The Influence of Weathering on the Mechanical Properties of Chalk: Study of the Saint Marguerite Chalk

The chalk cliffs of northern France are exposed to considerable erosion, resulting in a significant coastal retreat of up to 1 m per year on average. A key concern is how the mechanical properties of the chalk evolve under different weathering conditions. Previous research, based on a limited number of samples, has provided a preliminary understanding of potential changes in the mechanical properties of chalk in altered and unaltered states. As part of the DEPHY3GEO project, we conducted experiments on Saint Marguerite Chalk, which is part of the Newhaven Chalk Formation. Due to the inherent low strength of the chalk, some conventional displacement measurement techniques are inappropriate. Therefore, we used digital image correlation (DIC) coupled with basic acoustic measurements. Experiments were performed on chalk samples exposed to various weathering conditions, including salt solutions, fresh water, and thermal cycling. These experiments consisted of uniaxial and confined compression tests, which allowed us to evaluate the influence of weathering on the mechanical behavior of the chalk. Results show that water saturation of chalk rock significantly reduces by half or more its maximum compressive strength. Ongoing work will further investigate the weathering of chalk by studying its effect on micro- and macro-scale structures through structural analysis of cliff samples and scanning electron microscopy (SEM).