Collapses of underground cavities and soil-structure interactions:   influences of the position of the structure relative to the cavity
  This paper is focused on soil subsidence of small extend and amplitude caused by tunnel boring or the collapse of underground cavities, whether natural or man-made. The impact of the movements of the ground on existing structures is generally dramatic. It is therefore necessary to accurately predict these movements (settlements and horizontal extension or compression displacements). Even though it is obvious that the overall stiffness and weight of the structure influences the size and shape of the soil movement, the main features of this soil-structure interaction phenomenon are not well established. Caudron et al. (2006) developed an original small-scale physical model to take the soil-structure interaction into account. It is based on the use of the frictional Schneebeli material (assembly of small diameter rods) and a modified version including cohesion in order to reproduce a cohesive layer above a cavity. The displacements of the soil are obtained from digital images processing by particle image velocimetry (PIV). Interesting results were obtained, probing that the soil-structure interactions could be analysed by this experimental model. This article is focused in a first part on the influence of the position of the structure with respect to the cavity position. Consequences on the areas mainly concerned by horizontal compression or extension of the structure are determined. It appears that the stresses induced in the building are a superposition of several elementary loading (sum of the effects of the slope, the horizontal deformations and the curvature). The second part concerns the effect of the relative soil/structure stiffness on the ground movement during a cavity collapse by considering a second model of structure with similar dimensions but more flexible. 
Matthieu Caudron (INERIS), Marwan Al Heib (INERIS), Fabrice Emeriault   (LGCIE)