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.