温度影响的吸力循环过程GMZ膨润土持水特征

Temperature affected water retention characteristics of GMZ bentonite during suction cycle

为揭示核废料深地质处置库多重屏障系统运营过程中膨润土持水性能随水-热耦合作用的周期性变化规律,通过温控气相平衡法和PEG渗析法进行了一系列单次吸力循环及多次吸力循环试验,研究了在自由膨胀条件下吸力循环和温度对膨润土持水性的影响。基于试验所得数据对膨润土持水曲线预测模型Van Genuchten模型进行了修正及验证。研究结果显示:单次吸力循环试验中,膨润土在脱湿路径下的含水率始终高于吸湿路径,表现出回滞现象;随着温度的升高,膨润土的持水能力及回滞现象均呈减弱趋势;而随着吸力或循环次数的增加,回滞现象和温度对持水能力的影响均减弱;在多次循环试验中,每次循环中试样均可累积含水率,但多次脱湿-吸湿循环相比于多次吸湿-脱湿循环表现出更强的累积能力,且每次循环含水率的累积随温度升高或循环次数增加而减少。修正后的Van Genuchten模型同时考虑了温度效应和吸湿或脱湿路径的影响,并且该模型预测结果与试验数据误差在5%以内,证实了其可靠性。

To reveal the periodic changes in the water retention capacity of bentonite caused by the coupling of hydraulic and temperature during the operation of the multiple barrier system in the nuclear waste deep geological disposal repository,this work conducted a series of single/multiple suction cycle tests with temperature-controlled vapor equilibrium method and PEG dialysis method.The effects of the suction cycle and temperature on the water retention capacity of bentonite under free swelling conditions were investigated.Based on the test data,the Van Genuchten model for predicting the water retention curve of bentonite was modified and validated.Results show that in the single suction tests,the water content upon the drying path was always higher than that upon the wetting path,exhibiting hysteresis.As the temperature rising,the water retention capacity and hysteresis showed a decreasing trend.As the suction or cycle increasing,the hysteresis and thermal effect on water retention both decreased.In the multiple suction cycle tests,accumulation of water content was observed in each cycle.However,the multiple drying-wetting cycle accumulated more water content.As cycle increasing,the accumulation of water in each cycle decreased.The modified Van Genuchten model takes into account both temperature effects and the influence of suction paths.The predicted results have an error of less than 5%compared to the test result,which confirms the reliability of the modified model.