海底塌陷凹坑、扰动地层及再悬浮沉积物的波致土体液化成因探讨

Discussion on the Origin of Wave-induced Liquefaction in Collapse Depression,Disturbed Stratum,Re-suspended Sediment

在水下三角洲进行浅地层剖面测量中,经常发现存在塌陷凹坑和扰动地层,该地层通常被视为特殊工程地质条件。关于塌陷凹坑和扰动地层的形成,通常认为是海床液化所导致,但是缺乏有力的解释证据。本文根据在密西西比河与黄河水下三角洲的调查研究结果,结合实验室波浪水槽试验观察到的现象,提出了波致海床液化的观点,能合理地解释三角洲海底出现的塌陷凹坑和扰动地层:海底沉积物的液化振荡使得颗粒逐渐重新排列并压实,液化地层随之呈现厚度降低和强度变大的现象。同时也发现海底沉积物液化使得原来沉积底床深部的黏土析出进入水体,成为再悬浮沉积物。塌陷凹坑的波致液化成因可为海上构筑物建设的工程地质条件提供参考依据。

In the engineering geological survey on subaqueous delta,collapse depressions and disturbed strata are frequently found in shallow profile survey,which are usually regarded as special engineering geological conditions.Regarding the origin of collapse depressions and disturbed strata,it is commonly consi-dered that they are caused by the seabed liquefaction,but there is still lacking strong evidences.Based on the results of investigation in the subaqueous deltas of the Mississippi River and the Yellow River,this study,combined with the phenomena observed in the laboratory wave flume test,found that wave induced seabed liquefaction can reasonably explain the seabed collapse depressions and disturbed stratum in the delta.With the liquefaction oscillation of sediments,the particles are gradually rearranged and compacted,and the thickness and strength of the liquefied strata decrease and increase,respectively.Finally,we suggested that the liquefaction of seabed sediments makes the clay in the deep part of the original sediment bed precipitate into the water and become resuspended sediments.