For a dredging and reclamation site, excessive residual settlement due to the long term settlement after completion causes many problems. It is related to the big difference in the compression characteristics between the reclaimed clay ground and the sedimentary clay. For instance, the site formed by reclaimed clay in the upper area followed by soft ground is sold after improving according to the 10cm of residual settlement criterion. Here, it should be noted that the residual settlement is considered the primary settlement, not including the secondary settlement. Since this improved land shows a big residual settlement much more than expected, the dispute among the client, constructor, and the man who bought the land is intensified.
So far, the study about the reclaimed clay ground has not been systematically conducted. The reason is that the boring, investigation, and test on reclaimed clay are difficult compared to the sedimentary clay, and, thus, it is difficult to define the characteristics of reclaimed clay ground.
Therefore, to solve the problems, first, the physical, consolidation, and strength characteristics of reclaimed clay are analyzed using available data of reclaimed clay in this study. Moreover, the predicted settlement in design and measured settlements were analyzed. From the study results, the following things are redrawn.
The dredged reclaimed clay ground showed different stratum characteristics compared to the sedimentary clay. The reason is that the dredged reclaimed clay ground was formed quickly by re—deposition process after dredged seabed clay moved through conveying pipe. The dredged reclaimed clay ground showed a heterogeneity stratum layer where coarse particles deposited near the outlet location of conveying pipe, and small particles deposited far area from that. Thus the dredged reclaimed clay ground showed a big difference in physical properties compared to sedimentary clay. In other words, the dredged reclaimed clay ground's physical properties are dependent on the location of the discharge pipe and spillway.
According to measured settlement results of North container terminal distripark and Uudong distripark, the residual settlement of Undong distripark is bigger than that of North container terminal distripark. The difference in the consolidation waiting period between the two distriparks causes this result, even though the reclaimed clay ground is not much different.
The result of the settlement was analyzed using the entire data obtained during the consolidation waiting period after completion of the embankment and the partial data of the section with good linearity in the back part. It was found that there was a difference between them for the case of the North container terminal. Therefore, when analyzing settlement for evaluation of ground improvement, it is judged that the use of data of a section with good linearity in the back part rather than using the entire data after completion of the embankment is in good agreement with reality.
As a result of evaluating the degree of analysis according to the consideration of the amount of shear settlement occurring immediately after embankment completion, it was found that there is a difference when the amount of shear settlement is included. The shear settlement is a settlement that has the characteristics of causing not only vertical but also horizontal settlement. It is known that about 20 to 30% of the total vertical settlement is caused by shear settlement. In conclusion, it was found that the accuracy of the analysis result can be improved by excluding the shear settlement from the settlement analysis.