Study on the influence of disturbance on clay ground improved by sand drain with 120 cm diameter

摘要

The sand drain (SD) ships for offshore driving disappeared in Japan due to reduced demand, and the sand compaction pile (SCP) ships have been used for the construction of sand piles for SD method. In the quay construction project at the Nakano district in the Port of Sakai, the SD drains were constructed by SCP ship into the offshore alluvial clay layer. As there was a delay in the measured settlement compared to the prediction in the design, it is assumed that the diameter of the sand drain 120 cm caused the larger disturbance in the ground than that in the normal SD method. In this study, the decrease of the consolidation coefficient due to the ground disturbance was investigated from the analysis of measured settlement data at the site and the laboratory tests. It was found that, when the diameter of the sand drain is larger than that in the normal sand drain works, the settlement rate may be overestimated in the conventional design where the vertical coefficient of consolidation obtained by the laboratory consolidation test is used as the horizontal coefficient of consolidation in the field.