红黏土覆盖层水力参数演变规律与防渗设计讨论

以红黏土为对象,通过室内单元体并结合填埋场现场原位试验,从建设施工和建成后长期服役两个不同时间尺度对土质覆盖层水力参数开展了5 a的跟踪监测;分析对比了从实验室到现场、从建设施工到建成长期服役水力参数的劣化衰减规律。结果表明:(1)5 a长期服役中,无植被红黏土覆盖层入渗系数从10^-7 cm/s增大到10^-3 cm/s,增大4个数量级;有植被条件入渗系数从10^-7 cm/s增大到10^-6 cm/s,增大1个数量级。(2)自然气候长期服役覆盖层中大孔隙逐渐增多,降雨雨强过大(如暴雨)导致土质覆盖层防渗能力和储水能力下降。工程设计中应根据当地降雨参数进行适当放大调整。(3)自然气候下经历反复吸、脱湿滞回循环,土质覆盖层的储水能力与降雨前土层吸湿起点(或初始吸力)和吸湿路径有关。采用室内吸湿起点初始吸力-1500 kPa的主吸湿曲线设计偏于保守,结果相对安全。

Evolution laws of hydraulic parameters of red clay covers and design of seepage prevention

Through the laboratory unit and in-situ tests in landfill site,the hydraulic parameters of red clay soil covers have been monitored for more than five years on two different time scales of construction and long-term service.The degradation laws of hydraulic parameters from laboratory to field as well as from construction to long-term service are analyzed and compared.The results show that:(1) During the five years of long-term service,the infiltration coefficient of red clay covers without vegetation changes from 10^-7 cm/s to 10^-3 cm/s,with the variation fluctuated by 5 orders of magnitude,and the infiltration coefficient with vegetation is 2 orders of magnitude from 10^-7 cm/s to 10^-6 cm/s.(2) The macropores in the covers gradually increase in the long-term service of natural climate,and the excessive rainfall(such as rainstorm) leads to the decrease of water storage capacity of soil overburden.In engineering design,it should be adjusted according to the local rainfall parameters.(3) With the repeated cycles of moisture absorption and desorption,the water storage capacity is related to the initial matrix suction and path of moisture absorption before rainfall.The design of the main moisture absorption curve with the starting point of laboratory moisture absorption(initial matric suction) of -1500 kPa is conservative,and the results are relatively safe.