复合反滤渗滤液抽排竖井渗透-淤堵机理与淤堵防治

More than 20 thousands vertical extraction wells have been built in the MSW landfill of China, while clogging and low drainage rate has caused to the poor leachate level control effect. One type of vertical well was found to has good anti-clogging performance in practice, but the development and application of this type well has been impeded by the poor understanding of the seeping-clogging mechanism. This study is focused on the seeping and clogging mechanism of the composite filtration vertical extraction well. The seeping mechanism and seepage flow load distribution in the composite filtration is first studied by the unit cell model test, then the clogging is explored in the seeping process of the leachate with different physical-chemical-biological characteristic under some temperature, pressure and relative displacement condition, and the better composite filtration structure tried to be found. One long-term laboratory model test is conducted to inspect the clogging process of filtration and waste surrounding the composite filtration vertical extraction well, and different anti-clogging methods will be tried. The calculation model with clogging process to be considered for the vertical well will be established. Field tests will be carried out to validate and develop the composite filtration well. The findings may have significance for the understanding of seeping-clogging development mechanism of the composite filtration vertical well, and lays the foundation for its optimum development and application.

我国填埋场建有渗滤液水位迫降抽排竖井超过2万口，但其普遍存在淤堵快、出水流量低和水位控制效果差的问题。工程探索表明，一种具备复合反滤结构的渗滤液抽排竖井具有良好的抗淤堵性能，但其渗透-淤堵机理尚不清楚，难以进一步优化和推广。拟针对填埋场复合反滤渗滤液抽排竖井开展研究。通过单元体试验和模拟，研究复合反滤层的渗流机理，掌握各反滤结构层流量负荷分布规律，揭示其在不同物化生化特性渗滤液、温度、上覆压力、位移等因素作用下的渗透-淤堵响应，探索优化复合反滤结构；开展复合反滤抽排竖井长期室内模型试验，掌握其反滤结构及井周垃圾长期使用后的淤堵时空发展规律，试验探索淤堵防治技术；建立考虑淤堵时空效应的复合反滤抽排竖井井流计算方法；开展现场试验，验证和进一步探索复合反滤层抽排竖井出水效果、淤堵发展规律及淤堵防治技术。本研究可阐明复合反滤渗滤液抽排竖井的渗透-淤堵时空发展规律，有利于其进一步优化发展和推广应用

堆体内水位壅高会降低垃圾的有效应力，也会引起填埋气阻滞、气压增大，显著降低堆体的稳定性。填埋场采用抽排竖井强制降低渗滤液水位，常有三种形式：具有复合反滤结构的大口径竖井，具有复合反滤结构的小口径竖井，以及常规结构的大口径竖井。.广州兴丰填埋场降水实践表明，具有复合反滤结构的大口径和小口径竖井，单井平均产水量可达25m3/d，远大于常规降水竖井的5m3/d ~10m3/d，效果良好。但通过改变竖井结构，很难进一步提升出水量，原因是堆体内存在液气阻滞效应，降低了渗滤液自堆体向竖井内的运移速率，限制了竖井的产水量。现场监测表明，厚度40m左右的堆体，实测主水位埋深4m~10m，滞水位埋深3m~5m，气压达到225kPa，水、气压力大，阻滞严重。.基于此，研发了一种负压抽排竖井，除采用复合反滤结构，同时利用真空泵在竖井内形成负压，增大渗滤液的渗流梯度，弱化填埋气对渗滤液的阻滞，提高竖井产水量。在杭州天子岭填埋场建设负压抽排竖井并开展试验，结果表明：（1）定降深25 m抽水，井内负压由0 kPa增加至-30 kPa，qs由46.1 m3/d增加至66.3 m3/d，出水量显著提升。（2）将井内负压保持在-30 kPa时，降深由15 m增加至25 m，产水量由45.0 m3/d增加至66.3 m3/d。（3）定降深25m抽水，井内负压由0kPa增加至-30kPa时，距井5m处水位降深由7.3m增加至12.7m，距井30m处由1.2m增加至1.6m。影响半径平均由34.5m增加至37.2m。（4）井周边堆体内的负压随着深度和距井水平距离逐渐减少。随着深度的增加，堆体内负压逐渐衰减。当井内负压为-30kPa时，距井5m深度15m处负压为-14.7kPa，深度30m处负压为-3.5kPa。随着水平距离的增加，堆体内真空也逐渐衰减。（5）随着负压的增加，折算堆体内饱和渗透系数kw由1.41×10-6 m/s逐渐增加3.29×10-6 m/s。.研究表明，具备复合反滤结构的大口径、小口径竖井均取得很好的应用效果，尤其是小口径竖井，具有成井速度快、降水效果好的特点，已在深圳、广州、杭州、上海及西安等多地获得应用。负压抽排竖井可增大堆体内渗滤液的渗流梯度，弱化液气阻滞效应，提高竖井产水量，具有良好的应用前景。