Effect of Sampling on Behaviour of Weathered Chalk With Flints
Résumé
Due to its heterogeneous nature and the presence of flint nodules, weathered chalk can be difficult to recover offshore in an intact state. On an offshore wind farm site comprising medium to high-density Chalk with flint, several sampling tools have been deployed including Geobor s rotary coring, push sampling, standard vibrocore of 100mm diameter and large diameter vibrocore of 300mm and 500mm diameter. Results of laboratory tests show the impact of the sampling, the sub-sampling and sample diameter on the behaviour of the tested chalk. If the drilling tends to partially remould the chalk, the vibro coring tends to density the chalk, this effect seems to be less pronounced with the increase of core diameter. The different states of densification are difficult to see on the density measurement but more visible on the dilative behaviour observed during the isotropic consolidated triaxial tests. The variation of permeability and the effect of cycles on the behaviour of the chalk are also discussed in the paper.