| A suitable covering layer structure can effectively prevent rainwater infiltration,ensure the stability of the landfill,and reduce the cost of closing the landfill.Relevant engineering practice shows that adding an unsaturated drainage layer(UDL)to the traditional overburden structure can reduce rainwater entering the landfill and better ensure the safety and stability of the landfill.However,the water transport characteristics of overburden containing UDL in long-term service in humid climates are still unclear,which affects the better popularization and application of such overburden in landfills in humid areas.Based on the saturated-unsaturated finite element method,the paper numerically simulates the water transport law in the conventional capillary retardation overburden and the overburden containing UDL under the condition of rainfall.Moisture transport characteristics of overburden containing UDL under different influencing factors such as thickness,overburden slope,etc.Taking the climate of Changsha in 1997 as an example,the law of water transport in overburden containing UDL under humid climate conditions was analyzed,and the improvement measures for service performance of overburden containing UDL in humid areas was discussed.The main contents and conclusions are as follows:(1)Comparative analysis of moisture transport between overburden containing UDL and conventional overburden under rainfall conditions.Using the SEEP/W module of GeoStudio software,the numerical models of the conventional overburden composed of silty clay-crushed stone and the overburden composed of silty clay-sand-crushed stone were established respectively,and the moisture content of the overburden under the action of rainfall infiltration was compared and analyzed.Movement laws.The results show that:under the same rainfall conditions,the time of infiltration water breaking through the top of the UDL and seep into the gravel layer is delayed compared with the conventional overburden,and the length of the lateral guide is also longer,that is,the area that leaks to the gravel layer.Smaller;more water is drained out of the overburden through the drainage of the sand layer,and the leakage at the bottom of the overburden is also significantly reduced.(2)Research on the influence of different factors on the water migration in the overburden containing UDL.A finite element grid model with UDL overburden was established to analyze the influence of rainfall intensity,thickness of unsaturated drainage layer,thickness of silty clay layer,and overburden slope on lateral drainage length and overburden water balance.The results show that:when the total rainfall is equal,the effect of long-term light rain on the cover layer containing UDL is greater than that of short-term heavy rainfall;the effect of UDL thickness on the leakage of the cover layer is small;the thickness of the thickened silty clay layer can be increased.Significantly reduces the amount of leakage at the bottom of the cover;the steeper the slope of the cover,the less leakage at the bottom of the cover.(3)Moisture transport of inclined overburden containing UDL under rainfall-transpiration conditions.Using the VADOSE/W module of GeoStudio software,a numerical model of the overburden containing UDL under long-term rainfall,evaporation,and transpiration was established,and the evolution law of water transport in the overburden containing UDL under the climate conditions of Changsha in 1997 was explored.The results show that the distribution characteristics of rainfall in a typical year have a great impact on the rainfall infiltration of the cover layer;the annual rainfall infiltration amount of the cover layer is only 540 mm,and the infiltration water is basically consumed by soil evaporation and crop transpiration.No leakage oc curred at the bottom of the cover layer,and the anti-seepage performance of the cover layer containing UDL capillary block remained stable. |
PDF Full Text Request