浓缩液回灌对垃圾填埋体水位及稳定性的影响

成都长安填埋场渗滤液反渗透处理工艺日产260 t浓缩液,拟在填埋场进行回灌处理,回灌工程实施前需评估回灌工程对垃圾填埋体稳定性的影响.在该填埋场工程地质与水文地质勘查结果的基础上,利用GMS软件开展了垃圾填埋体非饱和一饱和三维渗流分析,模拟和预测了浓缩液回灌前后填埋体内渗滤液水位变化.基于渗流分析结果,利用Slope/W软件分析了浓缩液回灌对垃圾填埋体稳定性的影响,并提出回灌工程安全稳定控制措施.分析表明,现状水位条件下垃圾填埋体恰能满足稳定安全控制要求,现状水位线即为安全控制水位；若直接实施浓缩液回灌,全场渗滤液水位明显上升,垃圾填埋体稳定安全系数明显降低,不能满足稳定安全控制要求；如果预先将全场水位降低3 m后再实施回灌,回灌后水位低于现状水位,满足稳定安全控制要求.在该填埋场布设45口抽排竖井,预计实施渗滤液抽排3个月后可将全场水位降低3 m,满足浓缩液回灌工程稳定安全控制要求.

Effect of Concentrated Leachate Recirculation on Leachate Level and Slope Stability of Municipal Solid Waste Landfill

260 tons concentrated leachate per day is produced at the leachate treatment plant at Chang＇an landfill,which is considered to be recirculated into the landfill of municipal solid wastes.The effect of leachate recirculation on the slope stability of the landfill should be evaluated.The results from engineering geology and hydrogeology survey were firstly presented.Three-dimensional unsaturated-saturated seepage analyses were carried out by using GMS software to predict the change of leachate level as a result of the leachate recirculation.Based on the leachate levels and pore-water pressures obtained from the seepage analyses,slope stability analyses were carried out to evaluate the safety of the landfill.Some control measures were proposed to eliminate the adverse effect of leachate recirculation on the landfill safety.The analyses indicate that the factor of safety（FS） for the landfill with the current leachate level is slightly greater than the safety requirement（FS=1.3）,and the current leachate level happens to be the critical level.Direct leachate recirculation will result in a significant rise in leachate level,which will cause a significant decrease in the landfill safety.The landfill is likely to fail after a direct leachate recirculation.If the leachate recirculation is executed after the current leachate level is lowered down by 3 m and the resultant leachate level will be lower than the current leachate level,the landfill can remain safe.Vertical pumping wells are proposed to implement the drawdown work,and if 45 wells are used and pumping is conducfed for 3 mouths,the leachate level will decrease by 3 m,which meets the safety requirement.