某垃圾填埋场污泥坑外涌及其引发下游堆体失稳机理

中国许多垃圾填埋场接纳高含水率的市政污水污泥，对填埋场运营构成了严重安全隐患。介绍某填埋场污泥坑上堆填垃圾过程中引发污泥外涌及下游堆体失稳事故，根据填埋场失稳破坏现象及事故前后下游堆体边坡中渗滤液水位和顺坡向位移监测结果，对堆体失稳的力学机理及失稳过程进行反分析。现场监测数据与堆体失稳分析结果表明：在未加固处理的污泥坑上堆填垃圾会显著降低下游垃圾堆体的稳定性。其力学机理：①流态状污泥将上覆垃圾荷载等量转化为对周围垃圾体的侧压力（对下游垃圾堆体为下推力）；②污泥受压挤渗入周边垃圾和衬垫系统中导致堆体抗剪强度降低。垃圾堆体中高液气压力是造成堆体失稳的重要内因，降低堆体中渗滤液水位可显著提高污泥坑下游堆体的稳定性，有效控制失稳堆体继续滑移。污泥坑加固处理后再堆填垃圾，可显著降低发生失稳和污泥外涌的风险。

Failure mechanism of sludge pit and downstream waste slope of a MSW landfill

Sewage sludge pits exist in many landfills of municipal solid wastes (MSWs) in China, and their safety is particularly important. The failure of a sludge pit and the downstream waste slope during the waste filling over the pit is introduced. The presentation includes many failure evidences, contingency measures, field monitoring of leachate level, surface and deep horizontal displacements before and after the accident. Back analyses are also carried out to have the effect of the sludge pit on the stability of the downstream waste slope. The field monitoring and back analyses demonstrate that the surcharge loading of MSWs over the super-soft sludge pit significantly lowers the factor of safety of the downstream waste slope. The associated mechanism includes two aspects: firstly, the fluid-like sludge transfers the vertical loading of waste into a lateral pressure of the same magnitude acting on the downstream waste slope. Secondly, some fluid-like sludge is squeezed into the surrounding waste body as well as the interface between the waste and the underlying liner, leading to a decrease in the frictional strength. The high pressures of leachate and gas existing in the landfill are the internal and major factor for the failure. Drawdown of the high leachate level increases the factor of safety of the waste slope and prevents a further sliding of the slope. The risk of failure during the filling of MSWs will be significantly reduced if the soft sludge in the pit is firstly improved to a sufficient strength. Field monitoring of horizontal displacement on the waste body surrounding the sludge pit will provide an early warning of the accident.