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Determining rock quantities using swathe techniques on Maasvlakte 2

Huibert-Jan Lekkerkerk, Marnix Kol, Eric Peeters, René Roels, Tjebbe Westerbeek

 

For the Maasvlakte 2 extension of the Port of Rotterdama large amount of rock has to be placed underwater under tight specifications in relatively thin layers. The standard method for surveying rock levels (CUR 154) requires the use of a semi-spherical foot. As this technique is unusable under water or in the surf zone, echo-sounders are commonly used under water.

In the past research has been done into the effect of the survey technique on the surveyed level and volume of rock. Initial conclusions pointed towards lower volumes being detected using multibeam surveys than with the semi-spherical foot. The results of this research have been summarized in the booklet ‘Construction and survey accuracies for the execution of dredging and stone dumping works’.

As the rock gradations tested in earlier studies were limited and survey techniques have advanced, it was deemed necessary for the Maasvlakte 2 project to extend these studies. Therefore  a test-pit was constructed in which various gradations were placed. The test-pit was surveyed using ‘dry’ methods including the semi-spherical foot as well as helicopter- and crane-based LIDAR.

The test pit was then filled with water and surveyed using multibeam echo-sounders as well as a singlebeam echo-sounder. Each system was tested multiple times to obtain statistical significance.

The data has been processed using standard survey techniques augmented by statistical processing. The figure below shows the results of the trials[1].

The results obtained are in line with those from earlier tests and indicate a relation between the semi-spherical foot and multibeam echo-sounder which depends on the ‘median stone diameter (Dn50)’. The booklet mentioned has been updated with the results and is published as a CUR report. The results also form the basis of corrections applied to the surveyed rock levels at the Maasvlakte 2 project.

 

[1] In this abstract not all footnotes / discussion pertaining to the figure can be shown. As a result the image should be used with due care.