Thèse de Menes Badika Kiyedi

The shear behavior of rock-rock and concrete-rock interfaces is investigated for the design and structural stability assessment of geotechnical structures (tunnels, concrete-gravity dams). Most of the studies focused on the static shear behavior of rock-rock interfaces. These studies show that the shear resistance of rock-rock interfaces depends mainly on normal stress and roughness. However, the investigation of the static shear behavior of concrete-rock interfaces under low normal loadings shows that the concrete-rock bonds significantly influence the shear resistance beyond the normal stress and roughness. Despite this progress, more experimental and numerical work is required to further understand the shear behavior of concrete-rock interfaces. In particular, it is relevant to investigate the dynamic shear behavior of concrete-rock interfaces.

This thesis investigates the influence of roughness and concrete-rock bonds on the shear behavior of concrete-rock interfaces subjected to low normal loading. A two-fold approach combining experimental and numerical modeling is adopted. The experimental work includes a pioneering experimental campaign to investigate the dynamic shear behavior of concrete-rock interfaces focusing on impact shear loading.

The interpretation of recent experimental works, particularly concrete-granite interfaces, has distinguished the influence of the roughness scales on the shear behavior of concrete-rock interfaces. The unevenness (micro-roughness) is responsible for forming concrete-rock bonds. The waviness (macro-roughness) contributes to the shear resistance of concrete-rock interfaces through surface interlocking. The numerical modeling of these interfaces is based on this separation. The cohesive-frictional model simulates the influence of the unevenness and, therefore, the concrete-rock bonds. In contrast, the influence of the waviness is taken into account by the explicit representation of the 3D morphology of the interface through surface interlocking. This model is validated by performing a comparative evaluation of the results of experimental tests and the results of simulations of direct shear tests.

A new approach has been proposed to investigate the influence of roughness on the shear resistance of concrete-rock interfaces based on the validated numerical modeling. The approach consists of generating synthetic rough rock surfaces through random field simulations and performing simulations of direct shear tests of concrete-rock interfaces comprising the generated surfaces. The analysis of the results of these tests leads to the proposition of two failure criteria. The first is an analytical relationship, while the second is a neural network model.

The dynamic shear behavior of concrete-rock interfaces has been investigated as well. The dynamic shear loading is applied using a modified split Hopkinson pressure bar system with one input bar and two output bars. A modified confinement ring is used to generate low normal stresses. The outcomes of this study show that, like the static shear behavior, the dynamic shear behavior of concrete-rock interfaces depends on the concrete-rock bonds and friction. However, there is a double mobilization of concrete-rock bonds and friction in the pre-peak and the post-peak stages. The dynamic shear resistance is not strongly dependent on the normal stress. Furthermore, the dynamic shear resistance is three to four times the static shear resistance of interfaces.

The interpretation of the recent static experimental studies, the numerical simulations of rough concrete-rock interfaces, the analytical models proposed to estimate the shear resistance of concrete-rock interfaces, and the pioneering dynamic testing of concrete-rock interfaces have all provided new insights into the understanding of the shear behavior of concrete-rock interfaces.

Jury