Nowadays interest of environment protection and sustainable development is growing up, leading to improve natural resources management. Land settlement, and more precisely earthworks, is directly concerned with this new policy in order to limit using of external materials with an objective of " no adding - no waste ". Nevertheless, some crude soils as soft clays or clayed silt do not satisfy geotechnics criteria for a safe use. Several earthworks on North West of France have met difficulties with fine grained soils from high weathering sediment from Armorica massif. These soils do not check mechanical and swelling requirements even if they are treated with different common mixtures of lime and/or hydraulic binders. The multi-scale characterisation performed during this study allows us to understand the high water sensibility of these materials which is their main critical property. A composite effect between kaolinite and muscovite minerals responsible for their water sensibility is evidenced at macroscopic scale. It has been confirmed by clay minerals interactions in colloidal suspension. Improvements of soil cohesion obtained by lime treatment allow us to envisage their use on earthwork site if some cautions are taken. Discussions about different strength cohesion nature for crude and treated soils underline several hypotheses for explaining peculiar mechanical properties development compared with classical sustainable materials.
