波致孔压累积导致海床液化诱发的埋藏污染物释放过程研究

With the improved control of exogenous pollutant input into waterbody, the importance of endogenous pollution arises from the release of pollutants that accumulated in sediments through sediment resuspension attracts more attention. The effects of endogenous release of pollutants become more obvious, especially in the estuary area with complex hydraulic conditions. On account of the offshore oil exploitation activities, an obvious elevation of oil and heavy metal concentration was observed in sediments adjacent to the Chengdao oil field. The adsorption of fine-grained sediments in this area accelerates the enrichment of pollutants. Wave-induced sediment pore water pressure accumulation will lead to the seepage of pore water and even the bed-liquefaction. It is speculated that the release of endogenous pollutants will be greatly increased. However, the release law is not clear yet. Based on in-situ observation, indoor wave flume simulation, and numerical analysis methods, this project focuses on research about the relationship between sediment pore water pressure variation, re-suspended sediment concentration and granularity, and release amount of sediment pollutants under different wave intensity. The mechanism of sediment pollutants release under the influence of pore water pressure accumulation in different marine hydrodynamic conditions will be revealed. Moreover, a multi-parameter fitting function between the release amount of sediment pollutants, marine hydrodynamic parameters, pore water pressure, and concentration of re-suspended sediment will be established, which could provide scientific reference for the water quality management and pollution control of geological environment in the study area.

随着近海水体污染物的外源输入逐步得到有效控制，富集在海底沉积物中的污染物经再悬浮-释放途径产生的内源污染的重要性逐渐突出，尤其在水力条件比较复杂的河口地区, 受污染底泥的内源释放效应越来越明显。由于油田开采活动的影响，胜利埕岛油田海域沉积物中油类和重金属污染物含量上升，该区域细粒沉积物的吸附作用更加速了污染物的富集。波浪作用导致海底沉积物孔隙水压力累积，产生孔隙水渗流甚至海床液化时，推测内源污染物的释放量会大大增加，释放规律尚不清楚。本项目基于现场原位观测、室内波浪水槽模拟实验和数值分析方法，围绕不同波浪强度下沉积物中孔隙水压力变化、沉积物再悬浮颗粒浓度及粒度与污染物释放量之间的关系开展研究，揭示沉积物污染物在底床孔隙水压力变化影响下的释放机理，建立污染物释放量与水动力参数、底床孔隙水压力及再悬浮颗粒浓度的多维度拟合关系式，为研究区域水质管理和地质环境污染控制提供科学参考。

随着近海水体污染物的外源输入逐步得到有效控制，富集在海底沉积物中的污染物经再悬浮-释放途径产生的内源污染的重要性逐渐突出，尤其在水力条件比较复杂的河口地区，受污染底泥的内源释放效应越来越明显。波浪作用导致海底沉积物孔隙水压力累积，产生孔隙水渗流甚至海床液化时，内源污染物的释放量会大大增加。本研究利用室内波浪水槽模拟实验，以黄河口三角洲地区表层沉积物为研究对象，围绕不同波浪强度下沉积物中孔隙水压力变化、沉积物再悬浮颗粒浓度及粒度与重金属Cu及石油类污染物释放量之间的关系开展研究，探讨波致孔压累积导致底床液化过程中污染物的释放过程。结果表明：.(1) 固结阶段，沉积物中污染物向上覆水体迁移的途径主要是通过孔隙水的扩散作用完成的，另外，底床沉积物的固结排水作用也是促进沉积物中污染物向上覆水体中迁移的重要因素。.(2) 重金属污染沉积物位于底床表层的情况下，在波浪剪切力引起的沉积物再悬浮和波浪压力引起的孔隙水渗流的共同作用下，进入上覆水体中溶解态Cu浓度高于重金属污染物位于底床内部的情况。.(3) 底床沉积物未液化的情况下，波浪荷载对沉积物中Cu和总石油烃的释放促进作用不明显，且波浪作用后期由于悬浮颗粒的吸附作用，上覆水体中总石油烃的平均浓度低于静态扩散阶段。沉积物中污染物向水体迁移的主要途径是波浪作用下孔隙水的瞬态垂向渗流和孔压累积引起的单向累积渗流。.底床沉积物液化状态下，波浪扰动对沉积物中Cu向上覆水体中的释放有明显促进作用，水体中重金属污染物以颗粒态为主。沉积物液化对沉积物中总石油烃的释放同样有明显促进作用。上覆水体中总石油烃浓度为非液化阶段的5倍；沉积物液化加剧了沉积物中总石油烃垂向迁移及平面扩散迁移，总石油烃垂向扩散深度与液化深度基本一致。.液化状态下，上覆水体中悬浮泥沙粒度变小，孔隙水的累积单向渗流导致沉积物内部对污染物具有很强吸附作用的细颗粒物质再悬浮是内部污染物释放的主要途径。