressure is discussed.The research findings show that in plain reservoirs with geomembrane reservoir basin seepage control,when the infiltrated water is in contact with groundwater,a space of closed gas will be formed,and the rise of groundwater level will cause geomembrane air expansion.The rising groundwater level’s magnitude affects the air pressure distribution in the soil under the geomembrane membrane,and the air pressure under the membrane grows non-linearly with the rising groundwater level.When the rise of the groundwater level causes the increase in the pressure under the membrane,eight kinds of exhaust ditches with different spacing of 30~175 m are set,and the pressure under the membrane is compared and analyzed.It is found that the exhaust ditches can effectively slow down the pressure increase during the groundwater rising process and accelerate the gas migration under the membrane.At the same time,the distance between exhaust ditches affects the exhaust effect.The greater the distance between exhaust ditches,the smaller the drop in air pressure and the more unfavorable the dissipation of air pressure.For typical examples,exhaust ditches with 75 m spacing are recommended.