基于^(210)Pb、^(137)Cs分布和粒度特征的海床液化深度判定研究-以埕岛海域为例

Determination of sediment liquefaction depth based on ^(210)Pb,^(137)Cs distribution and grain-size characteristic:Take the Chengdao sea area as an example

黄河水下三角洲海床液化现象分布广泛,对海底工程设施造成了极大威胁,确定液化深度可为海上工程建设提供参考,具有很大的理论意义和应用价值。在黄河水下三角洲北部埕岛海域液化扰动区钻探取得柱状沉积物对其进行剖面图像扫描、放射性核素和粒度成分测试,获得图像分层特征、^(210)Pb、^(137)Cs活度及粒度剖面,在此基础上计算得到沉积速率。结果表明:埕岛海域受黄河1976年由刁口流路改道清水沟流路事件影响显著,这一时期沉积速率大幅减小并呈现阶段性特征;快速沉积时期表层沉积物频繁液化产生的砂层不断累积,从而形成密集砂层;通过分析^(210)Pb_(ex)、^(137)Cs活度剖面获得研究区液化历史的沉积记录,判定历史液化深度至少为5m,这一结论与前人研究相近。以^(210)Pb、^(137)Cs的活度为工具来判断沉积物液化历史及深度存在一定的可行性,具有很大的发展潜力。

The phenomenon of seabed liquefaction is widely distributed in the underwater delta of the Huanghe River,which poses a great threat to submarine engineering facilities.The determination of liquefaction depth can provide a reference for offshore engineering construction,which has great theoretical significance and application value.The columnar sediments were obtained by drilling in the liquefaction disturbance area of Chengdao sea area in the north of the Huanghe River Delta,and the profile image scanning,radionuclide and particle size composition testing were carried out to obtain the image stratification characteristics,^(210)Pb,^(137)Cs activity and particle size profile,and the deposition rate was calculated on this basis.The results show that the Chengdao sea area was significantly affected by the change of the Huanghe River from the Diaokou channel in 1976,and the sedimentation rate decreased significantly during this period and showed a phased character.During the rapid deposition period,the sand layer produced by frequent liquefaction of surface sediments accumulated continuously,thus forming the dense sand layer.By analyzing ^(210)Pb_(ex) and ^(137)Cs activity profiles,the sedimentary records of liquefaction history in the study area were obtained,and the historical liquefaction depth was determined to be at least 5 m,which is similar to previous studies.It is feasible to use the activity of ^(210)Pb and ^(137)Cs as tools to judge the history and depth of sediment liquefaction,which has great development potential.