The sticky property of Ypresian clays

Abstract

Construction sites may encounter many problems with the underlying soil, and excavating in soft soils is one of them. One major issue when managing soft soils is clogging, which occurs because cohesive soils tend to adhere to the cutting head of tunnel boring machines or to the cutting wheel of hydromills. This thesis focuses on Ypresian clays, which are highly adhesive. The adhesive properties of Ypresian clays can slow down excavation processes, causing economic loss to the construction companies. Studying the different mechanisms behind the clogging phenomenon and ways to qualitatively and quantitatively assess it makes it possible to evaluate the clogging potential of Ypresian clay and compare it to that of the Boom clay, a similar formation which is shown to be less sticky. The high plasticity index of Ypresian clays is proved to be an indicator of its high stickiness, and the cone pull-out test gives a value for adherence that quantifies the clogging potential. Ypresian clays also support the hypothesis that the Casagrande chart's U-line could be used as an evaluation method for clogging. In these ways, evaluating clogging potential is possible, but a standardized method has yet to be agreed on. The physics behind the evaluation methods, however, is not well understood. That is why this thesis discusses using a microscopic approach to study the origin of Ypresian clay's stickiness. Research still needs to be done to see if inter-scaling is possible between micro-, meso-, and macroscopic scales and to find out if the particles' interactions at microscopic scale can be interpreted at the macroscopic scale.