Numerical analysis of strain mechanisms of cavities excavated in jointed chalk

摘要

The fact that huge surfaces in North France are under lied by unexploited cavities implies a serious risk of damage on both people and constructions. Consequently, these cavities are not only required to avoid ultimate collapse, but also to satisfy limits of displacement, resistance, and stability. Thus a study of the behavior of these cavities is needed. Knowing that these cavities were excavated in chalk layers with stratified joints and discontinuities, an anisotropic behavior is induced. The major intention of this paper is to study the impact of joints on strain mechanisms and stability state of the cavities. First, an oriented yield criterion based on the theory of multi-mechanisms is used to account for the presence of joints in the chalk continuum. Then, a numerical technique is developed to study the stability state of these cavities. Since in shallow excavations dominating failure is often realized by shear, the approach used is based on the conventional shear strength reduction method. The effect of joint sets characterization on the shear strength reduction factor as well as on the strain profiles is analyzed. This illustrates the influence of induced anisotropy on the stability and failure mechanisms of the underground cavities excavated in jointed chalk layers of North France and its region.