A case study is presented on dynamic compaction of rockfill during construction of the new Stockholm Norvik container and ro-ro port, due to open in 2020. The compaction on land was performed with a 20-tonne pounder using a drop height of 20 metres. Because of the soil type, soundings could not be used to evaluate the compaction effect. The maximum depth of influence was therefore measured using inclinometers and extensometers and was found to be around 10 m, in line with expected depths. The dynamic response of the rockfill was measured with an accelerometer mounted on the pounder. From the derived stress vs. displacement curves, a displacement modulus was evaluated and incorporated in the superstructure design. The dynamic compaction under water was performed using the same pattern, but due to limited water depths the drop height was 10 m. An attempt to estimate the maximum depth of influence was made by adjusting the well-known Menard empirical relationship between drop height, weight and compaction depth. This was done to take into account the buoyancy effect and water resistance resulting in a lower velocity at impact. Accelerometer measurements of the underwater compaction was also performed to evaluate the dynamic response. As on land, the measurements were used to derive a stress vs. displacement curve intended to predict the deformations of the compacted rockfill during construction of the ro-ro quay Lwalls. The modulus of the rockfill after compaction was also evaluated by monitoring the craters created during compacting, followed by a back calculation of the change in density index. Based on the density index, the modulus could be assessed and compared to the same parameter from accelerometer measurements. Predicted and measured deformations will be compared during the construction of the L-walls as well as during placing of additional fill on the harbour area.
Subjects: dynamic compaction, accelerometer measurements, under water compaction
Author: Sölve Hov, Håkan Eriksson and Carl Wersäll
Publisher: DFI, EFFC